RELATIONSHIP BETWEEN IN VITRO DIGESTIBILITY AND FINENESS OF SUBSTRATE GRIND AS AN INDICATOR OF VOLUNTARY INTAKE OF HAY BY SHEEP

Abstract

Hay of two alfalfa varieties and four grass species harvested at six maturity stages each was fed to sheep. Voluntary intakes were measured in grams of dry matter daily per kg of metabolic size. Samples were ground coarsely and finely and digested in vitro. Fine grinding did not increase the digestibility of immature hay, but with advancing maturity the fine substrate was progressively more digestible than the coarse. This difference was inversely related (P < 0.05) to voluntary feed intake. The regression of voluntary intake of dry matter (g/day/kg0.75 body weight) on the difference of in vitro digestibility of organic matter in finely and coarsely ground substrate was −2.32 g in the alfalfa hay and −4.18 g in the grass hay. The coefficient of variation from regression was 14% in the alfalfa and 17% in the grass hays. Fine grinding had a greater effect on the in vitro digestibility of organic matter than of dry matter. This resulted in a higher significance of the relationship of intake with the effect of grinding on the digestibility of organic matter than on that of dry matter.