Intake and Diet Selection by Protein Supplemented Grazing Steers

Abstract

Nine esophageal-fistulated and 12 rumen-cannulated steers were randomly allotted to 3 equal supplement groups: cottonseed cake (CSC), ground, pelleted alfalfa hay (ALF), or no supplement (CON). Supplements were individually fed at isonitrogenous levels C1.7 kg * hd CSC vs 3.5 kg .hd 1 ALF) every other day. Animals were maintained on treatment from January through April 1983 while grazing blue grama (Bouteloua gracilis) rangeland in southcentral New Mexico. Esophageal samples were collected at 2 times during this period: early February and late March; intake was estimated from total fecal collections in late February and early April. Esophageal samples were analyzed in the laboratory for nitrogen (N) components, in vitro digestibility, fiber, and botanical composition. Animal selection for total grass content of the diet was not influenced (P>.10) by supplementation but declined from February to March (31.8% vs. 21.2%, respectively). Blue grama and mat muhly (Muhlenbergia richardsonii) comprised over 66% of the grass component. Total forbs selected was not influenced by supplementation but increased (P .49), type of supplement consumed, or sampling period (P>.90). Total organic matter intake however, differed (P<.05) between treatment groups because of addition of supplements. Results of this study indicate protein supplementation of wintering steers does not influence botanical or chemical composition of their diets or amount of forage consumed. Improved weight gains and reproductive performance of protein supplemented cattle grazing dormant rangelands are well documented (Parker et al. 1974, Langlands and Bowles 1974, Falvey 1977, Adams and Kartchner 1983). Satisfying dietary requirements for nitrogen is a major mechanism involved in improved livestock performance; however, responses primarily limited to intake and digestibility have been noted (Campling 1970, Conrad 1966). RitAt the time of the study authors were graduate assistants, professor, associate professor, range technician and assistant professor, respectively; Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003. Review of the manuscript by Dr. J.L. Holechek was helpful and we appreciate his efforts. Journal Article 1096, N.Mex. Agr. Exp. Sta., Las Cruces, N. Mex. 88003. Manuscript accepted September 13, 1984. tenhouse et al. (1970) reported forage intake increased upon addition of protein supplements to low-quality forage diets (<6% crude protein). However, results of other studies on the effect of supplements on forage intake have been varied (Weston and Hogan 1968, Rittenhouse et al. 1970). Effects of nitrogen supplementation on diet selectivity have not been investigated, although nutritional status has been proposed to influence preference (Heady 1964). The objective of this study was to evaluate effects of 2 protein supplements, cottonseed cake and ground alfalfa pellets, on diet selectivity from the standpoint of botanical and chemical composition and forage intake.