Determination of the number of replicates required to detect a significant difference between two means in rabbit traits

Abstract:

The number of replicates required to detect differences of variable size at several levels of significance, has been determined for growth, lactation and digestion traits from the equation: n ≥ s² x t² x 2/d². Residual standard deviation (s) values have been derived from results obtained with rabbits in our Research Department. An average value of s = 3.93 g/day has been obtained, for instance, in the case of average daily gain, for the average experimental conditions in our laboratory, and from a model including weaning weight as covariate and litter as block effect. This s value increased up to 5.38 when neither covariate nor block was considered in the model. Based on the s values obtained, the number of replicates needed to detect significant differences between two means for different traits were tabulated for several values of d and levels of significance. These values permit to decide the size of experiment according to the size of the differences to be detected. For example in our average experimental conditions, a sample size of 20 rabbits per treatment would allow to detect as significant differences (P = 0.05) of 3.0 g/day of average daily gain, 20 percentage units of mortality and 2 percentage units of dry matter digestibility during the fattening period.

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