Reproduction of Female Elephants
Basic anatomy and physiology, artificial insemination, parturition, and social aspects of reproduction
The study and research of reproduction in elephants is increasingly critical in consideration of the quickly dwindling population numbers and estimates. The current Asian elephant population is estimated to lie between 50,000-70,000 across the world, with 15,000 of these individuals in captivity. African elephant population numbers are low as well after serious culling through hunting and poaching. These numbers make the low reproduction rates a great concern as elephants do not currently sufficiently reproduce at an adequate rate to sustain population size.12
Reproductive Anatomy and Physiology of the Female Elephant
The vagina has multiple longitudinal folds and in size measures 30x15x10 cm approximately. In elephants, the penis does not physically penetrate the vagina during deposition of semen. During pregnancy, a thick vaginal mucus is present that works as a critical mechanical and infectious barrier. Nulliparous females contain a hymen that does not actually rupture by mating. The vaginal os has by two blind pouches by it that are considered to be possible remnants of Wollfian ducts. The clitoris is large and aids in guiding the penis during copulation. The ovaries are small in comparison to the overall size of the elephant, measuring approximately 7x5x2.5 cm in adults. Leading from these, the oviducts, at about 10 cm long, are positioned near the tip of the uterine horn at the ends of the oviducts. The ovaries contain multiple follicles displaying different stages of development, even in pregnant cows, with the dominant follicle usually being between 10 to 20 mm in size.13 The uterus is 0.8-1.5 m long has a short uterine body and longer uterine horns.14
Several hormones play a vital role in reproduction, the most notable being follicle-stimulating hormone (FSH) and luteinizing hormone (LH) produced by the pituitary gland, as well as estrogen and progesterone as formed by the ovaries.13 Progesterone levels raise 1-3 days after ovulation as the beginning of the luteal phase, 6-12 weeks in length, followed by the 4-6 weeks of the follicular phase, and concluded by the two distinctive LH surges. The first of these is anovulatory and takes place 19-21 days before the second, which is ovulatory. The vaginal lumen of the vagina is full with mucous that increases between the luteal and follicular phase and slowly recedes between the first and second LH surges. Excreted in the urine, the combination contains distinct pheromones that attract males.8 Females may be monocular or polyovular, with evidence to currently support either. Elephant ovaries have been collected and found to have evidence of singular follicle rupture, but in contrast the multiple corpora lutea (CL) found in ovaries of pregnant and non-pregnant cows open the possibility of it being polyovular, with the possibility that this...