Hormones that leak into streams from cattle feedlots are altering the sexual characteristics of wild fish, demasculinizing the males and defeminizing the females, according to a study.
The newly released study, which examined minnows in three streams that flow into Nebraska's Elkhorn River, suggests that cattle operations pose a previously unknown effect on the environment. About 30 million head of cattle are raised in U.S. feedlots each year, and nearly all are implanted with growth-promoting synthetic hormones.
A group of scientists from five U.S. institutions, led by the University of Florida in Gainesville, reported "significant alterations in the reproductive biology" of fish immediately downstream from a large Nebraska feedlot.
The male fish had about one-third less testosterone and testes about half as big as unexposed fish upstream, according to the study, which was published last week in the online version of the scientific journal Environmental Health Perspectives. The female fish had about 20% less estrogen and 45% more testosterone than females from the uncontaminated section of stream, the study found.
In addition, lab tests confirmed that feedlot effluent contained a complex and potent mix of androgens, the male sex hormones, and estrogens, the female hormones, said Edward Orlando, the study's lead author. He is now at St. Mary's College of Maryland in St. Mary's City.
The scientists said they did not know whether the damage was caused by natural hormones in cattle or by synthetic ones administered to the animals. Either way, their report says, the findings "clearly demonstrate" that effluent from feedlots is hormonally active. The discovery could fuel ongoing controversies over the safety of growth hormones in beef and increase pressure on the U.S. Environmental Protection Agency to tighten rules for livestock operations.
Cattle industry representatives, who have long maintained that hormone treatments are safe, called the study an unsubstantiated attack. They question whether the effluent came from the feedlots, rather than from septic tanks or sewage plants, which are known to release hormones from human waste into the environment. "It's very suspicious that they would indicate it is from feedlots, because there are long-standing regulations prohibiting discharge," said Gary Weber, executive director of regulatory affairs at the National Cattlemen's Beef Assn. "Feedlots are not allowed [under state and federal laws] to discharge into waters, so that raises the question of where are these materials really coming from?"
