CHICAGO – Two years after a devastating swine virus killed nearly 10 percent of U.S. hogs, farmers who built up herds to compensate are faced with a sober realization: they've produced too much bacon.

The aggressive ramp-up in hog production after the porcine epidemic diarrhea virus (PEDv) outbreak in 2013, which brought record profits for those whose pigs survived, has now created the greatest U.S. hog price collapse since the late 1990s. That was when overproduction sent prices plunging to 50-year lows.

Benchmark lean hog futures prices on the Chicago Mercantile Exchange have dropped 42 percent from their July 2014 record high of $133 per hundredweight.

And as herds continue to grow, and the strong dollar and competition from Europe and Canada blunts export demand, hog farmers are probably facing even lower prices in the months ahead, with December-delivery futures trading about 20 percent below current prices. The hog glut spells more trouble for a U.S. farm economy struggling with the lowest grain prices in five years.

La Mars, Iowa-based Tentinger Farms, which sells hogs to Tyson Foods, expanded its herd by about 20 percent to cash in on high hog prices and cheap feed costs, but record returns have eroded.

"Things are not real rosy out here. We're spending a lot of money and touching a lot of bases, handling and feeding more pigs, and not really making any money," owner Bill Tentinger said.

"Once we get past 2016, I think things are going to perk up a little bit … but it's not going to be gangbusters rolling ahead," he added.

With retail prices now at three-year lows, pork is stealing market share from other proteins: U.S. pork sales in June were up 12.5 percent over the previous month, while chicken rose 3 percent and beef fell 2.2 percent, according to the most recent industry data.

The number of piglets per litter hit a record high of around 10 in the spring, according to the U.S. Department of Agriculture (USDA), helped by steadily improving use of genetics and selective breeding. These animals take around six months to make their way to the meat case.

And when autumn weather arrives and sweet, freshly harvested corn begins filling feed troughs, reviving pig appetites, weights should climb back up to pre-summer levels.

The boom started when farmers who had lost millions of pigs to PEDv took advantage of cheap feed to plump up their hogs. Meat processors such as Cargill Inc. and Smithfield Foods Inc. were paying premiums for the extra weight.

As vaccines and strict biosecurity measures brought the virus under control, hog numbers exploded.

Some hog producers are still expanding as they reinvest last year's record profits. Construction permit applications for new and expanded swine buildings in Iowa, the top producing state where hogs outnumber people more than six to one, had nearly reached the 2014 total by mid-2015, according to state data.

Tyson Foods CEO Donnie Smith said in a recent conference call with analysts that he expects the domestic expansion to continue into 2016 resulting in 3 to 4 percent more hogs and pork on the domestic market.