The present thesis is a study of the factors that affect the assessment of rate and efficiency of gain in Yorkshire swine in the pre and post-weaning stages of growth. Calculations from metabolism data for growing swine and measurement of the milk production of Yorkshire sows were used to demonstrate the inability of a sow to produce sufficient milk (energy) for her suckling young about 12 to 20 days post-farrowing. A well balanced high energy creep ration was used in a commercial swine herd to

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... overcome the energy debt to suckling piglets and provide for attainment of maximum growth, and hence, reduce the time required by them to reach 200 pounds. The affect of subnormal hemoglobin levels on pre-weaning growth rates and weaning weights of suckling piglets was investigated. The need of a continuous supply of iron and energy (creep ration) for suckling piglets to produce normal hemoglobin levels and to permit them to grow at their genetic potential was demonstrated. Energy content of gain and resting energy metabolism data were used to calculate post-weaning feed requirements of four experimental litters that were 12½ percent inbred. The post-weaning growth studies show uniformity of litter averages for several economic characters of swine, but variations within litters were high as shown by large standard deviations. The relationship between post-weaning rate of gain, feed efficiency and dressed carcass is discussed. The results demonstrate the possibility of rapidly improving rate and efficiency of gain in swine if selection is based on the performance of individual animals.