The Genetic Analysis On Reproductive Traits In Corriedale Sheep

Data set of 1261 records of litter size, lamb survival, fertility, pregnancy maintenance and prolificacy from 668 Corriedale ewes and 1188 birth weight records of lambs were used to estimate genetic parameters. The GLM procedure of SPSS software was used to select non-genetic factors included in the genetic analysis models for dispersed reproductive traits. In the genetic analysis models, non-genetic factors were main effects of birth year, birth month, lambing year, lambing month, age and parity. Birth year, age, lambing year and parity had significant influence on litter size and prolificacy. Lamb survival and pregnancy maintenance were influenced by lambing month besides the above factors. Birth year, birth month, age, lambing year and parity affect fertility significantly. Threshold model was used for dispersed reproductive traits. Single trait and multiple traits Gibbs sampling were used to estimate genetic parameters for the traits. In multiple traits Gibbs sampling two traits were considered once, estimates of heritability and genetic correlation was averaged. Various Gibbs convergence diagnostic methods were used to supervise the convergence of Gibbs chains. The heritabilities for single trait and multiple traits Gibbs sampling of litter size, lamb survival, fertility, pregnancy maintenance and prolificacy were 0.097±0.052, 0.100±0.036, 0.119±0.058, 0.103±0.043 and 0.130±0.041, and 0.305±0.049, 0.296±0.047, 0.016±0.012, 0.015±0.010 and 0.261±0.045 separately. Genetic correlations between dispersed reproductive traits ranged from 0.004±0.357 to 0.982±0.007 except those between litter size and fertility (-0.008±0.384) , and prolificacy and fertility (-0.016±0.422). The estimates of repeatability for litter size, lamb survival, fertility, pregnancy maintenance, prolificacy and birth weight were 0.320, 0.435, 0.208, 0.476, 0.410 and 0.426 respectively. Using reproductive traits as threshold traits and birth weight as continuous trait to estimate genetic correlations between threshold and continuous traits, and heritability of birth weight. The fixed effects in the model were birth year (17 levels), birth month (3 levels), sex (2 levels) and birth type (2 levels) .The estimates of genetic correlation between birth weight and litter size, lamb survival, fertility, pregnancy maintenance and prolificacy were 0.142±0.364, 0.111±0.352, 0.208±0.343, 0.246±0.335 and 0.093±0.371 respectively. The mean heritability of birth weight was 0.004±0.025.