Relationship between feed efficiency and reproductive traits in precocious Nelore heifers

Residual feed intake (RFI) is one of the most used measure to assess feed efficiency. Animals with a negative RFI are considered more efficient, as they consume less feed than predicted for the observed weight gain. The RFI measures are commonly adjusted for subcutaneous fat thickness, however the energy efficiency detected by RFI may arise from reduced accumulation of visceral fat, an important energy storage for females during the reproductive cycle. Thus, the hypothesis evaluated here is that more efficient Nelore heifers have a lower body energy reserve, harming your reconception after the first calving as early primiparous (close to 24 months of age). Therefore, the present study aimed to evaluate whether there is a relationship between RFI adjusted for subcutaneous fat thickness and the reconception ability of early primiparous Nelore females and the relationships between growth, carcass traits, and reproduction according to RFI classification. Low and not significant correlations (phenotypic and genetic) were observed between RFI and reproductive traits, such as days to first conception (DFC), days to second conception (DSC), first gestation length (FGL), second gestation length (SGL), probability of second conception (PSC) and probability of second parturition (PSP). Reproductive traits exhibited low heritability (< 0.15), indicating limited potential for genetic selection in a tropical environment. In addition, the RFI classification had no influence on reproductive aspects. The results observed suggest that selection for more efficient animals did not affect the reconception of early primiparous females in the evaluated environment. However, these results can be affected by the environmental challenge imposed on these females. Therefore, obtaining similar data in other rearing environments would be interesting to explore the genotype by environment interaction in these traits' relationships. These findings are specific to the tested tropical environment, and the low heritability of reproductive traits may limit the potential for genetic improvement.