Estimation of (co)variance components and genetic parameters for growth and wool traits of Chinese superfine merino sheep with the use of a multi-trait animal model

The aim of the current study was to estimate genetic parameters for birth weight (BW), weaning weight (WW), weaning staple length (WSL), yearling liveweight (YLW), and greasy fleece weight (YGFW), staple length (YSL), mean fiber diameter (YFD), fiber diameter standard deviation (YFDSD) and fiber diameter variation (YFDCV) at first shearing, which are essential to design a selection breeding program for Chinese superfine merino sheep. Data was collected on progeny from eight birth years (2001–2008) in the Chinese superfine merino breeding flock maintained at Xinjiang Gongnaisi Fine Wool Sheep Breeding Farm, Xinjiang, China. (Co)Variance components and genetic parameters were estimated by average information restricted maximum likelihood (AIREML) with a multi-trait animal model, and primarily 6 single-trait models for each trait were used to determine the most appropriate model for multi-trait analyses with Akaike's Information Criterion (AIC). Estimates of direct heritability were 0.15 for BW, 0.27 for WSL, 0.16 for WW, 0.23 for YLW, 0.32 for YSL, 0.17 for YGFW, 0.22 for YFD, 0.02 for YFDSD and 0.09 for YFDCV. Maternal heritability estimates for BW and YGFW were 0.15 and 0.05, respectively. Direct genetic correlations among studied traits ranged from − 0.85 (YGFW–YFDCV) to 0.87 (WSL–YSL). Phenotypic and environmental correlation estimates were generally lower than those of genetic correlation. Low to moderate direct heritability estimates for growth at different age, fiber diameter, fleece weight and staple length imply that selection for these traits results in lower to moderate genetic gain. Our results herein lay a practical foundation for performing an optimal breeding program in Chinese superfine merino.