Periodicity in the Fecundity of Male Rabbits

¹ From the Department of Physiology, University of Illinois, Urbana, Illinois

Semen specimens were collected daily from 13 rabbits for prolonged periods during the course of 13 months. Total sperm count rose to a definite peak every 2–7 days (av. = 3.16 days) and then decreased again to values of from 79% to less than 1% (usually about 50%) of the preceding peak. In mature animals, the frequency of peaks was significantly different from the random distribution and significantly similar among individual animals. In pubescent animals, the intervals between peaks were consistently either longer or shorter than those found in mature animals, but the intervals were significantly different from the random distribution. The peaks were found not to coincide in different animals and were therefore not due to environmental influences. The number of collections made each day did not affect the daily pattern of total sperm counts. As daily total sperm count rose and fell sperm motility and the volume of liquid semen rose and fell with it, but this was not the case with the amount of coagulated semen.