Effect of the concentration of circulating prolactin on dairy cows' responsiveness to domperidone injection
Tong, J.J., Thompson, I.M., Zhao, X., Lacasse, P. (2018). Effect of the concentration of circulating prolactin on dairy cows' responsiveness to domperidone injection. Journal of Dairy Science (JDS), [online] 101(3), 2579-2587. http://dx.doi.org/10.3168/jds.2017-13828
Plain language summary
Although prolactin is a galactopoietic hormone in dairy cows, prolactin concentration changes throughout the year without similar changes in milk production, suggesting that the mammary gland’s sensitivity to prolactin is not static. To confirm that, we first injected cows with a moderate amount of the prolactin secretion inhibitor quinagolide or water for 2 wk followed by 3 wk of injection of the prolactin secretagogue domperidone. The milk production response to domperidone was enhanced by previous treatment with quinagolide. This supports the contention that the mammary gland’s responsiveness to prolactin is modulated by the chronic level of the hormone.
The objective of this study was to determine whether the responsiveness of the mammary gland to prolactin (PRL) is affected by the concentration of the hormone. After 1 pre-experimental week (d −7 to −1), 18 Holstein cows in mid to late lactation were injected intramuscularly twice daily with either 0.5 mg of quinagolide (QN) or 2 mL of water (control) for 2 wk (d 1 to 14; treatment period). After the treatment period, all cows received daily subcutaneous injections of 300 mg of domperidone (DOMP) for 3 wk (d 15 to 35; DOMP period). The cows were monitored for an additional 2 wk as a posttreatment period (d 36 to 49). Blood and milk samples were collected 3 times per week. Additionally, blood samples were collected during the a.m. milking on d −4, 14, and 35. Milk production was not affected by QN during the treatment period but was increased during the DOMP and posttreatment periods in the QN cows. With respect to milk composition, the treatments affected only the protein content, which was greater in the QN cows during the treatment period. Blood PRL concentration declined during QN injections and was lower in the QN cows than in the control cows between d 5 and 14. The basal concentration of PRL was increased by DOMP injections during the DOMP and posttreatment periods but was not affected by previous QN injections. Prolactin concentration in milk was not affected by the QN treatments but was increased by DOMP injections during the DOMP and posttreatment periods. Milking-induced PRL release was decreased by QN on d 14. On d 35, milking did not induce a significant release of PRL above the baseline for both treatments. In conclusion, the results of this experiment support the contention that the mammary gland's responsiveness to PRL is modulated by the previous level of the hormone.