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Effects of Forage Source on Ruminal Microbial Nitrogen Metabolism and Carbohydrate Digestion in Continuous Culture¹

University of Minnesota^,4, St. Paul 55108

Abstract

Eight single-flow, continuous culture fermentors were used in Exp. 1 to study the effects of forage source on ruminal bacterial N metabolism and carbohydrate digestion. Forages included alfalfa, cicer milkvetch, birdsfoot trefoil and sainfoin with respective CP concentrations of 26.0, 28.7, 26.3 and 20.0%. Each forage provided 100% of the substrate for microbial metabolism and supplied 2.6 g N/d. Ammonia-N, protein degradation and efficiency of ruminal bacterial protein synthesis were lowest (P < .05) for sainfoin. Protein degradation and efficiency of bacterial protein synthesis were higher (P < .05) for birdsfoot trefoil than for alfalfa. Effluent flow of amino acids was highest (P < .05) for sainfoin. Total nonstructural carbohydrate digestion tended to be highest for sainfoin and birdsfoot trefoil, whereas structural carbohydrate digestion was highest (P < .05) for alfalfa and cicer milkvetch. In Exp. 2, mixed diets were supplied to dual-flow, continuous culture fermentors with alfalfa, cicer milkvetch, birdsfoot trefoil and sainfoin contributing 85% of the total dietary CP. Each diet contained approximately 12.9% CP. Ammonia-N concentration in the effluent and CP degradation tended to be lowest with the sainfoin diet and highest with the birdsfoot trefoil diet. Effluent flow of amino acids tended to be highest with the cicer milkvetch diet and lowest with the alfalfa and birdsfoot trefoil diet. Total structural and nonstructural carbohydrate digestion was not different (P > .05) among forages. Results from these experiments indicate that bacterial degradation of protein was lower for sainfoin than for alfalfa. Birds-foot trefoil and cicer milkvetch appear to be comparable to alfalfa with regard to metabolism of N and carbohydrates by ruminal bacteria.

¹ Published as Paper No. 15,571 of the Scientific Journal Series of the Minnesota Agric. Exp. Sta. on research conducted under Minnesota Agric. Exp. Project No. 16-048.

² Address reprint requests to this author.

³ Present address: Nutrition Professionals, 4669 Hillcrest Dr., Middleton, WI 5 3562.

⁴ Dept. of Anim. Sci.