Corpora Lutea Variations of White-Tailed Deer

Abstract

The reproductive tracts of 404 female white-tailed deer (Odocoileus virginianus) were studied for information on size, shape, and coloration of corpora lutea. Corpora lutea in fawns are regarded as regressing if they are less than 4.0 mm in diameter at the time when the rut for that age-class is nearing its end. In all age-groups of does where fetal membranes or embryos are present, corpora lutea smaller than 6.0 mm are regarded as regressing. These small ones are regarded as corpora lutea of an earlier heat and not as corpora lutea of the current pregnancy. Regressing corpora lutea of a previous ovulation also appear to have an irregular surface shape. Color is not a dependable criterion for differentiation of the two types of corpora lutea. During an investigation of reproduction in white-tailed deer in Iowa, information was obtained on the physical characteristics of their corpora lutea. In attempting to correlate fertilization rate with ovulation rate, difficulty has been encountered in differentiating corpora lutea of ovulation of a previous heat from corpora lutea of pregnancy. In sheep, corpora lutea of ovulation are formed in ruptured follicles within 4 days following ovulation (Asdell 1946:366-367) and are fully developed by the eighth day following ovulation (Harrison 1962:169). In deer, corpora lutea of ovulation begin regressing after about 14-15 days (Cheatum 1949:285) if fertilization does not occur. When fertilization and implantation take place, corpora lutea of ovulation persist as corpora lutea of pregnancy (Amoroso and Finn 1962:454). The corpus luteum has a glandular function, secreting progesterone hormone which is essential for implantation and early development of the fertilized ovum. This hormone also suppresses further follicular development and ovulation. After parturition, corpora lutea of pregnancy regress and become corpora albicantia. Ability to identify corpora lutea of ovution of a previous heat from those of pregnancy of a later heat would eliminate a possible source of error when using corpora lutea counts as an index to reproductive rates of deer. Golley (1957) found the use of the corpora lutea dependable for determining the ovulation incidence of the black-tailed deer (Odocoileus hemionus columbianus) but detected an error when using the corpora albicantia to indicate ovulation. Golley used histological techniques to determine the differences between the two types of tissue. This paper will discuss gross size, shape, and color variations of corpora lutea in white-tailed deer ovaries as a possible means for distinguishing the two types. The assistance of Eldie Mustard, former Iowa State Conservation Commission Biologist, is appreciated. Several of Iowa's Conservation Commission officers and biologists also assisted materially by collecting reproductive tracts from wild deer. The cooperation of deer hunters who saved tracts for the study was indispensable. Calvin Rayburn, Ronald Schara, Harold Prince, and David Bolton, students 1Journal paper J-4604 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. A contribution from the Iowa Cooperative Wildlife Research Unit, which is jointly sponsored by Iowa State University of Science and Technology, U. S. Bureau of Sport Fisheries and Wildlife, the Iowa State Conservation Commission, and the Wildlife Management Institute. Financial support for Trauger was provided by the National Science Foundation Undergraduate Research Participation Program.