Estimation of genetic parameters and genetic trends for weight and body measurements at birth in sheep populations in Thailand

The main objective of this study was to estimate the genetic parameters and genetic trends for birth weight (BW),heart girth (HG), and body length (BL) at birth of sheep populations in Thailand. Data were collected during 1998 to 2011 fromfour livestock research and testing stations. Fixed effect testing showed that sex, herd, contemporary group and breed groupgreatly influenced on the investigated traits (P<0.05). The log likelihood ratio test showed that all traits significantly affectedby maternal additive genetic effect as well as covariance between animal effects. Estimated direct heritabilities from multivariate analysis of the model for BW, HG and BL were 0.32, 0.52 and 0.54, while estimated maternal heritabilities were 0.23,0.14 and 0.14, respectively. Positive correlations were found among direct additive genetic (0.29 to 0.97), maternal additivegenetic (0.23 to 0.95), and phenotype (0.18 to 0.96). Direct-maternal correlations within traits (-0.68 for BW, -0.92 for HG and-0.89 for BL) and between traits (-0.89 to -0.08) were antagonistic effect. Direct additive genetic trends for BW, HG and BL inthe second period (2005 to 2011) were significantly increased (0.02 kg/year, 0.89 and 0.73 cm/year) while maternal additivegenetic trends characteristically depicted significantly decreased (-0.01 kg/year, -0.92 and -0.72 cm/year).