Milk production of Holstein x Gyr cows in a dual-purpose system in the tropics

Objective. To determine the effect of breed group (BG), parity number (PN) and season of calving on lactation length (LL), milk production per lactation (MPL) and per day (MPD) of dual-purpose (DP) cows. Material and methods. Data from 160 Holstein x Gyr cows (0 to 75% Holstein) managed in a DP production system in the humid tropics of Chiapas, Mexico were used. Information for LL was analyzed using survival analysis, and that for MPL and MPD by general linear models. The model included the effects of BG (0-25%, 50% and 62.5-75% Holstein), PN and season of calving. Results. The means for LL, MPL, MPD were 219.3 +/- 39.6 days; 2125.1 +/- 568.7 kg; 9.66 +/- 1.96 kg, respectively. BG and PN affected all variables. The hazard ratio (HR) of 1.815 indicates that 0-25% Holstein cows had higher risk of being dry-off earlier than F1 cows, which had similar LL than 62.5 to 75% Holstein group. The HR was higher for cows calving in the windy-rainy season (HR=1) than those calving in the dry and rainy seasons (HR=0.448 and 0.446, respectively). The risk that a primiparous cow was dry-off was higher (HR=2.198). The LL of cows with 2 and >= 3 parities was similar. Conclusions. BG, PN and season of calving affected LL and milk yield of dual-purpose cows.