- 期刊
- OpenAccess
Effect of Environmental Factors from Birth to the Onset of Reproductive Function and Management in Indo-Brazilian Heifers
並列摘要
In order to evaluate factors that affect growth, age at first breeding (AFB) and age at conception (AC) 246 records of Indo-Brazilian heifers were used. An analysis of variance was performed with a model including the fixed effects of season of birth (SB), year of birth (YB), dam’s parity number (DPN) and breeding season (BS). Birth weight (BW), weaning weight (WW) and weight at first breeding (WFB) were included as covariates. The following interactions were also included, SBxYB, YBxDPN and BSxYB. The association of WFB with AFB and AC was analyzed by regression. The growth was described from birth to first calving with the Gompertz equation. AFB and AC were affected by SBxYB and BSxYB (p＜0.01). Differences in SBxYB for AFB of 16.56 and in BSxYB for AC of 17.24 months were detected. In average, heifers were bred at 32 months of age and became pregnant at 33, because some of them required two breedings. Variation in AFB and AC was due to SBxYB, BSrxYB and WFB (p＜0.01). Indo-Brazilian heifers with a higher WFB which are born and bred in spring will be the first ones to get pregnant. The most important sources of variation for WFB and AC were the interactions SBxYB, YBxDPN and BSxYB. Sire and mating year had a significant effect on the three parameters of the growth curve (p＜0.05). It is concluded that Gompertz equation is useful to describe the growth of Indo-Brazilian heifers because it allows adjustments during growth involving daily weight gain.