Researchers Jennifer Minick and Don Lay took a different approach to the problem, focusing on the interaction of the gilts and pigs that leads to crushing. "Typically you're looking at changes to the pen to try and figure out how to keep them from laying on the pigs," Lay said.

Minick and Lay presented results of the research at the Midwest meetings of the American Society of Animal Science and American Dairy Science Association, March 17-19.

The goal of the study was to measure the behavioral differences that may be responsible for fewer crushed pigs. If activities that prevent pig crushing could be discovered, the researchers figure that breeding stock could be selected based on those behaviors. They looked at time the gilts spent lying down, sitting and kneeling and the number of body turns and position changes.

Lay and Minick compared the behavior of two breeds of gilts -- Chinese Meishan and Yorkshire. Meishan sows have a lower incidence of piglet crushing compared to American sows. Yorkshire gilts were used as the representative breed in U.S. herds.

Sows of breeds typically raised in the United States crush an average of 1.2 to 1.5 pigs per litter. In Iowa, crushed pigs cost pork producers $8 million a year. A European study found a 5 percent survival advantage for the Meishan breed.

The gilts were placed in 5-by-7-feet pens to study their behavior in a more natural setting than a farrowing crate, said Minick, an ISU animal science senior. Lay added that Meishan gilts are not used to crates and sometimes "sulk" and refuse to eat when placed in them.

In the ISU study, the four Yorkshire sows each crushed one pig. Just one pig was crushed by all six Meishan sows and that was done during farrowing.

Less-active gilts that spent more time lying down had fewer opportunities to crush their pigs. The Yorkshire gilts were more active than the Meishan gilts and also spent more time sitting and kneeling, behavior that indicated discomfort. Minick said when the Yorkshire sows were sitting, pigs would typically run around under them, making them more vulnerable to crushing when the sows did lie down.

The Meishan gilts also performed a maneuver that seemed to protect their pigs from being crushed, Minick added. "The Meishan sows just flopped down, but they turned at least once before lying down to look for the pigs," she said.

Source: Iowa State University - March 1997