EFFECTS OF DIFFERENTIAL GRAZING OF ANNUAL PASTURES IN SPRING AND AGE OF SHEEP ON PASTURE AND SHEEP PRODUCTION

The effects of controlled grazing through spring on the production of young (age 1 year; liveweight 38.3 +/- 0.09 kg; condition score 3.0 +/ - 0.03) and mature (age 3 years; liveweight 61.9 +/- 0.36 kg; conditio n score 3.1 +/- 0.04) Merino wethers was examined. The grazing treatme nts involved adjusting sheep numbers to maintain green feed on offer n ear target amounts of 800, 1200, 1600, 2000, 2400 and 2800 kg dry matt er/ha. Liveweight and wool growth measurements were made on 8 sheep pe r plot, with additional animals added or removed as necessary to maint ain pasture near the target feed on offer. Changes in wool-free livewe ight were linear between days 0 and 42 (period 1), and days 42 and 111 (period 2) for both classes of sheep grazing low feed on offer treatm ents. Hoggets lost less liveweight than mature animals while grazing l ow feed on offer during period 1 and gained liveweight faster (P<0.05) than mature animals for any feed on offer during period 2. Curvilinea r relationships existed between feed on offer and clean wool growth ra te and fibre diameter, with feed on offer accounting for 65 and 81% of the variations in wool growth rate, and 65 and 73% of the variations in fibre diameter, for hogget and mature sheep respectively. There was no significant difference in wool growth rate between animal classes. Annual clean wool production, fibre diameter and staple length increa sed linearly (P<0.05) with increasing feed on offer. Staple strength w as higher (P<0.05) in mature sheep compared with hoggets, but was grea ter than 30 N/ktex for both classes of sheep irrespective of feed on o ffer. These results indicate that intensive grazing in spring to prede termined feed on offer is a useful tactic for manipulation of wool gro wth and fibre diameter, but factors other than feed on offer also cont ribute to liveweight change and wool growth.