Cowan C M, Larson L L
J Dairy Sci. 1979 Apr;62(4):546-50. doi: 10.3168/jds.S0022-0302(79)83288-9.
The relationship of the estrous cycle to milk composition was examined in 15 Holstein cows in first lactation which were approximately 45 days postpartum. Composite milk samples were collected twice daily and analyzed for progesterone, fat, protein, total solids, sodium, potassium, magnesium, calcium, and somatic cells. Milk progesterone was minimal (less than ng/ml) from day -1 to day 2 (day 0 = estrus) of the estrous cycle and then increased at a relatively constant rate through day 15. Milk yield and sodium and magnesium concentrations of the milk varied with days of the estrous cycle. Mean milk yield was highest and sodium and magnesium concentrations were lowest on day 1. However, sodium concentration of the milk was the only component that varied significantly during the 3 days centered on estrus (days -1, 0, and 1). No other milk component changed significantly during the estrous cycle. Although milk yield and composition varied during the estrous cycle, none of these components appeared to be a practical indicator of estrus.
对15头处于头胎泌乳期、产后约45天的荷斯坦奶牛，研究了发情周期与牛奶成分之间的关系。每天采集两次混合牛奶样本，分析其中的孕酮、脂肪、蛋白质、总固体、钠、钾、镁、钙和体细胞。在发情周期的第-1天至第2天（第0天=发情期），牛奶中的孕酮含量最低（低于纳克/毫升），然后以相对恒定的速率增加，直至第15天。牛奶产量以及牛奶中的钠和镁浓度随发情周期的天数而变化。第1天的平均牛奶产量最高，钠和镁浓度最低。然而，牛奶中的钠浓度是在以发情期为中心的3天（第-1天、第0天和第1天）期间唯一有显著变化的成分。在发情周期中，没有其他牛奶成分发生显著变化。尽管在发情周期中牛奶产量和成分会发生变化，但这些成分似乎都不是发情的实用指标。
