Botanical composition of sheep and cattle diets on a mature annual range

Abstract

Abstract: Botanical and chemical analyses of the diets of freely grazing range animals are essential in determining forage digestibility and nutritive values. The problem is further complicated by the fact that animals are selective in their grazing and thereby affect botanical composition of their range. Statements in the literature of forage intake and selectivity are often contradictory, or unsupported in fact, because of inadequate techniques for studying the problem. Methods based on hand sampling, observations, and stomach analyses are of questionable accuracy for evaluating quantitatively the dietary botanical composition of animals on range areas. The most recent techniques of determining diets employ esophageal and ruminal fistulas, of which the former appears to be the most effective method thus far developed for sampled diets. The objectives of this study were the utilization of esophageal-fistulated animals to (1) compare the dietary composition of cattle and sheep freely grazing together on a mature annual range; (2) to evaluate changes in dietary composition with changes in herbage availability; and (3) to determine differences and variability in diets selected in the early morning and late afternoon, during consecutive days, and throughout the summer. Percentage botanical composition on a weight basis of cattle and sheep diets, and preference ratings for certain plants, for animals grazing on a mature annual range are presented. Composition of the dietary samples was determined by the microscopic point method on forage material collected through esophageal fistulas. The same microscopic techniques were used to determine composition of herbage clipped in the field. Dietary comparisons are made between individual animals, cattle and sheep, morning and evening grazing, grazing on consecutive days, and between lightly and heavily used range. Individual sheep differed more in diet than did cattle. Differences in most dietary components among cattle and sheep decreased as herbage became limited.