Failure of Oxytocin to Initiate Prolactin or Luteinizing Hormone Release in Lactating Dairy Cows

Abstract

The relationship between oxytocin and release of prolactin was investigated in lactating cows. To minimize external stress on the animals, blood samples were withdrawn and treatment solutions administered via indwelling cannulas in the jugular vein. Serum concentrations of prolactin and luteinizing hormone were measured by radioimmunoassays. Injections of 10 or 50 IU oxytocin failed to change prolactin or luteinizing hormone concentrations in the serum. Milking caused a 4.8-fold increase in serum prolactin in some of the same cows that failed to release prolactin after an oxytocin injection. Oxytocin is not responsible for release of prolactin from the anterior pituitary.