Diet selection and voluntary forage intake by cattle, sheep, and goats grazing in different combinations

Abstract

Reciprocal influences of plants and animals were investigated in a study conducted in 1979 and 1980 by varying the ratio of cattle, sheep, and goats in five pasture grazing populations. Diet selection, voluntary forage intake, and herbaceous and browse forage availability were monitored in four trials for determining changes in botanical and digestible composition of livestock diets and quantity of forage consumed as affected by animal species combinations and quality and quantity of forage available. Cattle, sheep, and goats were grazed in pastures containing a diversified mosaic of grasses, forbs, and browse. The study area, located southwest of Brady, Texas, was well within limits of the Edwards Plateau, but vegetation reflected that of an ecotone between the Edwards Plateau, Rolling Plains, and Cross Timbers and Prairies vegetation areas. Livestock combinations included pastures stocked with cattle and sheep only, sheep and goats, and two combinations of cattle, sheep, and goats. A single dose rare earth marker technique and a one compartment model for fitting fecal marker excretion data were used for estimating fecal output of 10 grazing animals per livestock species present in each combination during the four trials. Estimates of voluntary intake were calculated from fecal output and in vitro dry matter digestibility. Diets collected from esophageal fistulated animals revealed seasonal and grazing combination differences in diet selection within and among livestock species for forage classes, plant species, and plant parts. Yearlong diet data indicate that cattle, sheep, and goats in this study selected diets similar to reports in the literature. Effects of grazing combinations suggested that cattle diets were affected little by the presence of other animal species, but sheep and goat diets demonstrated a decrease in the proportion of grass and an increase in the proportion of browse consumed as they were reduced in numbers of the pasture grazing populations. Yearlong undigested dry matter turnover and retention time was significantly different for cattle, sheep, and goats and demonstrated that the goat had a significantly faster turnover and shorter retention time than either cattle or sheep, except in the spring when sheep and goats were equal for retention time.