Estimation of genetic parameters for reproductive indices in sheep

This study aimed to estimate two reproductive efficiency indices in sheep based on the ratio between litter weight (at birth and weaning) and dam weight, as well as their genetic parameters. Phenotypic and pedigree data comprising the period from 1990 to 2018 were obtained from the Santa Inês sheep database of Embrapa Tabuleiros Costeiros. For estimation of the genetic parameters of the indices, a repeatability model was applied in single- and two-trait analyses by a Bayesian approach. The mean reproductive efficiency index was 0.069 ± 0.0163 and 0.43 ± 0.0955 at birth and weaning, respectively. These values indicate that, on average, ewes give birth to 69 g of lamb per kg body weight and wean 430 g of lamb per kg body weight. Described here for the first time, the heritability estimate obtained in single- and two-trait analyses was 0.24 for the index based on birth weights and ranged from 0.13 to 0.15 for the index based on weaning weights. The estimates indicate the possibility of genetic gain by selection and are similar to those reported for reproductive traits in sheep, representing an option for selection criterion. The genetic correlation between indices was positive and moderate (0.26). The repeatability estimates were high (0.49 for the birth weight index and 0.71 for the weaning weight index). These values indicate good prediction of future performance with few observations. The weaning weight index might be a good culling criterion of females.