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About 60% of the nutrient requirements for beef production in the U.S. are for maintenance of the breeding herd. In addition, the bovine female only produces about .7 of her body wt per yr in progeny wt. Thus, increasing the reproductive rate in beef cattle would have a major economic benefit. Although most bovine females are capable of gestating two calves, the natural frequency of twin births is low, ranging from less than .5% to 4% of the calvings, depending upon the breed of cattle. Several studies have indicated that the frequency of multiple births in cattle can be increased by gonadotropin hormonal therapy or by the artificial transfer of two 7- or 8-day-old embryos into the uterus. Unfortunately, the twinning response to these methods has been highly variable both within and among herds of cattle. The present study was conducted to identify causes for the variable twinning response in cattle to low dosages of gonadotropin therapy, to assess fertility in cattle that ovulate multiple oocytes (eggs), and to assess the relationship between number of fetuses and development of the fetus.