Relation of social dominance and body size to intake of supplements in grazing sheep

Abstract

The relations between dominance value, body measurements (liveweight, wither height, chest girth) and the estimated intake of three supplements (oats, chaff hay and molasses block) by grazing sheep were examined. Three groups of 15 Corriedale wethers, 3–4 years old, were rotated through three feeding periods of one week each, during which total intake of each supplement was estimated using chromium oxide. The feeding periods were separated by changeover periods of about 3 weeks. Agonistic encounters were observed for each group of animals during the feeding period on oats and chaff hay supplement. Animals were weighed at the start and end of each feeding period. Wither height and chest girth were measured at the end of the last feeding period. The three body measurements were closely correlated, particularly liveweight and chest girth. Dominance value was positively correlated with liveweight and chest girth, but not significantly with wither height. Intake of molasses block was correlated only with liveweight. This suggest that molasses block was not a limiting resource, its intake depending on the individual preference of particular animals. With intake of oats and chaff hay, dominance value generally had the highest correlation while chest girth had the lowest. In a multiple regression analysis, for intake of oats no variable explained significantly more variation after dominance value. For intake of chaff hay both dominance value and wither height were significant. The intakes of the different supplements were not significantly correlated. Thus it seems impossible to predict intake of one supplement from knowledge of intake of another.