Study Shows Choice White Grease Can Be Good Fat Source for Hogs

MANHATTAN - Kansas State University researchers recently studied the effects that choice white grease (CWG) and soybean oil have on hog growth performance and fat quality, said Justin Benz, Kansas State University swine nutrition graduate student.
calendar icon 1 March 2007
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The study showed that hogs fed diets containing CWG, which came from a Midwest source, had a more desirable fat quality when compared to hogs that were fed diets containing soybean oil, Benz said. CWG from the Midwest could be higher in saturated fat than CWG manufactured in other areas of the country. Saturated fat is more desirable than unsaturated fat because it is firmer, which is preferred in hog carcasses.

Soybean oil and CWG, which is a pork fat, are added to swine diets as economical energy sources, Benz said. Adding fat to hog diets also improves average daily gain (ADG) and feed efficiency in commercial settings.

“I think some producers question the quality of CWG and one of the big issues that we need to address is that CWG, when coming from a Midwest manufacturer, isn’t a bad fat source,” Benz said. “We believe CWG from the Midwest could be more saturated than some other areas of the country.”

In the Midwest, swine producers will generally add CWG or beef tallow to hog diets because they are a more economical fat source for that area of the country. In the southeast, Benz said, a lot of poultry fat is fed, which is more unsaturated. As a result, the CWG from pork in the southeast is softer than the CWG from pork in the Midwest.

“From a consumer standpoint, thinly-sliced bacon is popular, but ‘soft’ fat is harder to slice because it tends to tear easily,” Benz said. “When the bacon tears, packing plants lose product and have lower yields. Lower yields mean higher costs for consumers,” Benz said.

To test for fat quality, jowl (chin) samples were collected from 144 hog carcasses that had been fed corn-soybean meal-based dietary treatments. The hogs had an average initial 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 CWG and a corn-soybean meal diet with 5 percent soybean oil. The two diets with added fat were also fed for different time intervals – day 0 to 26, 0 to 54, 0 to 68 and 0 to 82.

The iodine value of jowl samples was used in the study to determine fat quality in the hog carcasses. The more saturated fat there is in a hog’s diet, the firmer its carcass fat will be, Benz said. By finding the iodine value, researchers can determine the amount of unsaturated fat, or soft fat, there is in a carcass. Carcasses with low iodine values will have a firmer and more desirable quality of fat.

While pigs that were fed CWG had a more desirable fat firmness, hogs fed soybean oil tended to have an increased average daily gain (ADG) and feed-to-gain ratio (F:G), Benz said. Results also show that increasing the feeding duration of CWG did not increase ADG, but did increase F:G and dressing percentage.

Dressing percentage is the percentage of a live animal’s weight that is carcass material, or the carcass weight divided by the live weight. The higher the dressing percentage, the more pounds of carcass an animal will yield.

“I think it’s pretty clear from our research that swine producers can use CWG as a fat source for any length of time without having any negative effects on the carcasses,” Benz said. “But, the use of any highly unsaturated fat would increase iodine values and make carcass fat softer.”

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