PSXII-4 The relation between oxytocin released by milking and expression of the oxytocin receptor in the mammary glands of Holstein, Jersey and Gir cows.

Abstract

Gir cows and their crossbred offspring can become better adapted to exclusive milking and increased milk yields. The present study evaluated the relation between milk ejection, oxytocin release and expression of oxytocin receptor in the mammary glands of Holstein, Jersey and Gir cows. Thirty-six experimental cows (12 Gir, 12 Jersey, 12 Holstein) were left in a Brachiaria brizantha grass pasture and received corn silage, mixed grains (corn, soybean meal, cottonseed meal) and a mineral-vitamin supplement. The same milking machine and milking procedures were used on all cows. Milk yield and milk composition were measured daily, and milk flow and residual milk were measured biweekly. On days 30 and 60 of lactation, we obtained milk samples before the cows were milked (3 minutes), during milking (1 minute after the start of milking) and after milking (3 minutes) for oxytocin analysis. The milk samples obtained during milking were used to measure oxytocin release, isolate milk somatic cells and study gene expression. Oxytocin in milk was measured by immunoassay analysis. The RNAm expression of the oxytocin receptor was analyzed by RT-PCR. Statistical analysis was performed by ANOVA using a MIXED model, and the level of significance was set at P < 0.05 for the primary effects and interactions. Oxytocin was significantly released in milk during milking by Gir, Jersey and Holstein cows compared with oxytocin measured before and after milking. In contrast, Gir cows exhibited significantly higher expression of the oxytocin receptor in their mammary cells than Jersey and Holstein cows. However, Gir cows produced significantly less milk, spent more time during the milking process compared with Jersey and Holstein cows. These results suggest that the relation between oxytocin and its receptor in mammary cells is relevant to improve milk ejection and milk yield of Gir cows.