Prolactin-inhibitor cabergoline hastened the mammary involution during drying-off in dairy cows

In ruminants, the early phase of drying-off is a period of mammary gland involution that is marked by the cessation of prolactin (PRL) release. The analysis of the changes of mammary secretion composition can providevaluable information about the speed of the mammary involution. To assess the effect of PRL inhibition by cabergoline on mammary gland involution, 14 Holstein dairy cows were injected with a single i.m. administration of 5.6 mg cabergoline (n = 7) or placebo (n = 7) at the first day of drying-off (D0). Mammary biopsy samples were collected one week before drying-off (D-6), at D1 and at D8 and used for RNA extraction and RT-PCR analyses. Mammary secretion samples were collected using a teat-cannula once during lactation (D-6) and at D1, D2, D3, D4, D8 and D14 after the drying-off. The mammary secretion samples were used for milk fat, lactose, true protein, a-lactalbumin, lactoferrin and citrate analysis. The decrease in lactose content of mammary secretionsseemed to be faster in cabergoline treated cows compared to controls, demonstrated by lower levels of lactose in cabergoline treated cows already by D1 than in control cows (P < 0.05). Cabergoline treatment tended to increase fat content at D3 after drying-off (P < 0.10), whereas an increase in fat content was only observed at D4 in the control group. The rise of lactoferrin was significant starting at D4 in the cabergoline treated cows whereas it only happened at D8 in controls, and overall there was a tendency towards greater lactoferrin content in cabergoline treated cows (P = 0.10). Cabergoline did not seem to alter citrate content. However, the decrease in lactoferrin/citrate ratio happened faster in cabergoline treated cows compared to controls on D1 (P = 0.01).No significant effects of cabergoline treatment were observed both in true protein and in a-lactalbumin contents in mammary secretions or in a-lactalbumin and k-casein mRNA levels in mammary tissues. These changes in lactose, lactoferrin, lactoferrin/citrate ratio and fat, indicate that cabergoline treatment was efficient to hasten the mammary gland involution without affecting milk synthesis in the mammary tissue.