Changes in Fish Tied to Feedlots

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?”

However, the scientists said the samples were taken from a site “directly connected to a retention pond” located at the base of a large feedlot, Orlando said. Several spots along the Elkhorn contained hormones, indicating that “this is not due to one farm in one location,” said co-author Louis J. Guillette Jr. of the University of Florida.

In their report, the scientists say that further investigation of livestock farms is “urgently needed if we are to understand the possible adverse effects of these compounds on aquatic ecosystem health.” A priority, they said, should be to identify the compounds that altered the fish, and determine whether they were natural or pharmaceutical in origin. “Cattle can be treated with any number of chemicals, or chemical combinations, including androgens and estrogens. We do not know what the cattle in this feedlot were treated with or what was in the effluent,” said Earl Gray, a reproductive toxicologist at the EPA’s health effects laboratory who also was an author of the study. “This is really the first study of this kind, and there are lots of questions, but few answers so far.”

Whether hormones implanted in cattle have any effects on people who eat beef is unknown. About 99% of the nation’s largest, factory-sized cattle feedlots and 90% of smaller ones use hormone implants, which stimulate growth in castrated bulls and help them produce more meat and less fat, according to a 1999 survey by the U.S. Department of Agriculture. Most implant-free cattle are raised on open rangeland instead of in feedlots.

In California, the nation’s seventh-largest beef-producing state, about half a million cows are raised in feedlots annually.

Some implants contain trenbolone, a potent androgenic steroid, and zeranol, a fake estrogen. In lab tests, trenbolone feminizes male fish and causes male-like characteristics in female fish. Some synthetic hormones, including trenbolone, last for months or years in manure piles and waste ponds, compared with natural hormones, which disappear within hours or days, Guillette said.

The ability of dozens of contaminants, mostly pesticides and pharmaceuticals, to mimic hormones has been a growing concern since the early 1990s, when scientists began finding mixed-up sexual characteristics in wild animals, including alligators and polar bears. In human beings, some studies have linked contaminants to lower sperm counts and premature puberty.

The European Union has banned U.S. hormone-treated beef. Because nearly all the study’s funding came from the European Commission, the beef groups said the researchers might have had an agenda.

But Guillette said that no U.S. funding was available and that the EU “was not looking for an effect; they were looking for data, given the complete lack of ecological data” related to cattle farms.