Changes in Serum Progesterone and Estrogen of the Nonpregnant Coyote during the Breeding Season 1

Abstract

Vulvar swelling and vaginal bleeding were monitored and blood collected at weekly intervals during proestrus, estrus, and diestrus in 16, captive wild, adult coyotes. Serum progesterone and estrogen were measured by RIA to characterize further the coyote estrous cycle. Coyotes have a prolonged period (2 to 3 months) of intermittent vaginal bleeding generally referred to as proestrus; however, this discharge can occur during estrus and metestrus in some nonpregnant coyotes. Vulvar swelling was extreme for 1 to 2 weeks and the midpoint of extreme swelling occurred about 4 days after the estradiol peak. Progesterone began to increase (P < 0.01) concomitantly with the estradiol peak and continued to increase, reaching its peak 3 weeks later. Progesterone then declined gradually toward basal concentrations at 9 to 10 weeks after the extradiol peak and remained at these concentrations through at least the 15th week. Thus, progesterone in nonpregnant coyotes remained above basal concentrations for a period that is about equivalent to that of normal gestation. The lack of progesterone increase from 10 to 15 weeks after the estradiol peak agrees that the coyote is monoestrus. A single estrus is advantageous for controlling reproduction of coyotes, but the distribution of estradiol peaks over a 2-month interval may require prolonged administration of antifertility compounds and thus limit their effectiveness.