Grazing management studies with Australian cashmere goats. 3. Effect of season on the selection of diet by cattle, sheep and goats from two tropical grass-legume pastures

Abstract

Oesophageally fistulated cattle, sheep and I goats were grazed together to study species diet preferences from 2 different tropical grass-legume pastures during 3 seasons (summer, autumn, winter). In one pasture, Brachiaria decumbens (signal grass) was the dominant grass and in the other pasture, Paspalum plicatulum. Each pasture had a common suite of tropical legumes, mainly Desmodium intortum (greenleaf desmodium), Macroptilium atropurpureum (siratro) and Macrotyloma axillaris (axillaris). Axillaris was the major legume available in summer and autumn and greenleaf desmodium was the major legume in winter. There was no significant effect in any season of the basal grass available on the composition of the diet selected by the different species. Both goats and cattle had a high preference for legume leaf during summer and autumn, with goats having a higher preference (34-75% of diet) than cattle (1245%). Sheep selected against legume (5-19% of diet) and had a high preference for grass leaf (58-74% of diet) in all seasons. Cattle selected grass in preference to legume (greenleaf desmodium) in winter. Goats showed the greatest discrimination against both grass and legume stem. In summer sheep selected a higher quality (in vitro digestibility) diet (62.7%) than did cattle (53.4%) and goats (51.2%). In both autumn and winter cattle and sheep selected diets of similar digestibility (range 58.6-63.6%). In vitro digestibility of the extrusa samples was significantly (P<0.05) correlated (r = 0.74) with the proportion of grass selected. It was concluded that in their grazing preferences, goats were more like cattle than sheep. The different preferences of sheep and goats for tropical legume leaf was associated with location of these legumes in the sward, goats browsing from the top down and sheep grazing from the bottom of the sward.