Genetic gains in clean fleece weight are not necessarily related to farm profitability per hectare, suggesting that increasing fleece weight may inadvertently compromise other traits of economic significance including stocking rate. While genetic gains in fleece weight are negatively related to body fat, and hence potentially stocking rate, we hypothesised that genotypes that achieve extra fleece weight from staple length growth rather than follicle density will still be fatter than expected due to a lower energy requirement for maintenance, and this could be due to a lower skin weight. Forty-four young Merino ewes (aged 20 months) were allocated to one of four treatment groups based on their Australian Sheep Breeding Values (ASBV) at yearling age for clean fleece weight (YCFW) and staple length (YSL). They were fed to maintain liveweight in individual pens on a pellet-based diet for 35 days to quantify the relationships between YCFW, YSL, proportion of body fat, wool and skin characteristics, residual feed intake and residual liveweight change. There were no significant differences in liveweight, percentage of body fat, skin weight, and residual feed intake between high and low YCFW or high and low YSL groups. However, at individual animal level, there was a significant negative relationship between YCFW and residual liveweight change, so sheep with higher YCFW lost more weight than expected based on their liveweight and feed intake. YSL did not affect residual feed intake or residual liveweight change and there was no associated change in whole body fat percentage between YSL groups. There was a tendency for residual liveweight change to increase with skin weight (P<0.05), but not residual feed intake. Overall, there was no evidence that higher YSL sheep may exhibit a better feed efficiency due to increased fat reserves or reduced skin weight.
Additional keywords: wool growth, staple length, feed efficiency, skin weight, skin thickness