Dairy cows look out from their feeding stalls Wednesday at Tim Forry’s Oregon Dairy Farm in Lititz, Pa. When a cow dies on Forry’s farm in Pennsylvania Dutch country, he dumps the carcass onto a 200-foot-long compost pile behind his barn, where dozens of dead cattle are slowly decaying in an above-ground tomb of manure, wood shavings, hay and leaves.

Lititz, Pa. ? A federal regulation aimed at preventing mad cow disease from getting into the food supply could create health risks of its own: many thousands of cattle carcasses rotting on farms, spreading germs, attracting vermin and polluting the water.

At issue is a Food and Drug Administration rule, set to take effect in April, that will prohibit the use of the brains and spinal cords of older cattle as ingredients in livestock feed and pet food.

Some of the rendering plants that grind up carcasses for use in feed have already announced they will stop accepting dead cattle from farms because it would be too costly to remove the banned organs. Other renderers are likely to raise the prices they charge farmers.

As a result, many farmers — especially now, with the economy in crisis — may simply bury dead cattle on their property or let them rot in the open, industry officials and regulators say.

“I think there will be some illegal disposal — animals that get dragged into the woods or into the back fields,” said Gerald F. Smith Jr., president of Winchester, Va.-based Valley Proteins Inc., which operates 12 rendering plants in seven states but will no longer remove dead cattle from farms come February. He said the fee per animal would have to go from $85 to $200 to cover the additional expense, and “I don’t think the farmers would be willing to pay.”

Farmers already routinely bury, abandon or compost millions of cattle carcasses each year without serious environmental problems, according to the FDA.

But the fear is that the new rule could lead farmers to put hundreds of thousands more dead animals into the ground, especially on dairy farms, which tend to have many more older cows than cattle ranches do, and are often closer to populated areas, too.

According to the FDA’s own environmental assessment of the new rule, abandoning dead cattle or improperly burying or composting them can cause foul odors; pollute soil, groundwater and streams; and attract insects and scavengers. Moreover, the infectious agent that carries mad cow disease may survive burial or composting, the agency said.

“In some areas of the country … adverse environmental impacts could be expected unless new disposal capacity is developed,” the FDA said.

For decades, farmers have sent their dead cows to rendering plants to be turned into pet food, soaps, cosmetics, toothpaste, lubricants and other products. The carcasses are ground to a uniform particle size, heated under pressure to separate fat, protein and bone, and then refined.

The FDA regulation is aimed at providing an added layer of protection against mad cow, a brain disease that has been linked to more than 150 human deaths worldwide, mostly in Britain.