If you’re adding fat to swine diets, consider choice white grease, according to a Kansas State University study. It may actually be preferred over soybean oil in terms of growth performance (average daily gain and feed efficiency) and carcass-fat quality, says Justin Benz, Kansas State University swine nutrition graduate student.

The study showed that hogs fed diets containing choice white grease, which came from a Midwest source, had a more desirable fat quality when compared to hogs fed diets containing soybean oil, Benz notes. The Midwest-based supply could be higher in saturated fat than choice white grease manufactured in other areas of the country. Saturated fat is more desirable than unsaturated fat because it’s firmer, which is preferred in hog carcasses.

“Some producers question the quality of CWG. But, when coming from a Midwest manufacturer, CWG isn´t a bad fat source,” Benz says.

In the Midwest, pork producers will add CWG or beef tallow to hog diets because they are economical fat sources for that area. In the Southeast, poultry fat is fed, which is more unsaturated. As a result, the pork fat originating in the Southeast can be softer than in the Midwest.

Fat firmness, of course, is important for bacon processing. “Soft” fat is harder to slice because it tends to tear easily. “When the bacon tears, packing plants lose product and have lower yields. Lower yields mean higher costs for consumers,” Benz says.

To test fat quality, he collected jowl samples from 144 hog carcasses that had been fed corn/soybean meal diets. The hogs started at an average weight of 88 pounds. Dietary treatments included a corn/soybean meal control diet with no added fat, a corn/soybean meal diet with 5 percent choice white grease and a corn/soybean meal diet with 5 percent soybean oil. The two diets with added fat also were fed for different time intervals — zero to 26 days, zero to 54 days, zero to 68 days and zero to 82 days.

Iodine values were used to determine fat quality. The more saturated fat there is in a hog’s diet, the firmer its carcass fat will be, Benz says. By finding the iodine value, researchers can determine the amount of unsaturated fat (soft fat) there is in a carcass. Carcasses with low iodine values will have firmer and more desirable fat quality.

He points out that, while pigs fed choice white grease had a more desirable fat firmness, hogs fed soybean oil tended to have increased average daily gain and feed-to-gain ratio. The trial shows that increasing the choice white grease feeding duration did not increase average daily gain, but it did increase feed efficiency and the carcass’ dressing percentage.

“It’s pretty clear from the study that pork producers can use CWG as a fat source for any length of time without having any negative effects on the carcasses,” Benz says. “But using any highly unsaturated fat would increase iodine values and make carcass fat softer.”