Metoclopramide induces preparturient, low-level hyperprolactinemia to increase milk production in primiparous sows

Inadequate milk production by sows often limits the growth of piglets. A successful lactation requires prolactin (PRL)-induced differentiation of the alveolar epithelium within the mammary glands of sows between days 90–110 of gestation. We hypothesized that induction of late gestational hyperprolactinemia in primiparous sows by oral administration of the dopamine antagonist metoclopramide (MET) would enhance mammary epithelial differentiation, milk yield, and piglet growth rate and that these effects would carry over into a subsequent lactation. Twenty-six gilts were assigned to receive either MET (n = 13, 0.8 mg/kg) or vehicle (CON, n = 13) twice daily from days 90–110 of gestation. The same sows were followed into their second lactation without additional treatment. On day 90 of gestation, circulating PRL concentrations peaked 45 min after feeding MET (P < 0.001) and then returned to baseline 3 h later. This response occurred daily out to day 104 of gestation (P < 0.05). Compared with CON, MET-treated gilts had enlarged alveoli on gestation day 110 (P < 0.05). Treatment with MET did not affect feed intake, body weight, or body fatness during pregnancy or lactation. Piglets born to MET-treated sows had both increased body weights and average daily gain on lactation days 14 and 21 (P < 0.05). Milk intake by piglets was estimated from deuterium oxide dilution. Although milk intake by piglets nursing MET sows was not statistically different from those nursing CON sows on day 21 of lactation (P = 0.18), there was a greater increase in milk consumption by piglets born to MET-treated sows between days 9 and 21 of lactation than for those in CON litters (P < 0.001). In one group of second parity sows (n = 11) that were treated with MET during their first gestation, milk yield increased by 21% during their second lactation (P < 0.05) in association with a 14% decline in body fatness across lactation compared with a 7% decline in CON sows (P < 0.05). These findings demonstrate that MET-induced hyperprolactinemia in primiparous sows during late pregnancy can increase milk yield and piglet growth rate, setting the stage for further large-scale studies.