Genetic group and maternal effects on pre- and post-weaning growth traits of four-breed cattle

Aim of study: To estimate variance components and genetic parameters for pre- and post-weaning growth traits in a four-breed composite cattle population, accounting for direct additive genetic, maternal genetic, and permanent maternal environmental effects under alternative genetic group classification strategies. Area of study: Animal breeding; crossbreeding design. Material and methods: Records for birth weight (BW), weaning weight adjusted to 210 days (W210), yearling weight adjusted to 365 days (W365), and post-yearling weight adjusted to 420 days (W420) from purebred, two-breed, and four-breed crossbred animals of the Purunã population were analysed. Genetic groups were defined using a conventional classification based on crossbreeding generation (GG) and an alternative classification based on crossbreeding pathways (GGI). Variance components were estimated via Restricted Maximum Likelihood (REML) using animal models including direct additive genetic and maternal permanent environmental effects. Model fit was assessed using likelihood ratio tests (LRT) and likelihood-based criteria (−2logL and Akaike Information Criterion [AIC]). Main results: The inclusion of maternal permanent environmental effects improved model fit for BW, W210, and W420 under both GG and GGI, and for W365 under GGI. Models excluding maternal effects yielded inflated direct heritability estimates. Maternal permanent environmental effects contributed to phenotypic variance beyond weaning, although their relative importance decreased with age. Direct heritability estimates were moderate for BW and lower for postnatal traits and were similar under both GG and GGI classifications. The GGI strategy provided better model fit in multi-trait analyses, as indicated by lower −2logL and AIC values (ΔAIC = 67.707). Research highlights: Accounting for genetic group origin and maternal permanent environmental effects improves the estimation of genetic parameters and enhances the reliability of genetic evaluation in composite cattle populations.