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1.
试验结果表明，用适量ＰＭＳＧ（１３５０－２０００ＩＵ）和纯化ＦＳＨ（５ｍｇ）均能诱导母牛产双胎，其双胎率分别为４２．９％（３／７）和３３．３％（１／３）。输精时注射ＬＲＨ－Ａ３双胎率为５０．０％（３／６），较对照组２５．０％（１／４）提高２５．０个百分点。  相似文献   

2.
本研究用生殖激素诱导母牛双胎进行了试验研究。ＰＭＳＧ处理组；选产后５０ｄ以上１２头参试母牛，按其发情顺序随机分为３个组。每组４头牛，三组牛在发情周期的第１０天分别ＴＫ ＥＭＮ  相似文献   

3.
选择本地母黄牛，应用ＬＲＨ－Ａ和ＰＭＳＧ进行提高母牛繁殖研究。结果表明，在母牛配种前５－６小时肌注ＬＲＨ－Ａ１５０μｇ／头，可使精期受胎率提高２５．３％（Ｐ＜０．０１）；为提高早期胚胎成活率，在配种后１１－１３天肌注ＬＲＨ－Ａ１００μｇ／头，使青年母牛受胎率提高２８．８％；应用ＰＭＳＧ和１５甲基－ＰＧＦ２ａ及抗ＰＭＳＧ血清，可诱导双胎率５３．３％，提高产活犊率６０％。  相似文献   

4.
将４１头产后４０－１００天卵巢静止奶牛分为四个处理组：ＯＩＵＰＭＳＧ（ｎ＝１２）、１０００ＩＵＰＭＳＧ（ｎ＝１２）、１２５０ＩＵＰＭＳＧ（ｎ＝１２）及１５００ＩＵＰＭＳＧ（ｎ＝５），处理后一周内的排卵率分别为０．０％、８３．３３％、９１．６７％及４０．０％（Ｐ＜０．０１），从处理到妊娠间隔时间分别为８９．１±３６．７天、２９．８±２且．７天、５１．９±２５．２天及６０．２±２９．６天（Ｐ＜０．０１）；２９头试验母牛又按产后４０－６０天及产后６１－１００天分为两组，处理后一周内的排卵率分别为９２．９％及６６．７％（Ｐ＞０．０５），从处理到妊娠间隔时间分别为５０．３±２７．０天及３８．５±２７．０天（Ｐ＞０．０５）。结果表明，ＰＭＳＧ处理卵巢静止母牛具有明显效果，其中以１０００ＩＵ为最优，处理时间的早晚对处理效果无明显影响。  相似文献   

5.
肌注ＰＭＳＧ＋ＣＨＧ、ＬＲＨ－Ａ或ＦＳＨ＋ＬＨ，能促使母果子狸发情、交配和产仔。ＰＭＳＧ５００ＩＵ＋ＨＣＧ２５０ＩＵ，ＬＲＨ－Ａ５０－１００μｇＦＳＨ１６０ＩＵ＋ＬＨ１００ＩＵ时催情效果较佳。使用上述药物，在每年１月３０日在若进行第１次催情，果子狸可比自然状态提早约１个月于４月５日前后产下第１胎仔狸。仔狸２０日龄断奶成活率较高。断奶后第１５ｄ对母猪第２次催情，７月中旬前后可产下第２胎仔狸，做到在较  相似文献   

6.
应用孕马血清促性腺激素诱导青年母牛发情试验   总被引：3，自引：0，他引：3  
对２０头黑白花青年母牛应用孕马血清促性腺激素（ＰＭＳＧ）处理诱发发情。结果：处理后１～９ｄ内出现发情的有１８头,发情率为９０％,未发情率为１０％;５头对照牛发情率为１０％,未发情率为９０％（Ｐ＜００１）。  相似文献   

7.
提高绵羊受胎率的研究——同期发情试验（二）   总被引：6，自引：0，他引：6  
５６只绵羊（海西２６只，海南２０只）经Ｐ＋ＰＭＳＧ和６２只绵羊（海西３０只，海南３２只）经ＰＭＳＧ处理后，１￣５ｄ内的同期发情率分别为７５．５％，（海西７９．９０％，海南７５．００％）和５６．５６％（海西６０．００％，海南５３．１３％），且Ｐ＋ＰＭＳＧ组与对照组间有显著差异（Ｐ〈０．０５），１０ｄ内的同期发情率为９５．７５％（海西９６．１５％，海南９５．００％）和９６．６６％（海西９３．３３，海南  相似文献   

8.
２４头太湖猪新生仔猪（二花×大白）分为四组，在出生后隔离并分别人工哺喂葡萄糖盐水（ＧＳ组，ｎ＝４），牛初乳（ＢＣ组，ｎ＝５），牛乳（ＢＭ组，ｎ＝６）４８ｈ和自然哺乳（ＰＣ组，ｎ＝９）。前３组在４８ｈ后回圈哺乳。初乳对新生仔猪血液蛋白电泳形态的影响，新生仔猪血清蛋白质浓度初生时平均为３１．８±１．８６ｍｇ／ｍｌ，ＰＣ组在出生后迅速增加，２４ｈ达８１．７８±８．６ｍｇ／ｍｌ此后略有下降。４８ｈ为５６．６７±１１．３６ｍｇ／ｍｌ，第７天为８７．６７±３．８９ｍｇ／ｍｌ。ＢＣ和ＢＭ组与ＰＣ组有相似的变化；而ＧＳ组在４８ｈ内一直下降，４８ｈ为６．２５±２．２８ｍｇ／ｍｌ，自然哺乳后，第７天上升为４７．７５±２．６８ｍｇ／ｍｌ。但ＢＭ、ＧＳ组在２４ｈ、４８ｈ和第７天血清总蛋白浓度显著低于ＰＣ组（Ｐ＜０．０１）。血清ＳＤＳ—ＰＡＧＥ电泳显示，清蛋白（ＳＡ）ＰＣ、ＢＣ、ＢＭ三组４８ｈ内持续增加，ＧＳ组２４ｈ后显著下降，并且ＧＳ组在高分子量区（１５０ｋｄ）出现非抗体蛋白和多肽的聚合，其他三组则未见到。实验中未观察到牛乳酪蛋白向仔猪血液中的转移。  相似文献   

9.
本试验采用三合激素（ＩＴＣ）为主的处理方案,对繁殖季节中１７９只母羊进行了同期发情处理。按５５ｋｇ以上体重的母羊第一次注ＩＴＣ２．０ｍｌ,间隔１４天,第二次注１．０ｍｌ;５５ｋｇ以下母羊第一次注１．５ｍｌ,第二次注０．８ｍｌ,于第二次注射同时随机分为６组。①ＰＭＳＧ１９０ＩＵ;②ＬＲＨ─Ａ＿２５０μｇ＋ＰＭＳＧ１５０ＩＵ;③ＬＲＨ－Ａ＿３５０μｇ＋ＰＭＳＧ１５０ＩＵ;④ＦＳＨ２０单位＋ＰＭＳＧ１５０ＩＵ;⑤ＬＨ５０单位＋ＰＭＳＧ１５０ＩＵ;⑥ＰＭＳＧ５００ＩＵ或ＬＲＨ－Ａ＿３１００μｇ。试验结果表明,第一次注射和第二次注射ＩＴＣ,第３组同期发情率较高（Ｐ<０．０５）,产羔率以第２组为高（Ｐ<０．０５）,成活则以第４组和第６组８为最高（Ｐ<０．０５）。试验初步结论为：三合激素与ＰＮＩＳＧ、ＬＲＨ─Ａ＿２配合处理,可利用于绵羊同期发情。  相似文献   

10.
IBDV VP2/VP243基因DNA疫苗表达质粒的构建与表达   总被引：2，自引：0，他引：2  
将传染性法氏囊病病毒（ＩＢＤＶ）ＶＰ２／ＶＰ２４３插入真核表达载体ｐｃＤＮＡ中,置于ＣＭＶ启动子的调控之下,构建成ＤＮＡ疫苗表达质粒ｐｃＤＮＡ ＶＰ２和ｐｃＤＮＡ ＶＰ０。分别转染ＣＥＦ细胞后,于２４、４８、７２ｈ取细胞裂解液进行ＥＬＩＳＡ、ＳＤＳ－ＰＡＧＥ和Ｗｅｓｔｅｒｎ ｂｌｏｔ检测,ｐｃＤＮＡ ＶＰ２于转染后２４ｈ呈阳性反应,４８ｈ表达量高于２４ｈ;ｐｃＤＮＡ ＶＰ０于转染后４８ｈ呈阳性反应  相似文献   

11.
在母牛产后第1次发情后第10d，给5头发情周期正常的母牛安装颈静脉血管导管；在母牛产后第2个发情周期进行挛生处理，即在产后第2次发情后第10d注射PMSG2000IU，2d后注射氯前列烯醇0．4mg第3次发情后注射抗PMSG抗体2000IU。自第1个发情周期第10d开始，每天间隔10min连续采血2h。发情当天间隔30min采血一次，直到第3次发情结束为止。挛生处理后采血间隔时间和方法与处理前不同。应用酶免疫测定方法测定血清中促性腺激素释放激素水平。结果表明：（1）牛外周血中GnRH释放具有脉冲性；（2)PMSG处理后外周血中GnRH水平升高，表现为脉冲频率增加，脉冲峰值升高。  相似文献   

12.
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.  相似文献   

13.
Application of AI in extensive beef cattle production would be facilitated by protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI). The objectives were to determine whether use of a controlled internal drug release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI in beef cows. Beef cows (n = 1,240) in 6 locations within the US Meat Animal Research Center received 1 of 2 treatments: 1)?an injection of GnRH [100 μg intramuscularly (i.m.)] followed by PGF(2α) (PGF; 25 mg i.m.) 7 d later (CO-Synch), or 2) CO-Synch plus a CIDR during the 7 d between GnRH and PGF injections (CO-Synch + CIDR). Cows received TAI and GnRH (100 μg i.m.) at 60 h after PGF. Progesterone was measured by RIA in blood samples collected 2 wk before and at initiation of treatment (d 0) and at PGF injection (d 7). Estrous behavior was monitored by Estrotect Heat Detectors. Pregnancy was diagnosed by ultrasonography 72 to 77 d after TAI. Plasma progesterone concentrations did not differ (P > 0.10) between synchronization protocols at first GnRH injection (d 0), but progesterone was greater (P < 0.01) at PGF injection (d 7) in cows receiving CO-Synch + CIDR vs. CO-Synch as a result of fewer CIDR-treated cows having progesterone ≤1 ng/mL at PGF (10.7 vs. 29.6%, respectively). A greater (P < 0.01) proportion of CO-Synch + CIDR vs. CO-Synch cows were detected in estrus within 60 h after PGF (66.7 vs. 57.8 ± 2.6%, respectively) and a greater (P < 0.01) proportion were pregnant to TAI (54.6 vs. 44.3 ± 2.6%, respectively). For both synchronization protocols, cows expressing estrus within 60 h before TAI had a greater pregnancy rate than cows without estrus. For cows with plasma progesterone ≤1 ng/mL at PGF injection, CO-Synch + CIDR increased pregnancy rate (65.2 ± 5.9 vs. 30.8 ± 3.4% with vs. without CIDR), whereas pregnancy rates did not differ (P > 0.10) between protocols (52.1 ± 2.1 vs. 50.0 ± 2.4%, respectively) when progesterone was >1 ng/mL (treatment × progesterone; P < 0.01). Inclusion of a CIDR in the synchronization protocol increased plasma progesterone concentration, proportion of cows detected in estrus, and pregnancy rate; however, the increase in pregnancy rate from inclusion of the CIDR was primarily in cows with decreasing or low endogenous progesterone secretion during treatment.  相似文献   

14.
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.  相似文献   

15.
Two progestin-based protocols for the synchronization of estrus in beef cows were compared. Cyclic, nonlactating, crossbred, beef cows were assigned by age and body condition score to one of two treatments. Cows assigned to the MGA Select protocol were fed melengestrol acetate (MGA; 0.5 mg x cow(-1) x (-1)) for 14 d, GnRH was administered (100 microg i.m. of Cystorelin) 12 d after MGA withdrawal, and PGF2alpha (25 mg of i.m. Lutalyse) was administered 7 d after GnRH. Cows assigned to the 7-11 Synch protocol were fed MGA for 7 d and were injected with PG on d 7 of MGA, GnRH on d 11, and PG on d 18. Transrectal ultrasonography was performed daily to monitor follicular dynamics from the beginning of MGA feeding through ovulation after the synchronized estrus. All cows exhibited estrus in response to PG. Mean interval to estrus was shorter (P < 0.01) for 7-11 Synch-treated cows (56 +/- 1.5 h) than for cows assigned to the MGA Select protocol (73 +/- 4.7 h). Mean interval from estrus to ovulation did not differ between treatments (P > 0.10). Variances for interval to estrus differed (P < 0.01) between treatments. Mean follicular diameter at GnRH injection, PG injection, and estrus did not differ (P > 0.10) between treatments. Relative to MGA Select, serum estradiol-17beta concentrations were higher (P < 0.01) for 7-11 Synch 2 d and 1 d before, on the day of GnRH injection, in addition to 4 d after GnRH, and 24 h after PG. Mean progesterone concentrations were greater (P < 0.01) for MGA Select cows from 4 d before to 7 d after GnRH. Forty-four percent of the variation in interval to estrus between treatments was explained by differences in estradiol-17beta concentrations 24 h after PG. This study suggests that follicular competence is likely related to steroidogenic capacity of the follicle and the endocrine environment under which growth and subsequent ovulation of the dominant follicle occurs.  相似文献   

16.
The efficiency of cronolone sponges in combination with either pregnant mare serum gonadotrophin (PMSG) or cloprostenol (PGF2alpha) for inducing and synchronizing the estrous cycle in Turkish Saanen does was investigated during the transition from non-breeding to breeding season. All does (n = 80) were treated with 20 mg cronolone sponges for 11 days and divided into 4 equal groups. In addition, each doe received an intramuscular injection of either 1.5 ml sterile saline solution, 0.075 mg PGF2alpha, 500 IU PMSG or 500 IU PMSG and 0.075 mg PGF2alpha, 24 h before the sponge removal. Cervical artificial insemination (AI) with frozen-thawed semen was performed once 16 h after the detection of the first accepted mount. The total estrous response for the first 24 +/- 4 h, total estrous response within 96 h, time to onset of the induced estrus, duration of the induced estrus and pregnancy rate was found to be 75.0%, 97.5%, 31.4 +/- 1.2 h, 29.3 +/- 1.2 h, and 33.3%, respectively. There were significant differences between the first two groups and the last two groups in terms of the onset of induced estrus and estrous response at the first 24 +/- 4 h (P < 0.05). These results indicate that the use of cronolone/PMSG was more effective than cronolone/PGF2alpha in the attainment of early and compact induction of estrus in Turkish Saanen does.  相似文献   

17.
The aim of this trial was to evaluate the effectiveness (fertility and lambing) of priming with a single injection of progesterone plus PMSG in anovulatory lactating Sarda ewes subjected to the ram effect (RE) in spring. Thirty ewes (P4 group) were i.m. injected with 30 mg progesterone and 500 IU PMSG 36 h before ram introduction (d 0). This treatment was compared to a 12-day treatment with fluorogestone acetate intravaginal sponges that was followed by injections of 350 IU PMSG upon sponge withdrawal (FGA group, n=30). All ewes responded to RE, showing plasma progestrone concentrations >1 ng/mL between d 6 and 12 (FGA) or 6 and 9 (P4). Eighty-nine percent of the P4 ewes conceived at first ovulation, and 11% conceived following a short estrus cycle. Lambings occurred on d 150.4 +/- 3.9, and the lambing rate was 100%. The fertility of the FGA ewes was 83% for the induced ovulation and was 7% for the second ovulation after a normal cycle. The FGA ewes lambed on d 149.8 +/- 4.4, and the lambing rate was 83%. Two abortions were recorded for the FGA ewes, which had higher prolificacy than the P4 group (2.2 +/- 0.8 vs. 1.8 +/- 0.4, respectively; P<0.05). Both fertility and the lambing rate were high in both groups, with a high degree of estrus synchronization, and there were no significant differences between the groups. We concluded that priming of lactating Sarda ewes in spring with P4+PMSG before RE is an effective and competitive method (cheaper and more practical than FGA+PMSG) of inducing fertile ovulations in these ewes.  相似文献   

18.
Sixty Simmental crossbred heifers 18 to 20 mo of age were detected in estrus and assigned at random to a 2 x 2 factorial design study with 30 controls, and 30 given FSH. Half of each group was given prostaglandin F2 alpha (PGF) i.v. and the rest i.m. Injections of follicle-stimulating hormone were started on d 7 to 14 of an estrous cycle and continued for 5 d or until ovariectomy; PGF was administered either i.v. or i.m. at 48 (25 mg) and 60 (15 mg) h after the initial FSH injection. Control females received a similar PGF treatment on a day between d 9 and 15 of the estrous cycle. Blood samples were collected from all animals immediately before PGF administration and every 12 h thereafter until ovariectomy. Within each of the four experimental subgroups, ovariectomies were performed at either 24, 48 or 72 h (five/time group) after initial PGF injection. Ovarian and corpus luteum (CL) weights were recorded as well as number and size of follicles and number of ovulations. Regression of the CL was slower (P less than .05) after administration of PGF i.v. than i.m. (CL weight was 2.6 vs 3.3 +/- .2 g for i.m. and i.v. groups, respectively). Exogenous FSH increased estradiol-17 beta (E2) concentrations, and FSH-treated heifers had more (P less than .05) early ovulations than control heifers did. Ovulations in FSH-treated heifers had begun to occur by 24 h after i.v. and i.m. PGF injection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

19.
Two experiments were conducted to determine whether dosage of estradiol valerate (EV) or day of estrous cycle when treatment was administered affected response to Syncro-Mate-B (SMB). Suckled beef cows received a 6-mg Norgestomet (NOR) ear implant (in situ 9 d) and a 3-mg NOR i.m. injection. In Exp. 1, 74 cows received NOR treatments concurrently with either 5 or 6 mg of EV administered i.m. on either d 1, 3, or 5 of an estrous cycle (estrus = d 1). In Exp. 2, 169 cows received NOR treatments concurrently with either 5, 7, or 9 mg of EV administered i.m. on either d 3 or 9 of an estrous cycle. In Exp. 1, 67, 50 and 92%, respectively, of cows receiving 5 mg of EV on d 1, 3, or 5 had functional corpora lutea (CL) at implant removal, whereas 42, 75, and 77%, respectively, of cows receiving 6 mg of EV had functional CL at implant removal (dosage P greater than .10; day P less than .05). Synchronized estrous responses were 50, 33, and 23%, respectively, when cows received 5 mg of EV on d 1, 3, or 5, and 67, 33, and 38%, respectively, when cows received 6 mg of EV (dosage P greater than .10; day P less than .05). First-service pregnancy rate was decreased (P less than .05) in cows treated on d 5 (33%) compared with cows treated on d 1 (63%), but dosage of EV had no effect on pregnancy rate.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
The objectives of this study were to evaluate replacing GnRH with hCG and the effects of 48-h calf removal (CR) on pregnancy rates of cows synchronized with the CO-Synch protocol. Suckled beef cows (n = 467) at two locations were assigned to treatment by breed, age, and calving date. Treatment included either GnRH with (n = 121) or without CR (n = 117) or hCG with (n = 115) or without CR (n = 114) using the CO-Synch protocol. On d 0 and 9, cows received either hCG (2,500 IU, i.m.) or GnRH (100 microg, i.m.), and on d 7 all cows received PGF2alpha (25 mg). At one location, blood samples were collected from all cows (n = 203) on d -14, -7, 0, 7, 9, and 16. Calves were removed on d 7 and returned on d 9 (48 h) from approximately half of the cows that received GnRH or hCG. Cows that were detected in estrus between d 6 and 9 were bred approximately 12 h later and received no further injections. Cows not observed in estrus by d 9 received a second injection of either GnRH or hCG and were timed-inseminated. The AI pregnancy rates for GnRH-treated cows with or without CR and hCG-treated cows with or without CR were 46, 49, 35, and 34%, respectively (P = 0.44). Pregnancy rates of cows differed by treatment x age interaction (P = 0.07), hormone (P = 0.09), and hormone x age (P = 0.01) but not by CR (P = 0.66) or CR x age (P = 0.33). Among 2-yr-olds, pregnancy rates were higher for cows treated with hCG without CR than for cows that received GnRH with calf removal, whereas cows treated with hCG with CR and GnRH without CR were intermediate. In addition hCG-treated 2-yr-olds had higher pregnancy rates than GnRH-treated 2-yr-olds regardless of calf presence, but the reverse was true for older cows. Overall, GnRH-treated cows (48%) had a higher (P = 0.09) pregnancy rate than hCG-treated cows (34%). Among anestrous cows, GnRH and hCG were similar (P = 0.40) in their ability to induce ovulation and corpus luteum formation after the first and second injections of GnRH (31 and 76%, respectively) or hCG (39 and 61%, respectively). More (P = 0.001) hCG-treated cows exhibited short estrous cycles following timed AI. We conclude that hCG is not a suitable replacement for GnRH to synchronize ovulation with the CO-Synch protocol in multiparous cows, although further evaluation among primiparous cows is warranted using hCG with the CO-Synch protocol.  相似文献   

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