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Removing Sources of Error in Lamb Feeding Experiments¹

University of California, Davis

Abstract

A method is proposed for conducting feeding experiments with lambs which removes much of the variation caused by composition of the body and weight of the gastro-intestinal tract contents. Carcass weight is obtained at the end of the experiment, specific gravity determined, and the weight adjusted to a standard weight equivalent in energy and protein content. This was shown to be a more reliable measure of animal performance than weight gain or weight gain in combination with dressing percent and carcass grade.

A study was made of the specific gravity method for the determination of carcass composition. It was found that the following multiple regression equations were suitable: Y= 436.8—398.7X₁+0.1756X₂, where Y=carcass fat, X₁=specific gravity, and X₂=carcass weight, in pounds. In the calculation of specific gravity the weight in air should be the warm carcass weight immediately after slaughter and the weight underwater should be that of a chilled carcass (preferably 24–48 hours) which has had all air pockets removed from under the fascia.

The following seems to be the most desirable method for obtaining the maximum amount of reliable information from lamb feeding trials:

1. Randomize the lambs to the treatments.

2. Take the initial weight after at least a 12-hour fast from feed and water and preferably a 24-hour fast from feed.

3. Obtain individual warm carcass weights at the end of the trial.

4. Determine specific gravity on each carcass and from this calculate the carcass composition.

5. Adjust the carcass weight to a corrected carcass basis equivalent in caloric content.

6. Analyze the data with an analysis of covariance to adjust the carcass weights to equal initial weights.

¹ This work is part of W-46, Western Regional Project on Environment stresses on range cattle and sheep production.

² Department of Animal Husbandry.