Department of Dairy and Animal Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
J Dairy Sci. 2011 Sep;94(9):4566-73. doi: 10.3168/jds.2011-4394.
Lactation can be induced successfully in 15-mo-old dairy heifers. Treatment of heifers induced into lactation with bovine somatotropin (bST) during an established lactation improved milk production; however, milk yields were still variable. The objective of the present study was to evaluate whether starting bST treatment during induction of lactation, rather than after lactation was established, would improve milk production beyond that of heifers induced into lactation but not treated with bST. Healthy Holstein heifers (n=32, 15 mo of age, 420±28 kg of body weight) were induced into lactation with subcutaneous injections of estradiol (0.075 mg/kg of body weight per d) and progesterone (0.25 mg/kg of body weight per d) for 7 d. Bovine somatotropin (500 mg) was administered to heifers (n=16) beginning on experimental d 1 along with the estrogen/progesterone treatment. Heifers continued to receive bST every 2 wk for 10 wk. Control animals (n=16) received no bST during this time. Milking began on experimental d 18, and milk production was compared through 53 d in milk (experimental d 70). Mean daily milk yield was 36% higher for bST-treated heifers than for control animals. A 15.5% difference in milk production between the groups was sustained through 305 d of lactation, even after control animals began bST treatment at 54 d in milk. Milk fat percentage was similar in bST and control heifers. Milk protein percentage was lower in bST-treated heifers (3.58%) compared with controls (3.99%) during the treatment comparison period and for the remainder of lactation (bST 3.25%, control 3.39%). Heifers treated with bST produced more total milk fat and protein compared with controls during the treatment comparison period. Throughout the induced lactation, heifers gained 0.87 kg/d and averaged 2.4 services/pregnancy; 30 became pregnant. Four heifers were culled during the induced lactation, and 28 heifers calved at 27.6±2.0 mo of age for a second lactation. Addition of bST to the lactation induction protocol was advantageous because it stimulated greater milk production.
成功诱导 15 月龄的奶牛泌乳。在已建立的泌乳期间，用牛生长激素（bST）治疗诱导泌乳的小母牛可提高产奶量；然而，产奶量仍然存在差异。本研究的目的是评估在诱导泌乳期间开始使用 bST 治疗，而不是在泌乳建立后开始治疗，是否会提高产奶量，超过诱导泌乳但未用 bST 治疗的小母牛。健康的荷斯坦小母牛（n=32，15 月龄，420±28kg 体重）接受皮下注射雌二醇（0.075mg/kg 体重/天）和孕酮（0.25mg/kg 体重/天）诱导泌乳 7 天。bST（500mg）于实验 d1 开始时给予小母牛（n=16），并与雌激素/孕酮治疗一起给予。小母牛每 2 周接受 bST 治疗 10 周。在此期间，对照动物（n=16）未接受 bST 治疗。实验 d18 开始挤奶，通过 53 天的产奶量（实验 d70）进行比较。bST 处理的小母牛的平均日产奶量比对照组高 36%。两组之间的产奶量差异持续到 305 天的泌乳期，即使在对照组在泌乳 54 天时开始接受 bST 治疗后也是如此。bST 和对照小母牛的牛奶脂肪百分比相似。bST 处理的小母牛的牛奶蛋白百分比（3.58%）低于对照组（3.99%），在治疗比较期间和整个泌乳期（bST 3.25%，对照 3.39%）。在治疗比较期间，bST 处理的小母牛比对照组产生更多的总牛奶脂肪和蛋白质。在整个诱导泌乳期间，小母牛每天增重 0.87kg，平均 2.4 次配种/妊娠；30 头怀孕。在诱导泌乳期间，有 4 头小母牛被淘汰，28 头小母牛在 27.6±2.0 月龄时产下一胎。在泌乳诱导方案中添加 bST 是有利的，因为它刺激了更高的产奶量。
