Genetic Parameters and Genomic Prediction for Calving Ease in Primiparous Nellore Heifers

The calving ease (CE) trait has recently been introduced in animal breeding programs, and studies on its genetic variability have proven essential for the genetic advancement of animals. An increase in dystocia rates in primiparous heifers has been observed due to the birth of heavier calves. As this is a new trait, no established model exists for its analysis. Thus, this study developed different statistical models to evaluate CE, aiming to estimate genetic parameters and perform genomic predictions for this trait. A total of 39,664 records of CE from primiparous Nellore heifers born between 2010 and 2017 were collected, belonging to the animal breeding program of the Nellore breed in Brazil, managed by the National Association of Breeders and Researchers (ANCP, Ribeirão Preto, Brazil). The results showed that direct heritability estimates ranged from 0.11 to 0.24, while maternal heritability estimates ranged from 0.09 to 0.11. Despite these low to moderate heritability estimates, the trait has potential for direct selection. Models incorporating the heifer category (HC) (early or traditional) and birth weight (BW), as well as the dam age at calving (DAC) and BW, were more suitable for estimating variance components. On the other hand, the model that considered only the HC and the model that included the DAC excelled in predictive ability, making them more appropriate for genomic predictions.