Context
Most Brazilian beef breeding programs perform selection for young bodyweight, which will inevitably increase mature weight due to the genetic correlation among weights at different ages.
Aims
The objective of the present study was to estimate genetic parameters for bodyweight from birth to maturity in Gir, Guzerat, Nelore and Caracu cows born between 1981 and 2014 at Centro APTA Bovinos de Corte, Instituto de Zootecnia, Sertãozinho, São Paulo, Brazil.
Methods
The model included the fixed effects of contemporary group (herd and year of birth), month of birth and previous reproductive status (calved = 1, or not calved = 0), the linear and quadratic effects of animal and cow age as covariates, and direct additive genetic, maternal genetic and maternal permanent environmental effects as random effects. The genetic parameters were estimated by univariate analysis of weights adjusted at birth, and at 120, 210, 378, 450 and 550 days of age, and annually from 2 to 10 years. In addition, multivariate analysis was performed considering weights at birth, and at 210 and 550 days, and at 5 years of age for all breeds.
Key results
For the different breeds, the heritability estimates ranged from 0.28 to 0.49 for birthweight, from 0.11 to 0.31 for weaning weight, from 0.25 to 0.43 for yearling weight, and from 0.25 to 0.69 for weights from 2 to 10 years of age. The genetic correlations were high and positive, indicating that selection at any age will affect weights at the other ages.
Conclusions
The results suggest the possibility of genetic progress for weights at different ages and the use of the young weights to monitor the mature weight of the animals.
Implications
As the trait most strongly correlated with mature weight was yearling weight, already used as the selection criteria for females in the breeding program of the Instituto de Zootecnia, selection indexes should be derived to keep the mature cow weight constant, since heavier cows could be undesirable for pasture-based Brazilian production systems.
