Estimation of genetic trend for body weight of Shal sheep

In this research genetic trends for body weight traits of Shal lambs, including: birth weight (BW), weaning weight (WW), 6-month weight (6MW), 9-month weight (9MW) and yearling weight (YW) were studied over a 16-year period. Genetic parameters were estimated using restricted maximum likelihood (REML) method under animal model and breeding values of animals were predicted with Best Linear Unbiased Prediction (BLUP) methodology with single-trait and five-trait animal models. Genetic trends were estimated by regressing the mean of breeding values on year of birth. Direct heritability for BW, WW, 6MW, 9MW and YW were estimated 0.32, 0.47, 0.32, 0.41 and 0.28, respectively. Genetic trends for these traits from both single- and five-trait analyses were estimated (-3 and 4), (32 and 35), (-18 and 10), (27 and 28), (-3 and 11) g per year, respectively, and were non-significant (P>0.05). Also, genetic progress for these traits from both single- and five-trait analyses were calculated (1 and 118), (316 and 918), (404 and 438), (522 and 672) and (60 and 379) g in studied period, respectively. The highest genetic trend was for WW, which had the highest heritability. Despite relatively high heritability for all studied traits, insignificant genetic trends for these traits indicate an undesirable selection program in Shal sheep.