Relationships between Concentrations of Porcine Prolactin in Blood Serum and Milk of Lactating Sows

Abstract

Concentrations of porcine prolactin (PRL) were quantified by a newly developed radioimmunoassay in blood serum and in milk collected from nine crossbred sows between 4 and 38 days after parturition. Litters were adjusted within 2 to 3 days after birth to 8, 10 or 12 pigs per sow. Blood and milk were sampled every 3 to 4 days following a 2-hr period of nonsuckling. Blood was collected by venipuncture of an ear vein after physical restraint. Following an intravenous injection of oxytocin, milk samples were collected by hand from a thoracic, abdominal and inguinal pair of teats on each sow. At the first sampling period, 4 to 6 days postpartum, serum and milk concentrations of PRL averaged 27 ± 5 and 33 ± 5 ng/ml, respectively. These concentrations declined to 9 ± 1 and 15 ± 1 ng/ml by the last sampling period, 35 to38 days postpartum. Over the entire lactation, the linear correlation between milk PRL and serum PRL was highly significant (r = .66, P < .001). When the effect of days postpartum was removed from each variable, there remained a significant correlation between milk PRL and serum PRL across all sows (r = .47, P < .001), as well as for sows with 10 and 12 pig litters (r = .78, r = .43, both P < .01). However, this relationship was different in sows with eight pig litters (r = −.35, P < .03). Both serum and milk PRL concentrations differed significantly (P < .05) among sows with different litter size. Milk sampled from different mammary locations on the same sow did not vary significantly in PRL concentrations. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.