Females with Phalli: The Effects of Low Doses of a Commonly Used Cattle Growth Promoter on Development in a Turtle with Temperature-Dependent Sex Determination

Abstract

Trenbolone acetate is a synthetic androgenic growth promoter used in conjunction with other steroidogenic compounds in the majority of beef cattle raised in the United States. It has been shown to disrupt normal reproductive development in many species. Because trenbolone and its metabolites pass through the urine and feces, aquatic species are likely to be exposed via runoff into water bodies adjacent to feedlots. The red-eared slider turtle (Trachemys scripta) has been used extensively in the past to model the effects of potential endocrine disruptors, like trenbolone, on normal development. It is an ideal model partly because it exhibits temperature-dependent sex determination, a condition which has been shown to be sensitive to exogenously applied estrogenic or androgenic compounds. In this study, the effects of low doses oftrenbolone on sex ratios were examined in turtles incubated at female or male biased temperatures. In addition to altering expected sex ratios, these first experiments resulted in male and female hatchlings with grossly hypertrophied phalli. A subsequent set of experiments was designed to compare the effects of trenbolone against two naturally occurring hormones, testosterone and 5a-dihydrotestosterone (DHT). DHT is the hormone responsible for phallus development in mammals and in many other vertebrate species. Trachemys scripta eggs were treated with identical doses of trenbolone, testosterone, or DHT and incubated at either a female-producing temperature or one that would normally produced mixed sex ratios. Trenbolone was shown to be more powerful than DHT or testosterone in its ability to reverse hatchling sex. It was the only compound to induce hypertrophied phalli in hatchlings. The benefits of using this compound in beef cattle should be reevaluated and weighed against its capacity to cause developmental abnormalities in exposed wildlife species.