Some aspects of growth rate as it is related to reproductive efficiency in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Science at Massey University

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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) S01'1E ASPECTS OF GRO\.JTH RATE AS IT IS RELATED TO REPRODUCT IVE EFFICIENCY IN DAIRY CATTLE. A thesis presented in partial fulfilment of the. requirements for the degree of Master of Philosophy in Veterinary Science at. Massey University. (Note: This thesis represents a thirty per cent component of the examinable material).. TAN Kim Sing. 1 9 79.

(3) ii. ACKNOWLEDGEMENTS. I a m greatly indebted to my supervisor, Professor E.D. Fielden for his guidance and help throughout the course of this study. My thanks go also to Dr K.L. Macmillan who willingly contributed advice and material and to Professor R.E. Munford for his assistance with the statistical analyses.. W.J.. Special thanks are extended to Professor. Pryor for his consideration when I first arrived at Massey. University.. Without the willing co-operation of the farm owners,and staff of the Ruakura Number Two Dairy Unit, the study would not have been possible to them. I. To Mr. am grateful. R.J,. Curnow for his invaluable help when weighing the cattle,. the Massey Library Staff for their assistance with obtaining literature, and Mesdames A. Low, V. Darroch and F. Wicherts for typing this thesis I give my thanks.. Finally I would like to acknowledge the financial and moral support given to me by my family and the forbea�ance shown by my flatmates, especially K,L. Chua,during my stay at this university..

(4) iii. ABSTRACT. The purpose of the study reported in this thesis was to evaluate whether live�veight, measured in Friesian yearlings immediately before the breeding season commenced and in parous cows of the same breed just before calving for the herd began, was related to reproductive performan�e during the first four weeks of the mating period.. Should such a relationship be confirmed 'target weights'. which .would ensure a high level of reproductive efficiency could be established for animals of this breed under normal husbandry conditions in New Zealand.. A pre-requisite to the investigation was that the. method(s) used should be easily applied in a commercial farming situation.. Body weight measurements for 184 yearlings (5 herds) and 283 parous cows (4 herds) which were at least three-quarter bred Friesian were taken at the times indicated above and related to submissio� rates ( S . R.) and pregnancy rates (P.R.) during the first four weeks of the f ollowing breeding season.. TI1e cows were bred by artificial insemination. with heat checks being made by experienced stock men;. yearlings were. mated to young bulls fitted with chin ball mating harnesses.. P.R. and. the dates of conception were confirmed by both pregnancy examinations at the conclusion of the breeding period and by subsequent calving information.. Reproductive performance in the yearling heifers was high with S.R. averaging 94% (range 88-100%) and P .R. 86% (range 71-100%) for the f ive herds.. The majority of the heifers were judged to be in good body -1-. condition with mean body weights for the herds ranging between23�27 and +. +. 277-22 kg (mean - S.D.).. Differences in liveweight between herds were. probably related to management during rearing although age variation &nd minor differences in the amount of Friesian 'blood' in each herd could have been contributing factors.. When individual herd effects were removed a positive but non significant linear relationship between liveweight and S.R. was achieved with the yearlings.. From the six points plotted on the regression it. was noted that the lightest group of animals had a submission rate of 76%.

(5) iv. whereas all other groups had submission rates in excess of 94% thus suggesting a threshold effect.. The IC'inimum liveweights for the. lightest yearling groups exceeding. a. 90% submission rate varied. from 204-229 kg depending on the herd. While a positive relationship between liveweight and pregnancy rate was noted in the yearling data this was neither linear nor significant - further investigations seem warranted to resolve this particular issue because of its importance in breeding management. The significant differences noted between herds in yearling pregnancy rates may have been due to differences in fertility of the bulls used. The reproductive performance of the three year-old and mature age groups of parous cows was satisf&ctory (S. R. averaged 87 and 8 6 % and P.R. 69 and 65% respectively ) but that of the two year-old cattle poor (S. R, 67% and P. R. 5 6%). herds.. Marked differences occurred between. Apart from the possible influence of liveweight before calving. on these parameters of performance analysis of the reasons for herd differences was beyond the scope of this study and not attempted. Differences in liveweight of the different age groups of cows both \vitldn and between herds was marked and, apart from the relation ship with age, could most likely be attributed to management during the late autumn and winter period before calving began.. Any. association bet\veen live\veight and subsequent reproductive performance was however generally poor and inconsistent and in retrospect it wa� concluded that the method that had been used for investigating any possible relationship was unsatisfactory.. A future investigation. in which variables are more effectively controlled has been suggested. Two year-old heifers experiencing their first lactation continue to be a problem group particularly under New Zealand dairy husbandry conditions.. Careful management commencing during r�aring and extending. through first mating, calving and second breeding is required if a high level of reproductive efficiency in this age group is to be achieved..

(6) V. TABLE OF CONTENTS. PAGE ii. ACKNOWLEDGEMENTS AB S T RACT. iii. L I S T OF TABLE S. vii. L I S T OF FIGURES. ix. INTRODUCTION. 1. LITERATURE REV IEW. 3. REPRODUCTIVE EFF ICIENCY AND PARAMETERS. 3. USED IN ITS AS SES SMENT i.. Calving Interval. 3. ii .. Days Open. 3. iii .. S e rvi c e s Per Concep t ion. 4. iv .. Non-Re t urn Ra te. 4. GROWTH RATE OF DAIRY YOUNG S TOCK. 5. i.. Body Weight and Pub e rty. 6. ii.. Conc e p t ion Ra te and Dy s t o c ia. 7. iii .. Milk Yield and Comp o s i t ion. 8. iv .. Longevi ty. 9 11. SUBMI S S ION RATE i.. The S ign if icance o f Submission Rate. 11. i i.. Body We ight and S ubmiss ion Rat e. 12. i i i.. Fac tors a f f e c ting Submis s ion Ra t e. 13. a.. E f f ic iency o f o es t rus d e t e c t ion. 13. b.. Ano e s t rous syndrome. 14. c.. P o s t -calving interval. 15. d.. Mul t ip l e suckl ing. 16. e.. Management fac t o rs. 17. BODY WEIGHT. AND. FERT ILITY. 17. i.. Phys iological Bas i s o f Nut r i t ional Inf e r t ility. 17. ii.. Par t i t ion of Nut r ie n t s. 19. iii .. Pa t t e rn o f L ivew e ight Change. 20. iv .. The R�lat ionship B e tween Body Cond i t ion and Fer t il i ty. 22.

(7) vi. PAGE v.. The Relationship Between Body Weight Change. 23. and Fertility vi.. Factors Which May Influence The Relationship. 25. Between Liveweight And Fertility a.. Protein-energy relationships. 25. b.. Yield level and fertility. 26. c.. Pre- and post-calving feeding. 26. d.. Level of feeding immediately arou�d the. 27. time of service TARGET BODY WEIGHTS. 27. i.. Target Body Weights For Maiden Heifers. 27. ii.. Target Pre-Calving Weights For Cows. 31 34. MATERIALS AND HETHODS i.. Location And Animals. 34. ii.. Records . And Measurement. 35. iii.. Method Of Analysis. 36. RESULTS. 39. DISCUSSION. 55. CONCLUSIONS. 64. REFERENCES. 66. APPENDICES. 76. I.. Coefficients and Diviso�s for Sets of Ortho. 76. gonal Comparisons in Regression Ila.. Submission Rate and Pregnancy Rate Responses for. 78. lib.. the Different Age Groups of Cattle within each Weight Classification F Values for Linear and Quadratic Components of the. 79. lie.. Response to Regression. (Herd Effects Ignored). Submission and Pregnancy Rates for Yearling Friesian. 81. Cattle According to Body Weight Before Breeding in Five Dairy Herds (Herd Effects Ignored) lld.. Submission and Pregnancy Rates for Two Year-Old Friesian. 83. Cattle According to Body Weight Before Calving in Four Dairy Herds lle,. (Herd Effects Ignored). Submission and Pregnancy Rates for Three Year-Old Friesian. 85. Cattle According to Body Weight Before Calving in Four Dairy Herds llf.. (Herd Effects Ignored). Submission and Pregnancy Rates for Mature Friesian Cattle. 37. .According to Body Weight Before Calving in Four Dairy Herds (Herd Effr;cts Ignored).

(8) vii. LIST. OF. TABLES. (. Table Liveweigh t s at various stage s o f deve l o pment o f Jersey and Fries ian Ca t t le ( kg). I. II. Page. 6. Gene ral e f fects of unde r feeding on p roduc t iv i ty of yo ung dairy ca t t le. 10. Ill.. 1be importance of C . R . and S.R . on sub sequent calving performance. 11. IV.. Rel a t ionship be tween b ody we i ght and 2 8�day submi s s ion ra te ( S . R . ). 13. .. V.. Ova r ian s ta tus o f s yndrome'. CO\vS. showing ' pre-se rvice anoe s trous. 15. VI .. The influence o f interval f rom calving to ma t ing on conce p t ion ra te s. 16. V I I.. E f fe c t o f change in body we ight on fer t i l i ty o f da iry cows. 24. VII I . Effec t s o f we igh t at b reeding age on reproduct ive pe r f o rmance o f heifers. 29. IX .. Targe t we ights immed iately p r ior to calving (kg). 32. Xa .. Mean body we igh t s of the yea r l ing he i fe r s immed iately be f o re ma ting in f ive he rds (kg). 41. Xb.. Analy s i s of va riance for he rd e f fec t s on body we ight o f the yea rl ing he ifers. 41. XIa. Mean body weigh t s o f the d ifferent age groups of parous cows measured be fore the f i r s t cow ca lved in each he rd (kg ). 42. X Ib .. Anal y sis o f var iance f o r herd and age e f fects on b o dy we igh t o f the parous c ows. 42. X IIa. Submi s s ion ra tes ( S . R . ) and p regnancy r a tes ( P . R . ) f o r a f o u r-week b reed ing period for yearl ing he ifers in f ive dairy her d s. 43. X I Ib . Chi- s q uare te s t o f independence f o r he r d d ifferences in subm i s s ion ra te and p regnancy rate f o r yearl ing he i fers using R x C me thod. 43. XI I Ia.Submi s s ion rate s and p regnancy rate s f o r a four-week b reeding per i o d f o r three age group s o f parous cows in four dairy herds. 44.

(9) viii. Pag e. Table XIIIb .. Chi- s quare tes t o f independ ence for h e rd dif f erences in s ubmi s s ion r a te and p r e gnancy r a t e with in each a ge c l as s if ic a t io n us ing R x C me tho d. 44. XIV.. S ubmi s s ion ra t e and p regnancy rate responses f o r the d i f f e rent age group s of c a t tle wi thin each we igh t cla s s i f ic a t io n. 45. XV.. F values for l inear and quad r a t ic components o f the response to regression (her d e f f e c t s r emoved ). 46. XVI .. Rela t ionship b e tween the p o s t -calving int erval and submi s s ion ra t e s for thr e e age g ro up s of cows in fQur d a i ry herds. 60. XVI I.. We i gh ing , calving and JOlnlng dates and weighing to c alving int erval for three age group s of cows in four dai r y herds .. 60.

(10) ix. liST. OF. F I GURES. Figure. Page. l.. The Effects of Nutrition on Reproduction. 1.8. 2.. Simplified Model to Describe the Relationship of Food to Milk and Live�veight in Dairy Cows According to Responses to Level of Intake. 20. 3.. Recommended Target Liveweights for Jersey and Friesian Cattle B etween Birth and Mating. 30. 4.. Recommended Target Liveweights for Jersey and Friesian Cattle Between Mating and Calving. 30. 5a.. Submission Rate for Yearling Friesian Cattle According to Body \.Jeight Before Breeding in Five Dairy Herds. 48. 5b.. Pregnancy Rate for Yearling Friesian Cattle According to Body Weight Before breeding in Five Dairy Herds. 48. 6a.. Submission Rate for Two Year-Old Friesian Cattle According to Body Weight Before Calving in Four Dairy Herds. 50. 6b.. Pregnancy Rate for Two Year-Old Friesian Cattle According to Body Weight Before Calving in Four Dairy Herds. 50. 7a.. Submission Rate For Three Year-Old Friesian Cattle According to Body Weight Before Calving in Four Dairy Herds. 52. 7b.. Pregnancy Rate For Three Year-Old Friesian Cattle According to Body Weight Before Calving in. Four Dairy Herds. 52. Sa.. Submission Rate for Hature Friesian Cattle According to Body Weight before Calving in Four Dairy Herds. 54. 8b.. Pregn&ncy Rate for Mature Friesian Cattle According to Body Weight Before Calving in Four Dairy Herds. 54.

(11) 1. INTRODUCTION. A concentrated c a lving per iod i s a unique feature o f the seasonal pattern of dairy farming i n New Zeal and .. I t i s t imed to. co - incide wi th the spring flush in p a s ture growth so a s to achieve maximum milk production at lowe s t cos t ;. in addi tion thi s prac t ice. s i mp l i f i e s management wi th respect to cows at d i f ferent stag e s of the i r annual reproductive and milking cyc l e a s wel l a s reduc ing prob lems a s sociated w i th cal f rearing . High bre eding e f f i c i ency o f d airy c attle in New Zeal and i s thus a s soci ated. w i th a short concentrated per i od o f mating usua l l y of about. n i ne weeks duration .. To achieve the obje c tive of high in c a l f rate s. during thi s short period o f time requ i res that as many anima l s as po s s ible i n the herd be bred during the f i r s t four we eks after mating commence s. ( i . e . a high submi s s ion rate ). and that sati s fa c tory. pregnancy r a te s be obtained at each breeding . Many f a c tors can a ffect submi s s ion rate and among the s e lack o f cycl ical activity as soc iated with a n i nadequate level o f nutri tion appears to be important i n many dairy herd s in thi s country .. Evidence. indicates that thi s problem is more f requent , and of greater magn i tude , in younger l a c tating an ima l s whi l e re cogn i s e ove r t oe strus ,. ' s i lent heat'. and/ or f a i l ure to. in add i t ion to l ack o f cyc l i c a l activity ,. contribute s i g n i f i cantly to the subm i s s ion rate prob l em in older anima l s i n the herd. ( F ie lden ,. 1 9 7 6 ; Fi.e.lden e t: al . , 1 9 7 6 ) .. Furthermore ,. fol l owing. a s tudy o� p l a nned animal hea l th schemes app l ied to dairy herd s , Mol l e r ( c i ted b y F i e l den et a l ., 1 97 6 ) h a s po inted o u t that there appears to. be a po s i tive re lationship between body weight and submi s s ion rate o f da iry anima l s under New Ze aland farming condi tions . There i s l i ttle doubt that under feeding of cattle can o c cur u nder an a l l grass grazing farming s y s tem .. P asture for examp l e var i e s. con s i derab l y i n both yield and qua l i ty wi th chang e s in season s .. An. over-e s timate of the feeding value o f forage , or of the feed intake under s e l f feeding cond i ti on s , can thus read i l y contribute to an . underfeed ing problem and ,. in addi tion , var i ations i n the s e a sonal. pasture growth pattern can seriously alte r the food suppl y that i s ava i l able a t any given time ..

(12) 2. S ince i n d airy cattl e ,. subm i s s ion rate i s mainly a probl em o f. anima l s returning to post-partum c yc l i c a l activity , a n d because p l an e o f nutrition i s a var iable which c a n b e read ily manipulated ,. the concept. o f a target we i gh t for anima l s at calving , which would corre l ate with sub sequent reproductive and productive perfo rmance , guide in management .. Such a concept ,. could be a u s e ful. i f practi cable,i s parti cu l arly. important s i n c e no immediate or even short term method of bene f i c i a l ly a f fec ting cycl i c a l activity has yet bee� described for anima l s which are i n a 'poor' reproductive state . foo d intake ove rcome the prob l em .. Nor doe s a short term boo s t in S i m i l arly , a target wei ght for. yearl i ngs at mat i ng is de s i r able in view of the fact that onset of puberty is mor e a function o f l ivewei gh t than age . The ob j e c tive of the study reported in th i s the s i s wa s to evaluate the r e l ationship betwee n submi s s ion and pregnancy rate s with that of body we ights of Fri e s ian year l i ng s prior to mating , and of F r i e s ian cows b e fore calving ,. in an e ffort to e stab l i s h a n optimum. target l ivewe ight for e f f i c ient reprodu c t ion .. An important cons idera tion. in r e spect to th e plan of the i nve stigation wa s that,whatever techn ique was adopted in o rder to e s tab l i sh the r e lationship1it had to be 'practical ' view .. in appl ication from the commercial dairy farmers po int o f.

(13) 3. LITERATURE. REVIEW. REPRODUCTIVE EFFICIENCY AND PARAMETERS USED IN ITS ASSESSMENT. I t is hard l y nece s sary t o s tre s s the economic importance o f reprodu c t ive e f f i c iency f or i t i s obvious that the a im o f dairy f arming is to ach ieve a calving rate of one c a l f per cow per year and so to renew milk product ion init iated through parturit ion . Reprodu c t ive e f f i c iency is l arge l y dependent upo n a s a t i s fac tory level o f he�d fer t i l i t y which in turn is a f fe c ted by b o t h gene t i c and environmental fac tors.. To be reprodu c t ive l y e fficien t , an animal m11St. be ab le to both c o n ceive and produce a v iable o f fspr ing at a calving in terval of about 1 2 mon ths .. Factor s a s sociated with this are bree ding. a t an early age, h i gh submis sion rates , h i gh concep t ion rates during the breeding per iod and l ow pos tnatal l o s se s . Major measures which are used for the a s sessmen t o f reprodu c t ive e f f i c iency include :. i,. Calving In terval. Th is represents the in terval from one c alving to the next and is a lmo s t always presented on a herd basis .. I t has been shown t hat a. 1 2 - 1 3 mon t h calving interval yields the highes t milk produ c t ion during the l i fe t ime of a cow (Har t i gen, 1 9 72) .. In a recent repor t the Mi l k. Marke t ing Board ( 1 975) ind icated that a 3 65-day calving in terval gave 3 0� the max imum � ilk yie l d s whi le produc t ion was depres sed where c a lving in terva l s were longer or shorter than 365 days . In actual pra c t i ce, mo s t s tudies in d icate that the usual f i gure f or c a lving in terva l s is nearer to 3 9 5 days though ex cep tions are no ted in seas onal supply dairy herds in both New Zea l and and Ire l and where calving interva l s of 364 and 363 days respec t ively have been repor ted (Shres tha,. 1 9 78 ) .. Calving interval i s the mos t import ant parame ter de s cr ib ing repro duc t ive e f f i c iency and it is ma in l y in f luenced by the t ime from calving to conception i . e. days open .. ii .. Days Open This is tl1e c alving t o c oncep t ion interva l .. le. o f fers a.

(14) 4. mean ingful analys i s o f the reproductive condition o f a herd and of individual cows w ithin th�t herd. {Lineweaver and Spe s sard ,. 1975) .. It. is h ighly corre lated with calving interval but it doe s not take account of lo s s e s wh ir.h may occur during a pregna.ncy after the e s t imate has been made . Days open i s made up of the calving to first s e rvice interval and the interva l from f irst s ervice to conception .. The re sumption o f. cyc l i cal act ivity a fter parturition i s a k e y factor a f fecting i t . Other influence s include management deci s io n s a s to when to first breeding , the e f f iciency of o e s tr us. begin. detection o n the farm and. the ferti l i ty level achieved once breeding has started . iii .. Service s Per Conception Thi s is one o f the primary measures u sed in eva luating. reproductive performance and herds that require mo re than two s ervices per conception are genera l l y cons idered to b e problem herds. et a l . , 1966 ) .. {Morrow. As the number o f service s p e r conception i s inver sely. related to the po st-partum interval be fore breeding commence s and Cooper ,. 1 97 0 ; Bri tt ,. 1975) ,. {Ol d s. a herd with a low servic e s p e r. conception index m a y have a long intercalvi ng i nterval , or vice versa . Thus calving i nterval is a more appropriate measure o f breed i ng e f f iciency .. A further diff icu l ty encountered with u s ing the parameter. of services pe r conception is that of determining the exact time when conception has occurred . iv .. Non-Re turn Rate This is a mea s ure o f. ' conception rate' and its e s t imation i s. ba sed o n the percentage o f anima l s bred that do not return for a furth er service with i n a spec i f i ed per iod . varie s from country to country .. Thi s speci fied period. In New Zealand , a 49-day non-return. rate is used as compared to 6 0-9 0 days in the Uni ted Kingdom and U.S . A (Pe l i s s ier ,. 1976 ) .. 'conception rate s',. et a l . , 1975 ;. Though non-return rate s are highly corre lated with as an e s t imate they are always higher. P e l i s s ie r ,. 1976). {Spal d i ng. owing to s uch problems a s po s t - s ervice. ano e s tru s in the absence o f a conceptus and incomplete records of return to service(Macrnil l an et a l . , 1 9 7 7b ) ..

(15) 5. N o n-return rate ha s to b e measur ed i n r elati o n to the post-partum period s i nc e the abi l i ty of a cow to c o nc eive increa s es as the po st partum period befor e s ervi c e l engthens .. Additiona l l y ,. rat e o nl y measures cows which have b een b r ed ,. no n- r eturn. and. as a n estimate o f. performa nc e i t should b e j udged i n co nju nc t i o n wi th the proportio n o f u nbred cows in the h erd in which the estimate i s being mad e .. GROWTH RATE OF DAIRY YOUNG STOCK Rearing of you ng dairy s tock i s carri ed out to provide herd r eplacements .. A sou nd hei f er r epla c em ent programme i s aimed at. keeping deaths to a m i nimum ,. s uc c es s fu l ly mat i ng the stock at a. des ired age and reari ng th em at a l evel so that subs equent milk produc t i o n and ferti l ity are not prej udic ed. ( Warner ,. 197 0ar. Davey ,. 197 6 ) . A lthough the growth potential o f a n a nimal i s l imited by its geno type,. the extent to which the animal expres ffSthi s pot ential i s. mainly determi ned b y nutri t i o na l factor s .. Thus , i t has b een po s s ib l e. to control growth o f h ei f ers b y manipulati ng their plane of nutr i t i o n ( Swa ns o n , 1 9 6 7 ; Pres ton a nd Wi l l i s ,. 197 4 ) .. Whi l e there a r e a vari ety of growth s t a ndardsfor dairy hei f er s , hei fer s of differ ent breedsc a nnot be bound to the s ame standard a nd even i ndividua ls with i n breeds may d i f f er a s much a s 2 0 - 2 5 % from a n average growth patter n ( Swanso n ,. 1967 ) .. I t is importa nt when cons ider i ng the question of l evel o f r earing t o have some conc epti o n o f normal o r average rates o f growth; a survey of livewei ghts at various stages of development of Jersey a nd F r i esian cattl e i s i l lustra t ed i n Tab l e I . I t should b e noted that the average age at first calvi ng wa s 2 0 - 2 4 mo nths for the Jer s eys a nd 2 8 - 3 2 months for the Fries i a ns .i n the data c ited in th is t ab l e . Early breed i ng o f catt l e has economic adva ntages s i nc e i t shortens the unproductive per iod o f th e a nimal ' s l i f e a nd at the same time i nc reases its l i fe time production provided it does not dec r ea s e lo ngev i ty .. Ther e appears nothi ng t o g a i n from a produc tion poi nt o f. vi ew in growing calves o r hei f ers too fa s t. ( Burt ,. 1 9 5 6; Lamo nd a nd.

(16) 6. Campbell,l968; Warner, 1970b).. For Jersey and Friesian breeds, from. birth to weaning, a gain in weight of 0.45 kg/day or slightly over, and after weaning to mating at 15 months a gain of 0.64 kg/day, are satisfactory for future productive purposes (Lamond and Carnpbell, 1968; Warner, 1970b).. TABLE I:. LIVE\'lEIGHTS AT VARIOUS STAGES OF DEVEWPMENT OF JERSEY AND FRIESIAN CATTLE (KG). Weight before W eight at first service first calving. Breed. Weight after first calving. Ma.ture weight. Friesian. 330. 509. 455. 568. Jersey. 218. 327. 291. 364. (after Broster and Leaver, 1969). It has been stressed that the most economic overall level of rearing will depend very much on the individual farm situation (Broster and Leaver,. 1969).. In New Zealand,. mating heifers at 15. months of age to calve at 24 months suits the seasonal nature of dairy farming. (Davey, 1976).. The question of the relationship between level of rearing, growth rate and adult performance has been reviewed by Allden. (1970).. The major productive issues are age at puberty, fertility when mating begins. (and at subsequent breeding periods), dystocia, milk. yield and life time in the herd. i.. Body Weight and Puberty Growth can be accelerated or delayed with little influence on. the final mature body size (Allden, 1970).. However, puberty, which is. the time at which reproduction first becomes possible. (Asdell,. 1968;. Roberts, 1971) is a function of liveweight and is relatively independent of age. (Sorensen et a l . , 1959;. Joubert, 1954, 1963).. Thus. onset of puberty as indicated by the occurrence of first oestrus is directly and positively related to growth r ate and level of nutrition (Joubert, 1963) ..

(17) 7. Using varied planes of nutrition, Sorensen et a l .,. ( 19 5 9 ) noted. that Holstein heifers reached puberty at widely different ages but at relatively constant weights.. The faster growing animals showed first. oestrus at higher body weights than those growing at slower rates which. is in contradiction to the results reported by Amir et a l . , and Dufour. ( 19 67). ( 1975 ) .. In Holsteins, at fast growth rates of 0 . 9 kg/day puberty appears at about 9 months of age, for average growth rates of 0 . 6 kg/day at 1 2 -1 3 months, and for slow growth rates of 0 . 4 kg/day puberty may not be observed until 17- 2 0 months of age et. a l . , 19 5 9 ; Swanson,. 1967) .. (Crichton. Ovarian cycles may occur before. (Sorensen et al . , 1 9 5 9 ) .. oestrus is observed in slow growing heifers. Weight at first oestrus in Holsteins has been reported to average from 2 5 0 - 2 74 kg. (Salisbury and Van Demark,. from 4 to 18 months ( 19 6 3 ) ,. (Fraser, 1971) .. 1961). while age varies. According to the data of Joubert. the weights at puberty of Jersey and Friesian heifers are in. the range of 1 2 1-2 2 9 kg and 2 07- 3 43 kg respectively. A fast-slow growth feeding regime seems to have an adverse. effect in that it delays sexual maturity (Crichton et a l., and reducesmature production. (Schultz, 196 9 ) .. Dufour. ( 1975 ). 1959) recently. observed that not only the duration but the time at which a fast growing regime is applied is important in attainment of puberty. Feeding regimes of high and moderate planes were imposed on Holstein heifers weaned at 5 months during two stages of growth:. q). an initial phase lasting lOO days and. b). a final phase immediately following the first and ending with ovariectomy at the second oestrus after puberty.. It was found that the high energy regime imposed after an initial phase of moderate growth was as effective in bringing about puberty as maintaining the high energy regime from weaning to puberty.. ii,. Conception Rate and Dystocia There is no evidence that growth restrictions in early life. will influence the reproductive performance of cattle once a normal diet has been restored. (Allden,. 1 970 ) .. Nevertheless, a slow growth. rate, because of a low level feeding regime, will delay the breeding.

(18) 8. date of an animal and subsequently delay the time at which it comes into production.. Besides delayed breeding, retarded growth may lead. to dystocia in heifers. {Broster and Leaver,. 1 9 69 ) .. Conversely,. liberal feeding, although it leads to early breeding, may also give rise to dystocia especially at the first calving {Wickershaw and Schultz, 1975) .. 1 9 63; Schultz, 19 69; Gardner and Schuh,. 1970; Gravert et a l .,. In fact, the increase in calving troubles is the most. consistent problem with early breeding even though heifers appear to be well-grown.. Reid et al . ,. 1964. {cited by Jl.llden,. 1 9 70 ) , feeding. a high, medium and low planeof nutrition to three groups of heifers from birth to first c alving, observed that at first calving the lov! group produced calves of lower birth weight and tended to have a In their. higher number of cases of dystocia than the otter groups.. subsequent performance, there were no significant differences between groups in respect to either calf weights or calf mortality. Additionally, a high conception rate at first service was observed in heifers reared on the low level of nutrition.. However, the authors. argued that high plane heifers could have possibly been bred earlier at weights similar to those of heifers on the low plane;. it is. possible under these circumstances conception rates may have been different.. Experimental results obtained at Cornell University and. quoted by Schultz. (19 6 9 ) agreed •.-vith the above findings except �or. conception rates which were found to be similar in all groups. Leaver and Yarrow. (1975 ). indicated that the relationship. between different levels of nutriti0n and conception rate was curvilinear with maximum conception rates {70%) (growth rates of 0 . 4-0.6 kg/day).. at moderate intakes. At lov1er and higher levels of. intakes conception rates declined. iii.. Milk Yield and Composition A low plane of nutrition during the rearing period is commonly. but not invariable associated with a reduced milk yield in the first lactation.. However, in subsequent lactation periods, low plane reared. animals were superior in yield to cows which of nutrition in early life {Allden,. 1 9 70 ) .. received a high plane. This apparent anomaly may. be attributed to faulty udder development as a result of high level feeiing since Swanson {1967). found that the udde�of overfat heifers.

(19) 9. at the end o f their s ec o nd lactat i o n po s s es s ed large depo s itions o f a di po s e ti s sue a nd undeveloped alveolar spaces . As fa r a s milk compo si tio n i s conc er ned , there i s evidence i ndicating that it is not affec t ed by lev el of r ear i ng exc ept for a sl ight i nc r ea s e in fat co ntent dur i ng the early part o f lac ta ti o n. wi th heifers r eared o n higher plane s o f nutritio n (Crichton e t a l . , 1960 ; Davey, 1976 ) .. It i s like l y that such a nimal s have uti l i s ed. body depot fat for mi lk synthes i s s i nc e they los t weight duri ng the early lactation period . Bro s t er and Leaver. po i nt out that maximum milk y i elds. ( 1969). had been obtai ned following re ari ng at 8 0-11 0 % norma l feed i ng standards . iv .. Lo ngevity Slowly r eared a nima ls have an apprec iably l o nger production. l i fe tha n rapidly reared a nimals 1970 ) .. In terms of economic s ,. ( Bro ster and Leaver , 196 9 ; Allden,. the average l ength of productive l i fe. o f da iry a nima l s is impor tant and an i ncrea s e in longevi ty could l ead to a greater suppl y of mi lk , a nd cheaper production ( Ki ng , 1970 ) . The decrea s e i n length o f produc tive l i fe with i ncrea s ed l evel s o f feed ing dur i ng rear i ng may be a s sociated with ear l i er a g e a t maturity and sub s equ ent ear l i er s tarti ng o f the agei ng proc ess .. Al t er natively. it may be due to the lo ng term effec t s of i ncrea s ed physiological s tress a s i ndicated by their higher heart and r espiration rates 1956; Allden,. 1970 ) .. Ki ng. ( 1970 ). a l so no ted tha t the averag e l ength. o f produc tive l i fe tended to b e s horter i n of produc t i o n .. However ,. h erds with a high l evel. A further obs ervat io n i s that there wa s l es s. s teril ity i n the cows r ea r ed 1970 ; Little,. ( Burt ,. on. a low plane o f nutri tio n (Allden,. 1973 ) . it must be borne i n mi nd that the advantages i n. lo ngevity o f slow rea r i ng may be mere apparent tha n real s i nce ther e are many envi ro nmental hazards that can r esult i n cows b ei ng c u l l ed f rom the herd. ( d i s ea s e , accid e nt ,. low produc tio n ,. poor fertility ) .. I n s ummar y the evi dence suggests that both very low a nd very high l evel s of feeding from weani ng to mati ng c a n have adver s e e ffects upo n productive and reproductive effi c i ency .. However,. und erfeed i ng is u ndoubtedly mor e of a prac tical problem tha �. M:J;"SSEY UNIV�RSITY LIBRARY.

(20) 10. oye:r:f eedi ng, a nd this i s es pecially true in a grazi ng s ituation like New. .Zealand's. ·�here c oncentra t e supplementati on i s rarely prac t i s ed .. An a s s essment by Davey. (1976). of the relative importance of vari ous. factors rela ted to the rai s i ng of dairy cattle over the growi ng peri od. is g iven i n Table II.. TABLE II.. GENERAL EFFECTS OF UNDERFEEDING ON PRODUCTIVITY OF YOUNG DAIRY CATTLE. A s s es sment o f importanc e. Effec t s. Ons et of pub erty a nd. Remarks. ++++. t i me of calv i ng Calvi ng d i f f i culti es. +. Weight of c a lf. + ?. Longevity. at extremes little evidenc e. M i lk produc ti on first lac ta t i on. ++. s econd lac tati on. 0. Und erf eeding immediately pri or to ca lvi ng. ++++. Underf eedi ng after ++++. c a lvi ng. ( after Davey ,. 19 7 6 ). u nless u nderfeed i ng extreme.

(21) 11. SUBMISSION RATE i.. The Significance of Submission Rate The objective o f mating management in New Zealand dairy farming. is to attain a concentrated calving i.e. 90% or more of the herd to calve in 6 weeks and with no more than 5% empty cows 1972b).. (�mcmillan,. Such a calving pattern facilitates herd management as cows. are at a. similar stage of lactation and have similar feed requirements. at any one time.. Moreover, time saved through a shortened calving. period means farmers can spend more time in caring for their calves. In order to achieve a concentrated seasonal calving pattern, a large proportion of cows in the herd have to be submitted for breeding during a 4-week breeding p eriod ( Flelden and Macmillan, et a l . , 1975).. 1973;. Macmillan. Submission rate (SR) can therefore be defined as the. percentage of the herd correctly identified in oestrus and bred during the first four weeks of the mating season.. The second important. factor which contributes to a concentrated calving is conception rate (CR) and it is defined as the percentage of cows which conceive to each insemination or mating within the breeding period (Macmillan, 1972a ; 1972b). The interaction and importance of these two factors on subsequent calving performance has been stressed by Macmillan. (1972b) and is. illustrated in Table III. TABLE III:. THE IMPORTANCE OF CR AND SR ON SUBSEQUENT CALVING PERFORMANCE CR. SR. 4-week calving. Farm A. 75%. 70%. 52%. Farm B. 55%. 90%. 52%. Farm C. 75%. 95%. 71%. (after Macmillan 1972b). •. It is noted that both CR and SR have a complementary effect on subsequent calving rate.. Conception rates in excess of seventy. percent however are difficult to achieve and thus SR becomes of very gre�t importance i f the herd is to get in calf over a relatively short period of time..

(22) 12. Fielden and Macmillan (1973), fro�.an inves tigat ion o f 14 dairy herds,repo rted that 2 1 % o f the two year-old cows were no t s ubmi t t ed during the f i r s t 2 8 days of r u at ing even though mo s t o f these cows had post-p ar t um in t erval s of mor e t han 60 days .. Th is was a much h igher. pro p o r t ion of an imal s within t h e herds than o c curred with the o ther age group s.. A survey b y Macm i l l an et aZ., ( 197 5 ) in the Taranaki. dis t r i c t of New Zealand confirmed this f inding in tha t s ubmi s s ion rate p r o b l ems o c c urred in herds of all s i z e s but tha t in mo s t cases the re wa s an age e f f e c t w i th two year-old he ifers showing lower submis s io n rates than older age group s . While the init ial ovar ian a c t ivity that o c curs p o s t -partum is connn o nly associa t ed with a high inc idenc e o f s il ent h e a t ( Morrow , et aZ., 19 6 6 ) , the lower submi s s ion r a t e s in young cows referred to above is ma inly a s so c ia t ed w i th a lack o f ovar ian ac t ivity ( Fi e l d en et a l , l 9 7 3) .. .. It i s t h e ma ture c ows which a p p e ar to.exp er i ence genuine s il en t heats und e r New Zealand husbandry cond i t ions (Macmillan, 1 9 7 2b) . Mo ller ( 1 9 70 ) has sugge s ted tha t in comp lete u t e r in e invo l ut ion may be the main reason fo r p o o r concept ion rates before 30 days p o s t partum wh ile anovulation , s i l e n t hea t and f a l s e heat a r e the main con t r ib ut o r s to poor conc ept ion rates f rom 30-40 day s p o s t-partum . ii .. is. Body Weigh t and Submission Rate a. Mo ller ( c i t ed by Fielden et a l . , 1 9 7 6 ) has poin t e d out that there p o s it ive relat ionship b e tween body we ight and submiss ion rate ( s e e. Tab l e IV).. The b ody weigh t s f o r yea r l ings in this s t udy_were meas ured. jus t p r io r to the beginning o f the ma t in5 p e riod wh i l e:tlo se o f the cowswe re t aken just b e fo re calving f o r the herd b egan . Though there is. limited informa t io n covering this assoc iation. there ap p ears to b e widesp read a c c ep tance that this r e l a t ionship b e tween body w e i ght and submission r a t e exi s t s ..

(23) 13. RELATIONSHIP BETWEEN BODY WEIGHT AND 28-DAY SUBXISSION. TABLE IV:. :RATE .. .. '. .. .. .. .. (SR). •. .. Jersey yearling. •. Weight. n 42. (kg). <180. Friesian x Jersey yearlings (heifers). (heifers) •. •. •. •. 0. •. 28 day SR. n. Weight. 76%. 16. (kg). <200. 28 day SR 81%. 34. 180-190. 82%. 20. 200-210. 95%. 44. 190-200. 93%. 26. 2 11-220. 96%. Friesian x Jersey 2 years . (Heifers). Jersey 2 years (heifers. 87. <275. 96. 275-300. 212. >300. 72%. 28. 85%. 62. 93%. 26. <325. 229. 325-375 >375. 313. 57% 74%. 300-350. 81%. >350. Mature Friesian x Jersey cows. .Mature .Jersey .cows. 179. <300. 78%. 27. 87%. 89. 88%. 77. <350. 70%. 350-400. 84%. >400. 90%. (after Fielden et a1.,1976). iii.. Factors affecting Submission Rate a.. Efficiency of oestrus detection. This is. a. major factor influencing submission rate.. Without. accurate oestrus detection, it is not possible to assess accurately the effect of other factors. (Macmillan,. 1972a, 1972b).. Inefficient. detection of o estrus will l ead to a false estimate of the submission rate either because cows which are in oestrus are not recognised or because cows. which are not in o estrus are wrongly diagnosed as being. in oestrus. The economic importance of oestrus detection has been well documented by Esslemont (1974a).. In New Zealand evidence suggests. that the standard of detection is high enough to ensure a calving.

(24) 14. int e rval o f 3 6 5 days;. this l ev e l of p e rformance is u s ua lly achieved. however by usin g l ib eral oes t rus d e t e c t ion methods and h igh cull in g rates (Macmillan, 1 9 7 6 ) .. The inc idence of short re t urn int ervals. ( 1 - 1 7 day s ) which inc reased f rom 1 1 % in 1 9 6 4 to 20- 2 5 % i n 1 9 70 r e f l e c t s t h i s t en dency to interpret oes t rus l ib erally, even though genuine short r e turn int ervals of l e s s than 1 7 days ( 9 - 1 1 day s ) do e x i s t (Macmill an, 1 9 76 ) .. I n Ireland, Hart igan ( 1 9 72 ) also ob served tha t the highe s t. inc idence of short cycles oc curred o n d a y s 9 to 1 1 of the c y c l e and that the incid enc e of such cyc l e s increased with incr�as ing herd s i z e . The d e t e c t ion of oestrus in dairy c a t t l e p re s en t s several p rob l ems to the f a rmer (Pop e et a l . , 1 9 7 6 ) .. Thi s can be ant i c ip a t ed s ince there. is grea t varia t ion in the in tens i ty of t he b ehavioural changes as socia t ed with the phenomenon ( E s s lemont and Bryant, 1 9 7 4 ) .. The. p rob l em is compounded by d i f f i c u l t ies in a l locat ing enough t ime for oestrus d e t e c t ion e s p e c ia l ly in larger herds ( Esslemon t, 1 9 7 4b ) . The important types of errors in oest rus d e t e c t ion and their ident ificat ion t o imp rove e f f i c iency of d e t e c t ion have b een d is cuss ed by Macmillan ( 1 976) . I t is wor th no t ing that the s tudy of Will iamson et a l . , ( 1 9 7 2 ) demons t r a t ed that v i sual ob s ervat ion a lone, exc ept when it is carried out con t inuously 2 4 hours a day, does not g ive a high d e t e c t ion e f f i c iency .. S in c e con tinuous ob s e rvat ion by farm work ers is not. a. p rac t ic a l solut ion und er New Z e a l and cond i t ions of f a rming, other d e t e c t in g devic es mus t b e used i n conj un c t ion with v i s ua l ob s ervat ions in ord e r to ob tain high d e t e c t ion rates .. S uch d evi c e s include the. use of vasec tomised marker b ul l s , heat mount detectors and tail p a in t ing all of which have been r epor t ed to p roduce good resul t s ( Shres tha, 1978) .. Tail p a in t ing as a me thod of d e t e c t ion is a p a r t icularly. convenient and low cos t t echn ique (Ma cmillan� and Curnow, 1 9 7 7 ) . b.. Anoes t rous Synd rome. Anoes t rus may be d e f ined as failure to show ove r t s igns of oestrus ( F ie lden et a l . , 1 9 7 6 ) ,. Def ined in this way i t i s not. neces s a r i l y synon)rmous wi th ovar ian ina c t ivity s inc e there may b e many f a c tors which can l ead t o the v i s ib l e s igns of heat in c a t t l e b e in g supp res s ed . this phenomenon .. 'Anoes t rous s ynd rom�' may thus b e a b e t t e r t erm for Convenien t l y, the 'anoes t rous syndrome' can b e.

(25) 15. c l a s s i f ied a s o f the pre -service or po st- s ervice type .. Obviou sly ,. submis sion rate w i l l be a ffected by pre - s ervice anoe stru s . An inve s tiga tion of 294 herds i n the Taranaki distr ict indicated ' pre - serv i c e anoe strous syndrome' wa s the major cause for cows. that the. not b e i ng submitted for mating during the 4 weeks of the breeding period; 1973 ) .. this problem was int e n s i fied in young animals. (Fie ldenarrl M:tcrniThn,. Addi tional f indings from a further i nvestigation of c ows in. herds i n the Manawatu/Wairarapa districts i s shmvn i n Table V .. TABLE V:. OVARIAN S TATUS OF COWS SHOWING 'PRE-SERVICEANOESTROUS SYNDROivlE'. Age a t calving. No . of examinations. % inac tive ovaries. 2 year. 1 028. 85. 3 year. 438. 74. 4 and over. 808. 47. ( af ter Fie lden et a l . , 1 976 ) The high incidence of i nac tive ovarie s in 2 year olds wa s a ttributed to the c ombined e f fe c ts of mee t i ng their nutritio�al demands for growth and lac tation as we l l as coping v1ith social stre s s e s within the h e rd. (Fielden et al . ,. 1 976) .. This problem of 'pre-servic e. anoes trous syndrome' al though o f temporary nature i s expensive i n t e rms o f time lost before breeding c a n commence a fter ca lving. Anoestrus in dairy cattle ha s been r eviewed by Morrow. ( l969a)and. furthe r considerations of the problem as i t exis ts in New Zeala nd can. be found in the reports of Fie lden et a l . , c.. ( 1976 ) .. Post - calving inte rva l. After partur i tion, anima l s n ee d some time for proper u terine i nvo lution and the re - estab li shment o f ovar ian ac tivity to occur . American worke r s. ( Marion and Gier,. 1 968; Wagner and Oxenreide r ,. 1 97 1 ). have indicated tha t the proc e s s o f u terine involu tion i s complete with i n 21 - 30 day s of parturi tion and tha t the first ovulation occurs with i n 40 days .. Ma ture cows ovulate ear l i e r in the post-partum. than the young cows .. Mo l l e r. ( 1 970 ). repor t ed that mature cows. pe riod.

(26) 16. exp e r ienced their f i r s t pos t-par tum ovula t ion a t an average of 36 days c omp ared with 52 days for 2 year and 3 y ear-old cows . Apa r t from the pos t-partum p er iod required before cycl ical act ivi ty r e c ommences in the cow a f t er she has calved, the post partum p e r iod that elaps es b e fore f irst mat ing after calving markedly i n f luences f e r t il ity .. Thus, when the in terval f rom. c alving to m a t ing is l e s s than 6 0 d ays, chanc es of conc ept ion are redu c ed ( Old s and Coop er, 19 7 0 ; 1974 ;. B r i t t , 19 7 5 ) .. Macmillan, 19 7 2 a ;. The inf luenc e. Wh i tmore et al . ,. of this in t erval on concept ion. rat e s is shown in Tab l e VI .. TABLE VI :. THE INFLUENCE OF INTERVAL FROM CALVING TO MATING ON CONCEPT ION RATES. Pos t-partum int erva l Und e r 4 0 days. 4 0 - 5 9 days. At l eas t 60 days. 2 year-old cows. 52%. 59 %. 65 %. Older cows. 40%. 58%. 68%. (af t e r Macmil lan, 19 7 2 a ) . B ri t t ( 19 7 5 ) in a review, e s t imat ed tha t fert i l i t y was 2 5 % for cows b re d during the f irs t 2 0 day s a f t e r calving, then in creased to about 6 0 % at 60 days pos t -par t um and s t ab i l i s ed the rea f t e r . Apparen t ly, mat ing cows wi thin 60 days p os t -p a r tum giv e s lowe r conc ep t ion r a t e s and r equires more s ervices / concept ion, b u t it has no c umulat ive det rimental e f f e c t on f er t i l i t y (Britt, 1 9 7 5 ) . d.. Mul t ip l e suckl ing. Macmillan ( 1 9 7 2b ) ind ica ted that mul t ip le suck l in g in creased both the duration of anoes t rus and the inc i d en c e of s i l en t hea t ..

(27) 1?. S aidudd i n e t a l . ,. (1967 ) worki ng w i th primi parou s Hol stei n c ows ,. noted that the mea n i nt erlal from parturi t i on to first oestrus wa s 30 d ays a nd 4 5 days for non- suck l ed a nd suckled c ows r es pectively . S imilarly ,. Baker. (1967) f ound a high cor r elation betwe en the l ength. of the suck l i ng peri od a nd the i nt erval t o f i r st oestrus .. I n his. subs equent studies however , when the body weight of the a nimals was s igni ficantly higher , thi s c orrelat i on was no. l onger s igni f icant .. Thus the qu esti on of whether the nutriti onal s ta tus of the animal can c ompensate f or th e the effect of suckl i ng is unres olved . Usi ng the criter i o n of ovarian growth , Mol l er ( 1970 ) noted highly s i g ni ficant dif f erenc es i n ov arian s i ze b etween c ows milked and c ows suckled twi c e per day or c onti nu ou s ly .. Thi s same author.. als o noted a 57% s i l ent heat occurr ence i n mi lked c ows when ovulat i on oc curred duri ng the first 60 day s after ca lvi ng as c om pared to a 100% occurrence i n the same per i od f or suck led c ows . The evidenc e then clearly demonstrates that the suck l i ng stimulus delays th e onset of ovarian a ctivity and the degree of thi s delay i s i nfluenc ed by the suckl i ng intensity . e.. Ma nagement fac tors. Managerial dec i s i ons can i nfluenc e submi s s i on rates ,. for. exampl e d ec i s i ons as t o whether a particular individual i n the h erd should be br ed or not .. Furthermor e, with the curr ent emphasis that. ha s b een placed on c onc entrated c a lvi ng patterns in New Z ealand , t ogether with the rea l i sation that a n i ni tial breed i ng of a c ow not i n. heat ha s l i ttle i f a ny d etrimental effec t (Macmi l la n et a l . , 1977a ) ,. liberal i nt erpretation of oestrus t ends to r esul t i n a n arti ficially high subm i s s io n ra te.. BODY W EIGHT AND FERT I L I TY i.. Phy si olog ical Ba s i s of Nu triti onal I nfert il ity There is no s im pl e r elati onshi p between nutri tion a nd. reproduc t i on ( Lammi ng , 1973).. The direct a nd s ome i ndirec t ef f ects. of nutri t i on on r eproduc tion c a n b e diagrarnatically repres ented as. in Figur e 1.. Not a l l the impl icati ons shown i n thi s figur e have. b een proven bey ond d oubt and thi s i s particularly true of those.

(28) 18. F igure 1 :. The Effects of Nutri tion on Reproduc tion. P sycho logical influence. /. /. /. /. ,.,�. Central ner,rou s sy s�ern. N U TRITION Hypotha larno hypophyseal c omp l e x. Target tis sue. Endocrine. gl ands. Thyroid Adrenal cortex. gonad +. ( pl acenta ) �====�==� Negative feedback. Proved relationship P o s sible r e l atio nship. (a fter Lammi ng , 1973). - - - -- ---- - ---- - - - --.

(29) 19. a spe c t s i nvolving the in fluence o f nut r i tion on gonadotropin secretio n and release. ( Lammi ng ,. 19 7 3 ) .. Man ipu lation o f nutrient i ntake ha s characteri s t i c e f fects on Thus Wiltbank et a l . ,. the ovary .. ( 1 964 ). a nd Lamond. ( 1 9 6 8 ) have. related r educed fol l i cular deve lopment to poor nutri e n t intake i n. A short-term low plane of nutrit ion has been a l so shown to. the cow .. reduce fo l l ic l e numbers and p l a sma prog e s t e rone leve l s i n be e f hei f e r s. ( Hi l l. et. a 1 . , 197 0 ) .. e f fe c t of undernut r i tion;. I t i s not c lear if thi s i s a pr imary. generally nutr i tional i n fluence s on. the a c ti v i ty of the gonads ar e b e l i eved to be mediated d irectly or i ndi re c t l y via the p i tuitary g l and rather than directly on the gonads ( Lammi ng , ii .. 197 3 ) .. P a r ti tion o£ Nutr i ents It is said tha t the cow d ivide s its food , ma i ntenance nee d s. apart ,. between milk produc tion a n d l ivewe i ght ( Bro s te r ,. 197 2 ) .. Further divi s ion o f nutr ients between milk production a nd l iveweight i s r e l a ted to the cow ' s mi lk y i eld potent i al , her s tage of lactation and her l evel o f food intake. ( Mo e et a l . ,. 1 9 7 1 ; Bro s te r ,. 197 2 ) .. However , under condi tions o f nutr itional i nadequac y , m i l k produc t ion i s atta i ned at the expen se o f body re serve s as seen in early l ac tat ion ( Bro s te r ,. 197 2 ;. B i ne s ,. 1976) .. Inadequacy in nutri tion may be due to. a frank short supply of feed to the an imal but it is generally a the consequence o f the genetic a bi l i ty o f/ a n imal to produc e milk dur i ng early la ctation whi ch exceeds i ts abi l i ty to inge s t s u f f ic i ent feed to mee t its requirements for ene rgy .. S ince production of milk dur ing. early l a c tation has a high pr iority in the dairy cow , produc tion o f milk may continue a t high l eve l s de spite a n insu f f i c i en t d i etary energy i ntake. ( Hoe et a l . , 1 9 7 1 ) .. Th i s i s po ss ible becau s e the cow. ha s the abi l i ty to draw upon i ts t i s sue r e serves to provide the energy which i s lacking in the diet . u sed. The amount o f t i s sue ene rgy. for th is purpose w i l l depend on the condition o f the COW at. the. time of partur i tion , the gene t i c po tenti a l of the a n imal for milk produc t i o n ,. the feed intake dur ing early lactation. (Moe. et. al . , 1 9 7 1 ). and the magnitude o f the neg a t ive e ne rgy balance which can exi s t w i thou t the produ c t ion o f keto s i s ( Chalupa ,. 1 9 74 ) ..

(30) 20. Understandably ,. l ivewe ight los s e s are a s soc iated with high. leve l s of milk produc tion and/or low leve l s of intake .. The manner. in which the cow's yield and rate o f l iveweight change respond independen t l y or jointly to the p lane of nutrition is i l lu s trated i n F igure 2 .. Cows o f gre ater d airy meri t produc e more milk and show. l e s s l ivewe ight ga in from a g iven amount of food .. Converse l y ,. the. low yielders increase in body wei ght at the expense of milk yield .. Simpli f i ed Mode l to De scribe the Relationship o f Food. Figure 2 :. to Milk and Liveweight in Dairy Cows accord i ng to Response s to Level o f I n take. ( Broster ,. 1976) .. -----. ,. I. c ow of low da iry merit cow o f high da iry merit. /. I I. ,. I I. .__..... tl. -. -. -. --. --. _,. .,.. , � , � "' , � .,.. __ __ _ -. iii. f ee d. Pattern o f Liveweight Change Chang e s in l iveweight of l a c ta t i ng c ows re sul t from a. combination of growth , pregnancy and a l ternate depo s i tion and subsequen t c a tabo l i sm of body fa t t i ssue Usua l l y ,. ( Mi l l er et a l . , 1 9 6 9 ) .. l o s ses of l iveweight are observed in e arly l a c ta tion where. milk yields are high a nd voluntary intake i s inadequate .. Hutton. ( 19 6 3 ).

(31) 21. observed that the i ntake o:f; pastu r e did not reach i t s maximum un t i l f ive months a f te r c a lving a n d tha t cows in e a r l y lacta t i o n were i n a state o f n egative energy balance and lost weight . gra s s fed cattl e .. H i s r eports appl ied to. Except ion s to thi s general rul e have been noted i n. he i fe r s severe l y under fed before c a lving ,. i n bee f h e i f e r s of low milk. y i e ld pote ntial , and in cows fed dried herbag·e and barl ey diets. 1976) .. (Broster ,. The reasons for thi s i nab i l i ty of c ows to consume enough food. to me e t the ir demand , parti c u l a r l y in early l a c tation ,. i s no t yet c lear .. Food intake actua l l y incre a s e s w i thin a few days after pa rturi tion but at a rate which is s lower in terrns o f e nergy i nput than the increa s i ng rate of e nergy output in milk. ( Forbe s ,. 1 9 7 0 ; B ine s ,. Remova l. 1976) .. of the foe tus and a s soc iated t i s su e s at parturi tion wi l l increa s e conside rab ly abdomina l capac i ty a nd thi s i n turn .,.,ould be expec ted to permi t a greater rumen f i l l .. P erhaps ,. as suggested by B i n e s. (1976) ,. f a t depo s i ted within the abdome n be fore calv i ng has to be mob i l i ze d be fore rumen f i l l c an b e maximi s e d . S tud i e s have shown that the increasing volume o f the ute ru s and fat depo s i ted within the abdomen both cau s e a reduc tion i n rume n capac i ty in the l a s t stages of pregnancy and l ead to a de c l i ne in roughage intake dur ing thi s pe riod. ( Forbe s ,. 1970 ;. Bines ,. 1 9 7 6 ; Journet a nd Remond , 197 6 ) .. Wi th die t s where i ntake is not th,:mght to be limited phy s i ca l ly ,. some. me tabo l i c fac to rs might cau s e the dec l i ne in intake ;a h igh l evel o f o e s trogen i s suspe c ted to b e such a facto r. ( Bi ne s ,. 1976 ) .. Anothe r. po s s ibi l i ty is that the rate o f m e tabo l i sm in both the rumen and other ti s sue s take s t ime to adapt a f t e r ca lving to the incre a s ed demand for nutri e n t s. ( B ines ,. 197 6 ) .. The long time n eeded for the breakdown o f. food i n to f ine particles b y chewing and b y rumen microb i a l digestion may a l s o be a l imitmg factor s ince in f e eding tria l s a rapid and s igni f i c a n t increa s e in the intake of pe l l e ted ground feeds , compa red to long forage s , has been noted a fter calving ( Journet a nd Remond ,. 1976) .. As the cow move s through l ac tation , m i lk yield and i t s re spo n s ivene s s t o var iation in i ntake dec r e a s e s. et al . ,. 1969) .. (Bur t ,. 1 9 56 ; Bro s te r. A greater re spo n s ivene s s in l ivewe ight c hange wou ld. ther e fo re · be exp ec ted but evidence that thi s is in fact so is l imited { Bros t e r et a l . ,. 1975 ) .. Neve r the l e s s ,. the weight of the cow genera l l y. stabi J . i s e s around t h e sixth wee k a f ter par turition and thereafter may.

(32) 22. be expected to s t a r t t o r i se a s mid- l a c ta tion proceeds B ro s ter ,. (Mi l l e r et al. l 9 6 9 ),. 1 97 3 ) .. The extent of the fa l l in weight in early lactation and the subs equent we i ght gain. depend both on the leve l of feeding o f fered. the an imal a s w e l l a s the type o f r a t i o n .. When a ration h i gh in. concentrate s wa s given a d l ibi tum to c ows a fter partur i t ion ,. a. s i gn i f icant increase in energy i ntake resulted thus reduc i n g the inte rval b e tween peak y i e l d a nd peak intake ;. a comp l e te balance betwe e n i ntake. and output of e nergy did not occur however and l ivewe ight lo s s e s s t i l l o ccurred in a l l an imal s. ( Broster and Strickla nd , 1 9 7 7 ) .. The e ff e c t o f feed ing varying l ev e l s o f suppl ementary concentra tes. to g�a z i ng d a i ry cows has been comprehens i ve l y revi ewed b y Leaver. et a l . ,. ( 1968 ) .. They conc luded tha t th ere wa s not a marked advantage. from feeding c o ncentrates to moderate yi e lding cows at gra s s . Simi lar l y ,. Taparia and Davey. ( 1969 ). found that feed ing conc entrat e s. depre s s ed vo luntary i n take of pastu r e and had l i ttle e f fe c t o n mi lk Thi s suppleme ntation with c o n c entrates re sul ted in a decrea s e. y i e ld .. o f about 0 . 6 5 kg pa sture d r y ma tter intake per k g concentrate dry matter consumed .. In add i t ion ,. the r e were no s igni f i cant d i f ferences. in l i vewe igh t ga in between concentrate supplemented groups at e i ther. 2 . 7 kg or 4 kg per day o f conc entrate p er head and the pas ture fed · a d l ibi t um. g r oup .. C l e ar l y , conc e n trate feed i ng i s wa ste fu l when such. feed- stu f f s become a sub s t i tute for pa s ture .. Howeve r ,. conc e n trate s. can play a u se ful role i n of fsetting short-term feed shortage s which are prone to o ccur under some s i tua t i o n s o f h i gh s tocking rate ( Leaver et a l . , 1 9 68 ) .. iv .. The Re l a tionship Between Body Condi tion and Fert i l i ty S i z e of animal v a r i e s betwee n a nd within. breeds .. Linear. measureme n t s such as he ight to w i th e r may be a better me asure o f s i ze but body we i ght is commonly used .. For g ra z i ng lactating cows , body. weight me a sur ements can provide a r ea sonable but crude e st imate o f their nutr i t ional state s .. The s e body weight measureme n t s c a n be. mi s leading i n he rds sub j e c t to marked changes in food typ e s. l97D ). .. A h eavy animal. good condi t io n .. does. . not n e c e s sar i l y mean. ( McClure ,. that i t i s i n.

(33) 23. The term body condition, o n the other hand, is the degree o f fatness shown b y the animal.. It i s independent o f the size of the the animal o r gut fill and it reflects janima� recent nutrit ional history. Investigations at the National Institute for Research in Dairying (Pope e t a l . , 1 97 6 ). with cattle classified as having poo r , moderate. and good or very good body condition had shown that the pregnancy rates ( 5 0 - 7 0 days after A . I.) o f maiden heifers were 4 2 , 6 3 % and of lactating cows,. 43 ,. 57,. 7 2 , 6 0 and. 63 and 4 6 % respectively in each. category of body condition. Body condition scoring is usually based on some numerical. At Ruakura, a scale of l - 1 0 is used and cows at grade 5 are. scale.. considered to be in ideal condition for calving (Trigg and Cook ,. 197 7 ) .. Also, a condition grade change of 1 is taken to be equivalent to about 3 0 kg liveweight in mature cows and 3 5 kg in heifers .. Understandably ,. visual ass essment of body condition is more re liable in experienced eyes.. v.. The Re lationship Between Body Weight Change and Fertility McClure. ( 1 9 6 5 ) from a study of Jersey herds in New Zealand , had. observed that the infertile cows were those which lost the most weight between calving and mating and/or were still lo sing weight at the time of mating.. In. ano'cher study , the same author. (McClure ,. that although weight change was rela�ed to fertility , was no t a strong one .. 1 9 7 0 ) found. the re lation ship. Two groups of cows which lost weight in the l as t. two weeks before mating at a rate o f 7 . 8 k g and 9 . 9 kg per cow per week still had normal non�re turn rates of 69% and 6 7 % respectively . King ( 1 9 6 8 ). in a study of 1 7 9 Ayrshire cows, similarly noted. that 9 8 cows which gained in body weight during the breeding period had a higher conception rate to first service 81 cows which lost weight ( 16 % ) .. (77 . 6% ). than did the. Additionally , in the latter group ,. none of the 8 cows which lost over 2 5 . 5 kg bodyweight held to service. (see Table Vll ) ..

(34) 24. TABLE V l i :. EffECT Of CHANGE IN BODY WE IGHT ON FERTILITY OF DAI RY COWS ( Ki ng ,. Total no . QQWS .. Q:f;. 1 9 68 ). ·. No . o f CO'tlS . . . conce ived. .. .. Change in body weight o v e r 4 . week period ( kg ). Conceptio n rate ( % ). Ri s e s. 2. 2. 4 7 . 7 and over. 100. 4. 4. 38 . 2 - 47 . 3. 100. 10. 10. 25 . 5 - 37 . 7. 100. 31. 24. 12 . 7. 51. 36. 25 . 0. -. 0 . 45. 77 . 4. 12 . 3. -. 70 . 6. Sub- total. 77 . 6. Fa l l s. 41. 11. 32. 2. 12 . 7. -. 25 . 0. 6.2. 8. 0. 25 . 5. -. 37 . 7. 0. 0 . 45. 26 .8. 12 . 3. -. Sub - total. I n a furthe r s tudy. ( Pope et a l . ,. 19 7 6 ) ,. 16 . 0. lasting from s i x wee k s. b e fore to s ix w e e k s a fter mating , h e i f e r s which were f e d t o gain w eight dai ly had a pregnancy rate o f 68% as c ompared to 45%. in a s ec ond group. whi c h were los i ng 0 . 2 5 kg/day . Further evidence for th i s po s i tive a s sociation between anima l s g a i ning weight a nd higher pregnancy rate s come s from work with b e e f c a tt l e reported by Wil tbank e t a 1 . � 1 9 6 2 ; Donaldson. 1 9 64 ) , Dunn e t a l . ,. ( 19 6 4 ). and. et a l . , ( 1967 ) .. In contr a s t to the above f inding s ,. Boyd. ( 19 7 2 ). reported tha t. whi l e there wa s a b e ne f i t to conception when the cow wa s ga i n i ng weight , thi s wa s not s ta t i st ic a l l y s ignificant a n d a l o s s o f l ivewe ight wa s not detrimental to ferti l i ty . top ic ,. S imi lar l y Bro ster. ( 1 97 3 ) ,. in a review o f the. sugge sted that there was no c o nc l u s ive relat ionship b e twe e n. f e r t i l ity and l iveweight change for c a t t l e rece iving moderate to g e n erous planes o f nutrition .. Furth e rmor e , based on h i s own work , he. found that a mod e rately inadequa te rat i o n in the first sixteen weeks.

(35) 25. o f lactation did no t a ff e c t the fertili ty o f Frie sian hei fers c a lv i ng for the f i r s t time a t about two-and -three -quarter years o f age . The abi l ity to conceive may be more a function of body we ight. per se and not a state of changing body we ight during the po s t -partum period. ( Richardson et a l . , 1 9 7 5 ) .. Supporting evidence for thi s wa s. noted in the work o f S tee nkamp e t a l . ,. ( 19 7 5 ). whi le Lamond. ( 19 7 0 ) , a l so. expre s se d the opi nion that fat he i fe r s may show good ra te s o f ferti l ity though currently los i n g weight .. Mol l e r and Shannon. ( 1 9 7 2 ) on the o ther. hand noted for cows mated 3 0 - 5 9 day s and mo r e than 5 9 days po s t -p a rtum that tho s e gaining we i ght had signi ficantly h igher non - r e turn rate s than those ma i ntaining body weight . Whi l e more i nformation i s yet required to c lari fy thi s relationship between body we ight change and f e r t i l i ty ,. i t i s c l ear that. animal s a t the lower end of the wei ght and body condi tion d i s t r ibution wi thin an age group a t the time of breedins have poorer bre eding per formanc e .. There may wel l be , however ,. some type o f thr e sho l d ab o ve. which such a r e l ationship doe s not app l y .. vi .. Fac tors which may Influence the Re l a t i o n ship between Livewei ght and Ferti l i ty . a.. Prote in - e n e rgy re lat ionships .. I t i s probably true tha t the pla�e o f nutri tion a f f e c t s reproduc tion b y virtu e of i t s carbohydrate a nd energy c ontent .. Howev e r ,. nutr itional infer t i l i t y may b e caused b y o th e r nutr ient de fic ienc ie s . Much o f the evidence r e l ating reduced fer t i l i ty to plane of nutri tion , a s outl i ned by Bro s t e r. ( 1 97 3 ) , Mc Clure. not a l low thi s d i s t i nc t ion to b e made .. ( 19 7 5 ). and Topp s. Roberts. ( 19 7 1 ). ( 1 9 7 7 ) , doe s based on c l in i cal. observa t ion s , has indi cated tha t mo st f i e l d c a s e s o f reduced fert i l i ty or ster i l i ty of nutr i tional origin are u s ua l l y due to mul t iple d e f ic iencie s . There i s an optimal bal ance between protein and energy .. Gould. ( 19 6 9 ) h a s sugge sted t ha t an exc e s s of pro te i n can lower the fert i l i ty statu s .. The primary e ffect o f thi s exc e s s o f crude pro tein i s to make. food unpala tabl e ; o f energy level s .. thi s re sults i n a reduc t i o n o f feed intake and thu s.

(36) 26. b.. Yield l evel and f e r ti l i ty. Op inions r e garding the r e la tionsh ip between produc tion and ferti l i ty rema i n. var ied and c o nc lusions confu s ed .. A ccording to a recent l it erature review by Shr e s tha. ( 19 7 8 ) , many. of the reports which ind i c a te an inverse relationship between production and f e r t i l i ty have been based on total milk produc t ion rather than the l evel o f produc t ion pr ior to and duri ng the ac tual breeding period . The problem i s tha t total m i l k produc tion can be s i g n i fic antly influe nced by l a c tation l ength and by the presence o r o therwise of a conc ep tu s .. It i s thus d i f f ic u l t to say i f high produc tion i s e i ther. the c au se or e f fe c t of poor conc eption r a te s . Other r eports rel a ting. ' conc eption rate '. to l evel o f production. prior to or dur i ng the breeding ;er iod have indicated that whe re negative corre l a tions exi s t they are sma l l and of l i ttle con sequence (Shr e s tha , c.. 1978 ) . Pre - and post-calv i ng feeding. P l ane of nutri t ion , both before and a fter par tur i tion , reproductive p e r formance :. W i l tbank et a l . ,. ( 1 964). influenc e s. observed in beef. cattle that the r e was a cumu l a tive e ffec t on fert i l i ty o f the l evel of f e eding dur i ng pregnancy wi th the l evel of feed ing during l a c ta t ion .. E i the r ,. i f inadequate ,. can reduce fer t i l i ty but the e ffect. o f low post-calving feeding i ncrea sed when i t fo l lowed a low level of f e ed i ng be fore calving .. H ight. ( 19 6 8 ). a l so noted tha t high pl ane s o f. nutr i t ion a fter c alving par ti a l ly overcome the in f e r t i l i ty e f fect caused by a low pl ane dur i ng late pregnancy .. Turman e t a l . ,. ( 19 6 4 ). found that a low nutri tive l evel for he i fers during the i r f i r s t pregnancy had a detr imental c arry over e f fect o n r eproductive performance at their second mati ng s e a so n . Furthermore ,. the time that the nutritional i nadequacy occur s. influences the ou tcome ;. thu s low inta k e s of food e nergy during the. p r e - c a lving period result i n an i ncreased time to the f i r s t po st-par tum oestrus whi l e low intake s o f food energy po st-calving have a more · sign i fi cant e f fe c t on the conception rate to first service et. a l . , 1 96 2 ;. 1964 ) .. ( Wi l tbank.

(37) 27. Level of. d.. Feeding Imme d ia te l y Around the Time o f Service. A r e l ation s!'lip be twe en the reproduc tive performance of sheep and the level o f feeding immediately prior to mating is .,.,.el l e s tabli shed ( Coop ,. 1966). Whe ther a similar relat ionship hol d s for cattle i s not. •. cl e ar . Lamond. ( 1 97 0 ). con s id e r s that very generous feeding before. s ervice might be of l imited value to anima l s i n poor condition but po s s ibly wa s te ful for a n ima l s alread y in good cond i tion .. F ielden. al so stre s s e s that short term a l teration s o f feed input appear. ( 19 7 6 ). to have. remarkably l i ttle e f fect on re turn to cyc l ical act ivity i f the anima l concerned i s in a and King. ( 1977 ). ' reproductively u n f i t '. cond i tion .. S imilar l y ,. Youdan. i nd icate that it i s unl ikely that an incre a s e in. nutr ient i nt ake at or abou t th e time o f s ervic e , w i th the ob j ec t o f rap idly increasing body weight , would improve fer t i l i ty . Brochard. ( c i ted by B ro ste r ,. 1 9 7 3 ) po i n te d out that the plane o f. n u tri tion immed iately a ft e r s e rvice m ight be cr itical to the survival of the fert i l i sed egg . wi th mice ,. McClure. ( 19 7 2 ) , c i ting evidence from stud i e s. s ta ted that s tarva tion immed iate l y before or a fter mating. r e duced fer t i l i ty ;. the pr imary biochemical change a s soc i ated with thi s. i n fertil i ty appeared to b e a f a l l i n blood g l uco s e .. Thi s same author. thus commen ted th at cows may behave l ike the l aboratory rodents s i nce hypoglycemi a had been noted in i n f e r t i l e cows .. TARGET BODY W E I GHTS The idea that ma iden he i fe r s should be wel l grown for age at the time of breeding and that cows should be i n good condi tion at c alving i s in l ine w i th the concept of Lamond Accord i ng to th i s author ,. ( 1 96 8 ;. 1 9 7 0 ) o f a target we ight .. each cow , d epend i ng on here d i ty ,. age ,. l a c tational status and time o f year h a s a high probabil i ty o f conception w i thin a certa in range of body weights and body c ond i tion . concept holds true ,. I f thi s. the n a ma i n concern i n management will be to. a c hieve the targe t weigh t for. a. part i cular c l a s s of cow u s ing a. f e eding · regime that wi l l be e c o nomically sound . i.. Target Body Weights for Maiden H e i f e r s . As d i s c us sed previously , hei fers mu s t a ttai n a certain we iqht.

(38) 28. b e fore they wil l show o e s trus ;. c alving probl ems a l so are rela ted to. the s iz e and phy s i c a l cond i tion o f the he i fer s . Brody ( quoted by Joub er t ,. Thus , according to. 1 9 54 ) , body weigh t r a ther than age should. be used as the cr i t e r i o n for first breeding of farm animal s ; dairy h e i fe r s should be f i r s t bred when they reach two- thirds of their expected mature body we ight . Hight. ( 1966 ). s hould we igh Young. ha s recommended that B r i t i s h bre ed bee f h e i f e r s. 2 7 3 t o 2 9 5 kg t o a l low mating a t fi fteen months .. ( 19 6 7 ) on the other hand ,. found that l ivewe ight at f ir s t mat i ng. had l i tt l e influence on the ab i l i ty o f h e i f e r s to become pregnant . Olds et a l . ,. ( 19 5 2 ). had also noted earl i e r that si. �� i�m. 182 to 4 5 5 k g. i n we ight caused l i tt l e or no e f fe c t on the f e rtil i ty o f F r i e s i a n heifer s . More recently , concept o f. Hanly and Mo s sman. ' critical m i nimum weights '. They d e f i ne the. ( 19 7 7 ). have put forward the. for mat i ng yea r l i ng be e f h e i fer s .. ' cr i t i c a l mi n imum weights ' a s the average weight o f. the breed o r cro s sbred required to attain a n 8 4 to 9 5 % pregnancy rate over a 42 to 45 day mat ing p er iod .. Any he i fe r ha s the po tential to. become pregnant once i t ha s reached puberty but what is more important is the r e -breed i ng p e r f ormance dur i ng the n e x t season according to these author s .. Mating year l i ng he i fe r s below a c ertain min imum we ight. wil l i nvi te reproduc t i ve problems anq increase the cull ing r ate o f s econd o r third calver s . Be tter per forma n c e s at hi gher body we i ghts have been reported by E l l i s. ( 1974 ) who found that the percenta ge of hei fers calving. incre a s ed l inear ly with incre a si ng j o i ni ng w e i ght from 1 7 5 to 2 6 5 kg a t the rate o f 7% for each 10 kg i ncrease in weight ;. increa sed. calvi ng rates with h i gher ma ting we ights wer e also observed by Buck. et al . ,. ( 19 7 6 ) .. Further s upport for thi s concept i s noted from the. work o f Harwin et a l . ,. ( 19 67 ) , Pope. ( 19 6 7 ). and Sparke and Lamond. ( 19 6 8 ). and the results o f two o f the s e groups o f authors are shown i n Tabl e VIn .. *. We i ght e s t ima ted f rom che s t g i r th by S a l i sb ury and Van Demark (19 6 1) .. *.

(39) 29. TABLE VIII : EFFECTS OF WE I GHT AT BREED ING AGE ON REPRODUCTIVE PERFORMANCE OF HE IFE RS. Age and breed. 2 year old Afrikand e r. We i ght. Calving rate (% o f tota l ). (kg). Harwin et a l . ,. 100. >318. Re f erence. 83. 2 5 0 - 3 17. ( 1967 ). <250. 60. 252. 74. Sparke and. Shorthorn -. 2 26. 55. Lamond. Devon c ro s se s. 191. 4. ( 19 6 8 ). <178. 0. 285. lOO. 2 year old. 3 year old. Sparke and. Shorthorn-. 236 - 254. 77. Lamond. Devon cro s se s. 216. 33. ( 19 6 8 ). For dairy he i fer s , Mol l er ( quoted by Fielden ,. 1976). has sugg e s ted. a minimum body w e i ght of 1 9 0 kg for Je r s e y yearl ings and 2 0 0 kg for Fri e s ian-Jer s e y c r o s s year l i ngs i n obt a i n ing optimal submi s s ion rate s when breeding the s e animal s at the age o f f i f teen month s . Davey. ( 1 9 7 6 ) , a fter having examined the re sul t s of experimental. and survey work both i n New Zealand and oversea s , has put forward hi s recommendation about the optimal weight for first breed ing at f i fteen mon th s , and between mating and c alving ,. for Jer s ey a nd Fri e s ian hei fer s. a s i l lu s trated i n Figures 3 and 4 . To reach these targets , ma iden Jer s ey hei fers need to grow at least at a rate of 0 . 4 kg/day from birth to mating ; Fri e s ians at s l ightly greater rates. ( Dave y ,. c ro s s e s and. 1 9 7 6 ; F ie lden ,. 1976) ..

(40) 30. 300. FRIE S IANS ---. 250. ,..... tT> :.:: E-1 :X:: (9 H. � � H. JERSEYS. 200. 150 weaning. 100. ...:!. 50. 0. 1. 2. J. A. S. 3. 0. 4. 5. 6. 7. 8. 9 1 0 1 1 12 13 14 1 5. N. D. J. F. M. A. M. J. J. A. S. 0. MONTHS Fig .. Recommended targ e t l ive weights for Jersey and Fries ian ca ttle. 3:. be tween birth and mating. ( Davey ,. 1976 ). Cal"ing. 450. tT> :.:: E-1 :X:: (9 H. � � H. - - - -- FRIESIANS JERSEYS. 400. 350. 300. ...:!. ,.. ,.. ,.. ,.. ,.. ,.. ,.. ,.. ,.. ,.. ,.. ,.. /. /. /. /. �. ,. //. 250. 200 1 6 l7 18 19 20 2 1 22 2 3 2 4 . N. D. J. F. M. A. M. J. J. MONTHS Fig .. 4:. Recomme nded target l ive weights for Jer sey and F r i e s ian cattle between mat ing a nd c alving. ( Davey ,. 1976).

(41) 31. Even though it has been s tr e s s e d that body weight i s the mai n cri terion for f ir st breeding o f c a tt l e ,. there i s a n age be low which. they should no t be hred s i nce rearing exper iments have shown that h e i f er s bred a t a very ear ly age have given d i sappointi�g milk yie lds in spite of hav ing achieved adequa te body weights at the time of breeding (A . D . A . S . ,. 1973 ) .. Thi s adv isory body in the Uni ted Kingdom sugge s t s. t h a t n o h e i f e r should be f i r s t b r e d be fore four teen months o f age . Wicker shaw a nd Schu l t z. ( 19 6 3 ). al so found that first lactation mi lk. and fat produc tion i ncre a s e s a s age a t first breed ing incre a s e s . a previous rev i ew o f early bre eding S chultz. In. ( 19 69 ) conc luded tha t. breeding a f t e r e leven mon ths was mor e de s irable than breeding earlier ; Warner. ( l9 7 0b ). added a further r ecomme ndation that breeding should. pre ferably be carried out a f ter the he ifers had exper i e nced two or · three o e s tr.ous cyc les . It i s wor thwhile. no t in g ·. that the nutr i e nt requireme n t s of. young stock ac c ount for about 1 5 % o f the total food supply o n the farm . Thus a moderate. increa s e in the l eve l o f feedi ng in order to atta i n. appropriate target weights at mating a n d at c alving a r e unl i k e l y to have profound e ffects on the overa l l feed suppl i es of the property ( Dave y ,. 197 6 ) .. S ince in a gra z i ng s i tuation the growth rate of h e i f e r s i s dependent upon the ava i lable pasture i t may b e j u sti fied t o u s e the supplements dur ing /period where there i s a shortage o f gra s s . Fo l lowing tr i a l s carried out at Ma s se y Unive r s i ty , Hal ford. ( 1976). suggested that meal feeding could b e the cheape st feas ible way o f achieving high growth rate s .. The u se o f me a l f e eding could then be. e xtreme ly u s e fu l to yearl i ng he i fe r s when the i r previous growth rates have been curta iled i f targe t we i ghts are to be achieved . ii .. Targe t P r e -Calving Weights for Cows Targe t l ive we ights immed i atel y p rior to ca lving a s sugge s ted. by Bryant. ( 19 7 7 ). are shown in Tab l e I X .. The s e can be achieved by. per iodic weigh i ngs of the animal s and appropria te feeding ..

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