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Expressing the Variability in Results of Metabolizable Energy Assays¹

G. M. Pesti^* and G. O. Ware

^* Department of Poultry Science Agricultural Experiment Stations, University of Georgia, Athens, GA 30602

In estimating the metabolizable energy of a food or feedstuff (ME_f), the ME of a reference diet (ME_r, containing glucose monohydrate) and the ME of a test (ME_t, containing the feedstuff substituted for glucose) are determined from a feeding trial:
where P is a proportion of substitution. Tradionally,
has been used in calculating the variance of ME_f as if it were measured without error, leading to an underestimation of the variance in ME_f. Variances of ME_f estimated by a method based on the variances
and ME_t were 4–11% greater for sample data. Underestimation of variances can lead to excess confidence in ME estimates. Too few replicates may be used for the desired confidence. Figures depicting the influence of replication and degree of substitution are included to help select the replication and proportion of substitution necessary to achieve acceptable results.

KEY WORDS: • metabolizable energy • bioassay • variance

¹ Supported by State and Hatch funds allocated to the Georgia Agricultural Experiment Stations of the University of Georgia.

Manuscript received 23 October 1985. Revision accepted 21 March 1986.