Evidence that hyperprolactinaemia is associated with ovarian acyclicity in female zoo African elephants

Abstract

African elephants of reproductive age in zoos are experiencing high rates of ovarian cycle problems (>40%) and low reproductive success. Previously, our laboratory found that 1/3 of acyclic females exhibit hyperprolactinaemia, a likely cause of ovarian dysfunction. This follow-up study re-examined hyperprolactinaemia in African elephants and found the problem has increased significantly to 71% of acyclic females. Circulating serum progestagens and prolactin were analysed in 31 normal cycling, 13 irregular cycling and 31 acyclic elephants for 12 months. In acyclic females, overall mean prolactin concentrations differed from cycling females (P < 0.05), with concentrations being either higher (n = 22; 54.90 ± 13.31 ng mL–1) or lower (n = 9; 6.47 ± 1.73 ng mL–1) than normal. No temporal patterns of prolactin secretion were evident in elephants that lacked progestagen cycles. In cycling females, prolactin was secreted in a cyclical manner, with higher concentrations observed during nonluteal (34.38 ± 1.77 and 32.75 ± 2.61 ng mL–1) than luteal (10.51 ± 0.30 and 9.67 ± 0.42 ng mL–1) phases for normal and irregular females, respectively. Of most concern was that over two-thirds of acyclic females now are hyperprolactinemic, a dramatic increase over that observed 7 years earlier. Furthermore, females of reproductive age constituted 45% of elephants with hyperprolactinaemia. Until the cause of this problem is identified and a treatment is developed, reproductive rates will remain suboptimal and the population nonsustaining.