Serum Concentrations of the Milk Proteins α-Lactalbumin and β-Lactoglobulin in Pregnancy and Lactation: Correlations with Milk and Fat Yields in Dairy Cattle

Abstract

Serum concentrations of α-lactalbumin and β-lactoglobulin in first pregnancy, parturition, lactation, involution, and second parturition in 37 Holstein cattle were determined and used as an index of mammary status and in predicting milk yield. During first pregnancy, serum α-lactalbumin increased in the last 3 mo and reached a peak at parturition (∼1100ng/ml). Changes in α-lactalbumin could not be described by a simple exponential equation, whereas changes in serum β-lactoglobulin were described by a single exponential from second trimester until 4 wk prepartum and reached a peak at parturition (∼460ng/ml). By 2 wk after parturition, α-lactalbumin had dropped to approximately 140ng/ml, and β-lactoglobulin dropped to approximately 25ng/ml. In late lactation, α-lactalbumin was approximately 70ng/ml and β-lactoglobulin approximately 20ng/ml. Short-term elevations were found after cessation of milking in both α-lactalbumin and β-lactoglobulin in serum. The concentrations of α-lactalbumin and β-lactoglobulin at second parturition were similar to those at first parturition with no differences found between parity. Both α-lactalbumin and β-lactoglobulin in serum were functionally associated with mammary growth and development. In heifers late in pregnancy, both serum concentrations of α-lactalbumin and β-lactoglobulin were positively correlated with mature equivalent milk and fat yields in the subsequent lactation. Serum β-lactoglobulin concentrations at 16 wk prepartum in heifers were highly correlated with the sum of first and second lactation milk (r = .60) and fat (r = .60) yields. The potential value of using serum β-lactoglobulin as an index for prescreening of heifers for lactation potential is discussed.