The objective of this study was to evaluate the environmental effects of contemporary groups (CG), Julian birth date (JBD), age of dam at calving (AD) and age of calf at weaning (AC) on pre-weaning performance traits: birth weight (BW), weaning weight (WW) and 205 days adjusted weaning gain (WG) of Devon cattle raised in Rio Grande do Sul. A total of 23,369 records on animals, born from 1980 to 2000, collected by PROMEBO - beef cattle improvement program of Associação Nacional de Criadores Herd Book Collares were used. Analyses were performed by PROC MIXED of SAS, using a model that included CG, JBD and AD as fixed effects and sire and residual error as random effects. Average BW of animals that were born in Oct-Nov was 3.15% higher than BW of animals that were born in Jul, which were respectively for WW and WG 11.51% and 9.99% heavier than animals that were born in Nov. Age of dam showed a quadratic effect with maximal response on all traits around eight years,. The age of calf effect was quadratic on WG and linear on WW. These results indicate environmental effects should be included in models used for genetic evaluations of pre-weaning performance traits in order to improve their precision and reliability.
beef cattle; contemporary groups; Julian birth date; pre-weaning weight gain; weights
