Larson J E, Thielen K N, Funnell B J, Stevenson J S, Kesler D J, Lamb G C
North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744, USA.
J Anim Sci. 2009 Mar;87(3):914-21. doi: 10.2527/jas.2008-1443. Epub 2008 Nov 7.
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.
我们确定了在先前已同步发情、人工授精未怀孕的奶牛中，排卵发情能否重新同步，同时又不影响前次同步排卵后的怀孕情况，也不影响在重新同步发情时进行人工授精的奶牛的怀孕情况。在6个地点，使用CO - 同步 + 孕酮植入物（控制内部药物释放；CIDR）方案，对937头哺乳肉用母牛进行了发情同步处理[在植入孕酮时注射100微克促性腺激素释放激素（GnRH），7天后在取出植入物时注射25毫克前列腺素F2α（PGF2α）；在PGF2α注射后60小时，母牛接受定时人工授精（TAI）并注射第二次GnRH]。首次TAI后，母牛被随机分配到4种处理中的一种：1）不处理（对照组；n = 237）；2）TAI后5天植入孕酮并在TAI后14天取出（CIDR5 - 14；n = 234）；3）TAI后14天植入孕酮并在TAI后21天取出（CIDR14 - 21；n = 232）；或4）TAI后5天植入孕酮并在TAI后14天取出，然后在TAI后14天植入新的CIDR并在TAI后21天取出（CIDR5 - 21；n = 234）。TAI后，每天观察母牛两次，直至TAI后25天，观察发情情况，并根据上午 - 下午规则进行人工授精。在TAI后30天和
