Risk factors and genetic analysis of pre-weaning mortality in Barki lambs

Abstract

Pre-weaning mortality (PM) of lambs is a worldwide economically trait of interest. It has a negative impact on the profitability of sheep farms. However, little is known about the genetic contribution of PM in Egypt and worldwide. In this study, a total of 21,280 records of 5317 Barki lambs descended from 153 rams and 1887 ewes were included. Based on the time of death, 4 binary traits were recorded; D0–3 was animals that were dead immediately or within 72 h after delivery, D4–60, D61–90, and D0–90 were lambs that were dead during 4–60 days, 61–90 days after birth and the full period (0–90 days), respectively. The average rate of mortalities for the corresponding traits was 4.6%, 5.4%, 4.3%, 2.2%, and 16.3%, respectively. A logistic regression model with a logit function implemented in R was used to assess the impact of the non-genetic factors on PM in Barki lambs. Bayesian threshold model and Gibbs sampling were used to investigate the genetic parameters and (co)variance components of the studied traits. Results showed that the PM traits were significantly (P < 0.05) influenced by damage, type of birth and birth weight of lamb. Direct heritabilities for PM traits ranged from 0.011 ± 0.01 to 0.02 ± 0.01. Maternal genetic effects for PM traits ranged from 0.13 ± 0.02 to 0.23 ± 0.01. Considerably, maternal effects had a large influence on variance estimates in case of PM trait, but these effects have declined as the lamb age increased. Permanent environmental effects for PM traits ranged from 0.06 ± 0.02 to 0.11 ± 0.02. The genetic correlations between the pairs of studied traits were positively moderate to high and ranged from 0.72 ± 0.07 to 0.95 ± 0.03, which suggested that different genes are contributed to lamb mortality at different ages. Notably, lamb mortality trait was found to be heritable and could be used as important criteria in breeding programs and genetic improvement strategies in Barki sheep. Additionally, improving management practices could also reduce lamb mortality. Results of this study may help animal breeders to reduce lamb mortality in Barki sheep.