Variables that influence outcomes of AI programs: Cow Biology

Transcription

1 Vribles tht influence outcomes of AI progrms: Cow Biology Sndy Johnson, Ph.D. K-Stte Reserch & Extension Northwest Reserch & Extension Center, Colby, KS Producers tht chieve excellent responses to AI progrms hve lerned to mnge number of detils. Vrious mngement decisions interct to influence cow s bility to resume norml estrous cycles before the strt of the breeding seson nd conceive erly in the breeding period. The gol of this pper is to review some of the fctors tht impct the cow s bility to respond with high fertility to synchroniztion protocols. A key determinnt of reproductive efficiency in beef cttle is the intervl from clving to the resumption of norml estrous cycles, lso known s the postprtum intervl to estrus. Fctors such s cow ge, genetics, nutrition, clving difficulty, bull exposure, suckling stimulus, nd mngement cn ll impct the postprtum intervl. For review see Short et l., 199 nd Yvs nd Wlton,. Nutrition is often the biggest limiting fctor in delyed rebreeding in commercil cow herds. Controlling winter feed costs re criticl to lowering overll cow herd production costs, yet must be done in wy to chieve profitble level of reproduction. Body condition score is n ccurte indictor of cow s body energy or nutritionl sttus. In generl, postprtum reproduction is impcted more by energy deficiencies before clving thn fter clving. The reltionship of body condition score t clving nd postprtum intervl to estrus is not uniform cross condition scores. Low post-clving nutrition hs less impct on the Figure 1. Reltionship of intervl from clving to estrus (PPI) nd body condition score (BCS) s ffected by levels of postprtum diets (Short et l, 199). 1

2 postprtum intervl to estrus in cow tht clves t body condition score of 6 thn one tht clves s 4 (Figure 1; Short et l, 199). Only moderte improvement (reduction) in postprtum intervl to estrus is expected when cow tht clves in body condition score of 3 receives high nutrition compred to dequte nutrition post-clving. Becuse first clf heifers hve dditionl nutrient demnds for growth, shortflls in nutritionl progrms re emphsized in their reproductive responses. First clf heifers tht clved t body condition score of 5 or Figure 2. Postprtum body weight of heifers with body condition <5 or 5 t clving nd fed to gin or mintin weight. Pregnncy rtes re on the right side of chrt. Adpted from Bell et l., 199. greter tht were fed to either mintin or gin weight for weeks fter clving hd similr pregnncy rtes (91 nd 94%, respectively; Figure 2; Bell et l., 199). Heifers with body condition scores less thn 5 t clving nd fed to gin weight were ble to compenste in body weight but not reproductive response. Pregnncy rte ws 36% in heifers tht hd body condition score less thn 5 t clving nd were fed to mintin weight, wheres those tht were fed to gin weight fter clving did so, but pregnncy rte (66%) ws still below those of heifers with body condition 5 t clving (> 9%). Tble 1. Predicted number of dys from clving to first estrus s ffected by body condition score chnge fter clving in young beef cows (Llmn et l., 1997) Clving Condition score chnge fter clving to dy 9 postprtum BCS Llmn nd co-workers lso evluted effects of body condition score chnges in young cows fter clving on the postprtum intervl to estrus (Tble 1). Thin cows tht gined s much s two body scores fter clving still could not chieve the postprtum intervl to estrus s those tht clved in body condition score of 5 or greter. Stevenson nd co-workers, 3, exmined the effects of body condition, cow ge, nd dys postprtum of lctting beef cows on the initition of estrous cycles nd their influence on the proportion of cows cycling before nd in response to synchroniztion protocols, s well s their effect on resulting fertility. Conception during the first week of the breeding seson is limited by the proportion of cows tht hve resumed norml estrous cycles (cycling) before the 2

3 beginning of the breeding seson. Only 54% of 3,269 beef cows studied were cycling before the onset of the breeding seson. Cow ge, dys postprtum, nd body condition score t breeding Percent cycling Figure 3. Effect of intervl between clving nd breeding on proportion cycling t the strt of the breeding seson < >9 Dys postprtum t breeding influenced the proportion of cows cycling before estrus synchroniztion s ssessed by concentrtions of progesterone in blood. Compred with mture cows (64%), fewer first clf heifers were cycling (55%), despite clving up to 23 dys erlier. In contrst, no difference in intervl to first postprtum estrus ws found between cows tht were 2, 3 or 4 yrs of ge (Cushmn et l., 7) when body condition score t breeding verged 6.1 for 2 yer olds (1.4 units bove Stevenson et l., 3). The percentge of cows cycling incresed in slightly curviliner fshion for ll cows regrdless of ge cross dys postprtum (Figure 3). Proportion cycling reched pek t 81 to 9 dys, nd tended to decrese therefter. Averge dys postprtum t the onset of the breeding seson were 86 for 2-yer old cows nd 68 for mture cows. The decresed percentge of cycling cows for those >9 d postprtum my be prtly reflection of reduced cyclicity in 2-yer old cows, which constituted 85% of the cows in this intervl. Similr to dys postprtum, the percentge of cows cycling incresed linerly with incresing body condition (Figure 4) indicting tht cows in lesser body condition were t greter Figure 4. Reltionship of cow body condition t breeding to cycling sttus before synchroniztion Percent Cycling < >6 Body Condition Score risk for not cycling t the onset of the breeding seson. No interctions were detected between cow ge nd body condition or cow ge nd dys postprtum. Percentge of 2 yer old nd mture cows cycling by 21 dy clving periods is illustrted in Figure 5. For 2 yer old cows, the cycling sttus t the onset of synchroniztion tretments ws not different mong the first three 21-dy intervls of the clving seson, but ws greter thn the very lte-clving cows (>63 d 3

4 into the clving seson). These results support the generl recommendtion to use shorter breeding seson for heifers to void problems with re-breeding lte clving heifers. In contrst, cycling rtes were greter for older cows tht clved during the first 42 dys of the clving seson thn for those tht clved fter dy 42. Erly clving is criticl becuse it llows more time for cows to resume estrous cycles before the breeding seson. The bility to induce ovultion in non-cycling cows is key to the effectiveness of some of the more recently developed estrus nd ovultionsynchroniztion protocols. Even in the best of situtions there re likely to be mix of cycling nd non-cycling femles to be bred. Ovultion ws induced most successfully in noncycling cows fter CIDR or 14-d feeding of melengestrol cette (MGA). Induction of ovultion ws limited in 2 yer old cows until body condition scores were 5. (Figure 6). In older cows, induction of ovultion incresed linerly with incresing body condition. In erly postprtum cows ( dys postprtum), progesterone from the CIDR ws more effective tht MGA (Perry et l., 4) for inducing ovultion nd resulted in higher proportion of lutel phses of norml length. More cycling nd non-cycling cows showed estrus fter synchroniztion protocols tht included progestin compred to protocols tht used only GnRH nd prostglndin or 2 injections of prostglndin (Stevenson et l., 3). Percent Induced Percent cycling Figure 5. Cycling sttus before synchroniztion by dys of clving period < > b yr >2 yr Cow Age b 172,b Synchroniztion protocols tht include CIDR or other progestin cn be used in noncycling cows to chieve pregnncy Figure 6. Proportion of non cycling cows induced rtes to fixed timed AI similr to to ovulte by synchroniztion protocol cycling cows, provided the noncycling cows re not too deep in nestrus. Severl studies hve 2 yr >2 yr found pregnncy rtes to fixedtime AI in non-cycling cows equl Prity BCS P<.5 to or even greter thn those in cycling cows (Dobbins et l., 75 9; Wilson et l., ). The 81 progestin in the protocol mimics the short rise in progesterone tht often precedes the first norml < length estrous cycle of either cows Body Condition Score or heifers trnsitioning out of period of nestrus. 4

5 Cows tht clve erly hve more time to resume norml estrous cycles before the breeding seson strts nd re more likely to conceive erly in the breeding seson. The cow tht clves on the first dy of the clving seson hs 82 dys until the strt of the breeding seson (Figure 7). A cow tht clves on dy 21 of the clving seson hs 61 dys from clving until the strt of the next breeding seson, Figure 7. Effect of clving dte on dys to strt of breeding seson Dys of clving seson 1 21 Feb 27 Cow A clves Mr Cow B clves Cow A Cow B April 29 Cow C clves Cow C Strt of Breeding Seson My Dys wheres the cow tht clves on the lst dy of dy clving period only hs 21 dys until the strt of the breeding seson. If this cow cycles for the first time t dys postprtum, she would hve dys to conceive in dy seson. Anlysis of postprtum intervl to estrus in Cycle VII t the Met Animl Reserch Center found rnge of 56 to 68 dys depending on breed when body condition score ws 6 or greter t the strt of the breeding seson (Cushmn et l., 7) Depending on the initil clving distribution, using synchroniztion protocol every yer cn grdully increse the proportion of cows tht clve in the first dys of the clving seson nd subsequently increse the pregnncy rtes to AI in prllel fshion. Dt shown in Figure 8 represent the proportion of the Figure 8. Clving distribution for the sme herd over five clving sesons Percent Clving st 2nd 3rd 4th 5th 6th Weeks of clving seson *Estrus ws not synchronized in 1998, single fixed-timed AI in ech following yer except in, 5 dys of AI. mture cow herd t the Agriculture Reserch Center in Hys tht clved ech week over 5 yers beginning in Only nturl service ws used during breeding in 1998 so tht the clving distribution in 1999 represents no estrus synchroniztion. In ech of the following yers, vrious single fixed-time AI protocols were used, with the exception of the breeding seson where there ws 5 dy period of AI fter observed estrus. The breeding seson ws dys long in 1999 nd nd finl pregnncy rtes were over 95%. The breeding seson ws shortened to 46 to 51 dys in subsequent yers with finl pregnncy rtes from 94 to 95%. 5

6 When ll cows re inseminted on dy 1 of the breeding seson in fixed-timed AI protocol, cows should hve 3 chnces to conceive within 45 to dy breeding seson. The following yer the lst cow to clve will hve more dys to resume norml estrous cycles thn in dy seson. Shortening the breeding period on 2-yer old cows nd mintining desired pregnncy rte my be hrder thn doing so for mture cows. Identifying lte clving cows with timely pregnncy dignosis, nd culling s pproprite, is one pproch to shorten the clving period. Mnging cows to chieve pproprite weight (first clf heifers) nd body condition by clving is key step in cost effective reproduction. Forge testing nd blncing rtions in dvnce of the third trimester of pregnncy on n nnul bsis gretly reduces the risk of missing cow condition trgets. Cows tht re less thn 45 dys postprtum on the first dy of the breeding seson will not respond s well to estrus synchroniztion s those tht clved erlier. Working towrd dy or shorter breeding seson utomticlly provides n opportunity for more cows to cycle erly in the breeding seson s compred to longer breeding sesons. 6

7 References Bell, D., R.P. Wettemnn, K.S. Lusby nd D.K. Bishop Effects of Body Condition Score t Clving nd Postprtum Nutrition on Performnce of Two-Yer-Old Heifers. OSU Animl Science Reserch Report MP-129 pp ccessed 1/4/. Cushmn, R.A., M. F. Alln, R. M. Thllmn nd L. V. Cundiff. 7. Chrcteriztion of biologicl types of cttle (Cycle VII): Influence of postprtum intervl nd estrous cycle length on fertility. J Anim Sci 85: Dobbins, C. A., D. R. Eborn, D. E. Tenhouse, R.M. Breiner, S. K. Johnson, T.T. Mrston nd J. S. Stevenson. 9. Insemintion timing ffects pregnncy rtes in beef cows treted with CO- Synch protocol including n intrvginl progesterone insert. Theriogenology. 72:9-16. Llmn, D.L., D. H. Keisler, J. E. Willims, E. J. Scholljegerdes nd D. M. Mllett Influence of weight nd body condition chnge on durtion of nestrus by undernourished suckled beef heifers. J Anim Sci 75:3-8. Perry, G.A., M. F. Smith nd T. W. Gery. 4. Ability of intrvginl progesterone inserts nd melengestrol cette to induce estrous cycles in postprtum beef cows. J. Anim. Sci. 82: Short, R. E., R. A. Bellows, R. B. Stigmiller, J. G. Berrdinelli, nd E. E. Custer Physiologicl mechnisms controlling nestrus nd infertility in postprtum beef cttle. J. Anim. Sci. 68: Stevenson, J. S., S. K. Johnson, nd G. A. Milliken. 3. Incidence of Postprtum Anestrus in Suckled Beef Cttle: Tretments to Induce Estrus, Ovultion, nd Conception. The Professionl Animl Scientist. 19: Wilson, D.J., D. A. Mllory, D. C. Busch, N. R. Leitmn, J. K. Hden, D. J. Schfer, M. R. Ellersieck, M. F. Smith, nd D. J. Ptterson.. Comprison of short-term progestin-bsed protocols to synchronize estrus nd ovultion in postprtum beef cows. J Anim Sci 88: Yvs, Y nd J.S. Wlton.. Postprtum cyclicity in suckled beef cows: A review. Theriogenology. 54: Heifer resources Dy, M. L., nd L. H. Anderson Current concepts on the control of puberty in cttle. J. Anim. Sci. 76(Suppl. 3):1-15. Ptterson, D.J. S. L. Wood nd R. F. Rndle.. Procedures tht support reproductive mngement of replcement beef heifers. J Anim Sci 77:1-15. Ptterson, D.J., D.A. Mllory, J. M. Nsh, nd M.F. Smith. 9. Estrus synchroniztion protocols for heifers. Proceedings Applied Reproduction in Beef Cttle, Aug. 5-6, 9, Nshville, TN. 7