Non genetic and breed group factors affecting weaning weight in a beef cattle system production in Pao de San Juan Bautista county of Cojedes state, Venezuela

To evaluate the effect of non-genetic factors and breed group on weaning weight (WW), 4455 records of calves that were grazing native and introduced pastures in tropical dry forest were analyzed. Data were analyzed using an additive linear model by restricted maximum likelihood method that included the fixed effects: year of birth (YB, 2001,.., 2007), month of birth (MB, January, February, October, November, December), age of dam at calving (AD, 3,.., 11 years or older), sex (S; female-male) breed group of the calf (BG1: Bos taurus crossbred Angus, Braunvieh, Carora, Holstein, Simmental, Romosinuano, Senepol; BG2: mainly Bos indicus breeds of Brahman, Nelore, Guzerat and Gyr) and calf age at weaning as covariate (linear and quadratic effects). The average WW was 156.4 kg at 228 days of age, and is considered low. All variables studied affected (P <0.01) WW, the most influential effects were YB (there was a difference of 27.5 kg, 16.2%, between extreme years), S (males were 5.7 kg; 3.6% heavier than females) and BG (BG1 and BG2 showed 159 ± 0.81 and 155 ± 0.50 kg, being BG1 heavier on 3.9 kg, 2.5%). The age of the calf at weaning had significant linear (0.47 kg) and quadratic (-0.000061 kg) effects. Was studied all possible interactions including only significant (P <0.05) YB*MB, YB*AD, YB*BG, S*BG, MB*AD. The results of this study suggest possible genotype by environment interactions (YB*BG and MB*BG) could indicate that the production of crossbred cattle must be accompanied by improvements in the environment.