Pregnancy Hormones and Parturition Diagnosis in Domesticated Asian Elephant
Faculty of Vet. Science, Chulalongkorn University
Female Asian elephant (Elephas maximum indicus) obtains sexual maturity at the age of 15-16 years old. Some reports pregnancy as early as 9 years old and continues to breed to the age of 55-60. Whereas most Asian male elephants reach their puberty at 12 years of age with fertile sperms when they are 18-20 years old.
The estrous cycle of the elephant last 16-19 weeks, based on measurement of urinary bioactive follicle stimulating hormone (FSH) levels. Ovulatory cycle can be defined into 3 phases: follicular, ovulation and luteal. Follicular phase (nonluteal, interluteal) in Asian elephants last 3.4-7.9 weeks. As in other mammals, FSH is assumed to be the main hormone in controlling folliculogenesis with estrogen and perhaps inhibin regulate the feedback control on hypothalamus and pituitary gland. Inhibin is produced by the follicular granulosa cells and Sertoli cells in the testes and act on the pituitary gland to suppress the production of FSH. In elephants, 90-96% of circulating estrogens are conjugated rapidly and cleared from the blood. Levels of unconjugated estrogen detected in the serum may not truly reflex estrogens production. Ovulation - There are luteinizing hormone(LH) surges in Asian elephants before and during the rise of progesterone. It has not been elucidated yet whether elephants are mono- or polyovulatory. Although they are generally monotonous, up to 22 corpora lutea are reported. The luteal phase - The multiple corpora lutea (average 11) may be the result of polyovulation, luteinization of the unovulated follicles and/or persistent corpora lutea from previous cycles. It is hypothesized that accumulation of corpora lutea from successive cycles are needed for the adequate amount of progesterone to maintain pregnancy. Radioimmunoassay (RIA) technique reveals the level of progesterone at 30-70 pg/ml during the follicular phase, and 400-700 pg/ml in luteal phase. Some report the correlation of testosterone with progesterone levels, suggesting the possibility of testosterone production by corpus lutea.
During pregnancy (20-22 months),the levels of serum progesterone rise to 1200-1670 pg/ml and rapidly fall to less than 100 pg/ml prior to parturition. It has been suggested that urinary progestagen profile closely followed that of circulating progesterone and commercial RIA test kit could be used diagnostically to detect urinary progestagen. Unconjugated estrogens levels in pregnant elephant are the same as in the nonpregnant ones (<50pg/ml) while total estradiol are significantly higher in pregnant elephants. Also urinary estrogen levels remained higher than cycling levels all through the gestation period.
Prolactin can be used to detect pregnancy after 4-7 months of gestation and the levels still remain elevated until parturition. Prolactin is increased to 50 ±7ng/ml during pregnancy while the level is 6.9±0.7ng/ml in nonpregnant animals. Some researcher reports Asian and African elephanturine testing to detect pregnancy using a test kit for human chorionic gonadotropin (hCG).
In our 3 years study, we have tried to make a practical approach to diagnose pregnancy and parturition in elephants by using the commercial test kits available for human. Plasma progesterone (n=5), estradiol(n=4) and prolactin (n=2) together with urinary progesterone (n=5) and estradiol (n=3) were analysed using electrochemiluminesence immunoassay (CMA). Urinary gonadotropin is monitored using color immunochromatographic assay for hCG (n=3).
From our study, the commercial test kit(for human) failed to detect prolactin and hCG. This may be due to the species immunospecificity of the glycoprotein nature of these two hormones. The plasma and urinary estrogens levels are tremendously fluctuated as most of the circulating estrogens are rapidly conjugated and the levels of free estradiol detected may not reflex the true estrogens production. Urinary progesterone levels are also not meaningful. Other researchers have learned that measuring unmetabolized progesterone in urine from Asian elephants was unsuccessful and that α- and β-pregnanetriol are major urinary progesterone metabolites in Asian elephant and can be measured using enzyme immunoassay (EIA).
Using the commercial test kits reveal that the high plasma progesterone levels proved to be the pregnancy attest after 4 months conception (1.01-1.96 ng/ml, n=3). In addition, lowering of plasma progesterone can determine that parturition would take place in a few days (0.06-0.03ng/ml, n=3). Gestation period in 5 elephant cows was 21-23 months.
Normally, fresh blood would best be monitored but physical or chemical restraint of elephant would be required for the collection of blood samples. Apart from the obvious danger to both the animal and the handler, physical or chemical restrain can elicit a stress response which impacts normal physiology and affects the levels of the hormones being studied. Urine progesterone level can be very useful and noninvasively assessing endocrine status during pregnancy and also the ovarian function.
The technique of detecting urinary progestagen, either EIA or RIA would be very much advantageous to monitor the ovarian cycle, pregnancy diagnosis and also signaled impending parturition. Especially in situations where elephants are not tractable.