Days to Calving of Nelore Cows From a Selection Experiment for Growth: I - Repeatability Model

[摘要] - Records of start of breeding season and subsequent calving, from 1,247 Nelore females raised at Sertãozinho Experimental Station (IZ ¾ SP, Brazil), selected for high (selection and traditional lines) and for average (control line) yearling weights were used to compute days to calving and to study the effect of selection for yearling weight on reproductive performance. Data sets of heifers, and cow and heifers were analyzed with and without non-calvers females. There were no significant differences among the performance of females from selection lines (selection and traditional) and those control line (NeC), although days to calving were higher in the selection line for all data sets. According to the results for the selection line effect, the weight at selection was significant only for cows and heifers including non-calvers females, and those with higher weight at selection showed smaller values for days to calving. Models without weight at selection showed equivalent results for line. The heritabilities were between 0.02 and 0.16, and the higher estimates were from data sets including non-calvers females, suggesting that the observation of reproductive traits only on fertile females can make-up the genetic differences between the animals and when this variability is re-introduced, assigning penalty for non-calvers females, the genetic differences appear. The results show that the selection for high yearling weight did not compromise female reproductive performance, even being raised under similar environmental conditions.

[学科分类] 兽医学

[关键词] reproductive performance;beef cattle;beef cows;reproduction;yearling weight selection    Introdução O peso corporal ou a taxa de crescimento continua sendo o critério de seleção primário para a maioria dos criadores de bovinos de corte em todo o mundo;e de outras espécies exploradas para produção de carne