Effect of the prolactin-release inhibitor quinagolide on lactating dairy cows

Abstract

In most mammals, prolactin (PRL) is essential for maintaining lactation, and yet the short-term suppression of PRL during established lactation by bromocriptine has produced inconsistent effects on milk yield in cows and goats. To assess the effect of the long-term inhibition of PRL release in lactating dairy cows, 5 Holstein cows in early lactation received daily intramuscular injections of 1mg of the PRL-release inhibitor quinagolide for 9 wk. Four control cows received the vehicle (water) only. During the last week of the treatments, one udder half was milked once a day (1×) and the other twice a day (2×). Blood samples were harvested at milking in wk -1, 1, 4, and 8. The daily injections of quinagolide reduced milking-induced PRL release but not the basal PRL concentration. Quinagolide induced a faster decline in milk production, which was about 5.3 kg/d lower in the quinagolide-treated cows during the last 4 wk of treatment. During wk 9, the inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the half milked 1×. Milk production was significantly correlated with the quantity of PRL released at milking. Quinagolide did not affect the release of oxytocin at milking. Serum concentration of insulin-like growth factor-1 was not affected by treatment or correlated with milk production. Serum concentrations of leptin and the calciotropic hormone stanniocalcin were not affected by the treatment. In conclusion, the chronic administration of the PRL-release inhibitor quinagolide decreases milk production in dairy cows. The effect is likely the result of the reduced release of milking-induced PRL and is modulated at the level of the gland by milking frequency.

LACTATION BIOLOGY SYMPOSIUM: Effects of photoperiod on mammary gland development and lactation1

“…The effect of melatonin would be expected to reduce both basal and milking-induced increases in PRL, although that remains to be confirmed experimentally. In a recent study, quinagolide, a PRLrelease inhibitor, was administered to lactating cows for approximately 8 wk to examine the effect of decreased PRL on milk yield (Laçasse et al, 2011). After 4 wk, quinagolide-treated cows produced less milk compared with controls that received vehicle.…”

In vivo inhibition followed by exogenous supplementation demonstrates galactopoietic effects of prolactin on mammary tissue and milk production in dairy cows

“…Although it has been well established in rodents and lagomorphs that PRL depletion reduces milk production, in ruminants the effects of PRL inhibition are less obvious, and the galactopoietic role of PRL has been a matter of debate for several decades (Knight, 2001). Several of the present authors recently showed that the long-term inhibition of PRL with a potent dopamine agonist, namely quinagolide (QN), reduced milk yield in dairy cows (Lacasse et al, 2011). However, a complete demonstration of the galactopoietic role of In vivo inhibition followed by exogenous supplementation demonstrates galactopoietic effects of prolactin on mammary tissue and milk production in dairy cows V. Lollivier,* † ‡ P. Lacasse, § J. Angulo Arizala,# P. Lamberton,* † S. Wiart,* † J. Portanguen,* † R. Bruckmaier,‖ and M. Boutinaud* † 1 PRL in ruminants requires showing that the effect of QN on the mammary gland is due to the inhibition of PRL secretion.…”

Unilateral once daily milking locally induces differential gene expression in both mammary tissue and milk epithelial cells revealing mammary remodeling

“…Plasma was separated by centrifugation at 4°C and 3,000 g for 15 min and then stored at Ϫ20°C for subsequent analysis. Plasma PRL concentrations were measured with an indirect competitive ELISA (31). Intra-assay variability was Ͻ2%, and inter-assay variability was Ͻ12%.…”