Stocking intensity and pastoral production: III. Wool production, fleece characteristics, and the utilization of nutrients for maintenance and wool growth by Merino sheep grazed at different stocking rates

Abstract

Summary: Wool production and wool characteristics are reported for a 5-year period in which sheep grazed Phalaris tuberosa–Trifolium repens pastures at stocking rates ranging from 2·5 to 37·1 sheep/ha. The utilization of nutrients for maintenance and wool production were calculated over shorter periods.Maximum wool production/ha was always recorded at the highest stocking rate attained. The highest annual maximum was 111 kg clean wool/ha in 1963–4. The decline in wool production/sheep/unit increase in stocking rate was greatest during winter and the amplitude of the seasonal rhythm in wool production increased with stocking rate.At high stocking rates wool count increased, staple length and character declined, colour and handle improved, soundness tended to decline and fibre entanglement (cotting) to increase particularly during drought. Live-weight gain/sheep also declined with stocking rate, the rate of decline being greatest during drought. Maximum live-weight change/ha was attained at a lower stocking rate than maximum wool production/ha.The maintenance requirement of grazing sheep was estimated to be 58·3 kcal metabolizable energy/day/kg live weight and did not vary consistently with stocking rate. The value was 79% greater than the requirements for penned sheep estimated from fasting heat production.Efficiency of wool production was defined as wool grown/100 g digestible organic matter intake (E_D) and as wool grown/100 g nitrogen intake (E_N). E_N declined linearly with increasing stocking rate but the intercepts differed between months, and were least in late winter and early spring. E_n declined with stocking rate in winter and increased during summer. At low stocking rates, E_D showed some variation throughout the year but this was much greater at high stocking rates.