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Influence of Supplemental Sulfur on in Vitro and in Vivo Microbial Fermentation of Kentucky 31 Tall Fescue^{1 ,2,}

University of Kentucky, Lexington 40506

Abstract

Experiments were conducted to ascertain if supplemental sulfur (elemental or L-methionine sulfur) would influence ruminal microbial fermentation of a Kentucky 31 tall fescue diet. An in vitro experiment indicated that cellulose digestion of fescue by ruminal microorganisms was stimulated by the addition of either .05 or .15% sulfur to the substrate dry matter which contained .20% sulfur. Lambs fitted with abomasal cannulas were used to determine if the levels and sources of sulfur used in the in vitro experiment would influence in vivo responses. Ruminal digestion of acid detergent fiber (ADF) and neutral detergent fiber (NDF) was improved by the addition of elemental sulfur or L-methionine to a chopped, dehydrated tall fescue diet. Complete gastrointestinal (GI) tract digestion of ADF, NDF and nitrogen was not affected by sulfur supplementation. The amounts of total nitrogen and nonprotein nitrogen reaching the abomasum daily were slightly higher for the control diet which contained no supplemental sulfur. Quantity of protein nitrogen reaching the abomasum daily was not affected by dietary treatment. Total plasma free amino acids were highest when no supplemental sulfur was fed and lowest in lambs receiving .15% added sulfur. Plasma concentrations (µM/100 ml) of isoleucine, leucine, serine and tyrosine were lowest when the sulfur-supplemented diets were fed. Molar percentages of plasma methionine and cystine were highest in lambs consuming the sulfur-supplemented diets. No differences between elemental sulfur and L-methionine were found in either the in vitro or in vivo experiment. These studies indicate that unavailability of sulfur in the forage may limit microbial fermentation in ruminants fed a tall fescue diet.

¹ This manuscript (77-5-3-57) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.

² This research was supported in part by a grant from the Sulphur Institute, Washington, DC 20006.

³ Present address: Department of Animal Science, University of Illinois, Urbana.

⁴ Department of Animal Sciences.

⁵ Department of Agronomy.