Biological Manipulation of Blackbrush by Goat Browsing

Abstract

Domestic goats were used to modify the growth form of blackbrush, a spinescent shrub occurring in nearly monospecific stands on several million hectares of rangeland in the southwestern USA. The objective of this research was to provide data on the responses of blackbrush, goats, and cattle to a biological manipulation program in which winter goat browsing was used to stimulate spring twig production in an attempt to improve fall and winter range for cattle. Goats were stocked at 4 intensities during each winter from 1977-1979. Resultant levels of use and spring twig production were determined, with increased use leading to increased twig production. Browsing improved the nutritional quality of blackbrush by stimulating twig production, and current season''s twigs collected during the winter contained more crude protein (6.5 vs. 4.6%), P (0.10 vs. 0.08%) and in vitro digestible dry matter (48 vs. 38%) than did older twigs. Cattle (heifers) browsed blackbrush pastures during Oct. of 1979. Heifers in pastures unbrowsed by goats consumed primarily older twigs while those in previously browsed pastures consumed primarily current season''s twigs. No statistically significant differences in weight response were recorded for heifers using pastures that were, or were not, previously browsed. In previously unbrowsed pastures the average heifer consumed 1.9 times more protein supplement than did her counterpart in previously browsed pastures.