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Comparative Digestion, Rumen Fermentation and Kinetics of Forage Diets by Steers and Wethers^1,2,3,4,

West Virginia University, Morgantown 26506

Abstract

Four rumen fistulated wethers and beef steers were used to evaluate differences in dry matter digestibility (DMD) between cattle and sheep. They were fed either perennial ryegrass or switchgrass hay at an ad libitum or restricted level for four experimental periods. Significant ruminant species x forage and ruminant species x level of intake (P<.05) interactions were observed for digestible dry matter. The steers digested the switchgrass 7 percentage units greater than the wethers while ryegrass was digested equally. Digestibility differences between the steers and wethers were 6 percentage units at the ad libitum level of intake and 1 unit at the restricted level of intake. Crude protein digestibility tended to be greater (P<.10) for sheep with a 7 unit difference for switchgrass and a 3 unit difference for ryegrass. The mean ruminal solids retention time of the digesta was approximately (P<.01) 50% greater (26.0 vs 17.4 h) in cattle, with no difference in ruminal liquid dilution rate (LD) between animal species. Total ruminal volatile fatty acid concentration differed (P<.01) with level of intake; however, no influence due to intake on the molar proportion of acetate (P>.10) or propionate (P>.10) was evident in spite of a difference (P<.01) in LD. Rumen pH (P<.05) and osmolality (P<.01) were affected by both level of intake and forage, with the ryegrass and high level of intake decreasing pH and increasing osmolality. No animal species differences were observed for in situ dry matter disappearance over time as measured using Dacron bags suspended in the rumen, suggesting that differences in DMD between ruminant species was related to solids retention time of digesta rather than differing rates of digestion.

¹ Published with the approval of the Director of the West Virginia Agr. and Forestry Exp. Sta. as Scientific Article No. 1807.

² This study was a contribution to Northeastern Regional Research Project NE-108, "Optimizing Intake and Digestibility of Forages by Ruminants."

³ The authors acknowledge the assistance of Dr. W. T. Thayne in the statistical analysis of the data.

⁴ Division of Anim. and Vet. Sci

⁵ Present address: Ruminant Nutrition Laboratory, USDA, Beltsville, MD 20705.

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