Kesler D J, Faulkner D B, Shirley R B, Dyson T S, Ireland F A, Ott R S
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
J Anim Sci. 1996 Dec;74(12):2885-90. doi: 10.2527/1996.74122885x.
The objective of this experiment was to determine the optimal interval from the last day of melengestrol acetate (MGA) feeding to prostaglandin F2 alpha (PGF2 alpha) treatment on pregnancy rates of beef heifers and cows. All females (149 heifers and 399 postpartum cows) were fed MGA (.5 mg) daily for 14 d and then administered PGF2 alpha (25 mg Lutalyse) 13, 15, and 17 d (Groups 1, 2, and 3, respectively) after the last day of MGA feeding. Females not in estrus the first 52 h after PGF2 alpha treatment were artificially inseminated 72 h after PGF2 alpha treatment. Females in estrus 0 to 52 h and 78 h to 6 d after PGF2 alpha treatment were inseminated at estrus. Blood sera (collected immediately before and 3 d after PGF2 alpha treatment) were assayed for progesterone concentrations. Pregnancy was determined 44 to 47 d after the 72-h AI by rectal examination. The intervals from MGA feeding to PGF2 alpha that had the highest 72-h AI pregnancy rates were 17 d for heifers (43%) and 15 d for cows (43%). Heifers with a 17-d interval had a higher (P < .05) 72-h AI pregnancy rate than heifers with 13-d and 15-d intervals, and cows with a 15-d interval had a higher (P < .05) 72-h AI pregnancy rate than cows with a 17-d interval. The 4-d synchronized pregnancy rates (the 72-h AI and the succeeding 3 d inseminations) for both heifers (44%) and cows (53%) were not different (P > .05) among groups. Fewer (P < .05) cows with a 17-d interval from MGA to PGF2 alpha had corpora lutea regression (by 72 h) after PGF2 alpha treatment than cows with 13-d and 15-d intervals. We interpret the results to indicate that the interval from MGA to PGF2 alpha treatment may influence 72-h AI pregnancy rates, that optimal intervals are 17 d for heifers and 15 d for cows, and that pregnancy rates are improved by insemination for 3 d after the 72-h AI.
本实验的目的是确定从醋酸美仑孕酮（MGA）饲喂的最后一天到前列腺素F2α（PGF2α）处理之间的最佳间隔时间，以探究其对小母牛和母牛妊娠率的影响。所有雌性动物（149头小母牛和399头产后母牛）每天饲喂MGA（0.5毫克），持续14天，然后在MGA饲喂的最后一天之后的第13、15和17天分别给予PGF2α（25毫克的律胎素）（分别为第1、2和3组）。PGF2α处理后最初52小时内未发情的雌性动物在PGF2α处理后72小时进行人工授精。PGF2α处理后0至52小时以及78小时至6天发情的雌性动物在发情时进行授精。检测PGF2α处理前即刻和处理后3天采集的血清中的孕酮浓度。在72小时人工授精后44至47天通过直肠检查确定妊娠情况。小母牛从MGA饲喂到PGF2α处理间隔17天（43%）以及母牛间隔15天（43%）时，72小时人工授精的妊娠率最高。间隔17天的小母牛72小时人工授精的妊娠率高于间隔13天和15天的小母牛（P < 0.05），间隔15天的母牛72小时人工授精的妊娠率高于间隔17天的母牛（P < 0.05）。小母牛（44%）和母牛（53%）的4天同步妊娠率（72小时人工授精及随后3天的授精）在各组之间无差异（P > 0.05）。从MGA到PGF2α间隔17天的母牛在PGF2α处理后（到72小时）黄体退化的数量少于间隔13天和15天的母牛（P < 0.05）。我们认为结果表明从MGA到PGF2α处理的间隔时间可能会影响72小时人工授精的妊娠率，小母牛的最佳间隔时间为17天，母牛为15天，并且在72小时人工授精后连续3天进行授精可提高妊娠率。
