Mackey D R, Sreenan J M, Rochet J F, Diskin M G
Teagasc, Research Centre, Athenry, Co. Galway, Ireland.
J Anim Sci. 2000 Jul;78(7):1917-29. doi: 10.2527/2000.7871917x.
The effects of calf isolation and restricted suckling on LH pulse characteristics and interval to first ovulation (postpartum interval) were studied in 52 multiparous beef cows, with or without exogenous progesterone. At 30 d postpartum, cows were randomly allocated to one of four treatments (n = 13/treatment): 1) Ad lib, ad libitum access of cows to calves; 2) CI/RS, calf isolation/restricted suckling, where suckling was restricted to once daily; 3) CI/RS+P4, same as CI/RS but cows received an intravaginal progesterone-releasing device at calf isolation for 6 d; or 4) CI/RS+P4+E2, as CI/RS+P4 but the intravaginal progesterone-releasing device had a 10-mg estradiol capsule attached. Daily ovarian scanning and twice-daily blood sampling were performed from d 25 postpartum until the day of second ovulation. A random sample of cows from each treatment (n = 31 in total) were blood-sampled at 15-min intervals for 10 h on d 29, 32, 35, and 38. Ovulatory response to treatment was regarded as ovulation of either the dominant follicle growing at d 30 or the subsequent DF. There was a treatment x day effect (P = .09) on LH pulse frequency, but neither progesterone (CI/ RS+P4) nor progesterone and estradiol (CI/RS+P4+E2) treatment suppressed the calf isolation/restricted suckling-induced increase in LH pulse frequency. The estradiol capsule (CI/RS+P4+E2) delivered sufficient estradiol to delay new follicle wave emergence (treatment x stage; P < .001) and the associated preemergence increase in concentrations of FSH (treatment, P < .05) in cows treated at the postselection stage of follicle wave development, prolonging dominance of the dominant follicle present at treatment initiation (P < .001). The number of cows that ovulated in response to treatment was greater (P < .001) in cows with calf isolation/restricted suckling than in cows suckled ad libitum. Hence, cows assigned to the Ad lib treatment had a longer postpartum interval (P < .001) than cows of the other treatments. Exogenous progesterone treatment increased the frequency of cows exhibiting clinical signs of estrus at first ovulation (P < .001) and reduced the frequency of short estrous cycles (P < .001). We conclude that, in beef cows with calves, a 6-d progesterone treatment does not suppress the calf isolation/restricted suckling-induced increase in LH pulse frequency. Hence, on progesterone withdrawal, the LH pulse frequency is sufficient to stimulate first ovulation, accompanied by overt estrous expression and elimination of a short estrous cycle in most cows.
在52头经产肉用母牛中研究了犊牛隔离和限制哺乳对促黄体素（LH）脉冲特征以及首次排卵间隔时间（产后间隔）的影响，部分母牛使用了外源性孕酮。产后30天时，母牛被随机分配到四种处理方式之一（每种处理13头）：1）自由接触组，母牛可自由接触犊牛；2）CI/RS组，犊牛隔离/限制哺乳组，即每天仅允许哺乳一次；3）CI/RS+P4组，与CI/RS组相同，但在犊牛隔离时给母牛放置阴道内孕酮释放装置6天；4）CI/RS+P4+E2组，与CI/RS+P4组相同，但阴道内孕酮释放装置附有一个10毫克的雌二醇胶囊。从产后第25天直至第二次排卵日，每天进行卵巢扫描并每天两次采集血样。在第29、32、35和38天，从每种处理中随机抽取部分母牛（共31头），每隔15分钟采集一次血样，持续10小时。对处理的排卵反应被视为在第30天生长的优势卵泡或随后的优势卵泡排卵。LH脉冲频率存在处理×天数效应（P = 0.09），但孕酮处理（CI/RS+P4）和孕酮与雌二醇联合处理（CI/RS+P4+E2）均未抑制犊牛隔离/限制哺乳引起的LH脉冲频率增加。在卵泡波发育的选择后阶段接受处理的母牛中，雌二醇胶囊（CI/RS+P4+E2）释放了足够的雌二醇来延迟新卵泡波的出现（处理×阶段；P < 0.001）以及卵泡波出现前促卵泡素（FSH）浓度的相关增加（处理，P < 0.05），延长了处理开始时存在的优势卵泡的优势期（P < 0.001）。犊牛隔离/限制哺乳的母牛对处理产生排卵反应的数量比自由哺乳的母牛更多（P < 0.001）。因此，分配到自由接触组的母牛产后间隔时间比其他处理的母牛更长（P < 0.001）。外源性孕酮处理增加了首次排卵时表现出发情临床症状的母牛频率（P < 0.001），并降低了短发情周期的频率（P < 0.001）。我们得出结论，在有犊牛的肉用母牛中，6天的孕酮处理不会抑制犊牛隔离/限制哺乳引起的LH脉冲频率增加。因此，在停用孕酮后，LH脉冲频率足以刺激首次排卵，同时在大多数母牛中伴有明显的发情表现并消除短发情周期。
