Estrus synchronization of gilts can be achieved by feeding the orally active progestogen altrenogest (AT) to cycling gilts at 20 mg/day for 14 to 18 days with gilts usually returning to estrus 4 to 8 days after the last feeding. In practice, gilts failing to exhibit estrus by 6 days after AT withdrawal may compromise weekly breeding targets. The cause of prolonged intervals to estrus are unknown but may involve prolonged suppression due to the release of progesterone (P4), and by extension AT, from adipose tissues. The present study examined relationships between gilt P2 backfat depth (<13.5 mm, 14–16.5 mm, >17 mm groups), the AT withdrawal to estrus interval, and subsequent reproductive performance in gilts. We noted longer intervals to estrus in gilts with greater P2 backfat depths (p < 0.0001), and higher serum P4 concentrations on the last day of AT feeding and at estrus detection (p < 0.05). Total born litter sizes were unaffected by backfat depth, but pigs born alive progressively decreased with increasing backfat depth with the fattest gilts producing the fewest liveborn pigs (p < 0.05). Taken together, these data suggest that adipose tissues may provide a reservoir of steroid, with its release from fatter gilts having potential negative effects on their subsequent reproductive performance.

中文翻译：

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背脂厚度和高脂糖母猪退出至发情的间隔对母猪繁殖性能的影响

母猪的发情同步可以通过将口服活性孕激素altrenogest（AT）以20 mg /天的剂量饲喂循环性小母猪14至18天来实现，通常在最后一次饲喂后4至8天，小母猪会回到发情期。在实践中，后备母猪停药后6天仍未发情，可能会损害每周的繁殖目标。发情间隔延长的原因尚不清楚，但可能由于脂肪组织中孕酮（P4）的释放以及AT的扩展而导致长时间的发情抑制。本研究检查了后备母猪P2背脂肪深度（<13.5 mm，14–16.5 mm，> 17 mm组），AT撤至发情间隔以及随后的后备母猪繁殖性能之间的关系。我们注意到，P2后脂肪深度更大的后备母猪发情间隔更长（p<0.0001），并且在AT喂养的最后一天和发情检测时血清P4浓度更高（p <0.05）。出生仔猪的总大小不受背脂深度的影响，但是随着背脂深度的增加，生猪的数量逐渐减少，而最肥的母猪生产的活仔猪最少（p <0.05）。综上所述，这些数据表明，脂肪组织可能提供了类固醇的贮藏，其从肥大的后备母猪中释放会对它们随后的繁殖性能产生潜在的负面影响。