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J. HANKS

Summary.

Aspects of reproduction in the African elephant in the Luangwa Valley in Zambia were studied in relation to the population dynamics of the species. The fetal and the secondary sex ratio up to 16 years of age did not depart significantly from equality. Males left family units soon after 16 years of age and joined bachelor herds. From 1964 to 1968, 88% of conceptions were in the rains, but in 1969 there was a shift in the breeding season peak to the dry months of the year. There was no evidence of seasonal breeding in the male elephant. Females reached maturity at 14 years, and males at 15 years, when the combined weights of the testes reached 650 to 700 g, and the mean seminiferous tubule diameter reached 90 to 120 μm. The mean calving interval was 3·5 to 4·0 years. In the population, 6% of the elephant were less than 1 year old. Apparent cycles of recruitment were considered to be artefacts caused by slight inaccuracies of the ageing technique used. Corpora albicantia accumulated at the approximate mean rate of 0·6/year, and the significance of this was examined in relation to comparative studies of population fertility. Reproductive senescence was a consequence of a combination of uterine defects and a reduction of oocyte number.

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J. HANKS and R. V. SHORT

Summary.

The uterus and ovaries of 617 elephants shot in Zambia were examined. Corpora lutea seem to be necessary for the development of the endometrial glands, and before conception can occur, a certain critical mass of luteal tissue has to be achieved by accumulating crops of cl from successive oestrous cycles. The elephant can be either monovular or polyovular, and ovulation is spontaneous. New ovulations do not occur during pregnancy, and the presence of an embryo prolongs the life of the cl. There is great variability in luteal size, small cl being commonest in non-pregnant animals and large ones in pregnant animals. The cl do not enlarge during gestation, and some of the smaller ones may regress. The number of cl in pregnant elephants varied with the age of the cow, the younger elephants having a significantly higher number. Larger cl ( > 20 mm in diameter) predominated in older animals. Very little progesterone appears to be secreted by the corpora lutea, and the hormone could not be detected in the peripheral blood during gestation. If progesterone is necessary for pregnancy, the elephant must be extremely sensitive to it, and may be forced to accumulate a large mass of relatively inactive cl before sufficient hormone is available to enable the animal to become pregnant.

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JANET G. SMITH, J. HANKS and R. V. SHORT

Summary.

Luteal tissue slices from an African elephant in early pregnancy have been shown to synthesize progesterone from added pregnenolone. The percentage conversion (2·4%/100 mg luteal tissue/hr) is very much lower than that found for human, bovine and porcine corpora lutea. It was possible to isolate a small amount of progesterone (0·18 μg/g) from a large quantity of luteal tissue taken from another pregnant elephant; this is far below the values found in the active corpora lutea of all other mammals.

The reasons for the relative inability of elephant corpora lutea to synthesize progesterone are not known. The elephant may be extremely sensitive to the action of progesterone, or the hormone may not be necessary for normal reproduction in this species.