Comparison of milk yield and of oxytocin and cortisol release during machine milking in Gir, Gir/Holstein and Holstein cows.

Gir cows (adapted to tropical conditions) and Holstein bulls (more productive) have been crossbred in Brazil to improve dairy production. In general, this crossbreeding program was a success and at present, many specialized farmers have Holstein cows with varying percentages of Gir blood. Although Gir cows and Gir/Holstein cows are reputed to be easily stressed and not well-adapted to machine milking, adaptation to exclusive machine milking has not been described in the literature for these cows. Taking this into account, 6 Gir cows (group G), 6 Gir x Holstein cows (F3; group GH) and 6 Holstein cows (group H) were used to evaluate the effect of exclusive machine milking on oxytocin (OT) and cortisol (CORT) release and on milk yield. Milk yield was recorded throughout lactation. Blood samples were taken on days 45, 48, and 51 of lactation, before and after milking. Plasma concentration of OT was measured by EIA method and CORT was measured by commercial EIA Kit (dslab Inc). As expected, milk yield was significantly higher in the H group (25.6 ± 3.3 L/day) than in the GH group (20.2 ± 1.7 L/ day), and the GH group produced more milk than the G group (13.1 ± 1.0 L/day). In contrast, all groups exhibited similar levels of OT, although OT increased more rapidly during milking of the H and GH groups (1 min) than of the G group (3 min). Simultaneously, CORT levels were significantly different for groups, the G group presented highest levels of CORT than GH and H groups. Our results indicate that G, G/H and H groups presented similar release of OT during exclusive milking, however CORT levels were inversely related to milk production. [ABSTRACT FROM AUTHOR]