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Factors Affecting Digestibility of Nutrients by Sheep¹

Utah State University, Logan 84322

Abstract

Digestion trials were conducted with growing lambs to compare digestibility of major organic components of the diet as related to (1) type of forage (legume or grass), (2) stage of maturity of forage, (3) digestible energy concentration or combination of ingredients (forage alone or 50% corn grain plus 50% forage diets) and (4) texture or form in which the diet was fed (coarsely chopped versus ground and pelleted). Chemical composition was the most important factor affecting nutritional value of the diets. Significant differences in apparent digestibility of structural components (cellulose, lignin, cell walls, neutral detergent fiber and acid detergent fiber) were found among forages of different types and stages of maturity and diets of different texture. Hemicellulose digestibility, however, was not related to diet factors. Apparent digestibility of structural components was not significantly changed in high energy forage-corn grain diets. Statistically significant energy x texture interactions were found for apparent digestibility of energy, dry matter, crude protein, cellulose, hemicellulose, cell walls, neutral detergent fiber and acid detergent fiber. Structural components were less digestible in unpelleted forage-corn grain diets than in forage alone, but pelleting of forage-grain diets improved apparent digestibility of structural components over that observed in all pelleted forage diets. Apparent digestibilities of available carbohydrate and crude protein were highly correlated with their content in the diet and were not influenced by ingredient source, processing method or texture of feed. Thus, these more chemically uniform components were also the most nutritionally uniform.

¹ Journal Paper No. 2479 of the Utah Agr. Exp. Sta. This research was supported in part by AID funds under contract No. AID/TA-C-1159, entitled "Increasing Livestock Production Through Improved Nutrition Information."

² Assistant professor, research assistant and professor and director, respectively, of the International Feedstuffs Institute, Anim., Dairy and Vet. Sci. Dept.