Influence of two native shrubs on goat nitrogen status

Abstract

In vivo digestibility trials were conducted in metabolism stalls at New Mexico State University to evaluate the influence of leaves of true mountain mahogany (Cercocarpus montanus Raf.) and fourwing saltbush (A trtriplex canescens [Pursh.] Nutt.) on nitrogen retention and digestibility by Angora goats. Each of the 2 shrubs were fed at 3% and 6% (air dry basis) of the diet along with prairie hay that was comprised mostly of blue grama (Bouteloua gracilis [H.B.K.] Lag. Ex. Griffhhs). High and low shrub diets contained about 12% and 8% crude protein, respectively. Nitrogen retention did not differ (P>0.05) among mountain mahogany and fourwing saltbush diets; however, goats fed the 60% shrub level had greater (P<0.05) nitrogen retention than did those fed the 3% level. Mountain mahogany diets had a greater soluble phenolic/-tannin content than fourwing saltbush diets, but this did not appear to influence nitrogen retention. Forage organic matter intakes averaged 2.0% of body weight and did not differ (P>0.05) among the 4 treatments. Total fecal output of nitrogen (g/d) was highly correlated (R2 = .71, n = 15) with nitrogen retention. Hence, total fecal nitrogen output may be useful as an indicator of grasing ruminant protein status. Digestible protein (%) and dietary crude protein concentrations were associated poorly with nitrogen retention in our study. Blood serum analysis showed no toxicosis problem for any of the 4 dietary treatments. We concluded that leaves from fourwing saltbush and true mountain mahogany have potential to he an effective source of protein for range livestock consuming low-quality grasses.