LINCOLN, Neb. (AP) — Researchers say environmental regulations have slowed the growth of large hog farms and helped some smaller ones survive.

Two agricultural economists at the University of Nebraska-Lincoln looked at how environmental regulations have shaped the industry in the top ten hog producing states.

A number of federal and state laws allow small hog farms with fewer than 2,500 animals to be except from rules that require manure storage plans and permits.

Also, zoning restrictions won’t allow large hog farms in many locations where small hog farms can operate.

The researchers say the number of small hog farms has declined 61 percent between 1976 and 2005, but without those kind of rules the decline would have been greater.

The number of large hog farms jumped 95 percent over the same period.