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Sources of Variation of Dry Matter Digestibility Measured by the Acid Insoluble Ash Marker

Department of Animal Science, Cornell University, Ithaca, NY 14853

ABSTRACT

Four experiments were conducted to describe and quantify variation of measurement of digestibility of dry matter by the acid insoluble ash method. Cattle fed diets of corn silage or corn grain and sheep fed silage or high fiber pellets did not exhibit a pattern of variation of digestibility associated with grab fecal samples. Except for cattle fed corn grain, differences were not significant between mean digestibilities determined by total fecal collection versus acid insoluble ash. Considerably more variation was associated with digestibility measured by acid insoluble ash when cattle were fed high grain diets, primarily because such diets contain little acid insoluble ash. Components of variance were estimated to quantify sources of variation and compute sampling sizes. Three grab fecal samples from each of 10 steers fed a high moisture corn diet or three grab samples from one steer fed a corn silage diet would be required for a 95% confidence range of 5 percentage units. Components of variance for sources of laboratory assay variation showed that two samples in each of two assay sets would be required to obtain a 95% confidence range of .1 percentage unit in mean acid insoluble ash content.