PLACENTAL LACTOGEN IN THE COW

Abstract

Placental lactogen secretion has been demonstrated in cows on days 36, 178, 182 and 270 of pregnancy by co-culture of cotyledonary tissue with mouse mammary gland explants. Bovine placental lactogen probably originated from the foetal cotyledon and showed no detectable cross-reaction in immunoassays for bovine prolactin or growth hormone. Peripheral plasma samples collected from seven primiparous heifers at 2-week intervals throughout pregnancy showed a seasonal rhythm in prolactin concentration, measured by radioimmunoassay, with high levels in the summer. Monthly samples were bioassayed for total lactogenic activity by a rabbit mammary gland organ culture method. Postive responses were obtained only when prolactin levels were high (greater than 70 ng/ml), indicating that levels of placental lactogen in the circulation are much lower in the cow than in sheep, goats or women.