Bovine mastitis in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand

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(1)Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author..

(2) Bovine mastitis in New Zealand. Kiro R Petrovski 2007.

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(4) Bovine mastitis in New Zealand. A thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand. Kiro Risto Petrovski 2007. Ill.

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(6) Abstract Th is thesis represe nts a n aggregation of knowledge o n bovi ne mastitis i n t h e N ew Zea l a n d dairy i nd u stry. Fi rstly, the thesis reviews the factors infl u encing the economic i m p a ct of bovin e mastitis. Second ly, it p rovides i nformation on the incidence of cli n ical a n d subclin ica l m astitis, as a p rereq u isite fo r estimating th ese costs. T h i rd ly, it investigates the effects of experi mental ly-i n d u ced Streptococcus uberis m astiti s early in the d ry period on milk p roduction in the su bsequent lactatio n . I n t h e review of factors i nfl uencing t h e cost of b ovi n e mastitis, it was c l e a r that n either fa rm ers nor fa rm advisors have a good u n d erstanding of its fu l l economic i m pact. In ord e r to better u n dersta nd these costs, it is necessa ry to h ave a clear idea of the incid ence and con sequences of clinica l and s u bcli n ical mastitis: areas of knowled ge which were id entified as being deficient. H ence, two studies were con d u cted to i nvestigate th ese a reas. In the first study, the incid ence of clin ical m a stitis in North l a n d, New Zea l a n d, was estimated . F u rthermore, the aetiological agents causing mastitis were el icite d and thei r chronologica l distrib utions in lactation were d escri bed . Th e average i n cid ence of clinica l m a stitis was 0.19 cases per 305 cow-d ays at-risk, which is h i g h e r than p reviously reported i n N ew Zea l a n d . There were a p p roxi m ately equal n u m bers of isolations of Staphylococcus aureus (23.7%}, and Strep. uberis (23.3%) from clinical cases: a p attern that is remarkably differen t to elsewhere i n the cou ntry. Clin ical mastitis due to S. aureus o r Strep. uberis d iffered between age grou ps, with the h igh est i ncid e nce of S. aureus isolations from older cows (0.043 cases per 305 cow- d ays-at risk) a n d lowest from 2-year old cows (0. 0 14). The i ncid ence of Strep. uberis was si m i l a r in fi rst calving (0.034 cases per 305 cow-days-at-risk) a n d older cows (5 yea r o l d : 0 . 03 9 cases, 6 year-o l d : 0.030 cases) . Ove ra l l, 12% of cows were tem porarily removed from supply and 1% were culled for m astitis. Th e differences b etween the stu d y i n N o rthland and th ese reported elsewhere from NZ highlight the need for a nati o n a l s u rvey on the aetiology and e p i d e m io logy of bovi n e m astitis. A secon d study eva luated the effects of Strep. uberis clinical mastitis in t h e e a rly d ry peri o d o n m i l k p roduction in the su bsequent lactatio n . I n a p revious stu dy,. V.

(7) Strep. uberis m a stitis was experim entally induced a n d then p rom ptly treated . This experi m en t p rovided a d ata set from which the i m pact of Strep. uberis cli n ica l mastitis ea rly in the d ry p e riod on m i l k p ro d u ction in the subsequent l a ctation cou ld be estimated. Resu lts of this study ind icated that an e a rly dry period cl i nical m a stitis due to Strep. uberis/ when p ro m ptly treated, d i d not affect production in the s ubsequent lactation. F o r cows that suffered m a stitis e pisode d u ring early d ry pe riod com pared to those t h at d id n ot, th ere was no differen ce in m i l k yield ( 5126 vs. 5010 l itres), fat yield (267 vs. 264 kg), and p rotein yield { 182 vs. 179 kg), respectively. lt was consid ered that the short d u ratio n of i ntra m a m m ary i nfection did not cause perm a nent d a mage to the m a m m a ry secretory tissue. lt was concl u d e d that the cu rrent esti m ates of the econom ics of m astitis i n N ew Zea l a n d a re p ro b ably u n d er-esti mating the real cost of mastitis to its dairy i n d ustry. This was based o n the higher incidence of clin ical m a stitis in North land tha n elsewh ere i n the cou ntry a nd a fai l u re of p revious stu d ies to take into consideration the costs associated with a n imals that were tem porarily removed from s u p p ly ( i . e. rather than c u l l e d ) . Additio n a l ly, as the h ighest freq uency of n ew i ntra mammary i n fections occurs i n the fi rst wee k or two after dryin g off, it m ay p rove beneficial for fa rmers to pay m ore attenti o n to ch ecki n g for clin ical m a stitis d uring the early d ry peri o d .. VI.

(8) Prefa ce lt is m o re than 3 yea rs ago that I started designing a p roject for my M asters degree. At that time I was working for Dr R oss D Woods in a mixed a n i m a l p ractice i n Da rgavi l l e, N o rth l a nd, New Zealand, a n d I h e ld a special interest in bovi n e mastitis a n d d a i ry cattl e re p roduction. I was fasci nated by h o w many cases of cli n ical mastitis or m a stitis pro bl e m herds were in the area. Anecdota l evidence fro m veterinarians and laborato ry workers fro m the region suggested that there might be d ifferent p atterns o f m a stitis i n N o rth l a n d t o those observed elsewhere i n N ew Zea l a n d . Th e i d e a t o con d u ct a study on t h e aetiology of bovi ne mastitis for the region was thus born. lt took m o re than a yea r to fi nd som eon e wi lling to provide fi nancial suppo rt a n d to start the first study. After th at, it was easier to fi nd extra fi nancial support. At this stage I contacted Prof Tim (Ti mothy) J. Parkinson, who invited Assoc Prof Cord Heuer a lso to be i nvolved. At th i s stage both veteri n a ry p ractices in Dargaville a m a lga mated causing a n a d d itional pressu re of cha ngi ng the working environm ent a n d h a bits. Cond ucting the study, I fou n d why people a re rel uctant to work o n larger sca l e stu d ies while e m ployed fu l l ti m e i n a p ractice. There was n o t i m e for a p rivate l ife, especially since I w a s recently marri e d . Fortun ately, my wife, P a u l i n a Rodriguez, was a lso p reoccu pied as she was preparing for the N ew Zealand N ation a l Veterin a ry Exa min ation registration exa ms. She d i d n ot complain ( h ugely) about the extra hours that I spent with m y "gi rlfriend" (my c o m p uter) o r with my "love" (dairy farms). O n ly d u e to the va l u ab l e time contributed by fa rm ers and farm perso n n el on the stu dy fa rms made it possib l e to cond u ct a n d complete this stu dy. I truly enjoyed the d iscussions with them and the fa rm visits. F u rt h ermore, browsi n g the literature, I fou n d that there is a great deal of literature avail a b l e on the economics of bovi n e m astitis, but there is a lack of revi ew/con t i n u i n g education articles t h a t p rovi d e a l i st of t h e factors associated with t h e cost o f bovi n e mastitis t o the dairy i n d ustry. This p rovided the inspiration for m e to review the l iteratu re for these factors a n d su bseq u ently write an article on conti n u i n g e d u cati o n . After a year or s o o f work, with h e l p o f two o f m y fri ends from my U n iversity days. -. P rof M etodija Trajcev a n d Prof Gjo ko Buneski of U n iveristy "St Cyri l a n d M eth o d i u s",. VII.

(9) Skopje, M aced on ia, the first version was sent to the ed itor of the J ournal of the South Africa n Veteri n a ry Association. In late J a n u ary 2006, my wife a n d I left Dargavi lle a n d moved to Palmerston North, wh ere I joined the tea m of the I n stitute of Veterinary, An imal and Biomedica l Science s, M a ssey U n iversity. M y close collaboration with Prof Norm a n B. Will iamson at M assey U n iversity com p l eted the expansion of my su pervisors team. My i nterest in the eco n omics of bovi n e mastitis formed the basis of the second study i ncluded i n th is t h esis - investigating the effects of clin ica l mastitis occurring in the early dry period o n t h e m i l k prod u ction i n t h e su bsequent season. A study on t h e efficacy o f a n experi m ental a n d a m od ified exi sting external teat sealant, conducted over a previous d ry p eriod by Cecilia Fern a n d ez, provided a great o p port u n ity to investigate a n y production effects after Streptococcus uberis challenge a n d i nfection. At this stage I started with my b iggest saga during the preparatio n of this thesis -th e a n a lytica l part o f the stu d ies. I l earned t h a t data preparation and proper a n a lyses are very i m p orta nt. Collectin g the d ata is easier than the d ata e ntry that can be a very d i ffic u lt task, p a rticularly when the collected data are on hand-written forms. This was s u ccinctly state d by Prof Ynte Sch u k ken from Cornell U n iversity, USA, at a February 2007 Epidemiol o gy worksh o p when he said "You enter your data preparing it for a n alysis, n ot j u st to be e ntered". This is something that I had to learn the h ard way, d urin g my M a st ers preparation. Ana lyses i n the second study were conducted with guidance a n d assistan ce o n the use of SAS software fro m Dr N icolas Lopez-Villalobos. Mr Alex Gri n berg was a lso i nvolved in t h e study, provi d i n g some i nformation in the absence of Cecilia Fernandez, who h ad returned to Arge nti n a . I fou n d computer software to be very hel pfu l a n d fast, h owever, I a m n o t s ure that i n m y next life I would l i ke to b e a statistician . This M asters proj ect h a s b een o n e of the m ost enjoya ble edu cational experiences that I h a ve u n d erta k e n . The k n owledge gain ed a n d the tech ni q ues learned (in p articu l ar b iostatistics), h a ve provided a n op portu n ity to i nvestigate problems that were previo u sly i m po s s i b le for me to tackle. I am n ow able to a pproach problems in a m ore l ogica l m a n n er. I h ave gained skills a n d confidence to learn m a ny more tech n i q u es of. VIII.

(10) the d isci p l i n e u nd e r my own gu i d a n ce a n d this will be basis for my fu rth er developm ent. Writing is a n essenti a l part of any resea rch and it is often very d ifficult to b r i n g the obse rvations and a n a lyses to other peop le, p a rticu l a rly in a foreign l a nguage as E nglish is my second (or so) l a nguage. Ross Woods, George Tha raka n, Kathy Dro p u lich, Kylie M a rtinovich, Dona ld Thom as, Graeme Ewe nson, Simeon Pol lock a n d J oyce D e Moulin from Dargaville, Prof Colin Holmes, Assoc P rof D u n can Mackenzie, M r Allan Th atcher, and my supervisors, at Massey h ave been of tremendous help rea d i ng p a pers, m a n u scri pts a n d this thesis and have s uggested u sefu l corrections. P rof W i l l i a mson once mentioned that my first versions of m a n u scri pts are in Maced o n i a n with E nglish words.. IX.

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(12) Dedicat i o n I wo u l d l i ke t o ded icate this thesis to m y p a rents Risto and Ve rica Petrovski for their guid ance a n d encou ragement through my life and m y wife Pau l i n a Rodriguez for her l ove a n d patience.. XI.

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(14) Ac knowl edge m e nts I wish to exp ress my sincere gratitude to my s u p e rvisors Prof Tim Parkinson, P rof N o rm W i l l i a mson. and. Assoc. Prof. Cord. H eu e r,. for. their patience,. sou n d. a dvice,. e n co u ragem ent, d edication and for l ea d i n g m e through the i ntricacies of a m a ster's degree thesis. I a m indebted to a l l the farm own ers and farm perso nnel in the e n ro l l ed d a i ry fa rms fo r the friendship, cooperation a n d interest i n my research. Without their fu l l s u p po rt a n d cooperatio n this work cou ld not have been carried out. I wo u l d also l i ke to th a n k the Oa rgavi lle Veteri n a ry Centre crew for their assista nce and encou rage me nt d u ring the field work o n the second study. I wou l d a lso like to tha n k the N ew Zea l a n d Veteri n a ry Pathology l aborato ry c rew of M ichelle M cKeany and Rae Pearson for their assista n ce in c u lturing the s a m ples a n d i d entification. Assoc Prof Ouncan Mackenzie and Prof Col i n H o l mes are a lso thanked for their guid a n ce and encouragement through my post grad u ate studies. Andrea Colem a n has p rovi d ed com p uter s u p p o rt a n d Or N icolas lopez-Vi llalobos, Or Richard laven a n d Kevi n Lawre nce h ave p rovided assista nce with t h e statistical analysis of the d ata. Oth e r I n stitute o f Veteri n a ry, An imal and Biomedical Sciences, M assey U n iversity staff, a lth ough not d i rectly i nvolved i n my stu dies, h ave a lso p rovided s u p port a n d fri e n dship through my stu d i es. The financial support p rovided by the. North land Com m u n ity Fou n dati o n i n. coo pe ration with t h e Northern Wairo a Vet Cl ub, Oargaville F i e l d d ays a n d M a n gata pere Vet Club for the Northland study i s also gratefu l ly acknowledged. Th e study o f the effects of early dry period m astitis o n m i l k p roduction in the subsequ ent season and the printing of this th esis were financi a l ly s u p p o rted by Bomac Laboratories Ltd .. XIII.

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(16) Table of co ntents Contents Abstract Preface Dedication Acknowledgme nts Table of conten ts List of Tables List of Figures List of Abbreviations. Page No. V VII XI XIII XV XVI I XIX XXI. Chapter one. 1.1 1.2. General introduction. 1. G e n eral l ntroduction References. 3 9. Chapter two A review of the factors affecting the costs of bovine mastitis. 2. 1 2.2 2.3 2.4 2. 5 2.6 2. 7 2.8. Abstract I ntrod u ction The cost of mastitis to the d a i ry i n d u stry Losses caused by mastitis Cost of mastitis control p rogra m m es Discussion a nd concl usions Acknowledgments References. Chapter three. 13 15 15 15 17 18 34 39 39 39 45. The Incidence and Etiology o f Bovine Mastitis in North/and, New. 3.1 3.2 3.3 3.4 3.5 3.6 3.7. Zealand. 47. Abstract I n trod u ction M aterials and methods Resu lts Discussi o n Conclusions Acknowledgm ents. 47 48 51 56 64 69 70. XV.

(17) 3.8. R eferences. 70. Chapter four Effects of Streptococcus uberis Clinical Mastitis in the Early Dry Period on Production in the Subsequent Lactation. 4. 1. I ntrod u ct i o n to the study used to p rovide data for analysis of p rod u ction effects Effects of experi m entally induced a n d t reated Streptococcus uberis m a stitis e a rly i n the d ry period o n p roduction in the subsequ ent l a ctation Abstract. 4.2 4.3 4.4 4.5 4.6 4.7 4.8. I nt rod u ction M ateri a l s a n d m ethods Resu lts Discussion Conclus i o n s Acknowledgments References. 4.a 4. 73 75. 77 79 79 80 82 83 85 85 85. Chapter five. 5.1 5.2. XVI. General discussion. 87. G e ne ra l d iscussion References. 89 93.

(18) list of Tab les Page N o.. Table. Content. 3.1. Diagnostic p rocedu res a n d their i m portance i n the diagn osis of clinical mastitis o n d iffe rent fa rms a s graded by t h e farm p e rson nel. 52. 3_2. N u mber of cows a n d m i l k p roduction per l a ctating cow per a n n u m among fa rms i n 3765 cows from dairy fa rms in Nort h l a n d, New Zealand.. 56. 3.3. Total n u mbe r a n d percentage o f m a st itis-ca using organisms isolated before and after re-classification (sampled 417 cows with clin ical mastitis). 60. 4.1. Least s q u a res means a n d standard errors of m i lk p roduction and somatic cell score cows affected and n ot affected with clin ical mastitis i n the ea rly d ry period. 83. XVII.

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(20) List of Figures Page No.. 1_1. Content Bovine m a stitis epidem iological triangle - cow, mastitis-ca using o rganisms and the cow. 1_2. Slid i n g scale from contagious to environ m enta l epidemiology of mastitis-causing organisms. 7. 3.1. Four-weekly movi n g average of the case i ncidence o f clin ical m astitis (cases per 305 cow-days-at- risk) in 3765 cows from 14 dairy farms i n North land, New Zeal a n d. 58. 3.2. Age related i n cidence of clin ical m astitis i n cows a n d q u a rters of 3765 cows from 14 dairy farms i n North l a n d, New Zealand. 58. 3.3. 305-days h e rd i ncidence of clin ical m a stitis i n 14 dairy farms in Northla nd, N ew Zealand. 59. 3.4. N u m bers of episodes of clinical mastitis per q u a rter position. 59. 3.5. Age related isolation of mastitis-causing organ isms i n 3765 cows from 14 d a i ry farms in North land, New Zealand. 61. 3.6. F o u r-weekly average distribution of culture isolates a n d no sam p li n g from cows with clin ical m a stitis, excluding cases caused by Staphylococcus aureus o r Streptococcus uberis. 61. 3.7. F o u r-weekly m ovi n g average of Staphylococcus aureus a n d Streptococcus uberis isolation ( n u mbers/305 cow-d ays a t risk). 62. 3.8. P e rcentage of h igh indivi d u a l cow, test day somatic cell cou nts (SCC>250, 000 cells/m !) a n d changes i n the pe rcentage of cows with high sec i ndividual somatic cell counts from l ow to high a n d h igh t o l o w a p p roximating rates of n ew and cure from subclin ical m a stitis t h rough lactation. 64. Figure. 4. XIX.

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(22) Li st of Abbreviations Abbreviation A.. Mea ning Arcanobacter. BTSCC. Bulk Ta nk Somatic Cel l Cou nt. CM. Clin ical Mastitis. CNS. Coagu l ase-negative staphyl ococci. CR-FVR. Case-ratio of c l i n ical mastitis in front versus rea r q u a rters. CR-RVL. Case-ratio of c l i n ical m astitis in right versus left q u a rters. DAR. Days at risk. DIM. Days i n m i l k. E.. Escherichia. E D PC M. Early D ry Period Clinical M astitis. HF. Holstei n-Friesia n. I CSCC. I ndivi d u a l cow somatic cell count. IMI. lntramamma ry I nfection. I VABS. Institute of Veteri n a ry, An i m a l and Biomedical Sciences. LIC. Livestock I m p rovement Corporation. M CO. Mastitis-Ca using Organ ism. MS. Milk solids. M UA E C. Massey U n iversity A n i m a l Eth ics Com m ittee. S.. Staphylococcus. SAS. Stati stical Analysis System. SCC. Somatic Cel l Co u nt. SCM. Sub-cli n ical Mastitis. SCS. Somatic cel l score. Strep.. Streptococcus. UK. U n ited K i n gdom. USA. U n ited States of America. XXI.

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(24) C h a pter o ne. Genera l Intro d u ction. 1.

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(26) 1. 1 Genera l Intro d u ction Bovi ne mastitis is defi ned as an infla m m ation o f the mammary gla n d mai nly i n reaction to i n fection by mastitis-ca using organisms (MCO). lt is one of the most p revalent econom ica l ly i m p o rta nt p rod uction d iseases affecting the dairy cattle indust ry world wide (Biosser 1979; Fetrow 1987; Gill et a l 1990; DeG raves a n d Fetrow 1993; Hort et and Seegers 1998; Seegers et a l 2003 ). Bovi ne mastitis is a m u lti-factorial and com p lex disease, resu lti ng from i nteraction between cows, m icroorga n isms a n d the e nviro n ment (Figu re 1 . 1; Watts 1988; Sch u kken a n d Krem er 1996). Most cases o f c l i n ical mastitis (CM) i n dairy cows a re infectious i n aetio logy (Craven 1987; San d h o l m et al 1990). Despite i ntensive resea rch and the i m p lementation of various m astitis control strategies over the d ecades, bovin e mastitis has n ot d isappeared a n d the red u ction i n t h e p revalence of sub-cli n ical mastitis (SCM) has been m i n imal (Pyorala 2002) to significa nt, country d e p e n d a nt. I n New Zea land the reduction of SCM i s evident from the decrease i n n ational bu l k m i l k somatic c e l l count t o a ro u n d 200,000 cells/ml lately. On th e other h a n d, t h e re h as been a considerable decrease i n the incidence of clin ical cases of bovi n e m astitis worldwide. More than 137 species of o rganisms have bee n i m p licated as ca usal agents o f bovin e mastitis (Watts 1988). M a ny bacteria, yeasts, viruses a n d fungi have bee n i s ol ated from bovi ne m a m mary glands but only a s m a l l gro u p of them ca use el evated s o m atic cel l c o u nts (SCC) and mastitis (Watts 1988; M a l inowski et a l 2002; Wel l enberg 2002). More t h a n 90% of all new i ntra mam mary i n fe ctions (IMI) are caused by a few M COs, n a m ely, Staphylococcus aureus, coagu lase- n egative sta phylococci (CNS), Streptococcus aga/actiae Strep. dysgalactiae, Strep. uberis a n d Escherichia coli. H owever, there a re many other m iscella neous species of o rga n is m s capable of causing m a stitis a n d fi n d i ng one o f t hese causing m astitis m ay be h ighly significant for a p a rticu l a r d a i ry herd . F i n a n c i a l losses d u e to mastitis are substa nti a l and arise from d i rect a n d i n d i rect l osses and expenditure. Bovin e m astitis is considered one o f the m ost eco n o m ically i m p orta nt d isea ses for the d a i ry i nd ustry in d evel oped cou ntries (Biosser 1979; F etrow 1987; G i l l et al 1990; Schepers a n d Dijkh uizen 1991; Mclnerney et al 1992; D e G raves. 3.

(27) a n d Fetrow 1993; Al lore and Erb 1998; Hortet and Seegers 1998; Fetrow 2000; Pyora l a 2002; Seege rs e t a l 2003). Ben n ett et a l ( 1999) esti mate that the total costs of each d isease can be m u ch h igher than the d i rect expenditure ( Ben n ett et a l 1999).. Figure 1.1. Bovine mastitis epidemiological triangle - cow, mastitis-causing organisms and the environment. M a stitis cost t h e U SA dairy i n d ust ry a pp roxi m ately US$ 2 billion/year i n 1992 and 1993 (M iles et a l 1992; C u l ler 1993). According to Ott (1999) the total production loss due to mastitis in t h e U S A is $ 108.00 per cow for herds with average B u l k Ta n k Somatic Cell Cou n t (BTSCC) of 200,000-399,99 9 cells/ml and $295.24 per cow for herds with average BTSCC 400,000 a n d above. Th is a m o u nts to losses of a p p roxim ately $1 bi llion to t h e USA d a i ry i n d u stry, based o n l y o n BTSCC, as a measure of SCM (Ott 1999). Mori n e t a l (1993), m on itori ng fou r I ll i n o i s herds for twelve months, reported mastitis associated eco n o m ic losses ra ngi n g from US$ 161.79 to $344. 16 per lactating cow/year. Si m i l a rly, the total fi n a ncial cost of mastitis to the average Scottish dairy herd i n 1996 w a s esti m ated to be £ 140/cow/year (Ya lcin 2000), o f which a loss of £ 100/cow/year w a s d u e to SCM i n high BTSCC h erds (Yalcin et al 1999). B ovi n e mastitis has been est i m ated to cost the N ew Zea l a n d dairy industry aro u n d NZ$180 m i l l io n/year i n 2 005/06 (Anonymous 2006) . M a ny factors h a ve been associated with the cost of m astiti s to the d a i ry i nd ustry a n d they h ave b e e n recently reviewed ( P etrovski e t a l 2006). The main facto r causing. 4.

(28) economic losses, due to both clinica l a n d SCM, is a more or less persistent decrease i n m i l k yi e l d . T h e pathogenesis of mastitis, i n m a n y cases, includes d a m age t o secretory tissue a nd its replacement with fibrous tissue, lead ing to a permanent d ecrease in m i l k yield from t h e affected q uarter (Benites et a l 2002) . Du ring m astitis episo d es a n d recovery periods m i l k com position is a l s o affected ( Bishop et a l 1984; DeG raves a n d Fetrow 1993; Auldist 1995; Seegers e t a l 2003) influencing yields o f milk solids. I n a case of m astitis d u ri ng lactation, u s u a l ly there wi l l be a short-term d e p ression in milk yield of variable severity. I n the case of no m icrobi a l cure a n d recovery, t h ere is a longer-lasting effect, someti mes carryin g over i nto the next lactation/s. Regarding short-term effects, it is gen era lly accepted that the earlier m astitis occurs in the lactation the greater the losses of m i l k yield (Beck et al 1992; Houben et al 1993; Hortet a nd Seegers 1998; Rajala-Schu ltz et a l 1999; Fetrow 2000). Lon g-term effects of CM o n milk yie l ds a re an a rea that need more attentio n from research (Petrovski et a l 2006), a lt h ough ava ilable esti mates general ly i n d icate that after a n episode of CM th ere are both short- a n d long-term d ecreases i n m i l k prod uction, particu larly associated with chronic bovi n e mastitis (Smith et a l 1968; Fetrow et a l 199 1; Lescou rret and Coulon 1994; Rajal a-Schu ltz et a l 1999; Fetrow 2000). Th e effects of CM d u ri ng the d ry period o n milk p roduction parameters d o n ot a p p ea r to h ave been systematica l ly investigated. Nonetheless, t h e d ry period is an i m port a nt part of the lactational cycle d u ri n g which the m a m m ary gland should recover a n d pre p a re for t h e n ext l actation. A clinica l case o f m astitis d u ring t h i s p eriod m ay therefo re be expected to d istu rb th e p rocess of normal invol ution a n d p reparation for lactogenesis. Most of the ava i l able estimates take i nto account o n ly a part of the real cost of mast i tis, as estimating the true costs associated with mastitis is notoriously diffic u lt. lt is even m o re d ifficult to q uantify the losses associated with SCM, beca use they a re n ot visible to farm owners. To avoid u n derestimating the consequences of m a stitis in eval u ations of econ o mi c-loss it i s i m portant to account for all o f the cost factors i nvo l ved.. 5.

(29) M a ny tech n i q ues a n d methods h ave been used to esti m ate p roduction losses from m a stitis in d a i ry cattle, but n o n e of the techniques used are perfect, due to lack of a d i rect m easu re o f how m u ch m i l k a cow would have produced if th ere had been no occu rrence of m a stitis d u ri n g l actation. F u rthermo re, all h ave a degree of i n h erent bias which, i n m ost cases, tends to u nderestimate the actual m i l k yield decrease that h a s occu rred (DeGraves a n d F etrow 1993 ). M ethods commonly used i nclude p roducer s u rveys, regression a n a lyses relati ng m i l k somatic cell cou nts, between-herd c o m p a risons, betwee n-cow yield com parisons, within-udder yield com p a risons, within-cow yield c o m p a rison a n d stud ies between identical twi ns. Estimation o f the eco n om ic costs associated with m a stitis depends on havi n g the fol lowin g data: 1. An estimate of the incidence and prevalence of mastitis in the population is a p re. req u isite for the estimation of its real cost to the d a i ry industry. Th ere is currently a general d emand t h rough regu l a r monitoring, recording and research to establish the i ncidence a n d p revalence o f mastitis. M cDougall (2002 ) reported the i n cid ence rate o f CM i n N ew Zealand d a i ry herds to be 14 cows/lOO cows per a n n um, with the m aj ority of cases occurri n g around ca lvi ng ( M cDougall 200 2 a ) . I ntervention stu dies in N ew Zealand fou n d that 10% of cows acqu i red new i n fections d u ri n g early lactation (Pan key 1982; M cDouga l l 1998). B rookba n ks (1966) repo rted that 3 2% of cows had a positive rapid m a stitis test ( RMT) d uring a study c o n d u cted in 130 h erds throughout New Zealand (Brookba n ks 1966). N o references t o other n ation-wid e surveys o f the incidence of clin ical or subcl i n ical mastitis were fou n d i n t h e l iteratu re. 2. The severity of the physical effects of mastitis on milk production, d e p ends o n m a ny. factors, such as type a n d virulence o f the M COs, stage of lactation, age of the cow a n d u dder d efen ce m e c h a n i sms. R esearch o n the d istribution of M CO i n N ew Zea l a n d is also limited . Ea rly surveys of M CO i n m i l k repo rted that 14 to 18% o f the cows were infected with Strep. agalactiae, 27 to 41% with 5. aureus 2 to 4% with Strep. dysgalactiae, fewer than 3 . 0% with Strep. uberis a n d 25% with CNS ( B rookban ks 1966; E l liot 1976). More recently, the. 6.

(30) p revalence of 5trep. aga/actiae a n d 5. aureus has fa l l en, wh i l st 5trep. uberis is now re p o rted as the m ost com mon cause o f bovi ne mastitis in New Zea land. Reports from i ntervention su rveys i n the Wai kato report the fol l owing p r o p o rtions of m a stitis causing o rga n isms from cows with C M : 27 to 75% of 5trep. uberis, 9 to 10% CNS, 2 to 5% col ifo rms, 1.5 to 4% 5trep. dysga/actiae and 3 to 5% 5. aureus (McDouga l l 1998, 2003}. M a stitis-ca using o rganisms are catego rised as contagious or e nvironmental, based on the source o f i nfection, mode of tra n smission and the tendency to cause persistent o r transient I M I ( B radley and G reen 2 001; M a kovec and Ru egg 2003). T h e p ri m a ry reservoir of contagious MCOs is the bovi ne m a m m a ry gland a n d they a re com mo n ly tra n s m itted a mong cows d u ri n g m i lking. 5. aureus and 5trep. agalactiae h ave h istorica l ly been most im portant. Lately, particularly in the USA, Mycoplasma s p p . a re i ncreasingly rep o rted to cause major m astitis p roblems in affected herds (Makovec a n d Ruegg 2003 }. Environ mental M COs h ave a primary reservoir i n t h e cow's enviro n m ent. The d ifference between contagious a nd enviro n m e ntal MCO is less clear than origi n a l ly thought (Figu re 1. 2), si nce envi ron m ental organisms have been s h own i n so m e cases to p e rsist in the mammary gl a n d throughout the d ry p e riod and beyo n d, a n d tra n s m i ssion fro m cow to cow has been p roven i n t h e case o f 5trep. uberis a n d 5trep. dysgalactiae (G romm ers et a l 1985; Zadoks et a l 2003). The most i m po rtant envi ron m e nt a l M COs are streptococci (other than 5trep. agalactiae), CNS and G ramnegative bacteria.. m ::s. :5:. ""'11. E. coli. 0 ::s. 3. (I) ::s. �. Figure 1.2. Sliding scale from contagious to environmental epidemiology of mastitis-causing organisms. Streptococcus agalactiae almost entirely transmitted cow-to-cow; Staphylococcus aureus largely. contagious, p a rtly environmental; Strep. dysgalactiae classified as environmental by some, as conta gious by others; Strep. uberis largely environmental, partly contagious; Escherichia coli ( almost ) entirely environmental.. Re-drawn from Zadoks and Schukken 2003. 7.

(31) Streptoccus uberis is a widely occu rri ng M CO wh ich is commonly isolated from I M is in many cou ntries, incl u d i n g N ew Zea l a nd, Austra l ia, the U n ited. Ki ngdom, the. N etherlands, the U n ited States, and Ca nada (Douglas et al 2000; P h u ektes et a l 2 001; Zado ks et a l 2003; McDougall et a l 2004). lt accou nts for a sign ificant p roportion of subc l i n i ca l a n d c l i n ical intra m a m m a ry infections i n l a ctating a n d nonlactati n g cows (Douglas et a l 2 0 00; P h ue ktes et al 2001). Strep. uberis is probably the most sign ificant cau se of bovi n e mastitis in N ew Zea land and Austra l ia, where the dairy i n d u stry is p redomi n antly p a stu re-based ( Pa n key et al 1996; Douglas et al 2000; P h u ektes et al 2001; McDo u ga l l 2002b) . 3. Identification of the prevention a n d treatment measures undertaken a n d estimates. of their efficacy. G eneral ly, there is n o difficu lty in fi n d i n g the expenditure o n m a stitis control but the i nfluence on the i ncidence of mastitis, its d u ration a n d the resu lting i m pact on prod u ction i s m o re d ifficu lt. 4. Valuation of the production losses, treatments and expenditures on prevention and control incurred. Estim ates of m i l k yield loss a re sti l l the subject of d ebate; however, they are l i kely t o be i nflu e nced by the age, breed a n d type of cow, m orphologica l characteristics o f the u d d e r, stage of l actation, pregn a ncy status, m i l k yield before mastitis occu rre d , m i l k p rice, prem i u m s a n d pena lties, MCO, infl a m m ation grade, d u ration and d i stribution, timelin ess of diagnosis ( i n relation to the onset of the o cc u rrence), trea t ment a n d p revention costs, feeding p ractices, season, recu rrence of m astitis d u ri n g the sa m e or a previous lactation, com parison model (what is the control grou p ) a n d the a n a lytica l model. Milk prod uct i o n l osses are typica l ly estim ated to a ccou nt for 7 0 to 80% of all m astitis losses in a h erd (Ki rk 1984; G i l l et al 1 990; Sche pers and D ijkh u izen 1991; DeG raves a n d Fetrow 1993; Morin 1993; Lehenbauer a n d Oltjen 1998; F etrow 2000). 5. Other cost factors- e.g. farm management, culling, replacement and fatalities.. Extra polating obse rvations from other cou ntries ca n be d ifficult due to the differences in the d a i rying system in N ew Zeal a n d where dairy farms a re past u re-based with seasonal p roduct i o n, l ower m i l k yields and shorter lactati o n periods.. 8.

(32) This thesis reviews the factors i n fluencing the cost of bovine m a stitis, p rovides i n fo rmation o n some of the p rereq u isites for esti m ation of the cost of bovi n e m a stitis to the New Zealand dairy i n d u stry a'n d reports the effects of experi m enta l l y i n d u ced a n d p romptly t reated Strep. uberis CM ea rly i n the d ry period (EDPCM) o n m i l k p roduction i n t h e subseq u ent l actation. In the review of the factors i nfl uencing the cost o f bovi ne mastitis, a reas of d eficient knowledge were i dentified and two stu d ies were conducted that contribute i n formation to the d eficient a reas of knowledge. The fi rst stu d y estim ated th e i ncidence of bovi n e c l i n ical mastitis in the N o rt h l a n d region o f N ew Zea l and a n d d escribes the aetiology a n d distribution i n lactation o f MCOs. The rati o n a l e for t h i s study is t h a t knowin g the i ncidence o f CM is o n e o f the m a i n pre-req u isites for estimation of the economic losses a ssociated with bovine m astitis. lt was u n d ertaken from the hypoth esis that the particular circ u m st a n ces of the d airy i n d u stry i n N o rt h l a n d would give rise to d ifferent p atterns o f m a stitis to those observed elsewh ere in N ew Zea l a n d (a view that was supported by a n ecdotal repo rts from veterin arians and laboratory workers of the North l a n d regi o n ) . T h e s eco nd study eva l u ated t h e effects of experim e ntally-in d u ced a n d p ro m ptly treated Strep. uberis CM i n the early dry p e riod o n m i l k production i n the subsequ ent lactation, by re-eva l uation of d ata from Fernan dez (2007). The ration a l e for t h i s i s the gen e ra l deart h of k nowledge about the effects of CM d uring the dry peri o d . lt i s well known that the d ry period i s an important p a rt of the lactational cycle d u ri n g which the m a m m a ry g l a n d p repares for next lactatio n . Th erefore, a n episode o f CM d u ri ng this p e riod may i m p ede the p rocess of m a m ma ry tissue remodelli ng, thereby adversely affecting m i l k yield in the subseq uent lactation. Streptoccus uberis was e lected for this stu dy as it i s regarded as the most com m o n cau se of mastitis i n N ew Zea l a n d ( D o uglas et a l 2000; M cDougall 2002b; McDouga l l 2002a).. 1.2 Refe re n ces !. ••. !. ••. !. ••. Allore HG, Erb H N . Partial budget of the discounted annual benefit of mastitis control strategies. Journal of Dairy Science 81, 2280-92, 1998. Anonymous. Cost of mastitis study. Final Report. N ational Mastitis Advisory Committee, 2006 A u ldist MJ, Coats, S., Rogers, G.L., and McDowell, G.H. Changes in the composition of m i l k from healthy and m astitic dairy cows during the lactation cycle. Australian Journal of Experimental A griculture 35, 427-36, 1995. 9.

(33) •!• •!• •!• •!• •!• •!• •!• •!•. Beck HS, Wise WS, Dodd FH. Cost benefit analysis of bovine mastitis in the U K. Journal of Dairy Research 59, 44 9-60, 1992. Benites N R, G uerra JL, Melville PA, Costa EOd. Aetiology and histopathology of bovine mastitis of spontaneous occurrence. Journal of Veterinary Medicine. Series B 4 9, 3 66-70, 2002 Bennett R M, Christiansen K, Clifton-Hadley RS. Estimating the costs associated with endemic diseases of dairy cattle. Journal of Dairy Research 66, 4 5 5-9, 1999 Bishop J R, Bodine AB, O'Dell GO, Janzen JJ. Retention data for antibiotics commonly used for bovine infections. Journal of Dairy Science 67, 43 7-4 0, 1984 Blosser TH. Economic losses from a nd the national research program on mastitis in the U nited States. Journal of Dairy Science 62, 119- 27, 1979 Bradley AJ, Green MJ. Adaptation of Escherichia coli to the bovine mammary gland. Journal of Clinical Microbiology 3 9, 184 5-9, 2001. Brookba n ks EO. A report on surveys of the incidence of m astitis infection in New Zealand dairy herds. New Zealand Veterinary Journal 14 , 6 2- 7 0, 1966 Craven N . Efficacy and financial value of a ntibiotic treatment of bovine clinical mastitis d uring lactation--a review. British Veterinary Journal 143 , 4 10-22, 1987. •!•. Culler JS. The control, treatment, and prevention of the various types of bovine mastitis.. •!•. DeGraves FJ, Fetrow J. Economics of mastitis and mastitis control. Veterinary Clinics of North. •!•. Veterinary Medicine 88, 5 7 1- 9, 1993 America, Food Animal Practice 9, 4 2 1-34 , 1993. Douglas. VL,. Fenwick. SG,. pfeiffer. DU,. Williamson. N B,. Holmes. CW.. Genomic typing of. Streptococcus u b e ris isolates from cases of mastitis, in New Zealand dairy cows, using p ulsed-field •!• •!•. gel electrop h o r esis. Veterinary Microbiology 7 5, 27-4 1, 2000 Elliot R, Tattersfield, JG, Brooksbanks, EO. N ew Zealand national mastitis survey:1965-6 3 . The microflora of bovine composite milk samples. New Zealand Veterinary Journal 24 , 80-4 , 1976. Fernandez C. The effect of external teat sealants on mastitis incidence during the d ry period u nder experimental challenge with Streptococcus uberis. Thesis submitted to Massey University in partial fulfi l ment of the requirements for the degree of Master of Applied Science in Animal. •!• •!• •!• •!• •!• •!• •!• •!• •!• •!• •!• •!• •!•. Production, 2007. Fetrow J, M a n n D, Butcher K, McDaniel B . Production losses from mastitis: carry-over from the previous lactation. Journal of Dairy Science 74 , 833 , 1991 Fetrow J, Anderson, K. The economics of M astitis Control. Compendium of Continuing Education of a Practicing Veterinarian 9, 1987. Fetrow J, Stewart, S., Eicker, S., Farnsworth, R., Bey, R. Mastitis: An econom i c consideration. I n : ' National M a stitis Cou ncil Annual Meeting Proceedings'. Atlanta, Georgia, U S A Pp 3 -4 7, 2000 Gill R, Howard WH, Leslie KE, Lissemore K. Economics of mastitis control. Journal of Dairy Science 73 , 334 0-8, 1 9 9 0. G rommers FJ, van de Geer D, in 't Veen CA. Duration of bovine intramammary infections in commerci a l d a i ry herds. Veterinary Record 1 16, 581-4 , 1985 Hortet P, Seegers H . Loss i n milk yield and related composition changes resulting from clinical mastitis in dairy cows. Preventive Veterinary Medicine 3 7, 1-20, 1998 Houben EH, Dijkhuizen AA, Van Arendonk JA, H uirne RB. Short- and long-term production losses a n d repeatab ility of clin ical mastitis in dairy cattle. Journal of Dairy Science 76, 256 1-78, 1993 Kirk J H . Progr a mmable calculator program for l i near somatic cell scores to estimate mastitis yield losses. Journal o f Dairy Science 67, 44 1-3 , 1984 Lehenb a u e r TW, Oltjen JW. Dairy cow culling strategies: making economical culling decisions. Journal of Dairy Science 8 1, 264 , 1998. Lescourret F, Coulon J B . M o d eling the i m pact of mastitis o n milk p roduction by dairy cows. Journal of Dairy Science 77, 2289-3 0 1, 1994. M a kovec JA, R uegg PL. Results of milk samples submitted for microbiological examination in Wisconsin from 1994 to 200 1. Journal of Dairy Science 86, 34 66-72, 2003 Malinowski E, Lassa H, Klossowska A. Isolation of Prototheca zopfii from inflamed secretion of udders. Bulletin of the Veterinary Institute in Pulawy 4 6, 295- 9, 2002 McDougall S. Efficacy of two a ntibiotic treatments in curing clin ical and subclin ical mastitis in lactating dairy cows. New Zealand Veterinary Journal4 6, 226-3 2, 1998. 10.

(34) !. • •. McDougall S. Bacteriology, cure rate and herd level risk factors for clinical mastitis in dairy herds In: 'Ann u a l Conference of the Society of Dairy Cattle Veterinarians of the New Zealand Veterinary Association'. (ed) TJ Parkinson. Pp 1-16,2002a. !. ••. McDougall S. Bovine mastitis: epidemio logy, treatment and control New Zealand Veterinary Journal 5 0 (supplement), 81-4, 2002b. !. ••. McDougall S. Ma nagement factors associated with the incidence of clinical mastitis over the non lactation period and bulk tank somatic cell cou nt during the subsequent lactation. New Zealand Veterinary Journal 5 1, 63-72, 2003. !. • •. M c Douga l l S, Parkinson TJ, Leyland M, Anniss FM, Fenwick SG. Du ration of infection a n d strain variation in Streptococcus uberis isolated from cows' milk. Journal of Dairy Science 87, 2062-72, 2004. !. • •. Mclnerney JP, Howe KS, Schepers JA. A framework for the economic analysis of d isease in farm livestock. Preventive Veterinary Medicine 13, 137-54, 1992. !. • •. Miles H, lesser W, Sears P M . The economic implications of bioengineered mastitis control. Journal of Dairy Science 75, 596-605, 1992. !. • •. M orin DE, Petersen, G. C., Whitmore, H. L., Hu ngerford, L. L., H inton, R. A. Economic analysis of a mastitis monitoring and control program in fou r dairy herds. Journal of The American Veterinary Medical A ssociation 202, 540-8, 1993. !. • •. Ott SL. Costs of Herd-Level Production losses Associated With Su bclinical Mastitis i n U.S. Dairy Cows. I n : 'Mational Mastitis Council Annual Meeting Proceedings' p 152, 1999. !. ••. Pankey JW, Pankey PB, Barker RM, Williamson J H, Woolford MW. The prevalence of mastitis in primi parous heifers i n eleven Waikato dairy herds. New Zealand Veterinary Journal 44,41-4, 1996. !. Pankey JW, Barker, R. M ., Twomey, A., Duirs, G. Comparative efficacy of dry-cow treatment. !. Petrovski KR, Trajcev M, Buneski G. A review of the factors affecting the costs of bovin e m a stitis.. • •. regimens against Staphylococcus au reus. New Zealand Veterinary Journal 30, 13-5, 1982 • •. Journal of the South A frican Veterinary Association 77, 52-60, 2006. !. ••. P h u e ktes P, Mansell P D, Dyson RS, Hooper ND, Dick JS, Browning GF. Molecular epidemiology of Streptococcus uberis isolates from dairy cows with mastitis. Journal of Clinical Microbiology 39, 1460-6,2001. • •. ! !. Pyorala S. New strategies to prevent mastitis. Reproduction in Domestic Animals 37, 211-6, 2002. ••. Rajala-Schultz PJ, Grohn YT, M cCulloch CE, Guard CL. Effects of clinical mastitis on milk yield in. !. S a n d holm M, Kaartin e n L, Pyorala S. Bovine mastitis--why does antibiotic therapy not always. d a i ry cows. Journal of Dairy Science 8 2 , 12 13-20, 1999 • •. work? An overview. Journal of the Veterinary Pharmacology and Therapeutics 13, 248-60, 1990. !. ••. Schepers JA, Dijkhuizen AA. The economics of mastitis and mastitis control in dairy cattle: a critical a nalysis of estimates pu b lished since 1970. Preventive Veterinary Medicine 10, 213, 1991. !. ••. Schukken YH, Kremer WDJ. M o n itoring udder health : objectives, materials and methods. I n : Herd h ealth and production management in dairy practice. Pp 351-426, 1996. !. ••. Seegers H, Fourichon C, Beaudeau F. Production effects related to mastitis and mastitis economics in dairy cattle herds. Veterinary Research 34,475-91, 2003. !. ••. S m ith A, Dodd FH, Neave FK. The effect of intra mammary i nfection d u ring the d ry period on the milk production of the affecte d quarter at the start of the succeeding lactation . Journal of Dairy Research 35, 287-90, 1968. !. Watts J L. Etiological agents of b ovin e mastitis. Veterinary Microbiology 16, 41-66, 1988. • •. :. Wellenberg GJ. The role of virus i nfections in bovine mastitis. Tijdschrift Voor Diergeneeskunde. :. Yalcin C, Stott AW, Logue ON, G u n n J. The economic im pact of mastitis-control procedures used i n. • •. 1 27,414,2002 • •. Scottish dairy herds with high bulk-tank somatic-cell counts. Preventive Veterinary Medicine 41, 135-4 9, 1999. :. Yalcin C. Cost of Mastitis in Scottish Dairy Herds with Low and High Su bcli nical M a stitis Problems.. :. Zadoks RN, Gillespie BE, Barkema HW, Sampimon OC, Oliver SP, Schukken YH.. • •. Turkish Journal of Veterinary and Animal Science 24, 465-72, 2000 • •. Clinical,. e pidemiological and molecul a r characteristics of Streptococcus u beris infections in d a i ry herds. Epidemiology and Infection 130,33 5-49, 2003. :. • •. Zadoks RN, Schukken YH.. Streptococcus. uberis:. environmental. or contagious. pathogen?. Proceedings of the 42ndAnnual Meeting of the National Mastitis Council,61-67, 2003. 11.

(35) 12.

(36) Chapter two. A review of t he fa ctors affecting the costs of bovi ne m astitis. Kiro R Petrovski\ Metodija Trajcei , Gjoko Bu neski. 2. 1/nstitute of Veterinary, Biomedical and Veterinary Sciences, Massey University,. Palmerston N orth,. New Zea land, a uthor for correspond ence. 2 Facu lty of Agric u ltural Sciences and Food, Un iversity "St. Cyril and M ethodius", Skopje, M acedonia. Publ is h e d : Journal of the South African Veterinary Association (2006}, 77(2} : 52-60. 13.

(37) References in t h i s chapte r a re u n u s u a l ly placed at t h e sta rt of the h e a dings/subhea d i ngs a ccordin g ly to the r u l es of publ i s h i ng i n st r u cted by t h e Journal of the South African. Veterinary. Association. Exa mple of the p ublish ed section is i n se rted : Cost of tlte drugs. (Refs t.l.lll. 11.14--16. 2l. �lt38..U. 4l.4\l,S2,.53). This part of the mastitis cost is easily calculated from the invoices of purchases of drugs on the {aTm. A similar calculation may be done for the expenditure on the treatment of individual cases.. Discarded milk. {Rill!: 1. a. 11. 14-16.23-25.:31, 3tl, 38. �. -42.43, 52. S3. &6. 67. 14, 78}. The assessment of th� cost of discarded milk should include the milk withdrawn during and after the treatment, which depends on the withholding periods of the drugs used and current regulations. The cost of discarded milk is usually estimated easily. In cases where mastitic milk is used for calf-rearing, estimation of the cost of mastitis should be carefully assessed. The system for accounting for. 14.

(38) 2. A review of t he fa ctors affecti n g the costs of bov i ne m a stitis 2.1 Abstra ct M astitis is o n e o f the m ost p revalent prod u ctio n diseases affecting the d a i ry cattle industry wo rld-wide. Its occu rrence is associated with d i rect a n d i n d i rect losses and expenditures. When estimating the cost of mastitis to the dairy i n d ustry the cost of the control p rogram mes must be added . Th e d i rect losses of mastitis a re the o n l y costs obvious to t h e fa rmer. The d ifference betwee n the costs of mastitis on o n e s i d e and the ben efits of m astitis control on the oth er side wi l l give us a p i cture of the economic efficacy of the m astitis control p rogramme. Co nti nuing education of the fa rm er is needed for better m astitis control p rogra m m es. This a rticle is an atte m pt to review briefly a l l relevant factors i ncluded i n the econ omics of bovi n e mastitis a n d to show the a uthors' view of some of the costs. Esti m ating the costs associated with m a stitis is n otoriously d ifficu lt. Th e eco n o mics of mastitis needs to be add ressed at the fa rm or herd level and d epends on l ocal, regi o n a l, e p idemiologicat m a n agerial and eco n o m ic co nditions. Some of the costs and expe nditu res are easy to calcu late and they s h o u l d be included i n resea rch p rojects dea l i ng with the modelling of the eco nomics o f the d isease. However, som e of the costs are n ot cou ntabl e, such as cases of h u m a n diseases, fa rmers' stress etc. To be able to consider the real cost of m astitis to the dairy industry, the p reva l e n ce a nd incid ence of m astitis o n a n ational l evel shou l d first be established . Then estim ations of all relevant co untable costs a n d expendit u re s should be m ade, and the last step wi ll be to incl u d e a l l of them i n one l a rge mod e l for m astitis cost estimation.. 2.2 Introd uction Mastitis i s d efined a s a n i n flammation of the m a m m ary gl a n d . l t is a com p l ex d isease i nvolving m a ny factors, which is m a i n ly caused by bacteria a n d th ere is no s i m ple mod e l t h at encom passes all possible facets (Schepers a n d Dijkhuizen 1991; Fetrow 2000). D espite i ntensive resea rch a n d the i m p lem entation of va rious mastitis control strategies over the decades, bovine m astitis has not disap p e a red and the red u ction in the p reva le nce o f sub-clinical m astitis has been m i n i mal ( Pyoral a 2002). On t h e other. 15.

(39) h a n d , there h a s been a co nsiderabl e decrease i n the i ncidence of clinica l cases of m a stitis worldwide as a result of these control measu res. Bovi n e m a stitis is consi d e red one of the most economically i m portant diseases for the d a i ry i n d u st ry i n d evel o ped cou ntries (Biosser 1979; Fetrow 1987; G i l l et al 1990; Sch e pers a n d Dijkhuizen 199 1; M c l nerney et al 1992; DeGraves a n d Fetrow 1993; Allore a n d E rb 1998; H o rtet a n d Seegers 1998a; Fetrow 2000; Pyorala 2002; Seegers et al 2003}.. M o ri n et al { 1993}, m onitoring 4 I llinois h erds for 12 months, reported. m a stitis-associ ated economi c losses ranging from US$161. 79 to $344.16 per lactating cow/year. The m agn itu d e of the economic losses to the dairy i n d ustry i n the USA due to m a stitis was a ro u n d $ 1 . 3 billion i n 1979 ( Blosser 1979) and aro u n d $2 billion in 1988 ( M i l e s et a l 1992) a n d 1993 (Cu l lor 1993) (not factored for inflation). The total financial cost of m a stitis to the average Scottish d a i ry herd i n 1996 was estimated to be £140/cow/yea r (Ya lcin 2000) of which a loss of £100/cow/year was d u e to sub-cli n ical mastitis alone in h igh B u l k Ta n k Somatic Cell Count (BTSCC) herds (Ya lcin et a l 1999). According to Ott ( 1999) the total p rod uction l oss due to mastitis in the USA is $ 108. 00 per cow for h e r d s with average BTSCC of 200,000-399,999 cells/m ! and $ 295.24 per cow for herds with average BTSCC 400,000 a n d above or losses of a p p roxim ately $1 bil l i o n to the USA dairy i n d ustry, based o n ly on BTSCC, as measu re of sub-cl i n ical m a stitis (Ott 1999}. There i s com m o n confusion between the terms ' loss' and 'cost', so it is i m portant to cla rify the term i n ology. In this article the fol l owing terms will be used as defined: a ) Loss i m p l ies a benefit that i s taken away (e.g. the p roduction loss exp e ri enced because conta minated. milk m u st be discarded ); a lternatively, it. represents a potential ben efit that is not realised (such a s an evident d ecrease in the m i l k yield ) ( M cl n e rn ey et a l 1992; Seegers et al 2003}. b) Expenditure represent some economic effects of disease that a re man ifested as extra i n puts i nto livestock prod u ction (such as treatment a n d p revention of m a stitis) ( M c l nerney et a l 1992; Bennett et al 1999; Seegers et a l 2003).. 16.

(40) c) Economic cost is the mon etary value of all the economic effects, both losses a n d expenditures, conseq uent u pon the occu rrence of d isease {Mcl nerney et al 1992; Be n n ett et a l 1999; Seegers et a l 2003 ). Th i s a rticle briefly reviews all the relevant factors i n fl u enci ng the economic cost of bovi n e m astitis.. 2.3 The cost of m a stitis to the d a i ry i n d u stry Th e re h ave bee n many articles p ublished worldwi d e on the economics of m a stitis . When consi dering the cost of a ny d isease, it m ust be kept i n m i n d that every d isease has d i rect and i n d i rect costs. Ben nett et al (1999) esti m ate that the total costs of each d isease can be much h igher tha n the di rect expe n d iture. Most of the available est i m ates take i nto account o n ly a p a rt of the real cost of mastitis, as esti mating the tru e costs associ ated with m astitis is n otoriously d ifficult. lt is even m o re difficult to q u a ntify the losses associated with sub-cli n ical mastitis, beca use they are n ot visible to fa r m owners. To avoid u n d erestimating the consequ ences of m astitis in eva l u ations of eco n o m i c-loss it is i m p o rtant to account for a ll of the cost factors i nvolved. Th e esti mation of the eco n o m i c costs associated with mastitis d epends o n having the fo l lowi n g data: 1. An estimate of the i ncidence and p revalence of m a stitis in the popu l ation i s a p re req u isite for the estim ation of its real cost to the d a i ry i n d ustry. There is cu rrently a ge n e ra l demand of regu l a r mon itoring, reco rd i n g a n d research to establish the i n c i d ence and p revalence o f mastitis . 2. Th e severity of the p hysical effects o f m astitis o n m i l k p ro d uction, which wi l l d ep e n d o n m a ny factors, such as virulence of t h e m astitis-causing o rgan isms, stage o f lactation, age o f t h e cow a n d udder defence mechanisms. 3. I d entification of the p revention a n d t reatment measures undertaken. lt is generally easy to calculate the expen d it u re o n m a stitis control . 4 . Va l u ation of the prod u ction losses, t reatments a n d expen ditu res on preventi o n a n d control i n cu rred . Prod u ction losses caused by mastitis a re l ikely t o b e infl ue nced by t h e a ge, b reed a n d type of t h e cow, stage o f lactation, m i l k yield before mastitis occu rred,. 17.

(41) m i l k p rice, p re m i u m s a n d p e n a lties, m astitis-ca using orga nism, inflammation grade and distrib ution, d iagnosis, treatment cost, prevention cost and a n a lytical model.. 5. Other costs' factors- e.g. fa rm m a n agement, culli n g, replacement and fatalities. M a ny tech n i q u es and methods h ave been used to estimate p rod uction losses from m a stitis in d a i ry cattle. M ethods com m only used a re: producer su rveys, regression a n a lyses relating m i l k somatic cell cou nts, between-herd com p a risons, betwee n-cow yield com parisons, within-udder yield com parisons, with i n-cow yield com p arison a n d stu dies between identical twi ns. De G raves and Fetrow ( 1993} state that none o f t h e tec h n i q ues u s e d a re perfect, d u e t o l ack o f d irect measure o f h o w m uch m i l k a cow wou ld h ave p ro d u ced if there was no occu rrence of m astitis d u ri n g lactation, a n d they all h ave a degree of i n herent b ias, wh ich, in most cases, tends to underest i m ate the act u a l m i l k yield d ecrease that has occu rred. The econom i cs of m astitis n eeds to be addressed at the fa rm or herd l evet and d e p e n ds on local, regional, e p i demiologicat ma nagerial and economic cond itions. At t h e h e rd levet a s stated by Seegers et a l (2003L some com pensation o r b uffer mechanisms ca n a ct a n d this should be taken i nto consid eration i n the estim ates. An exa m p l e is a far m e r who d ecides to cu l l cows with h igh so matic cell count (SCC), based on the BTSCC a n d the m i l k p ricing system, rather than on the a bsolute values of the i ndividual SCC resu lts of the cows. Another exam ple i s a farmer who decides to cull an extra cow to d ecrease the BTSCC a n d give up selling a h eifer (Seegers et al 2003 ).. 2.4 Losses ca u sed by mastitis 2.4. 1 Direct losses of mastitis Direct costs of m a stitis to the d a i ry i n d ustry i n c l u d e the costs of treatment (veteri n a rian's t i m e a n d d rugsL d isca rded m i l k (during both the course of treatment a n d with-hold i n g periods) herdsman's time, fata lities a n d the costs associated with repeated cases of m astitis. I n m a ny cases d i rect losses a re the o n ly cost of mastitis realised by the fa rmers.. 18.

(42) 2.4. 1 . 1 Treat m e nt cost. (Biosser 1979; Bishop et a l 1984; Kirk 1984; F etrow 1987; Lightn er 1988; H o l d away 1990; Fetrow et al 199 1; Beck et al 1992; M i les et al 1992; DeG raves and Fetrow 1993; M i l l er et a l 1993; Lesco urret and Coulon 1994; Kossaibati and Esslemont 1997; Leh enbauer and Oltjen 1998b; Fetrow 2000; Pyorala 2002; Seegers et a l 2003; B erry et a l 2004; S h i m et al 2004; Swi nkels et a l 2005 ) The cost of treatm ent of cl i n ica l cases is an i m porta nt element i n the expenditure o n mastitis. Very commonly, the size o f the vete rinaria n s' bills t e n d s t o be seen as 'the cost of d isease' in the fa rmers' eyes. I n fact, in genera l, the treatment of a d isease, such as m astitis, is o n ly a small p roportion of the disease cost (Kossaibati a n d Esslemont 1997). When est i m ating the treatment cost, the efficacy and cost effectiveness s h o u l d be taken i nto accou nt. For example Shim et a l (2004) comparing two treatment p rotocols fou n d that the ad dition of a nti microbials to supportive treatment is m o re effi cacious and cost effective than su pportive treatment alone, projected that cows witho ut mastitis wil l p ro d uce 8.265 kg of m i l k (305-days i n lactation). Cows t reated with s u p po rtive treatment o n ly prod u ced at 7838 (3.064-11.111) kg of m ilk, wh i l e cows with added a nti m icrobial to the treatment p rod uced 7975 (5.002- 1 1 . 163) kg, when d isca rded m i l k was i ncluded (Shim et a l 2004). Assu m i n g that n o ne of the u n m a rketable m i lk was fed to ca lves the cost of mastitis was 3 times h igher i n the gro u p treated o n ly with supportive treatment (Shi m et a l 2004). There a re two elem ents of the treatment cost: veterin arians' fees a n d the cost of d rugs. In a d d ition to the fi nancial consid erati ons, the treatment of cows with clin ical mastitis is d isru ptive to the normal m i lking routine ( H oldaway 1990; Fet row 2000). 2.4. 1 . 1 . 1 Veterinary time and consultation fees (Biosser 1979; Bishop et al 1984; Kirk 1984; Craven 1987; Fetrow 1987; Morse et a l 1987; Lightner 1988; Holdaway 1990; Beck e t al 1992; Hillerton e t al 1992; Cu l l o r 1993; DeG raves and F etrow 1993; M i l ler et al 1993; Morin 1993; Allore and E rb 1998; F et row 2000; S h i m et al 2004). 19.

(43) Th e veteri n a ry t i m e a n d consu ltation fees can vary considerably in a m astitis control progra m m e . These services a re charged on an hou rly basis, per-cow-per-yea r basis, or other m ethods. Th ey ca n be a p p lied to the i n d ivi d u a l cow, group of cows or the whole herd. Veterinary time for the treatment of i n d ivid u a l cows with cli n ica l m astitis usually i nvolves a m i n i m a l a m o u nt of herd-level consultancy and the cost per cow can be calcu lated from t h e i nvoices. The cost at the fa rm l evel may d epend o n the n u mber of visits by the vet e ri n a ri a n . For exam p l e in the N ordic countries a l l m astitis cases are atten d ed by a veteri n a rian. I n most othe r cou ntries, such as South Africa, USA, Aust ra lia a n d N ew Zea land, the veteri n a rians attend o n ly some cases of m astitis. I n such situations, t h e ca lcu lation o f costs on a per cow basis, from data collected a t the fa rm level, needs some modelling. G ro u p l evel service includes t reatment a n d p revention of mastitis in a speci fic gro u p, such as age-catego ries, h eifers o r newly p u rchased cows. I n this case, part of the veterinary ti m e i s clinical work, and u su a l ly there wi l l b e some consu ltancy ti m e as well. Ca lcu latio n of the estim ated cost per cow in such a case is d ifficu lt, as it is u n kn own how m uch cons u ltancy time has been spent per individ u a l an imal. The usual a p proach is to divide the a m o u nt on the invoice by the n u mber of anima ls attended. M ost of the ti m e when d e a l i n g with herd p roblems is spent on consultancy work, for exa m p l e dea l i n g with high BTSCC herds or mycoplas m a m astitis affected herds. I n this case o n ly a s m a l l a mo u nt of time is utilised as real veterinarian clin ical work. The calculation of t h e esti mated cost of this elem ent is from the invoices. Th e fees a re usually charged at the farm level, and if i n dividual cow-cost is req uired, then some model l i n g can be utilised, or the amount o n the i nvoices is si m p ly d ivided by the n u mbers of cows in the herd. 2.4. 1. 1.2 Cost of the drugs (Anderson a n d B lackshaw 1977; Blosser 1979; Kirk 1984; Craven 1987; Fetrow 1987; M o rse et al 1987; Lightn e r 1988; Holdaway 1990; H i llerton et al 1992; Cullor 1993; DeG raves and F et row 1993; M i ller et al 1993; Morin 1993; Lescourret a n d Coulon 1994; Al l ore and Erb 1998; Berry et a l 2004}. 20.

(44) Th is part of the m astitis cost is easily ca lcu lated from the i nvoices of p u rc h ases of drugs on the fa r m . A si m i l a r calculation may be done for the expe n d it u re o n the treatment of i n d ivid ual cases. 2.4. 1 . 2 D i scarded m i l k. (Biosser 1979; Bishop e t al 1984; Kirk 1984; Craven 1987; Fetrow 1987; M o rs e e t a l 1987; Lightner 1988; Holdaway 1990; Fetrow e t a l 1991; Beck et a l 1992; Cu l lo r 1993; DeG raves and Fetrow 1993; Morin 1993; Lescou rret and Co ulon 1994; Kossaibati and Esslemont 1997; Allore a n d Erb 1998; Fetrow 2000; Seegers et a l 2003; W i n kelman 2003; S h i m et a l 2004; Swin kels et al 2005} Th e assessment of the cost of d iscard ed milk sh ould incl u de the milk withd rawn d u ring and after the treatment, which depends o n the with hold ing periods of the d ru gs used and cu rrent regu lations. The cost of discarded m i l k i s usually esti m ated easily. I n cases where mastitic m i l k is used for ca lf-rearing, esti mation of the cost of m a stitis s h o u l d be ca refu l ly assessed . Th e system for acco u nting for the econo m ic costs associated with 'discarded m i l k' s h o u l d be transparent. No m atter wh ere it ends u p the m i l k is n ot sold, so it is a loss of i ncome. A possible solution is to budget for the eco n o m ic costs of mastitis to be debited with the full costs of the m i l k not sold and the calf reari ng budget to be cred ited with the va l u e of the milk as a rep lacement for a lternative sources o f feed. I f the esti mates of m i l k losses are calcu lated on basis o f BTSCC, then disca rded m i l k i n many cases is not taken i nto accou nt, lead i ng to u n d e restim ates of real m a stitis costs (Lightner 1988}. In many d a iry countries it is common p ra ctice for the fa rm own ers of h erds with average high BTSCC to with hold or d iscard t h e milk from t h e cows with highest sec aiming to control their bulk milk i n acceptable l evels. 2.4 . 1 . 3 labour cost. There a p pear to be two main a p p roaches in the literatu re for d ea l i n g with the exp e n d it u re on l abo u r fo r mastitis treatment. The fi rst one is to consider the l abour time as a d i rect cost o f the disease a n d i n c l u de it i n the calcu lations a s s u ch ( Biosser 1979; Bishop et a l 1984; Kirk 1984; Morse et al 1987; Lightner 1988; Mcl nerney et al 1992; C u llor 1993; DeG raves a n d Fetrow 1993; Miller et a l 1993; M orin 1993; Lescou r ret and Cou l o n 1994; Allore and Erb 1998; Seege rs et a l 2003; W i n k e l m an. 21.

(45) 2 003 ) . Th e secon d approach is to calcu late the labour cost if a farm specifica lly e m p loys a d d ition a l labo u r to man age treatm ent, segregation, or other aspects of m a stitis control ( F etrow 1987; Fetrow et al 1991; Fetrow 2000). The m ore usual case is t h at m astitis control a n d treatment are h a n d led by existing farm labou r (Mori n 1993) ( i . e . no labo u r reduction wou l d occu r if m astitis cases were red u ced). In a uthors o p i n ion, the workers' time should be included i n the calculations of mastitis cost. The estim ation of t h e time spend per case is va riable a n d will depend on many factors, such as type of m a stitis, m i l k yield, fa rm size, h i red labour, farm owner etc. For exa m p le, a peracute case of mastitis, a ssociated with general i l l ness, req u i res m ore time for treat i n g, n ursing a n d freq uent strip ping than m i ld subacute mastitis with o n ly changes i n t h e m i lk. 2.4.1.4 Fat a l ity. ( Ki r k 1984; F etrow 1987; Beck et al 1992; C u l ler 1993; M iller et al 1993; Morin 1993; Kossaibati and Esslem ont 1 997; Hortet a n d Seegers 1998a; Pyora l a 2002; Seegers et al 2003) Severe cases of m a stitis can lead to the d eath or e uthanasia of the affected cow. The cost of a fatality is greater than simply the val u e of the cow i n th e m arket, as it i n c l u des the lost m a rgin from the incom plete portion of its l actatio n . According to Kossaibati a n d Esslemont { 1997) it also i n cl u d es the cost of a replacement heifer. Th e mortality rate for clinical m astitis is usu ally low. Wilesmith et al ( 1986) reported between 0.3 a n d 0 . 6% of m a stitis cases to be fata l . Worldwid e, higher mortality rates caused by m astitis are seen in specific situations with a high p revalence of Gram negative i n fectio n s, p a rticu l a rly coliform mastitis. Men zies et a l (2003) recorded a fatality rate of 14% a n d a further 21% early culling because of the cond ition in a study involving 264 c a ses of acute and peracute toxic mastitis i n Northern I reland. In contrast, B radley a n d G reen {2001) reported a mortality rate of 0 .6%, in general, and 2.2% d u e to G ra m-negative o rganisms in 6 Somerset dairy herds. 2.4. 1.5 Repeated cases of m a stitis. Som e d a i ry cows suffer repeatedly from m astitis d u ring a single lactation. Kossaibati a n d Esslemont ( 1997) fou n d that a typically affected cow suffers on average 1 . 6 cases. 22.

(46) per lactation. The extra costs of that 0 . 6 repeat case shou l d be taken i nto a ccount wh e n assessing losses caused by mastiti s . For these repeated cases o n ly the relevant d i rect costs should be included (i.e. cost of drugs, h e rdsman's a n d/or veteri n a ri a n ' s t i m e a n d discarded m i l k ) . For t h e indi rect costs, i t is important t o calculate o n l y a d d itio n a l losses associated with fu rther decrease i n m i l k yield a n d i ncreased risk o f c u l l ing. The rest o f the indi rect costs usually have been a l ready taken into acco u n t .. 2.4.2 Indirect losses of mastitis I n d i rect l osses d u e to mastitis, p a rticularly the subclin ical form, a re n ot well-recogn ised by m a n y farm ers. lt is genera l ly a ccepted that subcli n ical mastitis accou nts for the m ajority of economic costs of mastitis. Education o n this m atter is necessa ry beca use u n-recogn ised i n d i rect losses can be a reason for d ifficult i m p l e mentation of m astitis control m easu res, as farmers usu a l ly h old an opinion that their own losses, d u e to m a stitis, are m uch lower than the estim ates p rovided for the i n d u stry by the e x perts ( B rown et a l 1988). I n d i rect l osses include the d ec reased m i l k p roduction d u e to clinical o r sub-cl i nical m astitis, decreased milk q u a l ity, increased c u l l i ng, l oss of premiu m s, pena lties, p re-term drying-off, a n i mal welfa re aspects and other associated health p roblems. 2.4. 2 . 1 Decrease i n m i l k yie l d. (Smith et a l 1968; Blosser 1979; Bishop et a l 1984; Kirk 1984; Craven 1987; F etrow 1987; Lightner 1988; Bartlett et al 1990; H o ld away 1990; Fetrow et al 1991; Beck et a l 1992; H illerton e t a l 1992; M c l n ern ey e t a l 1992; M i les e t a l 1992; C u l l o r 1993; DeG raves and Fetrow 1993; M i ller et a l 1993; M o ri n 1993; Kossaibati and Ess l e m o nt 1997; Allore and Erb 1998; Hortet a n d Seegers 1998a; Lehenba uer and Oltjen 1998b; Fetrow 2000; Pyorala 2002; Seegers et a l 2003; M u ngube et a l 2005; Swi n ke l s et a l 2005 ) The m a in factor i n causing economic l osses d u e to both clin ical a n d sub-cl i n ical m a stitis is a m o re or less persistent decrease in m i l k yiel d . Usually there will be a short-term dep ression i n yield of va riable severity and, i n case of no m icrobia l cu re and recovery, a lon g e r lasting effect, so m etimes carrying over i nto the next l a ctation/s. M i l k prod u ction l osses are typ ica l ly estim ated t o acco u nt for 7 0 t o 80% of a l l m astitis losses. 23.

(47) i n a typical h e rd ( Ki rk 1984; G i l l et al 1990; Schep e rs a n d Dij k h u izen 199 1; DeG raves a n d Fetrow 1993; M orin 1993; Lehenba uer and Oltjen 1998b; Fetrow 2000). Losses in m i l k yield (not i n cl u d i ng d iscarded mi lk) n eed to be assessed within several t i m e-fra m es. There a re the short-term effects on the cu rrent lactation and long-term effects, i n cl u d i n g carry-over effects i nto the next lactation o r beyond, that a re usually esti mated using several types of comparison or modelling a p p roaches (Hortet a n d S eegers 1998a; Seegers e t a l 2003} . Estim ates o f m i l k y i e l d loss a re stil l u n d e r debate a n d l i kely t o be i nfluenced b y t h e age, breed a n d type of cow, morphologica l chara cteristics of the u d der, stage of lactation, p regna ncy status, m i l k yield befo re m astitis occu rred, mastitis-causing o rga n ism, i n fl a m m atio n grade, d u ration a n d d istribution, d iagnosis (early or l ate after the occu rrenceL treatment, feed i n g p ractices, season, recu rrence of mastitis d u ri n g the s a m e o r p revi o u s l a ctation, com p a rison model (wh at is the control group) and the a n a lytical m o d e l . lt is generally a ccepted that m astitis occurring earlier i n t h e lactation wi l l l e a d to greater m i l k yield losses. Lescourret a n d Cou lon ( 1994) reported that m i l k production c u rves of about o ne third of the cows infected ea rly in lactation were l ittle a ffected a n d yield recovered in less than 5 weeks. The p roduction cu rves of the rest of the i n fected cows w e re m a rked ly a ffected or the cows were culled. In contrast, more than h a lf o f the cows i n fected from mid- to late-lactatio n were n ot affected by m a rked m o d ifications in their m i l k p ro d u ction cu rves and recovered i n less than 5 weeks (Lescou rret a n d Coulon 1994). lt has been reported t h at the m i l k yields of older cows were obviously a ffected if mastitis occu rred early in lactation, while you n ger cows' yie l d s a re sensitive with carry-over effects seen if mastitis occu rred after the peak of lactati o n ( Raja l a -Sch u ltz et al 1999; Fetrow 2000}. Raj a la-Schultz et al ( 1999) a n a lysed reco rds of over 24,000 F i n n ish Ayrshire cows, a n d reported that milk p roduction declined 4 weeks before the onset of clinical m astitis a n d d ropped fu rther below the cu rve of "healt h y" cows d u ring the fi rst week afterwards. M i l k yield n ever reached the pre-m a stitis l evel s if mastitis occurred i n ea rly lactation (before peak) (Raj a la-Sch u ltz et al 1999} . A d ecreased m i l k p ro d u ction before the occu rrence of clin ical mastitis was p res u m ably d u e to the effects of s ub-cl in ical i nfection.. 24.

(48) A higher level of m i l k yield prior to m astitis could be expected to be associated with higher losses in m i l k (both in absol ute va l ue and in percentage) (Lesco u rret a n d Co ulon 1994; Hortet and Seegers 1998a). Th e pathogenesis of mastitis, i n m a n y cases, includes damage to secretory tiss u e and its replace ment with fibrous tissue leading to a perman ent decrease in m i l k yi e l d from the affected q u a rter (Ben ites et a l 2002). I n addition, it is p robable that p a rt of the decrease of the milk prod uction is due to an increased dem a n d for energy by the i m m u n e system, a decreased appetite a ssociated with the infl a m m atory p rocess and lowered feed intake due to pain and decreased mobi l ity. Som e mastitis-causing orga nisms were s h own to have a more p rofo u n d im pact o n m i l k yie l d s t h a n oth e rs (DeG raves and Fet row 1993; Wi lson et a l 1997; Fetrow 2000}. M astitis caused by Staphylococcus aureus genera lly evolve i nto persistent but m o d e rate infections, u nl i ke mastitis ca used by coliforms. Thus, t h e m astitis-causing o rga n ism m ay contribute to the resi d u a l va riation of responses, as wel l as to the level o f i nten sity. Gen erally it is estimated th at the greater the infl a m m ation the l ess m i l k is p ro d u ced. There a re three broad gro u ps of co m p a rison models: ( 1) between h e rd com p a rison, (2) between-cow o r within- h erd com parison, a n d (3) between-q uarter o r with i n -udder com p arison. A co m parison of the relative yields of h e rds with va ryi n g l evels of m a stitis m a y be u sed to estimate the decrease in m i l k prod uction. H owever, in this type of stud y, factors oth er than m astitis m ay significa ntly co ntribute to a n y d ifference i n m i l k yi e l d that may be observed. The h erds i ncluded in t h e study m ust b e closely m atched for factors such as location, breed, a ge, and p l a n e of nutrition. The between-cow com pa rison model is also affected by some non-m astitis com p o u n d ing factors s u ch as age and breed a n d the cows m ust be closely match ed for such factors. With i n -u dder yield com pariso n s compare a mastitis-infected q u a rter with a n op posi n g mastitis-free q ua rter. Generally it is accepted that the contra-l ateral q u a rters of the u d d e r, when both a re un-infected, give approxi m ately the same volume o f m i l k. H owever, while with i n-udder compa rison avoids sou rces of variation which may confo u n d other est i m ates of d ecreased milk p rod uction, it is possible that with i n the infected cow, un i n fected q u a rters partially com pensate by p roducing more milk or both p roduce less as. 25.

(49) the cow i s sick. There is evi dence that mastitis-free quarters may com p ensate for q u a rters with m a stitis by increasing m i l k p roduction (Holdaway 1990; Holdaway 1993; M cDouga ll 2002). If com pensation d oes in fact occur, then this would cause over estimation of t h e a ct u a l milk loss as a resu lt of m astitis {DeG raves a n d Fetrow 1993; Holdaway 1993). H o rtet a n d Seegers { 1998}, usi n g a regression-mod elling a p p roach to a n a lyse d ata fro m 20 papers published worldwide, predicted the average m i l k-yield loss over t h e lactation was 300-400 kg (i.e. 4-6%) per treated case of clin ical m astitis in a H olstein F ries i a n cow p roducing a pp roxi m ately 7,000 kg/lactation. I n pri m i p a rous cows, the average l oss was l ower {200-300 kg) a n d m ild patterns of m astitis were m ore freq uent than i n m u lt i p a rous o nes. Cases occu rri n g before the peak of l actation were a ssociated with h igh er average losses {450-550 kg) than cases occu rrin g later. S i mi larly Seegers et al { 2003) esti mated loss of abo ut 375 kg {5%) per average cli n i cal case, occu rri n g in the s eco nd m onth of l actation in a H o lstein cow. The esti m ates n eed to be used with caution, especially for breeds oth e r th a n H o lstein F riesian or if u n u s u a l m astitis-causing o rganisms a re invo lved in clinical-mastitis cases ( Ho rtet and Seegers 1998 a ) . 2.4.2. 1 . 1 Short term effects ( Beck et a l 1992; Houben et a l 1993; Hortet a n d Seegers 1998a; Rajala-Sch u ltz et a l 1999; Fetrow 2000) For the estim a t i o n o f short term effects, it i s n ecessa ry to bear in mind t h at an i n fection can sta rt a n d the m i l k yield can be redu ced before the m astiti s is d etected. This may lead t o u n d e restimation of the real loss from mastitis ( Raja la-Schultz et al 1999). H o rter a n d Seegers {1998a) using regression models estimated that short-term l osses fro m c l i nical cases of m a stitis varied from 0 to about 3 kg/cow/day, but suggested that the estimates a re lower than expected. They s uggested that regression m odels u nd e restimate s h o rt-term losses, beca use of the d ifficulty in acco unting for va riabl e losses occu rrin g before a cli n ical diagnosis. Short-term red u ction i n m i l k yield is h igher for clinical mastiti s in ea rly lactation com pared to m a stitis i n mid to late lactation. Losses from 0 to 200 kg/cow/m onth. 26.

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