进口冷冻胚胎在贵州喀斯特地区的移植效果分析

为提高胚胎移植妊娠率,对影响移植妊娠率的受体品种、年龄、胎次、体况、黄体位置等因素进行试验。结果表明:初选合格率平均为49.50%,西+本牛初检合格率显著高于其他4个品种(本地牛,安×本牛,利×本牛,荷×本牛)(P0.05);发情率平均为88.17%,安+本牛高于其他4个品种,但各品种间差异不显著(P0.05);移植利用率平均为68.38%,妊娠率平均为46.8%,西+本牛移植利用率和移植妊娠率高于其他4个品种,但各品种间差异不显著(P0.05)。6～9周岁受体牛初选合格率显著低于2.5～6周岁和2.5周岁以下受体牛(P0.05),2.5～6周岁的受体牛在发情率、移植利用率和移植妊娠率高于6周岁的受体牛和2.5周岁以下的受体牛,但各组间差异不显著(P0.05)。5胎以上受体牛初选合格率显著低于0胎(育成牛)、1～4胎受体牛(P0.05);发情率、移植利用率和移植妊娠率1～4胎受体牛高于0胎(育成牛)和5胎以上受体牛,但各组间差异不显著(P0.05)。上等膘情受体牛发情率显著低于中上和中下等膘情受体牛(P0.05);移植利用率和妊娠率上等膘情受体牛最高,但与中上及中下膘情受体牛差异不显著(P0.05)。卵巢左、右有黄体侧移植妊娠率分别为48.48%、45.85%,两组间无显著性差异(P0.05)。     

非繁殖季节胚胎移植受体绵羊妊娠效果影响因素的研究

在非繁殖季节应用CIDR法和Progestagen Sponge法对受体绵羊进行同期发情处理后,进行冷冻胚胎移植,研究不同同期发情处理方法、卵巢状况、胚龄、移植方法和移植时间对冷冻胚胎移植妊娠率的影响,以期为当地实现绵羊胚胎移植产业化提供理论依据和技术参考。结果表明:经同期发情处理后,绵羊在去栓后24~72 h集中发情,在去栓后36~48 h发情最为集中;CIDR法和Progestagen Sponge法的同期发情率分别为91.11%和87.78%(P>0.05),同期发情绵羊移植利用率分别为82.93%和78.48%(P>0.05);单侧卵巢上含有1个和2个黄体其妊娠率分别为46.07%和48.78%(P>0.05);桑椹胚和囊胚的妊娠率分别为49.25%和42.11%(P>0.05);腹腔镜法和手术法的妊娠率分别为45.16%和48.52%(P>0.05);11月和12月进行冷冻胚胎移植的妊娠率分别为50.76%和43.08%(P>0.05),该试验的绵羊冻胚移植妊娠率为46.92%,基本接近国内冻胚移植水平,但低于目前国内羊鲜胚移植妊娠率(50%~60%)。由此可以得出,不同同期发情处理方法、卵巢状况、胚龄、移植方法和移植时间对胚胎移植妊娠率的影响均无显著性差异(P>0.05),大规模群体羊同期发情时,可选价格便宜的Progestagen Sponge法;只要受体绵羊黄体质量好即可移植胚胎;为了减轻受体绵羊的应激反应,降低术后子宫粘连的发病率,可广泛应用腹腔镜法进行胚胎移植;该试验的绵羊冻胚移植妊娠率低于目前国内羊鲜胚移植妊娠率,通过筛选高效低毒的抗冻保护剂,以及提高基层技术人员操作水平,则有望进一步提高绵羊冷冻胚胎移植妊娠率。     

受体因素对绵羊胚胎移植效果的影响

对绵羊胚胎移植过程中,受体不同发情方式、受体不同卵巢状态对妊娠率的影响进行研究,结果表明:在受体不同发情方式,同期发情组鲜胚妊娠率为59.46%,自然发情组鲜胚妊娠率为50.00%,两组无显著差异(P>0.05);在冻胚移植中,发情组妊娠率为46.22%,未发情组为16.00%,在妊娠率上两组差异极显著(P<0.01);其妊娠率发情组为46.22%,二情期返情组为25.88%,两组差异极显著(P<0.01)。有一个黄体的受体羊,妊娠率38.37%,有多个黄体的受体羊,妊娠率37.93%,2组差异不显著(P>0.05);有卵泡受体羊,妊娠率29.55%,无卵泡受体羊妊娠率40.51%,两组妊娠率差异不显著(P>0.05)。     

提高波尔山羊胚胎移植妊娠率研究

本文就波尔山羊胚胎质量、胚胎发育阶段、胚胎数量、受体卵巢黄体数、受体注射LRH-A3、供、受体发情同期化程度以及胚胎移植的方向等因素与受体移植妊娠率的关系进行了研究。结果表明:移植囊胚较移植1枚B级桑椹胚妊娠率高;A级桑椹胚妊娠率显著高于移植1枚B级桑椹胚(P<0.05);移植2枚B级桑椹胚妊娠率比移植1枚B级桑椹胚的高39.4%(P<0.05);受体注射LRH-A3有助于提高妊娠率;供、受体发情同步差在48 h以上组妊娠率显著低于0~24 h和24~48 h组(P<0.05);向子宫角前端方向的移植妊娠率比向子宫角基部方向的高12.2个百分点。     

不同受体牛对黑毛和牛冷冻胚胎移植的效果

[目的]选择不同品种牛,利用同期发情和自然发情后作为受体牛,进行日本和牛冻胚移植研究。[方法]选择奶牛20头和南德温杂种肉牛41头作为受体牛,利用CIDR+PG做人工同期发情处理,发情后的受体牛移植和牛冻胚。统计分析受体牛的同期发情率和移植后的妊娠率。[结果]试验结果表明奶牛和南德温杂种肉牛的受体牛同期发情率分别为90.00%和85.36%,差异显著(P<0.05);在同一牛场场使用不同品种受体牛进行冻胚移植试验结果表明,15头奶牛和27头南德温杂种肉牛受体牛妊娠率分别为46.67%和48.14%,差异不显著(P>0.05)。[结论]只要符合胚胎移植受体牛要求,奶牛和南德温杂种肉牛均可作为和牛胚胎移植受体牛。     

杜泊羊冷冻胚胎移植效果的影响因素及羔羊早期生长性能研究

为研究杜泊羊冷冻胚胎移植效果的影响因素以及羔羊早期的生长情况,本实验选用1 361枚质量合格的纯种黑头杜泊羊的早期冷冻胚胎作为供体,180只小尾寒羊和970只湖羊作为受体羊,采用同期发情和子宫角胚胎移植技术,研究季节(春季、秋季)、受体羊品种(小尾寒羊、湖羊)、卵巢上黄体个数(1个、2～3个)、受体羊的营养状况(中上等膘情、下等膘情)、胚胎发育阶段(桑椹胚、晚期桑椹胚、早期囊胚、囊胚和扩张囊胚)及移植胚胎数目(双胚和单胚)对于杜泊羊冷冻胚胎移植效果的影响。结果显示:秋季(11月)同期发情率显著高于春季(4月),但妊娠率没有显著差异;在春季,不同品种受体羊的同期发情率和妊娠率无显著性差异;受体羊卵巢上黄体个数对妊娠率无显著影响;中上等膘情受体羊的妊娠率显著高于下等膘情受体羊;移植扩张囊胚的受体羊妊娠率为30.0%,显著低于其他4个胚胎发育阶段;移植双胚的受体羊妊娠率低于移植单胚的受体羊。羔羊早期生长发育指标统计结果表明:在潍坊地区,小尾寒羊和湖羊均可以作为胚胎移植的受体,但是小尾寒羊体型偏大,每日饲料消耗偏多,湖羊作为受体羊在节约饲料方面更有优势。     

胚胎质量和发育阶段对奶牛胚胎移植妊娠率的影响

[目的]为了评估胚胎质量和发育阶段对奶牛胚胎移植妊娠率的影响。[方法]使用63头青年奶牛作为供体进行超数排卵,评估回收胚胎质量和发育阶段。选择334头青年奶牛作为受体鲜胚移植不同质量和发育阶段胚胎。对胚胎质量分布、发育阶段分布、不同质量胚胎和不同发育阶段胚胎移植30 d妊娠率进行统计分析。[结果]可用胚胎中A级胚胎比例(60.78%)显著高于B级和C级胚胎比例(36.70%和2.52%)(P<0.05);致密桑椹胚比例(54.36%)显著高于早期囊胚,囊胚和扩张囊胚比例(18.35%,25.0%和2.29%)(P<0.05)。A级和B级胚胎移植30 d妊娠率(63.55%和64.35%)显著高于C级胚胎移植30 d妊娠率(44.44%)(P<0.05);致密桑椹胚、早期囊胚、囊胚和扩张囊胚移植30 d妊娠率差异不显著(P<0.05),早期囊胚、囊胚移植30 d妊娠率高于致密桑椹胚、扩张囊胚移植30 d妊娠率(P<0.05)。[结论]选择不同发育阶段的A级和B级胚胎能够获得较高胚胎移植妊娠率,增加早期囊胚和囊胚阶段胚胎移植数量能够提高胚胎移植妊娠率。     

黑萨福克和杜泊羊新鲜和冷冻胚胎移植效率的研究

为提高优质肉用种用绵羊胚胎移植的效率,试验选取76只黑萨福克羊和27只杜泊羊作为供体,采用"CIDR+FSH+PMSG"法进行超数排卵处理。选取384只小尾寒羊为受体,采用"CIDR+PMSG"法进行同期发情处理,以探索供体胚胎发育阶段、胚胎冷冻处理、胚胎体外停留时间以及移植给受体时移植侧黄体数量等因素对胚胎移植妊娠率的影响。结果表明:移植新鲜囊胚的妊娠率极显著高于桑椹胚(P0.01);冷冻/解冻囊胚移植妊娠率极显著低于新鲜囊胚(P0.01),而冷冻/解冻桑椹胚移植妊娠率与新鲜桑椹胚无显著差异(P0.05);此外,移植桑椹胚时,移植侧有1个黄体的受体妊娠率极显著低于有2~3个黄体受体妊娠率(P0.01),但移植囊胚时两者间差异不显著(P0.05)。综上可知,子宫角移植桑椹胚和囊胚时,移植新鲜囊胚、移植冷冻桑椹胚效率较高;将新鲜桑椹胚移植给移植侧有2~3个黄体受体效果好于1个黄体受体。     

胚胎移植时卵泡和黄体对妊娠率影响的分析

本试验探讨在受体羊的卵巢上同时存在卵泡和黄体时进行胚胎移植对移植后妊娠率的影响。经试验得出:(1)胚胎移植时受体羊卵巢上有卵泡(卵泡的直径小于3mm)和无卵泡的移植后妊娠率差异不显著(P>0.05);(2)卵巢上有功能性黄体存在时,卵泡的直径(小于2mm)对胚胎移植妊娠率的影响差异不显著(P>0.05)。同期发情处理对卵巢上的黄体和卵泡有很大影响,处理效果直接影响受体羊的利用率和胚胎移植后的妊娠率,而当卵巢上有功能性黄体存在时,卵巢上卵泡的有无及其大小(直径小于3mm)对胚胎移植后的妊娠率影响不显著(P>0.05)。     

胚胎移植受体牛同期发情及受胎效果的研究

本试验分别采用CIDR+E2法和两次PGF2α子宫输注法,对胚胎移植受体牛做同期发情处理,鲜胚移植观察其妊娠情况。试验结果表明两种处理方法的受体牛在24~48h发情率分别为85.5%和51.6%,两者之间差异显著(P<0.05)。移植前对受体牛进行黄体检查,黄体合格率分别为79.3%和77.8%,差异不显著(P>0.05);受胎率分别为45.8%和42.4%,差异不显著(P>0.05)。24h后观察发情,6.5d直检,黄体A、B级者用于移植。     

高产奶牛性控雌性冻胚规模化移植试验

从美国引进高产奶牛性控雌性胚胎，在农村条件下，选择自然发情的黄牛作受体，移植合格受体牛648头。结果显示，自然发情黄牛924头中，经直肠检查合格受体牛648头，使用合格率为70．13％（648／924）；氯前列烯醇同期处理476头，使用合格率为36．13％（172／476），差异极显著（P〈0．01）。80～100d怀孕检查，自然发情移植成功率41．98％（272／648），同期发情移植成功率40．12％（69／172），差异不显著（P〉0．05）。自然发情黄牛不同黄体级别的移植成功率分别为：A级44．09％（41／93），B级42．43％（199／469），C级37．21％（32／86），差异不显著（P〉0．05）。单胚移植580头，移植成功率42．41％（242／580），双胚移植68头，移植成功率44．12％（30／68），差异不显著（P〉0．05）。正常胚胎单枚移植541头，移植成功率42．51％（230／541），裸胚单枚移植39头，移植成功率30．77％（12／39），裸胚比正常胚移植成功率低11．74％。怀孕牛已出生犊牛83头。其中母犊79头．公犊4头，母犊占95．18％，与自然发情的性比例（50％）相比较，差异极显著（P〈0．01）。     

Use of insulin-like growth factor-I during embryo culture and treatment of recipients with gonadotropin-releasing hormone to increase pregnancy rates following the transfer of in vitro-produced embryos to heat-stressed,lactating cows

An experiment was conducted to determine whether pregnancy rates following the transfer of in vitro-produced embryos to heat-stressed cows could be improved by 1) culturing embryos in the presence of IGF-I and 2) treating recipients with GnRH. Lactating Holstein cows (n = 260) were synchronized using a timed ovulation protocol. Embryos were produced in vitro and cultured with or without 100 ng/mL of IGF-I. On d 7 after anticipated ovulation (d 0), a single embryo was transferred to all recipients with a palpable corpus luteum (n = 210). A subset of recipients (n = 164) was injected with either GnRH or placebo on d 11. Plasma progesterone concentrations on d 0 and 7 were used to determine the synchrony of recipients. Pregnancy was diagnosed at d 53 and 81 by rectal palpation. Among all recipients, transfer of IGF-I-treated embryos increased pregnancy rate at d 53 (P < 0.05) and tended to increase pregnancy rate at d 81 (P < 0.06). Calving rate also tended to be higher for recipients that received IGF-I-treated embryos (P < 0.07). Among the subset of synchronized recipients (n = 190), pregnancy rate at d 53 and d 81 and calving rate were higher (P < 0.05) for IGF-I-treated embryos. The GnRH tended to increase pregnancy rate at d 53 for all recipients (P < 0.08) and the subset of synchronized recipients (P < 0.10). There were no effects of GnRH (P > 0.10) for pregnancy rate at d 81 and calving rate. The overall proportion of male calves was 64.3%. There was no effect (P > 0.10) of embryo treatment or GnRH on the birth weight or sex ratio of calves. Results of this experiment indicate that treatment of embryos with IGF-I can improve pregnancy and calving rates following transfer of in vitro-produced embryos. Further research is necessary to determine whether the treatment of recipients with GnRH is a practical approach to increase pregnancy rates following in vitro embryo transfer.     

Japanese Society for Animal Reproduction: award for outstanding research 2002. The development and prevalence of the transfer technique for frozen-thawed embryos of Japanese black beef cattle in Tochigi Prefecture

The conditions of embryo transfer by the stepwise method, in which frozen-thawed embryos are transferred on day 7 (day 0=onset of estrus), were investigated with the aim of increasing pregnancy rates in frozen-thawed embryo transfer. The use of a vaginal speculum to prevent bacterial infection when passing an embryo transfer gun through the vagina yielded a pregnancy rate equal to or higher than that with application of a sheath cover to the transfer gun. Administration of a sedative, xylazine, to recipient cattle for preventing movement at the time of embryo transfer improved the pregnancy rate. The influence of the time from thawing of frozen embryos to transfer and of the transportation of the recipient by truck upon pregnancy rate was investigated. Embryo transfer within 60 minutes after aspiration into a straw or transportation of the bovine recipient, 1.5 hours each way before and after transfer, had no influence on pregnancy rate. Relations of the embryonic developmental stage and morphological quality after thawing of frozen embryos to pregnancy rate were investigated in recipients of nulliparous Holstein heifers. The pregnancy rate increased as the embryonic developmental stage advanced from compacted morula, early blastocyst, and blastocyst in that order. The pregnancy rate obtained with blastocyst stage embryos was significantly (P<0.05) higher than that with compacted morula stage embryos, and there was no significant difference in pregnancy rates between excellent morphological quality and good morphological quality for compacted morula stage embryos. When correlation of luteal function and pregnancy rate was investigated in bovine recipients, pregnancy rate showed a tendency to increase with increasing blood progesterone (P) concentration on the day before (on day 6 after estrus) and the day of embryo transfer. The pregnancy rate in bovine recipients, which showed a blood P concentration of > or =2.5 ng/ml on the day before embryo transfer, was significantly (P<0.05) higher than that in those with a blood P concentration of <2.5 ng/ml. Pregnancy rate showed a tendency to increase with decreasing blood estradiol-17beta (E2) concentration on the day of embryo transfer. Activation of luteal function by administration of human chorionic gonadotropin (hCG) in cycling cattle was investigated for its effect on increasing pregnancy rate in bovine recipients. A follicle coexisting with cyclic CL ovulated and induced CL formed after injection of hCG 1,500 IU 5 days after ovulation. The blood P concentration was significantly (P<0.05) higher in the administration group than in the control group, and the blood E2 concentration rapidly decreased, showing a lower concentration than in the control group. These results suggest the possibility that the pregnancy rate could be improved by administration of hCG. Pregnancy rate following intramuscular injection hCG 1,500 IU was comparatively investigated in parous Japanese Black beef cattle receiving frozen-thawed embryos 7 days after estrus. Pregnancy rate was 67.5% in the group in which hCG was administered on day 6 after estrus, and was significantly (P<0.05) higher than that in the control group (45.0%) and the group in which hCG was administered on day 1 after estrus (42.5%), revealing that hCG administration facilitated pregnancy. Transfer of frozen-thawed embryos in the blastocyst stage within 60 minutes after the aspiration into a straw, with a vaginal speculum after administration of xylazine is suggested as a way of improving pregnancy rate in bovine recipients with favorable luteal function and in those with luteal function activated by administration of hCG on the day before embryo transfer.     

绵羊体外受精卵冷冻解冻后的移植

以含有10％乙二醇的磷酸缓冲液对体外受精的绵羊桑椹胚及囊胚进行防冻和冷冻处理后保存于液氮中。解冻后将胚胎分别以去除防冻剂后移植和连同防冻剂直接移植两种方法,将30枚桑椹胚和19枚囊胚先后以外科手术法移植到28只受体母羊子宫内。结果共有8只受胎,其中4只足月妊娠后产羔4只(♀1,♂3),另外4只分别在移植后2～3个月妊娠中断,其原因尚不清楚。解冻后连同防冻剂直接移植后的受胎率为50％(4/8),明显高于去除防冻剂后移植的结果20％(4/20),(P<0.05)。受体的发情同步化程度不同(-1～+1日)对受胎率无明显影响。     

Effect of GnRH pretreatment on reproductive performance of postpartum suckled beef cows following synchronization of estrus using GnRH and PGF2alpha

The effect of GnRH pretreatment on estrus detection rate, precision of estrus, and reproductive performance of postpartum beef cows synchronized to estrus using GnRH and PGF2alpha was evaluated. In Exp. 1, Angus cows (n = 87) were randomly assigned by parity, postpartum interval, and body condition score (BCS) to receive either 1) GnRH on d -7 and PGF2alpha on d 0 (GP) or 2) the GP treatment and an additional injection of GnRH on d -16 (GGP). Estrus detection and AI were conducted twice daily from d -3 to d 3. At 72 h after PGF2alpha, all animals not previously detected in estrus were bred by AI and received a concurrent injection of GnRH (TAI). Synchronized pregnancy rates were numerically increased (P = 0.15) in cows treated with GGP (55%) compared with those on the GP treatment (44%). In Exp. 2, 1,276 spring-calving, suckled beef cows in nine herds were randomized to treatments as described for Exp. 1, except that the initial GnRH injection for the GGP treatment was administered on d -14. Herd affected all indicators of reproductive performance (P < 0.05). The percentage of animals detected in estrus prematurely (d -3 to d 0; 7%) was not affected by treatment. Estrus response rate was influenced by postpartum interval (< 60 vs > or = 60; 61 vs 73%; P < 0.01) and a three-way interaction of parity, BCS, and treatment (P < 0.01). Within animals with a BCS > or = 5.5, the GGP treatment tended to increase the detection of estrus in primiparous cows (GP vs GGP; 76 vs 91%; P = 0.11) and decrease detection in multiparous cows (GP vs GGP; 78 vs 72%; P < 0.10). However, because conception rate to TAI in animals with a BCS > or = 5.5 was greater (P < 0.05) in the GGP than in the GP group (28 vs 8%, respectively), this interaction was interpreted to represent a shift in interval to estrus induced by the GGP treatment, rather than a reduction in the synchronization of ovarian function. Conception rates of animals inseminated to an observed estrus did not differ among treatments (P = 0.15). Synchronized pregnancy rate tended (P = 0.06) to be greater in GGP- (53%) than in GP-treated animals (47%). In conclusion, pretreatment with GnRH tended to increase pregnancy rates during a 6-d synchronization period, primarily through enhanced conception rates of cows bred by TAI. In contrast to our hypothesis, GnRH pretreatment did not increase the percentage of animals detected in estrus or the precision of estrus expression.     

绵羊胚胎移植受体同期发情方法的比较

为了比较CIDR＋PG与CIDR＋PG＋PMSG两种激素处理方法对于受体同期发情以及胚胎移植的效果,将103只小尾寒羊作为胚胎移植受体分为两组,分别使用上述两种方法进行同期发情处理。其中,CIDR＋PG组83只,CIDR＋PG＋PMSG组20只。在对供体羊人工输精后第6．5天获取移植囊胚,分别移植到两组受体子宫内。统计受体的发情率、黄体生成情况,以及移植后的妊娠情况。CIDR＋PG组与CIDR＋PG＋PMSG组受体羊发情率分别为87．95％、90．00％;有黄体羊的比例分别为37．35％和75．00％,平均黄体数为1．81和1．93个;两组受体胚胎移植后妊娠率分别为77．41％和86．67％。结果表明,使用CIDR＋PG＋PMSG进行同期发情效果较好,且胚胎移植后妊娠效果较好。     

Effectiveness of GnRH plus prostaglandin F2alpha for estrus synchronization in cattle of Bos indicus breeding

Postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding at three locations were studied to determine the efficacy of GnRH + PGF2alpha combinations for synchronization of estrus and(or) ovulation. Cows were equally distributed to each of three treatments by body condition score at the start of the experiment (d 0). All cows received 100 microg of GnRH on d 0 and 25 mg of PGF2alpha 7 d later. The three insemination protocols included 1) AI 12 h after exhibiting estrus during d 7 to 12 of the experiment (Select-Synch; n = 197); 2) timed-AI + 100 microg of GnRH on d 9 of the experiment (CO-Synch; n = 193); 3) AI 12 h after exhibiting estrus during d 7 to 10 of the experiment. Cows not exhibiting estrus by d 10 were timed-AI and injected with 100 microg of GnRH on d 10 of the experiment (Hybrid-Synch; n = 200). The percentage of cows exhibiting estrus during d 7 to 12 of the experiment was lower (P < 0.05) for CO-Synch (17.6%) cows than for Select-Synch or Hybrid-Synch (45.2 and 33.0%, respectively) cows, which did not differ (P > 0.05). For the Select-Synch and Hybrid-Synch cows that exhibited estrus during d 7 to 10 of the experiment and were artificially inseminated, conception rates were similar across treatments (50.5%). Pregnancy rates were greater (P < 0.01) for CO-Synch and Hybrid-Synch (31.0 and 35.5%, respectively) cows than for Select-Synch (20.8%) cows. A greater (P < 0.01) percentage of cycling cows became pregnant (34.5%) than noncycling cows (25.9%) across all treatments. The CO-Synch and Hybrid-Synch synchronization protocols resulted in greater pregnancy rates compared with the Select-Synch protocol in postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding.     

Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d -10), PGF(2alpha) (d -3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF(2alpha) were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF(2alpha) were TAI at 72 h and given GnRH (100 mug). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF(2alpha) did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF(2alpha) than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.     

Synchronizing estrus and(or) ovulation in beef cows after combinations of GnRH, norgestomet, and prostaglandin F2alpha with or without timed insemination

Three experiments were conducted to induce estrus and(or) ovulation in 1,590 suckled beef cows at the beginning of a spring breeding season. In Exp. 1, 890 cows at three locations were allotted to three treatments: 1) GnRH on d -7 + prostaglandin F2alpha (PGF2alpha) on d 0 (Select Synch); 2) GnRH on d -7 + PGF2alpha on d 0 (first day of the breeding season) plus a norgestomet implant (NORG) between d -7 and 0 (Select Synch + NORG); or 3) two injections of PGF2alpha given 14 d apart (2xPGF2alpha). More (P < 0.05) cycling cows were detected to have been in estrus after both treatments that included GnRH, whereas, among noncycling cows, the addition of norgestomet further increased (P < 0.05) the proportion in estrus. Pregnancy rates were greater (P < 0.01) among noncycling cows after treatments that included GnRH. For cows that calved >60 d before the onset of the breeding season, conception rates were greater (P < 0.01) than those that calved < or =60 d regardless of treatment, whereas days postpartum had no effect on rates of detected estrus. When body condition scores were < or =4 compared with >4, rates of detected estrus (P < 0.05) and conception (P = 0.07) were increased. In Exp. 2, 164 cows were treated with the Select Synch + NORG treatment and were inseminated either after estrus or at 16 h after a second GnRH injection (given 48 h after PGF2alpha). Conception and pregnancy rates tended (P = 0.08) to be or were less (P < 0.05), respectively, for noncycling cows inseminated by appointment, but pregnancy rates exceeded 53% in both protocols. In Exp. 3, 536 cows at three locations were treated with the Select Synch protocol as in Exp. 1 and inseminated either: 1) after detected estrus (Select Synch); 2) at 54 h after PGF2alpha when a second GnRH injection also was administered (Cosynch); or 3) after detected estrus until 54 h, or in the absence of estrus, at 54 h plus a second GnRH injection (Select Synch + Cosynch). Conception rates were reduced (P < 0.01) in cows that were inseminated by appointment. An interaction of AI protocol and cycling status occurred (P = 0.05) for pregnancy rates with differing results for cycling and noncycling cows. Across experiments, variable proportions of cows at various locations (21 to 78%) were cycling before the breeding season. With the GnRH or GnRH + NORG treatments, ovulation was induced in some noncycling cows. Conception rates were normal and pregnancy rates were greater than those after a PGF2alpha program, particularly when inseminations occurred after detected estrus.