Factors Affecting Rate of Gain and Their Relation to Allotment of Pigs for Feeding Trials1

Abstract

The rates of gain by 601 pigs in the Record of Performance work of the Iowa Agricultural Experiment Station were studied to determine the relative importance of breed, litter, sex, initial weight and previous performance in allotting pigs for feeding trials. It was found that breed and litter must be carefully considered. Differences between sexes were very small although real. Neglecting sex in the allotment will increase the experimental error only a little, except where carcass characteristics are a prime object of study. The intra-litter correlation between initial weight and rate of gain was .24 in these data, indicating that initial weight is not important in allotment when the available pigs do not vary much in weight. Differences in initial weight might well be handled by analysis of covariance. The intra-litter correlation between gain in a 30-day preliminary period and rate of gain in the final feeding period was .32, which is only a little more than was found for initial weight. The large component of variance for error indicates that, although careful allotment does increase the precision of the experiment, the precision cannot become extreme even by perfect allotment. Further refinements must be sought in the techniques of feeding and management if nearly perfect precision is to be attained. Copyright © . .