DETERMINATION OF REPRODUCTIVE CYCLICITY AND PREGNANCY IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS) BY RAPID RADIOIMMUNOASSAY OF SERUM PROGESTERONE

Abstract

The stages of the reproductive cycle and pregnancy of 15 Asian elephants (Elephas maximus) at Busch Gardens in Tampa, Florida were determined by measuring serum progesterone concentrations using a commercial radioimmunoassay (RIA) kit with a sensitivity of 40 pg/ml of serum. Blood samples were collected and analyzed weekly for a 45-mo period. Serum progesterone concentrations ranged from nondetectable (<40 pg/ml) in nonpregnant elephants to 2,110 pg/ml in pregnant elephants. The highest concentration of progesterone during the estrous cycle was 1,490 pg/ml. The length of the estrous cycle ranged from 10 to 23 wk, with an average (?SEM) of 15.1 ? 0.3 wk for 103 estrous cycles. One elephant had a consistently longer estrous cycle length (18.6 wk). The duration of the nonluteal phase was 4.6 ? 0.2 wk, and the duration of the luteal phase was 10.5 ? 0.2 wk. The serum progesterone concentration during the estrous cycle was 214.0 ? 5.2 pg/ml. The individual elephant average cycle length was used to estimate the time of estrus and ovulation. During the nonluteal phase, elephant cows were placed with a bull for mating. Two weeks after estrus began (based on rising progesterone at the end of the nonluteal phase), the cow was separated from the bull. Ovulation was predicted to occur during the first week after estrus began. Serum progesterone analyses were continued weekly to determine pregnancy or the next estrus. Eight elephants became pregnant, with a serum progesterone concentration of 554.6 ? 16.4 pg/ml and a range of < 40-2,110 pg/ml. These results confirm that weekly measurement of serum pro gesterone by RIA can be used to characterize the luteal and nonluteal phases of the Asian elephant estrous cycle. Using this information, cows can be managed and placed with a bull at the appropriate time for breeding. Serum concentrations of progesterone also can be used to confirm pregnancy and to monitor and evaluate potential problems during pregnancy. The approximate date of parturition can then be predicted from average gestation length data, thus allowing staff to prepare facilities and be ready to assist with delivery.