Timing of Ovulation and Implantation in the Cottontail Rabbit


Reproductive behavior of individually marked cottontail rabbits (Sylvilagus floridanus) confined in large pens was studied in the spring and summer of 1963. The author observed coitus, which immediately follows parturition, and thus determined the timing of ovulation and implantation. Ovaries of postparturient females were either collected 8-18 hours after copulation for histological treatment, or the females were subjected to one or more laparotomies and their reproductive status determined by macroscopic examination of ovaries and uteri. The findings of this study indicate that cottontail rabbits ovulate between 10 and 11 hours postcoitus and that implantation is grossly visible by the 8th day postcoitus. The earliest time at which implantation sites are visible was not determined. This paper, on the timing of ovulation and implantation in the cottontail, presents the kind of information that is a fundamental prerequisite to ecological studies involving the reproductive performance of female cottontail rabbits. I wish to express thanks to Dr. R. D. Lord, Jr., United States Public Health Service, Atlanta, Georgia, for encouragement in initiating this study; to W. R. Edwards, Dr. G. C. Sanderson, and Helen C. Schultz, Illinois Natural History Survey, Urbana, and to Dr. J. H. Sather, Western Illinois University, Macomb, for guidance and assistance in manuscript preparation; and to 1 This paper represents part of a study submitted in partial fulfillment of the requirements for the degree of Master of Science at Western Illinois University, and is a contribution from Federal Aid Project W-66-R, the Illinois Department of Conservation, the U. S. Bureau of Sport Fisheries and Wildlife, and the Illinois Natural History Survey, cooperating. rted here and in the ea lier paper. The ick dermis on older male goats probably i es some protection during short fights en only a few blows are exchanged. In l-out battles old males still get severely ctured and lacerated. The rump shield thick dermis f old male goats appears be a defense gainst t e sharp h rns of specifics. It remains to be seen whether ale goats carry as thick a hide as males , and whether th dermis of male goats creases in thickness with ge a present is paper, on the tim ng of vulation implantation in the cott n ail, presents a st sub itted e ire e ts for the punctures, 23 were located poste ior e sternum; of 14 punctures on t e hind , 10 were located on the median sides. quite evident that most blows landed e goat’s ventral and rear parts. This ir s results of an earlier autopsy (Geist ctive perfor ance of female ournal of Wi dlife Manag ment, Vol. 31, No. 1, January 1967 This content downloaded from on Wed, 12 Oct 2016 04:24:07 UTC All use subject to http://about.jstor.org/terms OVULATION AND IMPLANTATION IN COTTONTAIL * Casteel 195 Dr. Jean W. Graber, University of Illinois, Urbana, for preparing slides from ovary tissue. MATERIALS AND METHODS A study of the reproductive behavior of individually marked cottontail rabbits confined in a 2-acre fenced enclosure located approximately 3 miles northeast of Urbana, Illinois, was conducted during the spring and summer of 1963. The rabbits were obtained by trapping with box traps from January through August, 1963, near Urbana. The 2-acre enclosure was divided into two adjacent square pens of %5/ acre each and a rectangular, %-acre pen. The observation facilities, techniques, and behavioral results are reported elsewhere (Casteel 1965). Nonfertile copulations were avoided by using only males with large scrotal testes which were considered to be indicative of sexual activity. Males placed in the observation pens were periodically checked throughout the season to determine their testicular status. Newly captured males were used as replacements in preference to those being held in reserve. Females 8 or more days pregnant were recognized by palpation. Proficiency at palpation was acquired and it became possible to make accurate embryo counts in this manner. The kidneys, urinary bladder, large intestine, caecum, and pellets in the descending colon were also distinguishable. However, care was necessary to distinguish between pellets in the descending colon and newly implanted embryos. It was usually possible to ascertain by palpation whether or not parturition had recently taken place. Normally, when an adult or sexually active juvenile female was not obviously pregnant, the uterus was turgid and coiled posteriorly, whereas for a short time after parturition it was flaccid and stretched anteriorly. Lactating females could be recognized by gross observation of the mammary glands. Behavioral acts which preceded copulation became recognizable to the investigator and proved useful in predicting the imminence of copulation. Does observed in coitus were either sacrificed and their reproductive status determined histologically or were subjected to laparotomies and macroscopic examinations of ovaries and uteri. Females were killed between 8 hours 52 min and 18 hours 45 min postcoitus. Reproductive tracts were preserved in 10 percent buffered formalin solution. Drawings of ovaries and uteri examined during laparotomies were sometimes made to augment word descriptions. Preserved material was fixed at least 14 days. After fixation, ovaries were carefully dissected from the mesovarium. The University of Illinois Animal Science Histology Laboratory subjected the ovaries to routine histological procedures, sectioned them at 10 micra, mounted every tenth section in an interrupted series, and stained the sections with Delafield’s hematoxylin and eosin.