Direct and maternal genetic components for body weight traits in Markhoz goat.

The aim of the study was to estimate the (co)variance components and genetic trends of direct and maternal genetic effects in Markhoz goat using random regression (RR) models. A total of 16,283 body weight trait records from birth to 400 days of age were obtained from 3476 Markhoz kids. Kids were from 223 bucks and 1217 does raised in the Markhoz goat breeding station in Sanandaj, Iran. The fixed effects were gender, year of birth (1992-2014), age of dam (2 to 7 years old), and type of birth (single or twin). RR models based on Legendre polynomials of age at weight recording included direct and maternal genetic and permanent environmental effects. Heterogeneous residual variances were considered along age of recording. According to the Akaike information criterion (AIC), the Bayesian information criterion (BIC) and the likelihood ratio test (LRT), adding covariance between direct and maternal genetic effects, resulted in significant improvement in the level of fit. After examining models with different order of fits, the most suitable model consisted of the fourth-order polynomial for direct genetic effect and the third-order polynomial for maternal genetic, individual permanent environmental, and maternal permanent environmental effects. The direct heritabilities ranged from 0.21 at birth to 0.55 at 400 days of age. The largest (0.25) and the lowest (0.17) maternal heritabilities were estimated at birth and 60 days of age, respectively. Generally, negative direct-maternal genetic correlations were estimated between different ages, which might cause fluctuations of direct-maternal genetic trends along the years. It was concluded that selection at 100 days of age could reduce the impact of the antagonist relationship between maternal and direct genetic effects.

Variation in autosomal and sex-linked genetic effects for growth traits in Markhoz goat using multivariate animal models.

The present study was conducted to estimate autosomal and sex-linked genetic parameters by restricted maximum likelihood method using four different multivariate models for growth traits in Markhoz goat. Data were collected over a period of 23 years (1992-2014) from the breeding station of Markhoz goat. The studied growth traits were birth weight (BW), weaning weight (WW), 6-month weight (6WT), 9-month weight (9WT), and 12-month weight (12WT). The best model was determined by Akaike's information criterion. Based on the best model, direct autosomal heritabilities of 0.18, 0.10, 0.12, 0.22, and 0.24 were obtained for BW, WW, 6WT, 9WT, and 12WT, respectively. On the other hand, estimates of direct sex-linked heritability for BW, WW, 6WT, 9WT, and 12WT were 0.02, 0.01, 0.002, 0.03, and 0.04, respectively. The maternal permanent environmental component was remarkable for growth traits. Direct autosomal additive genetic correlations among the traits were positive and varied from 0.11 between BW and 9WT to 0.95 between BW and WW. The positive correlations were also estimated for direct sex-linked additive genetic effect except between BW-6WT (- 0.07) and WW-6WT (-0.19). The result of this study indicated that sex-linked chromosome effect had more considerable influence at post-weaning traits.