Analysis of the genetic relationship between litter size and weight traits in Segurena sheep

A selection program is being implemented to improve meat production in the Segurena breed of sheep. Increasing litter size per ewe is the main objective, but possible repercussions on weight traits of lambs should be considered. The aim of this work is to determine the relationship between litter size and weight at birth, weaning and at 90 d. Records of 8117 animals, during 11 yr of production, taken from 1981 to 1991 in an experimental flock, were used to estimate heritabilities, repeatability, and genetic and environmental correlations by means of single-trait and multitrait linear models. Heritability estimates for litter size were approximately 0.08, and repeatability estimates were 0.14 and 0.11 for single-trait and multitrait models, respectively. Heritability estimates of weight traits obtained with single-trait and multitrait models were similar. Genetic correlations were 0.18 between litter size and birth weight, 0.48 between litter size and weaning weight, and 0.36 between litter size and weight at 90 d. Environmental correlations between litter size and weight traits were close to zero. Because genetic correlations between litter size and weight traits were all positive, no deterioration of breeding values of weight traits could be expected, when selecting for litter size.