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Effect of Sample Grinding Size on Forage Quality Estimates of Smooth Bromegrass Clones¹

Particle size of ground forage influences in vitro digestibility and the concentration of cell wall constituents. Little information is available on the effect of ground forage particle size on the relative rankings of genotypic or phenotypic values for quality of ground forage. Our objective was to determine the effect of two grinder screen sizes on the relative rankings and repeatability of forage nutritive value estimates of smooth bromegrass (Bromus inermis Leyss.) clones. Dried forage of 75 smooth bromegrass clones was ground through a 2-mm screen, from which a sample was reground through a 1-mm screen. Neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose, cellulose, and ash were determined on duplicate samples of fine- and coarse-ground forage. All traits except ADF and hemicellulose had average absolute values of duplicate differences reduced significantly by fine grinding. The correlation between duplicate samples was increased by fine grinding for each trait, except hemicellulose and ash. Fineness of grind severly affected the relative rankings of ADL and hemicellulose; NDF, ADF, and cellulose were also more highly correlated with one another when forage was ground finely. The interactions between particle size groups and clones raises the question of which size provides a better predictor of animal performance potential. We concluded that forage breeders should grind forage samples fine enough to obtain adequate repeatability unless it can be shown that coarser grinds give results more highly correlated with animal performance.

Key Words: Bromus inermis (Leyss.) • Cell walls • Particle size • Repeatability

² Assistant professor, Univ. of Wisconsin-Madison and professor, The Pennsylvania State Univ.

Received for publication February 2, 1984.