Genetic parameters of lamb weights and ultrasonic muscle and fat depths in Beulah Specklefaced sheep

Genetic parameters for live weight at 8 weeks and day of scanning (mean age 151 days), ultrasonic muscle (UMD) and fat (UFD) depths were estimated using data from Beulah Specklefaced sheep in a sire reference scheme. Heritability estimates were 0.17, 0.16, 0.18 and 0.17 for eight week weight, scan weight, UMD and log10 UFD, respectively, with corresponding estimates of maternal heritability of 0.05, 0.17, 0.07 and 0.18. Estimates of the proportion of phenotypic variance explained by permanent and temporary environmental effects for eight week weight were 0.17 and 0.14, respectively, and ranged between 0.04 and 0.08 for scan traits, with no significant (P > 0.05) variance due to permanent environmental effects for log10 UFD. Correlations between direct and maternal additive effects ranged between −0.54 and −0.80. Genetic correlations among scan traits were moderate (0.33–0.51) and estimates of maternal, permanent and temporary environmental correlations were not significantly different from one (P > 0.05). These estimates generally support the structure of the selection index currently used in the Beulah breed; however, further information is required concerning the importance of the covariance between the direct and maternal additive effects.