Variation between Merino ewes in pasture intake 2. Within-flock genetic parameters for intake and some production traits

Abstract Genetic parameters were estimated for pasture feed intake, liveweight, ultrasonic fat depth, clean wool growth and clean wool growth efficiency of approx. 300 grazing adult Merino ewes in each of 2 years, over four seasons representing different stages of the annual reproductive cycle. Measurements were made on a total of 515 individual ewes (with 87 measured in both years), the progeny of 126 sires. The genetic parameters were estimated using a sire model REML analysis. Digestible organic matter intake (DOMI) had a heritability of 0.12 ± 0.07, pooled across seasons. Adjusting for liveweight did not affect the pooled heritability estimate. The pooled heritability estimates for liveweight, fat depth, clean wool growth and wool growth efficiency were 0.67, 0.47, 0.41 and 0.21, respectively. Clean wool growth, liveweight and fat depth had moderate to strong positive genetic correlations with DOMI in all seasons except spring (mid-lactation). Wool growth rate and wool growth efficiency had a strong positive genetic association (0.77 ± 0.34, pooled across seasons), as did liveweight and fat depth (0.54 ± 0.14). It was concluded that selection for wool growth will result in genetic improvement in efficiency and some increase in intake. Optimising responses in efficiency will require more precise estimates of genetic parameters.