Assessing Minimum Amounts and Form of Roughages in Ruminant Diets: Roughage Value Index System

Abstract

Ruminants require adequate amounts of coarse-textured feeds to avoid metabolic disorders and, in the case of dairy cows, reduced milk fat production. Coarse-textured feeds help to maintain both proper muscle tone in the digestive system and proper rumen pH, both of which contribute to productivity and health. Texture of feeds is quantitatively reflected in the chewing activity of ruminants, and chewing stimulates saliva secretion. Saliva contains bicarbonates and other buffers that alter rumen environment and help avert disorders. Because chewing time reflects feed texture, a series of experiments were conducted in which feed intake, chewing time and milk and fat production were measured. Roughage value indexes (RVI) were partitioned for feed ingredients from regression equations. In addition, an equation was developed that predicts RVI from sieving and chemical data: RVI = 10.86 + PS (21.59) − DMI (1.91) + NDF (.541), where RVI is minutes/kilogram, PS is particle size in mean diameter, DMI is dry matter intake in kilograms and NDF is neutral detergent fiber percentage. The minimum RVI for the production of 3.5% fat milk was determined. By coupling an RVI requirement of 31 min/kg with feed RVI, one can formulate, by computer, diets for lactating cows that not only are nutritionally adequate, but also are adequate in roughage value, and thus avert metabolic disorders. The RVI procedure is ready for field testing.