The dopamine antagonist domperidone increases prolactin concentration and milk production in dairy cows

Abstract Text: In previous studies, we have shown that inhibition of prolactin (PRL) secretion by the dopamine agonist quinagolide reduces milk production of dairy cows (Domest Anim Endocrinol 43:154). The objective of this study was to determine the effects of the administration of a dopamine antagonist and feed restriction on basal and milking-induced PRL concentrations in blood and milk production in dairy cows. Twelve mid-lactation Holstein cows received daily subcutaneous injections of either domperidone (300 mg, DOMP, n=6) or canola oil (CTL, n=6) for 5 wk. During the 5^th wk, all cows were fed at 65% of their DMI of the previous wk. Blood samples were collected prior to morning milking 3 d a wk from d-8 to d42 (7d after the last injections). In addition, blood samples were collected during morning milking at d1 (before the 1^st injection), 2, 29 and 35. Basal PRL concentration was similar among both groups before the start of treatments. Domperidone injection caused a gradual increase (P<0.001) in basal PRL concentration which averaged, on the wk prior the feed restriction, 32.2 and 13.9±2.1 ng/mL for DOMP and CTL, respectively. Feed restriction did not affect basal PRL concentration in DOMP cows but reduced it in CTL cows (P<0.05), averaging 28.0 and 7.9±2.4 ng/mL, respectively. Concentration of PRL was still elevated (P<0.05) in DOMP cows 7d after the last injection averaging 19.4 and 10.8±2.7 ng/mL for DOMP and CTL, respectively. In CTL cows, the milking-induced PRL above premilking concentration (AUC) was similar at d1, 2 and 29 but was reduced (P<0.05) during feed restriction (d35). In DOMP cows, AUC was similar at d1 and 2 but was reduced (P<0.05) at d29 and 35. Milk production was similar for both groups prior to the start of treatments. There was time*TRT interaction (P<0.001) for milk production during the treatment period. Milk production was similar during the first 2wk of treatments but was greater (P<0.02) in DOMP cows during the 2 following wk, averaging 38.0 and 35.0±0.6 kg/d at wk3 and 38.0 and 35.3±0.7 kg/d at wk4 for DOMP and CTL, respectively. Milk production declined in both groups during feed restriction but remained greater (P<0.05) in DOMP cows. Milk production of both groups became similar again 5d after the last injection. Milk composition and DMI were not affected by DOMP. These results support the hypothesis that PRL is galactopoietic in dairy cattle.

Keywords: feed restriction
prolactin