Blood plasma and milk prolactin, and effects of sampling technique on composition of milk from suckled ewes.

Relations of techniques of sampling milk to its composition and concentrations of prolactin in blood plasma and milk from 59 suckled ewes were compared; Prolactin in milk and blood samples 0 to 2 h (hour 0) after removal of lambs did not differ significantly within autumn or summer, but both were doubled in summer. After the hour 0 sampling (summer only), one side of the udder of each of 12 ewes (group 1) was milked hourly for 4 h, and the opposite side was milked only at 0 and 4 h. Group 2 ewes were milked only at 0 and 4 h and blood was collected from both groups at 0 h and 4 h. Concentrations of prolactin were correlated in pairs of milk or blood samples from the same ewe and in plasma and milk of ewes in group 2 but not in group 1. Prolactin in milk increased between 0 h and 4 h in groups 1 and 2. Although milk lactose and prolactin concentrations differed among hourly samples, their average was similar to that of milk accumulated in the contralateral side for 4 h (group 1). Variations among ewes in progesterone of plasma indicated luteal activity during autumn and none during summer. Prolactin was unchanged in milk stored at -23 C for 30 days. The hour-0 milk-sampling technique was satisfactory to compare among individuals the concentrations of prolactin, total protein, or somatic cells in milk but not percentage fat and lactose, or milk yield due to variable time from last suckling to milking at hour 0.