Distillers dried grains with solubles (DDGS) can be fed in swine diets at an inclusion rate of up to 30% without negatively affecting pig growth performance. However, DDGS contains high levels of polyunsaturated fatty acids (PUFA), which may promote deposition of unsaturated dietary fatty acids in adipose tissue. Consequently, inclusion of DDGS at more than 20% has been shown to result in increased fat iodine values (IV) and soft belly production.  The disadvantages of this decrease in fat quality include reduced shelf life, increased susceptibility to oxidative damage, and reduced belly sliceability.

An experiment was performed to determine if the addition of different sources of saturated fat would improve belly fat quality in pigs fed a DDGS-based diet. In addition, the hypothesis that the iodine value product (IVP) of the diet can be used to predict backfat IV and belly fat IV of pigs fed diets containing DDGS was tested.

Belly fat quality

A total of 36 barrows and 36 gilts were used in the experiment. The pigs were fed one of six diets. The control diet was a corn-soybean meal-based diet that contained no DDGS and no added fat.  A second diet contained corn, soybean meal, and DDGS and the remaining  four diets were similar to the second diet with the exception that they contained 15% corn germ, 3% tallow, 3% palm kernel oil, or 5% glycerol.

Fat quality was measured using a belly flop test. In this test, the belly is draped lengthwise, skin side down, over a suspended  metal rod. The distance from skin surface to skin surface is then measured at a standardized point 10 cm down from the top of the rod. A larger flop distance indicates a firmer belly.

As expected, pigs fed the control diet had firmer bellies than pigs fed the DDGS-containing diets (Table 1). No difference in flop distance was observed among pigs fed the diets containing DDGS. Addition of corn germ, tallow, palm kernel oil, or glycerol to DDGS-containing diets did not affect belly softness.

Predicting backfat and belly fat iodine values

The IV of ingredients, diets, belly fat, and backfat were calculated based on fatty acid analysis. The IVP of each ingredient was calculated by multiplying its IV by the lipid concentration (%), and then by 0.10.

The IVP of the diets was calculated using 2 different equations. Dietary IVP 1 was determined as follows:

Dietary IVP 1 = IVP of each ingredient × concentration of each ingredient in the diet

Dietary IVP 2 was determined using the following equation (Madsen et al., 1992):

Dietary IVP 2 =analyzed IV of diet oil × analyzed dietary lipid (%) × 0.10.

The IVP of each diet calculated by each of the 2 procedures wasthen used to predict the IV of backfat using the following equations:

IV_backfat = 47.1 + 0.14 × dietary IVP / day (Madsen et al., 1992).

IV_backfat = 0.315 × dietary IVP + 52.4 (Boyd et al., 1997).

The use of the Madsen and Boyd equations with dietary IVP 1 showed a tendency for a positive correlation (r = 0.79, P = 0.06). There was no correlation between actual and predicted backfat IV using either equation with dietary IVP 2, nor was either equation able to predict belly fat IV.

Using dietary IVP 1 and dietary IVP 2, the relationship between the calculated IVP of the diet and backfat/belly fat IV was calculated using regression equations.Dietary IVP 1 explained 63% of the variability (P < 0.06) in analyzed backfat IV. Dietary IVP 2 explained 52% of the variability (P = 0.11) in analyzed backfat IV. Belly fat IV was not explained using either dietary IVP 1 or dietary IVP 2.

Key points

• Use of distillers dried grains with solubles at inclusion rates of more than 20% can lead to soft belly production.
• Addition of corn germ, tallow, palm kernel oil or glycerol did not ameliorate the problem with soft belly production. No difference in belly quality was observed among pigs fed any of the DDGS-containing diets.
• Iodine values for belly fat cannot be predicted from dietary IVP values.
• Dietary IVP is only a weak predictor of backfat IV.

Table 1. Belly quality of pigs fed experimental diets

^a,b Values within a row lacking a common superscript letter are different (P < 0.05).

Table 2. Iodine value (10 g/100 g) of backfat and belly fat

Figure 1. Relationship between the calculated iodine value product (IVP) of the diet and backfat IV

Figure 2. Correlations (r = 0.79; P = 0.06) between actual and predicted backfat IV calculated using the Madsen and Boyd equations and dietary IVP 1 values

This research report is based on unpublished research by J. W. Lee, D. Y. Kil, B. D. Keever, J. Killefer, F. K. McKeith, R. C. Sulabo, and H. H. Stein.