Chemical and botanical composition of the diets of oesophageally fistulated sheep, cattle and goats in a semi-arid Eucalyptus populnea woodland community.

Abstract

Diet samples collected from oesophageally fistulated sheep, cattle and goats on six occasions over a 12 month period were analysed for botanical and chemical composition. Angus steers, Merino wethers and feral goats were used in the study which was conducted in a poplar box (Eucalyptus populnea) woodland community near Cobar in northern N.S.W. Over 90 species, including trees and shrubs, were available to the livestock but only 18 species were eaten and of these, only five were of major consequence. These were the grasses, Eragrostis lacunaria and Stipa variabilis and the chenopods, Bassia diacantha, B. convexula and Chenopodium anidiophyllum. Other species to figure prominently in the diet were the composite forbs Calotis spp. and the shrub Acacia aneura. Diet quality was generally low with percent N in the range 0.98-2.10% and in vitro digestibility values ranging from 42-61%. The diet quality varied throughout the year and between animal species at any one time of year. Sheep selected diets which were higher in nitrogen and which were more digestible than those selected by either cattle or goats. Shrubs and trees were a major component of the diets of all three livestock species when the herb layer plants had been reduced to low levels of availability (< 180 kg/ha). Goats ate more trees and shrubs than either sheep or cattle at all times (P < 0.05) and these plants contributed up to 55 per cent of the goat's diet on occasion. The maximum contribution of shrubs to sheep and cattle diets was 22% and 34% respectively. Management implications are discussed in the light of the ephemeral nature of the herbage layer and the nutritional needs of the livestock.