Effect of Reserpine on Milk Production and Serum Prolactin of Cows Hormonally Induced into Lactation

Two studies were to examine the effect of reserpine administration during hormonally induced lactation on serum prolactin and milk production. Previous investigations have shown reserpine injection causes prolonged elevation of prolactin concentration in serum. Ten animals in study I were given 17β-estradiol (.1 mg/kg body weight per day) and progesterone (.25 mg/kg body weight per day) on days 1 to 7 and dexamethasome (20 mg/day) on days 18 to 20. Five animals were designated controls, and five were given reserpine (5 mg/day) on days 13 to 16. In study II, nine animals were given injections of 17β-estradiol, progesterone, and dexamethasone as in study I. Four animals were designated controls and five were given reserpine (5 mg/day) on days 8, 10, 12, and 14. Prolactin concentrations in serum during estrogen-progesterone injections (days 1 to 7) were below 30 ng/ml. Prolactin increased in control cows on days 14 to 21 but was variable. Prolactin concentrations of reserpine treated groups were elevated during the period of reserpine administration. Both reserpine groups had higher peak milk yields and greater milk production to 100 days than respective controls. Peak milk yields of reserpine groups ranged from 10 to 21 kg/day for study I and 16 to 24 kg/day for II. Results were consistent with hypothesis that prolactin may be limiting in those cows which fail to lactate following the estrogen-progesterone treatment to induce lactation.