USDA, ARS, US Meat Animal Research Center, Clay Center, NE 68933-0166, USA.
J Anim Sci. 2011 Dec;89(12):4023-31. doi: 10.2527/jas.2011-4097. Epub 2011 Jul 15.
Seventy-four Angus and Angus × Hereford heifers were used in 2 successive years (yr 1, n = 43; yr 2, n = 31) to determine if luteal function of heifers during acute submaintenance feeding is related to variation in utilization of feed as determined by residual feed intake (RFI). Residual feed intake was determined for heifers beginning at 12.3 ± 0.1 mo of age in yr 1 and at 9.1 ± 0.1 mo of age in yr 2. Heifers were assigned to dry-lot pens (n = 6 to 9 heifers/pen) with electronic gates to measure individual feed intake of a total mixed ration for 70 and 72 d in yr 1 and 2, respectively. Residual feed intake was calculated as the difference between actual DMI and expected DMI from linear regression of DMI on mid-test BW(0.75) and ADG. At 14.4 ± 0.1 mo of age, all heifers were provided a restricted amount of feed to supply 40% of their maintenance energy requirements for 21 d. Estrous cycles of heifers were synchronized with PGF(2α) on d -10, 0, and 11 relative to start of restriction. Concentrations of progesterone in plasma on d 14 to 21 of restriction were used to determine if heifers ovulated. Overall ADG and ADFI were 0.83 ± 0.02 and 7.37 ± 0.67 kg/d, respectively, for yr 1; and 0.50 ± 0.02 and 5.66 ± 0.09 kg/d, respectively, for yr 2. There was no correlation between RFI and BW, ADG, ADFI, or ultrasound measure of backfat, nor was RFI related to concentrations of IGF-I in plasma. All heifers lost BW and had reduced backfat (P < 0.001) at the end of restricted feeding. All heifers had reproductive cycles before dietary restriction started. During acute nutritional restriction, 4 heifers became anovulatory. Sixteen heifers had concentrations of progesterone in plasma during restricted feeding that were atypical of normal luteal function. There was no relationship between luteal function during nutrient restriction and RFI of heifers. Circulating IGF-1 was greater at weaning and after restricted feeding in heifers with a smaller RFI (>0.5 SD below the mean) than heifers with a greater RFI (>0.5 SD above the mean). It is concluded that RFI is not related to luteal function during acute submaintenance feeding, but that short-term restriction of nutrient intake can alter luteal function that may compromise fertility, even in heifers that exhibit estrus and ovulate.
在连续两年（第 1 年，n = 43；第 2 年，n = 31）中，使用了 74 头安格斯和安格斯×赫里福德小母牛来确定小母牛在急性亚维持饲养期间的黄体功能是否与通过剩余饲料摄入量（RFI）确定的饲料利用变化有关。在第 1 年，小母牛从 12.3 ± 0.1 月龄开始，在第 2 年从 9.1 ± 0.1 月龄开始，确定了小母牛的剩余饲料摄入量。小母牛被分配到干草场围栏（每栏 6 到 9 头小母牛），配备电子门，以分别测量 70 和 72 天的全混合日粮的个体饲料摄入量。剩余饲料摄入量是通过 DMI 与中期测试 BW（0.75）和 ADG 的线性回归计算得出的实际 DMI 与预期 DMI 之间的差异。在 14.4 ± 0.1 月龄时，所有小母牛都被提供了限量饲料，以满足其 21 天维持能量需求的 40%。用 PGF(2α)同步小母牛的发情周期在限制的开始前 10、0 和 11 天。在限制的第 14 天到第 21 天期间，使用血浆中孕酮的浓度来确定小母牛是否排卵。第 1 年的总体 ADG 和 ADFI 分别为 0.83 ± 0.02 和 7.37 ± 0.67 kg/d；第 2 年分别为 0.50 ± 0.02 和 5.66 ± 0.09 kg/d。RFI 与 BW、ADG、ADFI 或背部脂肪的超声测量值之间没有相关性，RFI 也与血浆中 IGF-I 的浓度无关。所有小母牛在限制饲养结束时体重下降，背部脂肪减少（P < 0.001）。所有小母牛在开始限制饮食前都有生殖周期。在急性营养限制期间，有 4 头小母牛无排卵。在限制饲养期间，16 头小母牛的血浆孕酮浓度异常，与正常黄体功能不一致。在营养限制期间，黄体功能与小母牛的 RFI 之间没有关系。在 RFI 较小（小于平均值的 0.5 SD）的小母牛中，断奶后和限制饲养后循环 IGF-1 较高，而 RFI 较大（大于平均值的 0.5 SD）的小母牛中，循环 IGF-1 较高。因此，RFI 与急性亚维持饲养期间的黄体功能无关，但短期限制营养摄入会改变黄体功能，从而可能损害生育能力，即使在表现发情和排卵的小母牛中也是如此。
