The d ata analysed i n this study were i n itially gen erated by Ceci lia Fernan dez d u ring the a n i m a l p hase of her i nvestigations on "Th e effect of extern al teat seala nts on m a stitis i ncidence d u ring the dry period un der experimental challenge with Streptococcus uberis. " (M aster of Applied Science thesis, subm itted, 2007). The d ata u sed i n the p resent study were extracted from the regu lar herd tests i n the fo llowi n g lactation from the fa rm that was used in her stu dy.
The work of Fernandez was u nderta ken to assess the efficacy of two d ifferent substances used at d ryi ng off as extern al teat seala nts in prevention of I M I fol l owing experim ental challenge of the teats with Streptococcus uberis i n the early dry period. The p roducts used for sea ling teats were based on a com mercia l ly available teat sealant (tetra hyd rofura n : DryFiex) and on a wou nd sealant for use in h u m a n s (2- octylcya noacrylate: Ban d-Aid ).
Her study was cond ucted based on the following:
1. There are two main periods of high suscepti bi lity to mastitis d u ring the d ry period, namely the periods of active i nvo lution and colostrogenesis.
2. From the 1960s the use of d ry cow th erapy a ntimicrobials has been p racticed i n order to eli minate existing a n d p revent n ew I M I duri ng t h e d ry period .
3 . Th e extensive use of a ntim icrobials to treat and control mastitis h as con seq uences for h u man health, through a n i ncreased risk of i ntroducing resid ues i nto the food chain and the em ergence of a nti microbi al-resista nt orga n isms.
4 . Non-antibiotic means for the treatment and prevention of mastitis h ave the potential to create widespread ben efits from red ucing the n eed for a ntibiotics. One h u nd red a n d seventy five cows with four fu nctional quarters, low ICSCC a n d no evide nce of clinical mastitis were enrolled in the study, a few d ays p rior to d ry-off. Single-q uarter milk samples were taken for microbiological cu ltu re, fou r and o n e days before dry-off, and a gain on two occasions within four days after calvi ng. At drying off,
e n rolled cows were split i nto two grou ps, with 88 cows receiving mod ified "DryFiex", external teat sea lant available on the USA ma rket, and 87 receiving "Band Aid", liquid bandage, i n two contra-latera l quarters (i.e. LF a n d R H ), while the other two q uarters were left as u n t reated controls. All cows were challenged on two occasions with a b roth culture of Strep uberis, by dipping a l l quarters, two and fou r days p ost d ry-off a n d treatment. Assessment for clinical mastitis was su bsequently performed d aily o n all quarters.
The results fro m this stu d y demonstrated that the high est frequency of mastitis occu rred b etwee n Days 6 a n d 11 after dry-off and treatment. After adjusting for the effects of treatment and i n d ividual cow-level, the daily hazard of clinical m astitis in cows identified as i nfected at dry-off was 1.64 {95% Cl 1.10 to 2.44) times that of u n infected cows. Modified DryFiex provided p rotection agai nst the bacterial challenge for 5 0% of the q u a rters for fou r days. At the gro u p l evel, th ere were 35 CM events out of 176 treated q u a rters with modified D ryFiex, com pared to 83 events i n the u ntreated q u a rters { 176). For the Band Aid treated gro u p, 67 CM events occu rred in 174 treated quarters, com p a red to 64 events in the u ntreated quarters {174).
Based on the resu lts from this study it was concluded that the application of D ryFiex at d rying-off was b eneficial in reducing mastitis caused by Strep. uberis chal lenge. Contrari ly, the use of Band a i d at d ry-off had no benefit in reducing the incid ence of m a stitis followi n g two experim ental Strep. uberis exposu res.
All of the cows that develo ped clinical m astitis were treated (with antimicrobials i ntra m a m m a ri l y or systemically when all fou r quarters affected) p romptly, resu lting in a clinical cure within {3-4) d ays.
This study gen erated a su bst a ntial group of cows that had had a b rief period of clinical mastitis in their early d ry period. As most of these cows { 165) rema ined i n the herd for a fu rther lactation, the o p portun ity was p resent to eva luate various parameters of their l actational performance. This was u n d ertaken, as d escri bed in the rem ai nder of this chapter, by co mparing the performance of cows that developed m astitis with those that d i d n ot.
Effects of Experi menta l ly I n d uced a n d Treated
Streptococcus
uberis
Mastitis Ea rly i n the Dry Period on Pro d u ction i n theSubseq uent Lactation
Ki ro R. Petrovski§, Norman B. Williamson, Cecilia Ferna ndez, Alex G rinberg, N icolas Lopez-Vi lla lobos and Timothy J . Parkinson
Institute of Veterinary, Biomed ical and Veteri nary Scien ces, Massey U n iversity,
P a l m erston N o rth, New Zealand,
§ Author for Co rrespondence
P u blish ed:
4. Effects of Experi menta l ly In d uced a n d Treated
Streptococcus
uberis
Mastitis Ea rly i n the D ry Period on Prod uction i n the Subseq uent Lactation4.1 Abstract
Th e effect of experimenta lly ind uced cl i n ical mastitis in the early dry period (EDPCM) u pon the milk p roduction in the su bseq uent lactation was exam i ned. An imals with low somatic cell cou nts at herd test (n=165) were experim enta l ly exposed to Streptococcus uberis in their early dry period i n an efficacy study of two external teat sealants. Ani m a ls that d eveloped EDPCM after ch allenge (n =127) were treated with an a ntibiotic after o bservation of clinical m astitis. Tota l lactation yields of m i l k, fat, protei n a n d m i l k solids were a na lysed with respect t o treatment grou p (fixed effect) a n d the covariab les: ca lvi n g week (l in ear), pa rity (linear and quadratic) and proportion of Holstein-Friesian genes (lin ear). For animals that suffered EDPCM and th ose that did not, there was no difference in p roduction ( m i l k yield ; 5126 vs. 5010 litres, fat yield; 267 vs. 264 kg, protein yield ; 182 vs. 179 kg). lt was concl uded that prom ptly t reated EDPCM due to Strep. uberis did not affect pro d u ction in the su bseq uent lactatio n .
4.2 Introd uction
Bovi ne m astitis is one of the most economica l l y im portant d iseases affecti n g t h e dairy cattle industry internationally (Hortet and Seegers 1998; Seegers et a l 2003). M astitis was estimated to have cost the New Zealand dairy ind ustry a ro u n d N Z$ 180 m i l lion/year in 2005/06 (Anonymous 2006). M any factors have been associated with the cost of mastitis, incl u d i ng stage of lactation, p regn ancy status, p rior yield, m a stitis causing organism, severity, di agnosis (ea rly or late after occu rrence), treatment and recurrence of m astitis. The main factor (70-80% of all losses) is red uced m i l k yield . M oreover, as the pathogenesis of mastitis resu lts in irreplaceable loss of secretory tissue, this loss of milk yield can be permanent (Benites et al 2002}.
Short-term depression i n milk yield occu rs when cows d evelo p mastitis d u ring lactation, with more severe losses occu rri n g if it occurs early in lactation and there is a fai l u re of microbial cu re or when the effects of the mastitis carry over into su bsequent
l a ctations ( Houben et al 1993; Hortet and Seegers 1998; Rajala-Schu ltz et al 1999). Adverse effects on m i l k com position (Seegers et al 2003) increase economic losses. P roduction effects of clin ical mastitis res u lt from both short- and long-term decreases in milk p roduction, particularly associated with chronic mastitis (Sm ith et al 1968; F etrow et a l 1991; Raja la-Sch u ltz et al 1999).
Less is known a bout the effects of clinical mastitis du ring the d ry period, on milk p roduction i n s u bseq u ent lactations. Th e dry period is an important part of the l a ctational cycle d u ring which the m a m mary gland p repa res for the next lactation. Clinical m astitis d u ring this period may slow the process of m a m m a ry tissue remodelling, there by adversely affecting m i l k yield in the subseq uent lactation.
Streptococcus uberis is the most significant cause of clinical bovi n e m astitis in N ew Zealand and Austra lia (Pan key et a l 1996; Douglas et al 2000; Phu ektes et al 2001; M cDouga l l 2002) where the dairy industry is p redominantly pastu re based . Information is l a cking a bout the effects of clinical mastitis in the e arly d ry period ( E D PCM) on m i l k p roduction in the subsequent lactation. A p reviously cond ucted study with different o bj ectives p rovided an o p portunity to fu rther understand any im pact of treated Strep. uberis mastitis on p roduction parameters in the following lactation . I n t h i s post h oc a n a lysis, t h e effects o f experi menta lly induced and p rom ptly treated
Strep. uberis c l i n ica l mastitis early in the d ry period on m i l k p rod uction in the subsequent lactation have been analysed.
4.3 Mate ri a l s and m ethods
4.3. 1 Animals and experimental design
A total of 175 cows (H olstei n-Friesian ( H F ) and H F-J ersey crossbreds ) were selected fro m the M assey Un iversity #4 herd, located i n the M a n awatu Region of N ew Zealand to p a rtici pate i n a p rospective, ra ndomised, control led field trial of the efficacy of two external teat s e a l a nts. Ten cows were excluded from analysis i n this study due to missing p roduction d ata, leaving 85 cows (modified DryFiex) and 80 (i nvestigation al external teat sea lant). The herd was managed at pastu re, with s u pplementary hay/si lage as req u i red. Selection criteria for cows in this trial were :
(ii) fo u r functional quarters a nd,
(iii) no cl inical signs of mastitis or teat abnormalities at enrolment.
All a n i m a l mani p ulations were approved by Massey University Animal Ethics Comm ittee (M UAEC 04/165 ).
4.3.2 Challenge protocol
The Strep. uberis strain used for the chal lenge was initially isolated by Douglas et al (2000) in the Horowh enua district, Wel li ngton regio n, p henotypica lly id entified as 99.9% p robable to be Strep. uberis, by means of biochemical tests, and kept frozen at - 80QC at the Institute of Veteri nary An imal and Biomed ical Sci ences M icro b iology Laboratory. All cows were exposed to the cha l lenge broth on two occasions, two and fou r d ays after dry off, by dip ping of each teat, entirely, fo r 1-2 seconds in a suspension of 1. 1 5x 108 cfu/ml of the cha l lenge stra in.
4.3.3 Milk sampling
Qua rter milk sa m ples were aseptically collected, following N ational Mastitis Council (NMC) recommendations (and stored on ice) b efore m orning milking on 4 occasions:
(i) 4 days befo re d rying off, (ii) one day before drying off, ( i i i ) the day of ca lvi ng and,
(iv) 3-4 days postpartu m .
Sam p les were subjected to routine m icrobiologica l cult u re and examination o n t h e day of collection following N M C recom mendations.
4.3.4 Clinical assessment and treatment
All q u arters were exa m i ned d aily by an experienced d airy tech nician for the p resence of m a stitis from the time of the first exposu re u ntil 29 days later. Individ ual q u a rters were observed a n d pal pated for' the clinica l signs associated with mastitis, i . e. h eat, swelli ng, redness, painfu l quarter/s and if req uired, by an examination of the secretion. Each quarter was su bjectively j udged as mastitic o r non-m astitic accord ing to the above criteria. M astitic quarters were sa m pled for microbiological cu ltu re before
treatm ent was i n itiated. After sampling each affected quarter was treated as for lactating cow c l i nical mastitis with penici l l i n based a ntibiotics as p rescribed on the label.
4.3.5 Statistical analysis
Total yields of m i lk, fat a n d p rotein were estimated from herd-test data d u ring the p rod u ction season (2005-06}, which is the season after the Strep. uberis chal lenge. Somatic cell score (SCS) was calcu lated as n atural log (somatic cell count +1) for each h e rd-test record.
Statistica l ana lyses were performed using SAS (Statistical Ana lysis System, version 9 . 1; SAS I n stitute I nc., Ca ry, N C, USA). Freq u encies of EDPCM between treatment gro u ps were compared using Fish e r's exact test.
Tota l lactation yields of m i l k, fat, p rotein and m i l k sol i ds a n d average SCS were a na lysed with t h e M I XED proced u re using a linear model that considered the fixed effects of treat m e nt gro u p (mod ified DryFiex and investigational external teat sealant), EDPCM occu rren ce (cows that suffered EDPCM and those that did not), their i nteraction and the covariables calving week (linear), pa rity (linear and quadratic) and proportion of Holstein -Friesian gen es (linear). Least squares and their standard errors were used for m u ltiple com pa risons.
4.4 Resu lts
4.4. 1 Early dry period mastitis occurrence
After Strep. uberis exposu re, 1 27 of 165 cows developed ea rly d ry period clinical m astitis (76.97%). Sixty fou r of 85 (75. 29%) that d eveloped EDPCM were from modified DryFiex a n d 63 o ut of 80 (78.75%) fro m the investigational external teat sealant group. The difference between grou ps was not sign ificant (p=0. 13).
Milk production parameters
M il k p roduction d ata a n d SCS are given in Table 4. 1. Th ere was no difference i n m i l k yield, fat or p rotei n p roduction between cows that suffered EDPCM and those that d i d
not. Th ere was a statistical ly sign ificant d iffe rence (p<O.OS) i n the SCS observed i n cows that suffered EDPCM and those that d i d not.
Th ere was no d ifference in the m i l k prod uction parameters between treatm ent grou ps.
Ta ble 4 . 1 . : least squares means and standard errors o f milk production and somatic cell score (SCS) of cows affected and not affected with clinical mastitis in the early dry period
Group
Affected
(EDPCM)1
Unaffected
Days in milk M ilk yield (L}
277.6 ± 1.4 5126.8± 73
275.4 ± 2.7 5010.2± 135.9
1 early dry period clinical mastitis
4.5 Discussion
Milk solids yield
(kg) Fat yield (kg) 449.5± 6.5 267.1± 4.2 443± 12 264.3± 7.8 Protein yield (kg) scs 182.4± 2 . 5 4.45± 0.07 178.6± 4.7 4. 17± 0.12
The b ovi ne m a m mary gland is particularly suscepti ble to new i nfections early a n d late in the d ry period, due to i nvolution and colostrogen esis respectively (Bra d l ey and Green 2004). The pathogenesis of mastitis inclu des, in some cases, d a m a ge to secreto ry tissue and its replacement with fi b rous tissue, leading to a perm anent d ecrease i n m i l k yield from the affected quarter (Ben ites et a l 2002). lt is p ro b a b l e that part of the decrease i n m i l k p ro d uction seen when clinical mastitis occu rs d uring lactation is d u e to an i ncreased demand for energy by the i m m u n e system, a decreased a p p etite associated with the inflammatory p rocess a n d lowered feed intake due to pain and decreased mobility (Petrovski et al 2006). These factors m ay also infl u e nce the n ormal i nvol ution of the bovi ne mamm ary gland after drying off. If the normal i nvol ution is affected there is a possi bility of decreased m i l k prod u ction in the subsequent lactation.
P revious stu d i es reported less th a n 20% milk yield l osses i n s ubseq uent-' actations for cows affected with clinical mastitis ( Fetrow et al 1991; Houben et al 1993; H o rtet and Seegers 1998). In the p resent stu dy, no significant effect of i n duced and treated Strep. uberis mastitis soon after d ryi n g off was fou n d i n cows u p o n subsequent lactation yields.
Reasons that the resu lts of the present study differ from earlier investigations are not readily a p p a rent. Possibilities include the orga n isms i nvolved, time of i nfection, natu re and p athogenesis of the intra mamm ary i nfection ( I M I ) and the duration of the clin ical mastitis episode. All p revious reports were based on the n atura l occu rrence of clin ica l