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Reproduction is an important economic trait in beef cattle production. The average percent calf crop for the United States has been estimated between 80 to 85%. Approximately 60% of the reduction in calf crop can be attributed to fertilization failure and embryonic death. We conducted several studies to determine at what stage of the reproductive cycle losses were incurred in normal reproducing cows and heifers and in cows and heifers that failed to reproduce. In addition, we measured hormone levels in normal range cows and heifers and used techniques like embryo transfer and culture to study the development of the embryo.