Università degli Studi di Milano, Dipartimento di Scienze e Tecnologie Veterinarie per la Sicurezza Alimentare, via D. Trentacoste 2, 20133 Milan, Italy.
J Dairy Sci. 2011 Aug;94(8):4081-9. doi: 10.3168/jds.2010-3611.
The overall goal of this study was to investigate milk flow traits in Italian Holstein-Friesian cows and, in particular, the bimodality of milk flow, defined as delayed milk ejection at the start of milking. Using a milkometer, 2,886 records were collected from 133 herds in northern Italy from 2001 to 2007. All records included 5 time-period measurements for milk flow, somatic cell score (SCS), milk yield, 8 udder type traits, and the presence or absence of bimodality in milk flow. Genetic parameters were estimated using linear animal models for continuous traits such as milk flow, udder type, SCS, and milk production, whereas bimodality was analyzed as a categorical trait. With the exception of decreasing time (which had a very small heritability value of 0.06), heritability values for milk flow traits were moderate, ranging from 0.10 (ascending time) to 0.41 (maximum milk flow). In addition, moderate to high genetic correlations were estimated between total milking time and other time measures (from 0.78 to 0.87), and among time flow traits (from 0.62 to 0.91). The decreasing time was the trait most genetically correlated with udder type traits, with correlation values of 0.92 with rear udder height, 0.85 with rear udder width, and 0.73 with teat placement. Large udders with strong attachments were also associated with greater milk production. Heritability estimated for bimodality was 0.43, and its genetic correlation with milk flow traits and SCS indicated a sizable genetic component underlying this trait. Bimodality was negatively associated with milk production; shorter milking times and greater peak milk levels were genetically correlated with more frequent bimodal flows, indicating that faster milk release would result in an increase in bimodal patterns. The negative genetic correlation of bimodality with SCS (-0.30) and the genetic correlation between milk flow traits and SCS suggest that the relationship between milkability and SCS is probably nonlinear and that intermediate flow rates are optimal with respect to mastitis susceptibility. Quicker milk flow over a shorter period would increase the frequency of bimodal curves in milking, whereas the correlation between bimodality and both ascending and descending time was less clear.
本研究的总体目标是研究意大利荷斯坦弗里生奶牛的牛奶流动特性，特别是牛奶流动的双峰性，定义为挤奶开始时牛奶的延迟排出。使用乳脂计，从 2001 年至 2007 年，从意大利北部的 133 个牧场中收集了 2886 条记录。所有记录都包括 5 个时间周期的牛奶流量、体细胞评分（SCS）、牛奶产量、8 个乳房类型特征，以及牛奶流动是否存在双峰性。使用线性动物模型估计了连续性状（如牛奶流量、乳房类型、SCS 和牛奶产量）的遗传参数，而双峰性则作为分类性状进行分析。除了下降时间（具有非常小的遗传值 0.06）外，牛奶流动性状的遗传值适中，范围从 0.10（上升时间）到 0.41（最大牛奶流量）。此外，还估计了总挤奶时间与其他时间测量值（从 0.78 到 0.87）以及时间流动性状（从 0.62 到 0.91）之间的中度至高度遗传相关性。下降时间是与乳房类型特征最具遗传相关性的性状，与后乳房高度的相关性值为 0.92，与后乳房宽度的相关性值为 0.85，与乳突位置的相关性值为 0.73。大乳房和牢固的附着也与更高的牛奶产量相关。双峰性的遗传值估计为 0.43，其与牛奶流动性状和 SCS 的遗传相关性表明，该性状具有相当大的遗传成分。双峰性与牛奶产量呈负相关；较短的挤奶时间和较高的峰值牛奶水平与更频繁的双峰流动具有遗传相关性，表明更快的牛奶释放将导致双峰模式增加。双峰性与 SCS 的负遗传相关性（-0.30）以及牛奶流动性状与 SCS 的遗传相关性表明，产奶力与 SCS 的关系可能是非线性的，中间流动速率对乳腺炎易感性是最佳的。在较短的时间内更快的牛奶流动会增加挤奶中双峰曲线的频率，而双峰性与上升时间和下降时间之间的相关性则不太清楚。
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