The primary efforts of the Reproduction Research Unit are directed toward improving the reproductive efficiency of beef cattle, sheep, and swine. Because of high fixed resource requirements associated with maintenance of the nation's breeding herds, small increases in reproductive efficiency will have a major impact on the efficiency of red meat production. Research on reproduction includes both sexes and involves physiology, endocrinology, behavior, molecular biology, neuroendocrinology, biochemistry, nutrition, and genetics. Increased understanding of factors that influence puberty, estrus, sexual behavior, ovulation, fertilization, implantation, embryonic and fetal mortality, parturition, and early postnatal mortality is required for improving reproductive efficiency. Specific research efforts involve regulation of follicular and testicular development, ovulation rate and sperm production, embryo and fetal interrelationships with uterine function, and identification of quantitative trait loci in both cattle and swine.