ENVIRONMENTAL FACTORS AND BREED PROPORTION AFFECTING BIRTH WEIGHT, WEANING WEIGHT AND AGE AT FIRST CALVING IN MEXICAN BROWN SWISS CATTLE

Abstract

The effects of some environmental and genetic factors on birth weight (PN), weaning weight adjusted to 240 days of age (PD240) and age at first calving (EPP) in Brown Swiss cattle were evaluated. The statistical model used to analyze the dependent variables, after eliminating the non-significant two-way interactions, included ranch as random effect nested within region and the fixed effects of year (Y) and season of birth (BS), sex of the calf (for BW and WW240), breed upgrade, the YxBS interaction, as well as the linear and quadratic effect of age of the cow at calving (for PN and PD240). The analyses were performed using mixed models. The means for PN, PD240 and EPP were 37.7 ± 5.1, 233.8 ± 46.9 kg and 1209.6 ± 338.0 days, respectively. All main effects were significant (P<0.05) with the exception of season for PN and PD240. In conclusion significant effects for region, sex, breed upgrade, and year by season interaction were found, this suggests the importance to include them into the models before perform genetic evaluation for PN, PD and EPP in Brown Swiss cattle in Mexico.