Abstract

The Houston toad (Anaxyrus houstonensis) was the first amphibian to be protected by the Endangered Species Act and less than 300 toads are estimated to remain in the wild. In 2007 the Houston Zoo began a head start program involving over 500 captive assurance toads; however, natural breeding was poor and hormone-assisted breeding became necessary to produce animals for reintroduction. Hormone-assisted propagation is accomplished in a 5-day sequence. Absolute intracoelomic doses of hormones are used with the median weights of females and males at 75 g and 55 g, respectively. On days 1 and 4, females are primed with 100 IU of chorionic gonadotropin^a (hCG). On day five, both sexes are treated. Females receive 500 IU hCG and 16 µg of luteinizing hormone-releasing hormone^b (LHRH) and males receive 300 IU hCG and 8 µg of LHRH. Pairs of toads are then placed in breeding tanks. In 2015 this protocol resulted in a fertility rate of 88% and the release of over 450,000 fertilized eggs. While not a significant cause of mortality, oviductal or bladder prolapses remain the most common reason for post-breeding hospital presentation. Refinement of this protocol has improved fertility and reduced post-breeding mortalities since 2010. Adjustments include changing hormone dosing and frequency and decreasing time in breeding tanks. The current protocol is under constant reevaluation. The next areas of investigation include exploring methods to evaluate fertility of individual matings and to determine efficacy of a shorter treatment interval with a different class of hormone.

Endnotes

a. hCG, 5000 IU/ml ,Chorulon, Intervet, Inc., Millsboro, DE.
b. LHRH, 0.2 mg/ml, Sigma Aldrich, St. Louis, MO.