The production of faster growing, more efficient, leaner pigs is of primary interest in the swine industry. Boars grow faster, convert feed more effi ciently and have less fat than barrows. The higher rate of gain seen in intact males relative to castrates is related to differences in endogenous testosterone levels.
Positive correlations exist between growth and blood concentrations of testosterone.
The early determination of testosterone levels in addition to other criteria represents a novel approach to identify superior breeding animals. Swine producers also recognize that litter size has important influences on efficiency and revenue. Two factors affecting number of pigs born alive are ovulation rate and embryo survival. Variation in natural ovulation rate may result from differences in FSH concentration and ovarian sensitivity. Female reproductive traits are lowly heritable, but moderate to high heritabilities have been reported for testosterone and testicular measures in boars.