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Digestibility and Metabolism of Kenhy Tall Fescue Harvested at Three Stages of Physiological Maturity^{1 ,2,}

University of Kentucky, Lexington 40546

Abstract

Kenhy tall fescue was harvested at three dates during the growing season to study the relationship of stage of physiological growth to digestibility and metabolism when fed to growing lambs. The three maturity stages were characterized as early vegetative, dough and regrowth vegetative. Crude protein was highest in early vegetative (17.6%), lowest in dough (7.7%) and intermediate (11.1%) in regrowth vegetative forage. Organic matter was similar for forages of all three maturities. Acid and neutral detergent fiber and lignin were considerably increased in tall fescue harvested at the dough stage. Concentrations of all macro-minerals studied were also lowest in forage at this stage of growth. Average N retention values of 2.7, –2.1 and .6 g/day were observed for lambs fed early vegetative, dough and regrowth vegetative forages, respectively. Apparent digestibility of crude protein, organic matter, neutral detergent fiber and acid detergent fiber were highest for lambs fed tall fescue in the early vegetative stage of growth and lowest for those fed fescue in the dough stage of maturity. Plasma glucose tended to be higher when regrowth vegetative forage was fed. Plasma urea nitrogen and rumen NH3-N were highest in lambs fed early vegetative forage and lowest in those fed tall fescue harvested in the dough stage. Total ruminal volatile fatty acid concentrations were greatest for lambs fed early vegetative forage and lowest for those fed forage in the dough stage of maturity. Average daily retention of individual minerals among the three stages of forage maturity tended to correspond to intake levels of each. Apparent digestibility coefficients of minerals most notably influenced by stage of maturity were those for Mg and S, which were decreased when dough stage tall fescue was fed, and Ca, which was highest for lambs fed fescue in the regrowth vegetative stage of physiological maturity.

¹ This paper (79-5-3-130) is published with the approval of the Director of the Kentucky Agr. Exp. Sta.

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

³ Dept.of Anim. Sci.

⁴ Present address: Lilly Research Lab., Greenfield, IN 46140.

⁵ Dept.of Agron.

⁶ USDA-SEA-AR and Dept. of Agron.