Alpha-lactalbumin in bovine serum: relationships with udder development and function.

Concentrations of alpha-lactalbumin in blood from cattle in various physiological states were measured as an index of udder development and function. Included were primiparous heifers during gestation and the peripartum period, nonlactating, nonpregnant cows hormonally induced into lactation, and cows milked two or three times daily in early, middle, or late lactation. Concentrations of alpha-lactalbumin in serum increased in two phases during gestation. Initial values (7.3 ng/ml, up to 120 d prepartum) rose, then leveled at 29.9 ng/ml on d 120 to 30 prepartum. Concentrations subsequently increased, averaging 133.2 ng/ml over the 30 d prior to parturition. During the peripartum period, alpha-lactalbumin rose from 221.2 ng/ml on d 4 prepartum, peaked at calving (918.8 ng/ml), then declined, stabilizing at approximately 500 ng/ml (1.5 to 3 d postpartum). Concentrations of alpha-lactalbumin in cows induced to lactate were low on d 1 to 9 of hormone treatment (15.7 ng/ml), rose to a maximum on d 17 (803.4 ng/ml), then fell to a plateau (185.8 ng/ml) on d 21 to 25. alpha-Lactalbumin concentrations were higher in early (101.9 ng/ml) than in middle or late lactation (81.4 and 79.2 ng/ml, respectively). Concentrations were also greater in twice versus thrice milked cows (101.9 vs. 73.0 ng/ml). Changes in alpha-lactalbumin concentrations in serum are associated with developmental and functional status of the udder. The measurement provides a noninvasive method to assess mammary gland activity.