Effects of level and physical form of cottonseed hulls on microbial protein synthesis in the rumen of steers fed high concentrate diets

A. Yusof Hamali, R. Pucala and F. N. Owens

Abstract

Six steers fitted with ruminal and duodenal cannulas were used in a replicated 3 x 3 Latin square. Ruminal igestion and efficiency of microbial protein synthesis were measured. Three corn based diets were formulated to contain the following percentages of cottonseed hulls (CSH) and effective neutral detergent fiber (eNDF): a) 18% CSH and 10.4% (eNDF), b) 18% CSH (ground) and 6.1% (eNDF) and c) 25% CSH and 14.1% (eNDF). Mean ruminal pH values increased as eNDF content of the diet was increased. Ruminal NH3-N, peptide-N, and amino acid-N were similar among treatments averaging 96.4, 1.56, and 2.56 mg/L. The efficiency of microbial protein synthesis in the rumen was unaffected by the concentration of eNDF, and averaged 13.67 g of microbial N/kg of organic matter (OM) digested for all treatments. Increasing eNDF increased true ruminal OM and starch digestion in the rumen. Grinding CSH reduced ruminal starch digestion. Reducing the eNDF content of the diet depressed rumen pH less than expected and did not reduce efficiency of microbial growth to the degree proposed by NRC (1996).

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