Formation, Function, and Persistence of the Corpora Lutea of the African Elephant (Loxodonta africana)

Between 1956 and 1967, 146 female African elephants were collected in Uganda and 23 sets of ovaries from pregnant animals were collected in Zambia. These were examined for number and diameter of corpora lutea, corpora rubra, and Graafian follicles. Histological sections were made of corpora lutea, corpora rubra, and ovarian stroma. In each corpus luteum 15 microscopic fields were examined. In each field 100 points were examined and cells at each point were classified as one of four classes. Presence of vascularity and cytoplasmic vacuolation was noted. Follicular development is repressed during gestation, especially in the 5 to 16 months of gestation. Lactation has little apparent influence on follicular development. Ovaries of all pregnant elephants contained more than one corpus luteum. In the Zambian collection the mean number of corpora lutea with stigmata of ovulation (2.4 was significantly different, P < .01) than the mean number without stigmata (3.5). Mean diameter of corpora lutea with stigmata was significantly (P < .01) larger than those without stigmata. Corpora lutea resulting from ovulation are formed in the first few months of pregnancy, whereas corpora lutea formed by luteinization of nonovulated follicles can be formed at all stages. The elephants of this sample had approximately 2.2 estrous cycles before becoming pregnant. The mean number of corpora lutea from 41 pregnant elephants was 6.0. There was no difference in the number or diameter of corpora lutea from the first or second halves of pregnancy. The mean number of corpora rubra in pregnant animals was 10.8 and the mean maximum diameter was 7.1 millimeters. In the ovaries of some animals in the late stages of pregnancy or shortly after parturition, there were no corpora rubra. The number of corpora rubra in the last half of pregnancy was not significantly greater than those in the first half. The average time of persistence of corpora rubra was about 77 months. Cell types within corpora lutea are heterogeneously distributed within individual corpora lutea. Within a single elephant there may be two or more groups of similar corpora lutea. Typical lutein cells were less abundant in the late stages of pregnancy. Cell types were not correlated with the presence or absence of stigmata of ovulation. Cytoplasmic vacuolation was more abundant in the second to thirteenth month of gestation. The corpora lutea of elephants are probably secreting hormones most actively during 2 to 14 months of gestation.