Proposed Use of Adjusted Intake Based on Forage Particle Length for Calculation of Roughage Indexes

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Abstract
Effects of forage intake and particle length on chewing time were investigated. Two ratios of forage to concentrate, 33:67 and 50:50 and 3 lengths of forage particles were compared in two 3 .times. 3 Latin squares repeated a 2nd yr. Distribution of forage particle length was determined with an oscillating screen particle separator. Weighted mean particle lengths, 0.31, 0.43 and 0.51 cm, were measured for the 3 forages. Actual intakes of forage dry matter and fibrous constituents were multiplied by mean particle length of the forage to obtain intakes adjusted (kilogram centimeters) for particle length. Although there were no differences in intake of forage dry matter, or of neutral detergent fiber and acid detergent fiber between forage particle lengths, adjustment for particle length revealed that total chewing time was associated with mean particle length of the consumed forage. Total chewing time affected concentration of rumen volatile fatty acids, pH and milk fat percentage between ratios of forage to concentrate. Roughage indexes based on adjusted forage intake or intake of forage fibrous constituents are reported. The quadratic equation that described the roughage index (.cxa.Y) for the adjusted forage intake was .cxa.Y = 365.2 -69.6X + 4.73X2.