Herbage intake and production of Merino sheep grazing native and improved pastures at different stocking rates

Abstract

Estimates were made of the herbage intake, nutritive value of the diet, liveweight, wool production, efficiency of wool production and fleece characteristics of fine wool merino sheep grazing native pastures at stocking rates of 1.9, 3.7 and 5.6 sheep ha-1. The effects of increased stocking rates on these variables, and differences between improved and native pastures were examined by regression analysis. Organic matter digestibility declined with increasing stocking rate and was consistently less on native than on improved pasture as were the N content and the ratio, N : organic matter digestibility in the diet. Organic matter intake/sheep did not differ between pasture types or stocking rates, but digestible organic matter, digestible nitrogen and nitrogen intakes were less on native pasture, and paralleled seasonal changes in nutritive value, minimum values being recorded in late winter. Both wool production/sheep and liveweight were greater on improved pastures. Wool production ha-1 was 4 to 10 times greater on improved than on native pastures at stocking rates at which wool production/sheep were similar. Efficiency of wool production expressed as g wool/100 g digestible organic matter consumed was greater on improved pasture but when expressed/100 g nitrogen intake, sheep grazing native pasture were more efficient. Possible reasons are discussed. The maintenance requirements for energy appeared to be similar on both types of pasture. Fleeces produced on native pastures were generally lighter with shorter staple lengths, and appeared to be one spinning count finer than those produced on improved pasture. They were also superior in terms of softness and colour but were less uniform.