The fecundity of the immature rat following induced superovulation

It was shown by Smith & Engle [1927] and Engle [1927] that ovulation could be induced in adult rats and mice by the daily implantation of anterior pituitary tissue. The numbers of eggs which were obtained by this process, from twenty to forty-eight from each animal, were well in excess of those observed after spontaneous ovulation. Furthermore, when mice treated in this way were mated many of them became pregnant and were found to have from nineteen to twenty-nine implanted embryos. These results seemed to hold promise that a method might be developed for materially increasing the prolificacy of animals, a procedure which would be valuable if it could be applied to certain classes of livestock. The method was simplified by Cole [1936] who was able to induce the ovulation of up to fifty-four eggs with a single injection of unfractionated pregnant mares ' serum. He also noted that immature rats were more satisfactory for this purpose than adult rats. Cole [1937] later obtained supernormal pregnancies by mating the treated immature rats, but the results were no better than those recorded by Smith & Engle. The largest number of embryos observed in any one rat was twenty-eight, while th