An Appraisal of Ovarian Analyses in Determining Reproductive Performance of Black-Tailed Deer

During investigation of the reproductive performance of the Columbian black-tailed deer (Odocoileus hemionus columbianus) in western Washington (Golley, 1954), some information was obtained on the limitations of determining reproductive performance by analyses of structures in ovaries collected during the anestrous period. The data also suggest a need for further research to refine the technique of analyzing ovaries originally established by Cheatum. (1949). One aspect of Cheatum's technique was designed to measure reproductive performance from pregestation ovarian data obtained during hunting seasons. Significantly large numbers of does for statistically reliable measurements of reproductive performance usually can be collected only during this period of the year. The first part of the technique consists of determining i.e., the number of eggs ovulated per doe during the estrous cycle in which conception occurs. This is done by counting corpora albicantia of corpora lutea of pregnancy. Corpora albicantia are connective tissue resulting from degeneration of luteal tissue. These structures may or may not be pigmented. The corpora albicantia formed after parturition from corpora lutea of pregnancy are frequently designated as pigment scars or pigment spots. In applying the technique, it is necessary to assume that corpora albicantia of corpora lutea of pregnancy (1) persist until fall, when ovaries are collected during hunting seasons, and (2) can be distinguished from other pigmented corpora albicantia that might occur in the ovary. Cheatum identified corpora albicantia of corpora lutea of pregnancy by eliminating pigmented resulting from other so rces on the basis of the following assumptions: (1) corpora albicantia of corpora lutea of pregnancy persist in the ovary for at least eight months after parturition, (2) corpora albicantia formed from corpora lutea of estrus (ovulation without ensuing pregnancy) do not become pigmented, and (3) corpora albicantia of corpora lutea of pregnancy can be distinguished from corpora albicantia of luteinized, nonovulated follicles on the basis of their larger size. Having established the ovulation incidence, Cheatum multiplied this figure by the frequency of fertilization, the percentage of corpora lutea represented by embryos in the uterus, to obtain the production of fawns per doe. Frequency of fertilization is based on data from road-killed deer or limited collections made during the gestation period (usually the posthunting season). It is with the determination of ovulation incidence that the present paper is primarily concerned.