During the past few years substantial progress has been made in the induction of multiple ovulation in cattle by hormone treatment. The practical results, however, have been unsatisfactory. Hitherto, only about 30% of treated cows ovulated the limited number of eggs (two or three) likely to lead to the birth of twins or triplets. In many cases only one egg could be obtained or the animals failed to ovulate; in others, four or more eggs were ovulated, and normal embryonic development did not ensue.The following investigations deal with the problem of inducing twin pregnancies by the ovulation of only two or three eggs. Forty-seven cows of the Max Planck Institute were treated with different sex hormones. All cows had been shown to be fertile in tests extending over the previous two or three years. They were kept under the same environmental conditions and fed individually. During the trial,
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