Edwards J P, Jago J G, Lopez-Villalobos N
DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
J Dairy Sci. 2014;97(1):259-69. doi: 10.3168/jds.2013-7051. Epub 2013 Nov 7.
The objective of this study was to describe the variation in milking characteristics, and factors associated with these traits, in grazing dairy cows milked without premilking stimulation. Milk yield, duration, and average and maximum milk flow rate data were collected from 38 farms in New Zealand at 2 time points (spring and autumn) during the 2010 to 2011 season. Subsequently, a second data set, allowing the generation of daily milk flow profiles, was collected from 2 farms in the 2011 to 2012 season. Corresponding animal data, such as breed, date of birth, and ancestry information, were extracted from the New Zealand Dairy Industry Good Animal Database (New Zealand Animal Evaluation Ltd., Hamilton, New Zealand). Residual milking duration (deviation from the regression line of milk yield on milking duration) was calculated, allowing the identification of fast-milking cows independent of milk yield. Variance components for the milking characteristics traits were estimated using an animal linear mixed model. The average milk yield was 10 kg/milking and the average milking duration was 360 s. The average milk flow rate was 1.8 kg/min and maximum milk flow 3.3 kg/min, with 44% of milk flow curves being classified as bimodal. Primiparous animals exhibited different milk flow profiles, with a lower maximum flow, than multiparous animals, possibly due to differences in cisternal capacity. Residual milking duration was shortest (-10s) in mid-lactation (121-180 d) and was 13s longer for Jersey compared with Friesian cows; however, it was 19s shorter when adjusted for energy content. Residual milking duration had a negligible genetic correlation (-0.07) with milk yield, indicating that selection for cows with shorter residual milking duration should have a negligible effect on milk yield. A heritability of 0.27 indicated that residual milking duration could be valuable as part of a breeding program. Knowledge of the distribution of milking durations for a given milk yield allows farmers to choose appropriate cluster-on time when using a maximum milking time strategy to improve milking efficiency.
本研究的目的是描述在不进行挤奶前刺激的情况下，放牧奶牛的挤奶特征变化以及与这些特征相关的因素。在2010至2011年季节的两个时间点（春季和秋季），从新西兰的38个农场收集了产奶量、挤奶持续时间以及平均和最大奶流率数据。随后，在2011至2012年季节从2个农场收集了第二个数据集，用于生成每日奶流曲线。相应的动物数据，如品种、出生日期和系谱信息，从新西兰乳业优质动物数据库（新西兰动物评估有限公司，新西兰哈密尔顿）中提取。计算了剩余挤奶持续时间（产奶量与挤奶持续时间回归线的偏差），从而能够识别出与产奶量无关的快速挤奶牛。使用动物线性混合模型估计挤奶特征性状的方差分量。平均产奶量为10千克/次挤奶，平均挤奶持续时间为360秒。平均奶流率为1.8千克/分钟，最大奶流为3.3千克/分钟，44%的奶流曲线被归类为双峰型。初产动物的奶流曲线与经产动物不同，最大奶流较低，这可能是由于乳池容量的差异。剩余挤奶持续时间在泌乳中期（121 - 180天）最短（-10秒），与弗里生奶牛相比，泽西奶牛的剩余挤奶持续时间长13秒；然而，在根据能量含量进行调整后，其短19秒。剩余挤奶持续时间与产奶量的遗传相关性可忽略不计（-0.07），这表明选择剩余挤奶持续时间较短的奶牛对产奶量的影响可忽略不计。0.27的遗传力表明剩余挤奶持续时间作为育种计划的一部分可能具有价值。了解给定产奶量下挤奶持续时间的分布情况，有助于奶农在采用最大挤奶时间策略提高挤奶效率时选择合适的集群开启时间。
