Methods of Restoring Carcass Firmness and Other Post-Harvest Traits in Finishing Pigs Fed a High Level of Distillers Dried Grains with Solubles (DDGS)

The large demand for corn for ethanol production has resulted in marked increases in corn prices and a resulting increase in feed costs for swine producers. The large amounts of distillers dried grains with solubles (DDGS), one of the major by-products of ethanol production, is now a viable and less expensive alternative feed ingredient for use in swine feeds. Questions are being asked regarding the amount of DDGS that can be used in swine feeds without causing reduced performance of pigs or soft bellies that are discriminated against by pork processors.

Previous research funded by the National Pork Checkoff showed that growing-finishing pigs could be fed as much as 45% DDGS in the diet with only a slight (2-3%) reduction in pig performance. However, this amount of DDGS in the diet caused softer bellies and high iodine values (a measure of the relative amount of unsaturated fatty acids in the carcass fat). However, in another study funded by the National Pork Checkoff, it was found that processing characteristics of pork bellies and eating quality of bacon, sausage, and loin chops were not negatively affected by this feeding this high dietary level of DDGS.
The objective of this study was to determine if withdrawal of a high level (45%) of DDGS from the diet during the final 2, 4, or 6 weeks of the finishing period or if the addition of a harder, more saturated fat (tallow) to a diet containing DDGS would prevent the softer bellies and high iodine numbers that occur when high levels of DDGS are fed. In addition, the study allowed us to further evaluate the effects of dietary inclusion of DDGS on the processing characteristics of cured bellies, physical characteristics of sliced bacon, and eating quality of bacon and loin chops.

An experiment involved 168 crossbred pigs was conducted at the University of Kentucky. Seven dietary treatments were evaluated, which included a corn-soybean meal control diet, a similar diet with 45% DDGS fed continuously to the end of the experiment, or three treatments in which the DDGS was removed during the final 2, 4, or 6 weeks of the experiment followed by a corn-soybean meal diet. Two additional treatments were the same two diets with 5% added tallow. Each treatment was evaluated with six replications of three or five pigs per pen. Diets were fed in three phases from 81 to 267 lb body weight. The two diets without added tallow were formulated on a true ileal digestible (TID) lysine basis with 0.81, 0.70, and 0.55% TID lysine during the three phases. Adjustments were made in diets containing tallow to maintain the same TID lysine:ME ratio across all diets. The experiment was terminated on a replication basis when the average weights reached 265 lb. Three pigs per pen were killed for carcass information.

Over the entire experiment, average daily gains and daily feed intakes were reduced (P < 0.05) by about 8 to 9% in pigs fed DDGS continuously, but efficiency of feed utilization was not affected. Daily gain improved linearly (P < 0.05) with increasing time of DDGS withdrawal. Tallow addition to the DDGS diet prevented the growth reduction, and feed efficiency improved (P < 0.05) with tallow addition to both diets. Carcass yield was reduced by DDGS feeding, but withdrawal of DDGS improved dressing percent. Belly flex measurements were negatively impacted by DDGS feeding, but they improved to those of the control pigs when DDGS was withdrawn for 6 weeks. Polyunsaturated fatty acids (PUFA) in the fat increased (P < 0.05) when DDGS was fed, but the changes were moderated (linear, P < 0.05) with DDGS withdrawal time. Iodine values (IV) followed similar trends. Tallow addition had no positive effect on iodine values.

Bellies from the pigs were pumped with brine, smoked, and sliced into bacon at a commercial plant. Bacon slices were scored for shatter, then fried and scored for distortion, cook loss, and shrink, then evaluated by a trained sensory panel. DDGS inclusion had no affect on slicing yield of smoked bellies and it improved shatter scores (P < 0.05) of the bacon. After frying, there was more distortion, cooking loss, and shrink (P < 0.05) of bacon from pigs fed DDGS, and withdrawal time had no effect. Tenderness and flavor of bacon was not affected by DDGS. Tallow did not consistent affect any of the measures. Sensory attributes of loin chops were not affected by DDGS, but tallow increased off-flavor (P < 0.05).
In summary, this study clearly shows that some of the belly firmness problems and elevated iodine values in carcass fat that are associated with the feeding of high levels of DDGS in the diet can be overcome by withdrawing the DDGS from the diet during the final 4 to 6 weeks of the finishing period. A 4-week withdrawal produced acceptable iodine values (mean of backfat and belly fat of approximately 70). The addition of a hard fat such as beef tallow to the diet, however, was unsuccessful as a means of improving belly firmness and elevated iodine values of pigs fed DDGS at high dietary levels. Under the conditions of this study, the softer bellies, increased polyunsaturated fatty acids, and higher iodine values did not negatively impact bacon processing or eating quality of bacon or loin chops in pigs fed a high level of DDGS.

This study was supported with the National Pork Checkoff. For further information, contact Dr. Gary L. Cromwell, Animal and Food Sciences Department, University of Kentucky, Lexington, KY 40546 (gcromwel@uky.edu).