不同处理方法对受体牛同期发情效果的比较研究

[目的]为了进一步促进人工授精技术广泛应用以及提高胚胎移植效率，为酒泉本地胚胎移植选择高效的同期发情方法。[方法]本试验分别采用PRID＋PGF2α法和PGF2α＋PGF2α法对胚胎移植受体牛做同期友情处理。[结果]表明：两种方法处理受体牛，其同期发情率和移植妊娠率之间差异无统计意义（P〉0．05），但是用PRID＋PGF2α法处理受体牛同期发情率和移植妊娠率均高于PGF2α＋PGF2α法。[结论]在奶牛养殖及生产上，在考虑移植成本和生产效益的情况下，在农区大面积对牛只进行同期发情技术处理，应优选PGF2α＋PGF2α法处理受体牛。     

郏县红牛与夏南牛同期发情定时输精效果分析

[目的]探讨“同期发情定时输精”技术在不同群体中的实施效果,提升郏县红牛和夏南牛的繁殖效率,发挥地方良种的繁殖力。[方法]试验以100头郏县红牛和198头夏南牛为研究对象,采用戈那瑞林和PG 079同期发情方案对其进行处理,分析同期发情定时输精效果。[结果]100头郏县红牛的平均受胎率为76.4%,198头夏南牛后备母牛的受胎率为100%。[结论]同期发情定时输精处理的后备牛受胎率高于经产牛。     

不同处理方案对肉牛同期发情率和情期受胎率的影响研究

为了筛选出合理的肉牛同期发情处理方案,试验选用健康能繁母牛90头,随机分为5组,采用黄体酮阴道栓(P)、孕马血清促性腺素(PMSG)、注射用促黄体素释放激素A_3(A_3)、氯前列醇钠注射液(PGF)4种药物,按5种不同方案(P/PGF/PMSG、P/PGF/A_3、PGF/A_3/PGF/A_3、PGF/PGF/PMSG、PGF/PMSG)进行同期发情处理,母牛发情后用细管冷冻精液输精,测定其同期发情率、情期受胎率和处理牛受胎率。结果表明:方案一(P/PGF/PMSG)情期受胎率最高,方案四(PGF/PGF/PMSG)处理牛受胎率最高,方案五(PGF/PMSG)情期受胎率和处理牛受胎率均最低。说明方案一到方案四均可用于肉牛的同期发情处理。     

新疆褐牛同期发情和同期排卵—定时输精效果

[目的]新疆褐牛是新疆北疆牧区养牛业主导品种,夏季放牧区新疆褐牛人工授精集中冷配点模式的广泛推广,对新疆褐牛选育提高和新品系培育起到了积极作用,为探索新疆褐牛同期发情和同期排卵—定时输精最佳处理方法。[方法]试验选用2胎以上45头牛,分3组,A组,PG+PG法;B组,PG法;C组,CIDR+PG法,比较3种同期发情处理方法效果,同时选用2胎以上20头牛,分2组,D组,GnRH+PG+GnRH+AI法;E组,CIDR+GnRH+PG+GnRH+AI法,比较2种同期排卵—定时输精方法效果。[结果]结果表明,3种不同同期发情处理方法母牛集中在12～24 h内发情,其中12～24 h内A组和C组处理方法母牛发情率极显著高于B组处理方法(P0.01),C组比A组高出32.3%,B组和C组母牛总发情率差异不显著(P0.05),A、B、C 3组总发情率分别达到86.7%,40.0%,93.3%;发情母牛经人工授精配种后,情期受胎率3组差异不显著(P0.05)。2种同期排卵—定时输精方法中,E组发情牛排卵率显著高于D组,D组和E组总受胎率差异不显著(P0.05)。[结论]综上所述,新疆褐牛同期发情处理应采用B组方法,即2次PG法,即降低了成本,有可取得较好的效果;同期排卵—定时输精宜采用D组方法,成本低,且受胎率较好,适宜在牧区集中人工授精冷配点推广。     

CUE-MATE诱导新疆褐牛同期发情试验

[目的]为了探索新疆褐牛同期发情处理的有效时间段和最佳处理方法.[方法]采用CUE-MATE孕酮栓+PGF2α法进行新疆褐牛同期发情试验,[结果]表明:同期发情主要集中在取栓后的2 d,平均发情率为72.5%,情期受胎率为66.7%;3月的同期发情率显著高于5月和7月(P＜0.05),达到90.8%,但情期受胎率低于5月和7月,为61.0%,差异不显著(P＞0.05);母牛卵巢上以有黄体的同期发情率最高,达到95.3%,其次是有卵泡的,无黄体、卵泡的最低,三者差异显著(P＜0.05);有卵泡的情期受胎率略高于有黄体的,差异不显著(P＞0.05),无黄体、卵泡的同期发情率和受胎率都最低,差异显著(P＜0.05);育成牛的同期发情率略高于经产牛,为92%,差异不显著(P＞0.05);育成牛的情期受胎率显著高于经产牛(P＜0.05),为73.9%.[结论]环境温度、营养水平及母牛卵巢上有无黄体、卵泡影响发情率的高低,CUE-MATE孕酮栓+PGF2α法可用于诱导新疆褐牛的同期发情.     

寒冷条件下西门塔尔牛同期发情效果及提高受胎率措施的试验

为了研究新疆地区在寒冷条件下西门塔尔牛的同期发情效果与如何提高受胎率的措施方面展开试验。采用氯前列烯醇(PGF2a)一次法和孕马血清促性腺激素(PMSG)一次法进行试验,剂量分别是PG为0.8 mg/头,PMSG为500 IU/头;共分为2组,A组89头牛;B组为121头牛。结果表明,A组:PGF2a一次法的同期发情效果为82.2%,受胎率为67.6%;PMSG一次法的同期发情效果为72.7%,受胎率为53.1%。B组:PGF2a一次法的同期发情效果为80.0%,受胎率为66.7%;PMSG一次法的同期发情效果为73.8%,受胎率为51.1%。通过本试验为新疆地区在寒冷条件下开展类似的工作提供借鉴。     

外源性生殖激素对卵巢功能异常奶牛的影响

应用50μg促排卵素3号(IRH—A3)给排卵延迟母牛肌肉注射,0．4mg氯前列烯醇给持久黄体的母牛注射,结果表明,注射LRH-A3的母牛情期受胎率、总受胎率显著高于对照牛,注射氯前列烯醇的母牛发情率、情期受胎率、总受胎率显著高于对照牛。表明LRH-A3,氯前列烯醇均能提高卵巢异常牛的繁殖力。     

同期发情技术在奶牛胚胎移植中的应用研究

本文研究了同期发情技术在奶牛胚胎移植中的应用,以提高牛胚胎移植的效率和受胎率。根据以往的胚胎移植数据,分析了自然发情与PGF2α诱导的同期发情受体牛的冷冻胚胎移植受胎率,结果表明两者之间的受胎率没有差异。使用同期发情方法可以使受体牛集中发情,有利于集中观察发情和开展胚胎移植,节省时间并降低劳动强度,提高移植工作效率。本文同时研究分析了低温气候对同期发情效果和受体牛可用率的影响,结果表明在平均气温为-1~1℃,最低气温为-5℃时,可以采用PGF2α进行同期发情处理,发情率可达70%,可用率达到三分之一以上;但在平均气温达到-5℃,最低气温达-10℃时进行同期发情,发情率只有50%,可用率只有18.42%,表明在极端低温条件下,同期发情的效果较差,受体牛的可用率很低,影响胚胎移植工作效率。     

氯前列烯醇诱导黄牛同期发情效果试验

氯前列烯醇是PGF2α的类似物,在目前常用的PGF2α及其类似物中,其活性最高。本试验应用氯前列烯醇对农牧民分散饲养的母牛进行同期发情效果观察。结果表明在24~72 h内92%的母牛发情,经直肠检查发情母牛排卵率为86%,情期受胎率为62%。说明氯前列烯醇对诱导母牛同期发情处理效果显著。     

非繁殖季节母驴诱导发情、排卵效果的研究

[目的]研究前列腺素F2α（PGF2α）、孕马血清促性腺激素（PMSG）、人绒毛膜促性腺激素（hCG）3种激素在不同处理方案下对内蒙古通辽地区乏情期母驴卵泡生长情况、排卵率、发情率、受胎率与妊娠率的影响。[方法]将50头2～6岁、体重接近、体况良好、处于乏情期的母驴随机分为A、B、C、D4组,其中D组为未使用任何激素的空白对照组。首先,采用PGF2α、PMSG进行诱导发情试验,对A、B、C3组母驴注射2mL／头PGF2α,连续处理5d,第6天对A、B组母驴分别注射PMSG 1000IU,头和500IU,头;C组不做PMSG处理。诱导发情后将A、B组再细分为A1、A2和B1、B2组,当A1、B1、C3组中母驴卵泡直径大于35mm时注射hCG（总量1500IU）进行诱导排卵;A2、B2不做hCG处理,由卵泡自然发育至排卵。对所有诱导发情后有发情表现的母驴进行自然本交。同时,在试验期间利用直肠检查和B超检查对母驴的卵巢发育进行监测。『结果]c组发情率为30％,经PGF2α处理第5天时卵巢黄体基本全部消退;A组和B组的发情率分别为93．33％和86．66％,二者差异不大,但均明显高于C组。A1、B1最终的排卵率为100％和77．78％,而A2和B2的排卵率为60．00％和50．00％。A,组受胎率和妊娠率最高,分别达到了88．89％和80．00％,其次是B,组分别为66．67％和60．00％,B2、C2组的受胎率和妊娠率都较低,D组虽然有1头母驴发情,但配种后未妊娠。[结论]单独使用PGF2α对非繁殖季节母驴诱导发情效果不明显,但其对消除母驴黄体有明显作用;PGF2α与PMSG联用对诱导乏情母驴发情效果较好。使用PGF2α与PMSG对处于乏情期的母驴诱导发情后,注射hCG对母驴卵巢上优势卵泡具有明显的促进排卵作用,能加快优势卵泡的排卵,且明显提高母驴的排卵率。该试验确定的最佳方案为：注射0．2mgPGF2α连续处理5d,第6天注射PMSG 500lU,当优势卵泡直径达35mm时注射hCG 1500lU,排卵后配种。     

育成和经产母牛肌肉注射PGF2a同期发情对比试验

[目的] 探讨应用氯前列烯醇诱导母牛同期发情的方法。 [方法] 选择育成母牛和经产母牛,一次性肌肉注射2支(0.2mg/支),通过发情数量、时间、同期率、受配率等情况对比同期发情率的差异。 [结果] 结果表明,在牛体格、生理状况和饲养管理条件大体一致的情况下,育成牛发情比经产牛早3-5h;在发情持续时间上,育成牛比经产牛早结束2-3h,症状显著,而相对持续时间较短,受配率育成牛多于经产牛。 [结论] 用一次PG法处理繁殖母牛可获得较高的同期发情率,育成牛同期发情效果稍优于经产母牛,体况因素也是母牛发情的重要影响因素之一。     

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.     

Conception rates to artificial insemination in primiparous, suckled cows exposed to the biostimulatory effect of bulls before and during a gonadotropin-releasing hormone-based estrus synchronization protocol

The objective of these studies was to evaluate whether exposing primiparous, suckled beef cows to the biostimulatory effect of bulls alters breeding performance associated with an estrus synchronization protocol that included GnRH followed 7 d later by PGF(2alpha) and fixed-time AI (TAI). This was a composite analysis of 3 experiments that evaluated (1) the effects of bull exposure at different days after calving (yr 1); (2) the biostimulatory effects of bull excretory products (yr 2); and (3) the biostimulatory effects of familiar and unfamiliar bulls (yr 3) on the resumption of ovarian cycling activity. In all studies, cows were exposed (biostimulated; n = 94) or not exposed (nonbiostimulated; n = 67) to bulls or excretory products of bulls for at least 60 d before the beginning of the estrus synchronization protocol. Average calving day did not differ among years and was 52 +/- 5 d. Year did not affect the proportions of biostimulated and nonbiostimulated cows that were cycling at the beginning of the estrus synchronization protocol; however, a greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows were cycling at this time. In each year, cows were given GnRH followed by PGF(2alpha) 7 d later. Cows were observed for estrus twice daily (am and pm) after PGF(2alpha). Cows that exhibited estrus before 54, 60, and 64 h after PGF(2alpha) were inseminated by AI 12 h later in yr 1, 2, and 3, respectively. Cows that failed to show estrus were given GnRH and TAI at 62, 72, and 72 h after PGF(2alpha) in yr 1, 2, and 3, respectively. Conception rates were determined by transrectal ultrasonography 35 d after TAI in each year. The percentages of cows that exhibited estrus after PGF(2alpha) and before TAI, the interval from PGF(2alpha) to estrus, and the percentages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows and were 51%, 54.7 +/- 7.3 h, 35%, and 65%, respectively. Conception rates for cows bred by AI 12 h after estrus did not differ between biostimulated and nonbiostimulated cows; however, the TAI conception rate was greater (P < 0.05) for biostimulated cows (57.6%) than for nonbiostimulated cows (35.6%). We conclude that TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF(2alpha) may be improved by the biostimulatory effect of bulls in postpartum, primiparous cows.     

Effect of addition of a progesterone intravaginal insert to a timed insemination protocol using estradiol cypionate on ovulation rate, pregnancy rate, and late embryonic loss in lactating dairy cows

The objectives of this study were to determine the effects of incorporating a progesterone intravaginal insert (CIDR) between the day of GnRH and PGF2alpha treatments of a timed AI protocol using estradiol cypionate (ECP) to synchronize ovulation on display of estrus, ovulation rate, pregnancy rate, and late embryonic loss in lactating cows. Holstein cows, 227 from Site 1 and 458 from Site 2, were presynchronized with two injections of PGF2alpha on study d 0 and 14, and subjected to a timed AI protocol (100 mixrog of GnRH on study d 28, 25 mg of PGF2alpha on study d 35, 1 mg of ECP on study d 36, and timed AI on study d 38) with or without a CIDR insert. Blood was collected on study d 14 and 28 for progesterone measurements to determine cyclicity. Ovaries were scanned on d 35, 37, and 42, and pregnancy diagnosed on d 65 and 79, which corresponded to 27 and 41 d after AI. Cows receiving a CIDR had similar rates of detected estrus (77.2 vs. 73.8%), ovulation (85.6 vs. 86.6%), and pregnancy at 27 (35.8 vs. 38.8%) and 41 d (29.3 vs. 32.3%) after AI, and late embryonic loss between 27 and 41 d after AI (18.3 vs. 16.8%) compared with control cows. The CIDR eliminated cows in estrus before the last PGF2alpha injection and decreased (P < 0.001) the proportion of cows bearing a corpus luteum (CL) at the last PGF2alpha injection because of less ovulation in response to the GnRH and greater spontaneous CL regression. Cyclic cows had greater (P = 0.03) pregnancy rates than anovulatory cows at 41 d after AI (33.8 vs. 20.4%) because of decreased (P = 0.06) late embryonic loss (16.0 vs. 30.3%). The ovulatory follicle was larger (P < 0.001) in cows in estrus, and a greater proportion of cows with follicles > or = 15 mm displayed estrus (P < 0.001) and ovulated (P = 0.05) compared with cows with follicles <15 mm. Pregnancy rates were greater (P < 0.001) for cows displaying estrus, which were related to the greater (P < 0.001) ovulation rate and decreased (P = 0.08) late embryonic loss for cows in estrus at AI. Cows that were cyclic and responded to the presynchronization protocol (high progesterone at GnRH and CL at PGF2alpha) had the highest pregnancy rates. Incorporation of a CIDR insert into a presynchronized timed AI protocol using ECP to induce estrus and ovulation did not improve pregnancy rates in lactating dairy cows. Improvements in pregnancy rates in cows treated with ECP to induce ovulation in a timed AI protocol are expected when more cows display estrus, thereby increasing ovulation rate.     

广西本地黄牛同期发情定时输精的研究

1984年对68头和1985年对97头本地黄牛用“18—甲”进行同期发情。试验分组比较了“18—甲”结合不同激素的同期发情效果,并对母牛被处理后的同期发情率、卵泡明显发育率、排卵率、第1情期受胎率和总受胎率进行了检查和统计。结果表明:埋植“18—甲”药管同时肌注少量“18—甲”可提高处理效果;“18—甲”药管埋植7天后取出同时子宫内灌注2mg15—甲PGF_(2α)是一种效果较好的处理方法。     

Influence of premature induction of a luteinizing hormone surge with gonadotropin-releasing hormone on ovulation, luteal function, and fertility in cattle

We tested the hypothesis that luteal function and fertility would be reduced in cattle induced to ovulate prematurely compared with those ovulating spontaneously. Estrus was synchronized in 56 beef cows (24 that were nonlactating and 32 that were nursing calves). At 6.4 +/- 0.1 d after estrus, all follicles > or = 5 mm were aspirated (day of aspiration = d 0) with a 17-gauge needle using the ultrasound-guided transvaginal approach. On d 1.5 and 2, cows were administered 2 luteolytic doses of PGF2alpha. Ovarian structures were monitored by transrectal ultrasonography from d -2 to 12, or ovulation. Emergence of a new follicular wave occurred on d 1.7 +/- 0.1. When the largest follicle of the newly emerged wave was 10 mm in diameter (d 4.8 +/- 0.1), cows were assigned on an alternating basis to receive 100 microg of GnRH (GnRH-10; n = 29) to induce ovulation or, upon detection of spontaneous estrus, to the spontaneous (SPON) treatment (n = 24). Cows were bred by AI at 12 h after GnRH (GnRH-10) or 12 h after the onset of estrus (SPON) as detected using an electronic surveillance system. Blood samples were collected every other day beginning 2 d after ovulation until pregnancy diagnosis 30 d after AI. Ovulation and AI occurred in 29/29 cows in the GnRH-10 and in 24/24 cows in the SPON treatment. Ovulation occurred later (P < 0.05) in the SPON (d 7.7 +/- 0.1) than GnRH-10 (d 6.8 +/- 0.1) treatment. Double ovulations were detected in 47% of cows, resulting in 1.5 +/- 0.1 ovulations per cow. Diameters of the ovulatory and the second ovulatory (in cows with 2 ovulations) follicles were greater (P < 0.05) in the SPON (12.0 +/- 0.3 mm and 10.5 +/- 0.4 mm, respectively) than in the GnRH-10 (10.7 +/- 0.1 mm and 9.2 +/- 0.3 mm) treatment. Cross-sectional areas of luteal tissue and plasma concentrations of progesterone during the midluteal phase were greater (P < 0.05) in the SPON (3.62 +/- 0.2 cm2 and 6.4 +/- 0.3 ng/mL) than in the GnRH-10 (3.0 +/- 0.2 cm2 and 5.4 +/- 0.2 ng/mL) treatment. The conception rate to AI in the SPON (100%) treatment was greater (P < 0.05) than in the GnRH-10 (76%) treatment. The animal model used in this study resulted in unusually high conception rates and double ovulations. In conclusion, premature induction of the LH surge reduced the diameter of ovulatory follicle(s), the luteal function, and the conception rate to AI.     

Effects of standing estrus and supplemental estradiol on changes in uterine pH during a fixed-time artificial insemination protocol

Cows that exhibit estrus within 24 h of fixed-time AI have elevated concentrations of estradiol and greater pregnancy rates compared with cows not in estrus. Our objective was to determine whether estradiol, estrus, or both had an effect on uterine pH during a fixed-time AI protocol. Beef cows were treated with the CO-Synch protocol (100 mircog of GnRH on d -9; 25 mg of PGF(2alpha) on d -2; and 100 mircog of GnRH on d 0). One-half of the cows received an injection of estradiol cypionate (ECP; 1 mg) 12 h after PGF(2alpha). Cows detected in standing estrus within 24 h of the second GnRH injection were considered to be in standing estrus. Uterine pH was determined in all animals 12, 24, and 48 h after the PGF(2alpha) injection. For Exp. 1, pH was also determined 72 and 96 h after the PGF(2alpha) injection; in Exp. 2, pH was also determined at 54, 60, 66, 72, 78, 84, 90, and 96 h after the PGF(2alpha) injection or until ovulation. A treatment x time interaction (P < 0.01) influenced concentrations of estradiol. All cows had similar (P > 0.15) concentrations of estradiol at the time of ECP administration, but after ECP treatment all cows treated with ECP and control cows that exhibited estrus had greater (P < 0.01) concentrations of estradiol compared with nontreated cows that did not exhibit estrus. In all animals, estradiol diminished 48 h after the PGF(2alpha) (time of the second GnRH injection), but ECP-treated cows, regardless of estrus, had elevated (P < 0.02) concentrations of estradiol compared with control cows. There was a treatment x time interaction (P < 0.001) on uterine pH. All cows had similar uterine pH (P > 0.19) 24 h after the PGF(2alpha) injection. Control cows that did not exhibit estrus had a greater uterine pH compared with control cows that exhibited estrus (P < 0.01) and ECP cows that exhibited estrus (P = 0.05) 48 h after the PGF(2alpha) injection (7.0 +/- 0.1 vs. 6.7 +/- 0.1 and 6.8 +/- 0.1, respectively). Estradiol cypionate-treated cows not exhibiting estrus were intermediate (6.8 +/- 0.1; P > 0.05). All cows had similar uterine pH 72 h after the PGF(2alpha) injection through ovulation (P > 0.06). In summary, uterine pH was similar among all animals that exhibited estrus, regardless of treatment with ECP.     

Influence of a controlled internal drug release after fixed-time artificial insemination on pregnancy rates and returns to estrus of nonpregnant cows

We determined whether an ovulatory estrus could be resynchronized in previously synchronized, AI nonpregnant cows without compromising pregnancy from the previous synchronized ovulation or to those inseminated at the resynchronized estrus. Ovulation was synchronized in 937 suckled beef cows at 6 locations using a CO-Synch + progesterone insert (controlled internal drug release; CIDR) protocol [a 100-microg injection of GnRH at the time of progesterone insert, followed in 7 d by a 25-mg injection of PGF(2alpha) at insert removal; at 60 h after PGF(2alpha), cows received a fixed-time AI (TAI) plus a second injection of GnRH]. After initial TAI, the cows were assigned randomly to 1 of 4 treatments: 1) untreated (control; n = 237); 2) progesterone insert at 5 d after TAI and removed 14 d after TAI (CIDR5-14; n = 234); 3) progesterone insert placed at 14 d after TAI and removed 21 d after TAI (CIDR14-21; n = 232); or 4) progesterone insert at 5 d after TAI and removed 14 d after TAI and then a new CIDR inserted at 14 d and removed 21 d after TAI (CIDR5-21; n = 234). After TAI, cows were observed twice daily until 25 d after TAI for estrus and inseminated according to the AM-PM rule. Pregnancy was determined at 30 and 60 d after TAI to determine conception to the first and second AI. Pregnancy rates to TAI were similar for control (55%), CIDR5-14 (53%), CIDR14-21 (48%), and CIDR5-21 (53%). A greater (P < 0.05) proportion of nonpregnant cows was detected in estrus in the CIDR5-21 (76/110, 69%) and CIDR14-21 (77/120, 64%) treatments than in controls (44/106, 42%) and CIDR5-14 (39/109, 36%) cows. Although overall pregnancy rates after second AI service were similar, combined conception rates of treatments without a CIDR from d 14 to 21 [68.7% (57/83); control and CIDR5-14 treatments] were greater (P = 0.03) than those with a CIDR during that same interval [53.5% (82/153); CIDR5-21 and CIDR14-21 treatments]. We conclude that placement of a progesterone insert 5 d after a TAI did not compromise or enhance pregnancy rates to TAI; however, conception rates of nonpregnant cows inseminated after a detected estrus were compromised when resynchronized with a CIDR from d 5 or 14 until 21 d after TAI.