The botanical and nutritive composition of goat diets on lightly and heavily grazed ranges in the Edwards Plateau of Texas

Abstract

The yearly diets selected by Angora goats were compared on heavily and lightly grazed ranges in the Edwards Plateau region of Texas. Comparisons were based on the botanical and nutritive composition of dietary samples collected in two adjacent pastures by esophageally cannulated goats over an 11-month period in 1967. Forage available for consumption was measured at each of four seasons, and animal response to the two grazing treatments was measured by weight gains or losses of non-fistulated goats. Results indicated highly variable diets over the year, in terms of nutritive and botanical composition. However, seasonal trends were usually similar in the two pastures for most dietary components. Under both grazing treatments, grass and browse constituted approximately equal proportions of the winter diets, but browse in the diets was replaced by increasing proportions of grass throughout the spring and summer. Animals on heavily grazed range selected slightly more grass and less browse during summer than did animals on lightly grazed range. Browse replaced grass in the diets in late autumn. Forbs were of limited availability on the ranges at all seasons, but they contributed significantly to spring diets on lightly grazed range. Leaves were the predominant plant part in both diets throughout the year. The nutritional composition of diets on the two ranges reflected the botanical composition. Diets containing large proportions of grass were high in cell wall content, hemicellulose, and cellulose, and were relatively digestible in vitro, whereas, diets containing large proportions of browse contained relatively high concentrations of lignin and cell contents, and were usually less digestible in vitro. Diets high in forbs and immature browse contained the greatest concentrations of crude protein and cell contents and the least concentrations of structural carbohydrates..