Prediction of milk yields from serum beta-lactoglobulin concentrations in pregnant heifers.

The serum concentration of beta-LG at wk 26 of pregnancy was determined in Holstein heifers of known genetic merit to evaluate use of a single blood sample as an index to predict their subsequent milk yield. Concentrations of beta-LG varied widely (16 to 1200 ng/ml) in the serum of the heifers at this stage of pregnancy. Subsequent measures of lactation performance showed that heifers with high beta-LG concentrations in pregnancy produced more milk than those with low beta-LG in serum. Previous studies have shown that the concentration of beta-LG in serum shows a log-linear increase during pregnancy, which is consistent with correlation to the growth of the mammary parenchyma. Therefore, the logarithm beta-LG concentration was used as the index in this study. The correlations of this index were .46, .54, and .48 for first lactation 305-d yields of milk, fat, and protein, respectively. The results suggest that serum concentrations of beta-LG estimated from a single blood sample at this stage of pregnancy can be used to predict milk yield. Analysis showed that an explanation of future milk yield was significantly improved by use of serum beta-LG and parent average. Serum beta-LG can be used as a physiological marker to prescreen heifers for lactation potential.