Efficiency of wool production of grazing sheep. 1. Differences between merino sheep selected for high and low fleece weight

The intake, wool production, and efficiency of wool production (wool production per unit intake) of rams drawn from two flocks selected for 13 years for high (Fleece Plus) and low (Fleece Minus) fleece weights were estimated while the rams grazed three pastures differing in the amount of herbage available. In a second experiment the rams were fistulated at the oesophagus and determinations were made of the digestibility and nitrogen content of the samples collected while the sheep grazed two pastures. The wool production, intake, and efficiency of the Fleece Plus rams were greater than those of the Fleece Minus on all pastures. Variability in wool production was primarily attributable to variability in efficiency. Differences between flocks in wool production and efficiency increased when herbage availability and wool production were high.