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

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Abstract
Two studies examined the effect of reserpine administration during hormonally induced lactation on serum prolactin [PRL] and milk production. Previous investigations showed reserpine injection causes prolonged elevation of serum PRL concentration. In study I, 10 animals were given 17.beta.-estradiol (0.1 mg/kg body wt per day) and progesterone (0.25 mg/kg body wt per day) on days 1-7 and dexamethasone (20 mg/day) on days 18-20. Five animals were controls, and 5 were given reserpine (5 mg/day) on days 13-16. In study II, 9 animals were given injections of 17.beta.-estradiol, progesterone and dexamethasone as in study I. Four animals were controls and 5 were given reserpine (5 mg/day) on days 8, 10, 12 and 14. PRL concentrations during estrogen-progesterone injections (days 1-7) were < 30 ng/ml. PRL increased in control cows on days 14-21 but was variable. PRL 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 10-21 kg/day for study I and 16-24 kg/day for study II. PRL may be limiting in those cows which fail to lactate following estrogen-progesterone treatment to induce lactation.