PARENT SESSION

(T182) URINARY ESTROGEN PATTERNS ASSOCIATED WITH THE ESTROUS CYCLE OF THE ASIAN ELEPHANT.

Graham, Laura¹, Gray, Charlie², Buhr, Mary¹, ¹ University of Guelph, Guelph, ON, Canada² African Lion Safari, Cambridge, ON, Canada

ABSTRACT- The endocrinology of the estrous cycle in the elephant is unusual in that there are two waves of follicular growth during the non-luteal phase, each terminated by an LH surge. The first LH surge follows the growth of two to four follicles to 14mm and is anovulatory while the second LH surge follows the growth of a single follicle to 21 mm and induces ovulation. It is unknown what the function of the anovulatory surge is and what controls the timing of the two surges. Also unknown is the relationship of circulating estrogens to the LH surges because serum estrogen patterns have been difficult to elucidate in elephants. In the present study we investigated urinary estrogen patterns associated with the estrous cycle in Asian elephants. Matched urine and serum samples were collected from four females during the estrous cycle (n=24 cycles). Serum samples were assayed for progestagens and LH and urine samples were assayed for estrogens. Cycle length was 109.6±3.5 days. The first and second LH surges were identical in concentration (2.5±0.2 ng/ml) and occurred 20.1±0.2 days apart. Serum progestagen concentrations were 1.5±0.1 ng/ml during the non-luteal phase and 6.2±0.6 ng/ml during the luteal phase. There were significant elevations in urinary estrogens for four to six days prior to each LH surge. There was no difference between the estrogen peaks associated with the anovulatory and ovulatory LH surges (14.7±0.4 vs 15.9±0.7 ng/mg creatinine; P>0.05). Urinary estrogens also peaked during the mid-luteal phase indicating there is follicular growth during the luteal phase and/or there is production of estrogens by the corpora lutea. In conclusion, the concentrations of serum LH and urinary estrogens associated with the anovulatory and ovulatory LH surges are identical in Asian elephants. We hypothesize that the group of two to four follicles preceding the first LH surge collectively produce enough estrogen to induce the LH surge but individually are not mature enough to respond to the LH surge with ovulation and luteinization. In contrast, during the second wave of follicle growth the resulting single large follicle is capable of producing enough estrogen to induce an LH surge only once it is fully mature and capable of responding to the LH surge with ovulation and luteinization.

KEY WORDS: elephant, estrogens, estrous, LH