Cassandro M, Carnier P, Gallo L, Mantovani R, Contiero B, Bittante G, Jansen G B
Department of Animal Science, University of Padova, Italy.
J Dairy Sci. 1995 Dec;78(12):2884-93. doi: 10.3168/jds.S0022-0302(95)76919-3.
This study evaluated the adequacy of an alternate a.m.-p.m. testing scheme for milk yield in comparison with the official test method based on weighing two milkings within 24 h. A total of 88,558 single test day milking weights from 15,670 Italian Friesian cows in 610 herds in the province of Milano (Italy) were collected between September 1991 and October 1992. Ratios were computed for daily milk yield to a.m. and p.m. milking weights (direct yield ratios) and ratios of a.m and p.m. milking weights to daily milk yield (inverse yield ratios). Analysis of variance indicated that the milking interval is the most important source of variation for yield ratios. Factors for estimating daily milk yield from single milking weights adjusted for milking intervals were derived through regression analysis of direct and inverse yield ratios on the length of the milking interval. Daily milk yield was estimated more precisely and accurately when adjustment factors were used than when single milking weights were doubled. The doubling of a.m. and p.m. milking weights overestimated and underestimated (5% on average) daily milk yield, respectively. For 305-d lactation yield, accuracies of these methods were comparable. In conclusion, alternate recording of a.m. and p.m. milking weights led to reliable estimates of milk yield. Effects of the alternate a.m.-p.m. testing scheme on estimates of milk components and genetic evaluations of dams of sires should be investigated.
本研究评估了一种交替上午-下午测试方案用于产奶量的适用性，并与基于24小时内两次挤奶称重的官方测试方法进行了比较。1991年9月至1992年10月期间，收集了意大利米兰省610个牛群中15,670头意大利荷斯坦奶牛的总计88,558个单次测试日挤奶重量。计算了日产奶量与上午和下午挤奶重量的比率（直接产奶率）以及上午和下午挤奶重量与日产奶量的比率（逆产奶率）。方差分析表明，挤奶间隔是产奶率变异的最重要来源。通过对直接和逆产奶率与挤奶间隔时长进行回归分析，得出了根据调整挤奶间隔后的单次挤奶重量估算日产奶量的因素。使用调整因子时，日产奶量的估算比将单次挤奶重量加倍时更精确、更准确。上午和下午挤奶重量加倍分别高估和低估（平均5%）了日产奶量。对于305天泌乳期产奶量，这些方法的准确性相当。总之，交替记录上午和下午挤奶重量可得出可靠的产奶量估算值。应研究交替上午-下午测试方案对牛奶成分估算以及种公牛之母本遗传评估的影响。
