"Fat Canadian cattle, Mexican cattle being trucked to our slaughterhouses and sold on our streets," he said.

Meanwhile, a drought in northern Mexico and the collapse of the peso, combined with the free trade pact, have driven substantial numbers of Mexican cattle into the American market.

Making the problem worse is a general meat glut nationwide - too much pork and too much chicken as well, along with low-cost Mexican cattle.

Nonetheless, he had chanced to look up one morning as they were trailing a herd of Mexican cattle through Lonesome Dove.

For awhile, his wild, rangy, Mexican cattle were prized, and he profited from driving them all the way to San Francisco.

They assert that the increase in trade in Mexican cattle, which has led to higher numbers of infected carcasses in American meat-packing plants, is a warning sign.

He buys some cheap Mexican cattle which, unknown to him, are infected with foot-and-mouth disease.

Instead, Mexican cattle developed immunities to the two types of tick that most threaten American herds, the cattle fever and southern cattle varieties.

Frank and Tom McLaury had a ranch outside of Tombstone that they used to buy and re-sell stolen Mexican cattle.

Over the last three years, an influx of Mexican cattle and increased concern over high-fat diets have led to a 35 percent drop in cattle prices.