Spanish goat diets following manipulation of South Texas mixed brush

Abstract

Forage availability and diet selection by Spanish goats were monitored seasonally from summer 1983 to spring 1984 to determine the influence of selected brush management treatments and range site on botanical composition and nutritive value of goat diets on mixed brush rangeland. Brush treatments applied in the spring 1983 to gray sandy loam and clay loam range sites included: no treatment, shredding, broadcast application of tebuthiuron pellets (2.2 kg a.i./ha), and picloram foliar sprays (1.2 kg a.e./ha). Total available forage (oven dry) varied from 900 to 2080 kg/ha during the course of study. Grasses dominated (>46%) available standing crops, especially on the chemically-treated plots. Forb production was markedly reduced on plots treated with herbicides, compared to no treatment and shredding. Proportions of available forage as browse varied from near zero to 34% depending on treatment and season. Species identified in goat diets by fragment counts included 17 shrubs and subshrubs, 14 forbs and 18 grasses. Forbs were minor contributors to composition of goat diets (<13%) throughout the study period. Browse consistently dominated diets selected on untreated and shredded plots (>50%), except in winter when freezing temperatures severely reduced availability of both browse and forbs. Diets selected on chemically-treated plots contained more grasses than those from untreated and shredded plots. Proportions of dietary grasses were inversely related to browse availability. Browse was highly preferred by goats, regardless of treatment and season, while grasses and forbs tended to be avoided on the untreated and shredded plots but were selected in proportion to their availability on chemically-treated plots. Crude protein (CP) contents of diets selected on untreated and shredded plots were consistently greater than CP contents in diets from chemically-treated plots. High CP contents were directly related to proportions of browse in diets and inversely related to proportions of grass. In contrast, dietary IVDOM varied little among treatments and seasons.