Effect of age at first conception as a selection criterion on growth and carcass traits in Nellore cattle
Abstract
The aim was to identify predictive traits of relatively easy measurement and which can be
recorded early in life (age at first conception - AFCo), besides estimating its genetic correlations with
growth and carcass traits in Nellore cattle. Age at first conception was considered the age at which the
female had the first positive diagnosis for pregnancy. The estimation of (co)variance components and
genetic parameters was performed using a linear animal model in two-trait analysis. The estimates
of heritability were moderate, enabling genetic selection for growth-, carcass-, and sexual precocityrelated traits. The genetic correlation obtained between AFCo and age at first calving (AFCa) was high
(0.88), indicating the feasibility of using AFCo as a selection criterion for early calving heifers. Genetic
correlation estimates between AFCo and AFCa with weight at 120, 210, 365, and 450 days of age and
carcass traits were moderate and negative (-0.33 to -0.62). Thus, genetic selection for animals with
early AFCo and AFCa would enhance carcass yield, fat deposition, and growth performance, despite
not affecting birth weight or daily weight gain. The results of this study encourage the use of AFCo in
Nellore cattle since this trait displayed enough genetic variability in Nellore cattle, and can be used as
selection criteria to improve sexual precocity. When the objective of genetic selection is to increase
heifer sexual precocity, we could use the first trait as a criterion, as the measurement of this trait
occurs at a lower AFCa.
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