Lactoferrin (LF) and milk fat globule (MFG) are 2 biologically active components of milk with great economical and nutritional value in the dairy industry. The objectives of this study were to estimate (1) the heritability of mid-infrared (MIR)-predicted LF and MFG size (MFGS) and (2) the genetic correlations between predicted LF and MFGS with milk, fat, and protein yields, fat and protein percentages, and somatic cell score in first-parity Canadian Holstein cattle. A total of 109,029 test-day records from 22,432 cows and 1,572 farms for MIR-predicted LF and 109,212 test-day records from 22,424 cows and 1,559 farms for MIR-predicted MFGS were used in the analyses. Four separate 5-trait random regression test-day models were used. The models included days in milk, herd test date, and a polynomial regression on DIM nested in age-season of calving classes as fixed effects, random polynomial regressions on DIM nested in herd-year of calving, animal additive genetic and permanent environment classes, and a residual effect. Regression curves were modeled using orthogonal Legendre polynomials of order 4 for the fixed age-season of calving effect and of order 5 for the random effects. Moderate overall heritability estimates of 0.34 and 0.46 were estimated for the MIR-predicted LF and MIR-predicted MFGS, respectively. These heritability estimates were similar to the ones estimated for the direct measure of MFGS in a previous study. The genetic correlations between predicted MFGS and fat percentage (0.53) and between predicted LF and protein percentage (0.41) were both moderate and positive. Predicted LF and somatic cell score showed a weaker correlation (0.06) compared with other studies. The moderate genetic correlation between MIR-predicted MFGS and fat percentage and between MIR-predicted LF and protein percentage suggests that MIR predictions of MFGS and LF are not simply a function of the amount of fat and protein percentage, respectively, in the milk (i.e., the prediction equations are not simply predicting fat or protein percentages). Thus, these MIR-predicted values may provide additional information for selecting for fine milk components in Holstein cattle.

中文翻译：

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荷斯坦牛中红外预测的乳铁蛋白和乳脂球大小的遗传参数估计。

乳铁蛋白（LF）和乳脂球（MFG）是乳制品中的两种生物活性成分，在乳制品行业中具有巨大的经济和营养价值。这项研究的目的是估计（1）中红外（MIR）预测的LF和MFG大小（MFGS）的遗传力，以及（2）预测的LF和MFGS与牛奶，脂肪和蛋白质产量之间的遗传相关性，头胎加拿大荷斯坦牛的脂肪和蛋白质百分比以及体细胞评分。分析中使用了来自MIR预测的LF的22,432头奶牛和1,572个农场的109,029个测试日记录，以及使用MIR预测的MFGS的22,424头奶牛和1,559个农场的109,212个测试日记录。使用了四个独立的5性状随机回归测试日模型。这些模型包括牛奶天数，牛群测试日期，以及在犊牛年龄季节嵌套的DIM多项式回归作为固定效应，在犊牛畜群年嵌套的DIM随机多项式回归，动物累加遗传和永久环境类别以及残差效应。对于产犊效应的固定年龄季节，使用4阶正交勒让德多项式对回归曲线进行建模，对于随机效应，其回归阶数为5阶。MIR预测的LF和MIR预测的MFGS的中度总体遗传力估计分别为0.34和0.46。这些遗传力估计值与先前研究中直接测量MFGS的估计值相似。预测的MFGS和脂肪百分比（0.53）之间的遗传相关性以及预测的LF和蛋白质百分比（0.41）之间的遗传相关性均为中度和阳性。与其他研究相比，预测的LF和体细胞评分显示出较弱的相关性（0.06）。MIR预测的MFGS和脂肪百分比之间以及MIR预测的LF和蛋白质百分比之间的中等遗传相关性表明，MIR预测MFGS和LF不仅分别是牛奶中脂肪和蛋白质百分比的函数（即，预测方程式不只是预测脂肪或蛋白质的百分比）。因此，这些MIR预测值可为选择荷斯坦牛的优质牛奶成分提供更多信息。MIR预测的MFGS和脂肪百分比之间以及MIR预测的LF和蛋白质百分比之间的中等遗传相关性表明，MIR预测MFGS和LF不仅分别是牛奶中脂肪和蛋白质百分比的函数（即，预测方程式不只是预测脂肪或蛋白质的百分比）。因此，这些MIR预测值可为选择荷斯坦牛的优质牛奶成分提供更多信息。MIR预测的MFGS和脂肪百分比之间以及MIR预测的LF和蛋白质百分比之间的中等遗传相关性表明，MIR预测MFGS和LF不仅分别是牛奶中脂肪和蛋白质百分比的函数（即，预测方程式不只是预测脂肪或蛋白质的百分比）。因此，这些MIR预测值可以为选择荷斯坦牛的优质牛奶成分提供额外的信息。