For most pork producers in North America, the use of distillers dried grains with solubles (DDGS) is now common. However, research and on-farm studies have shown that while DDGS is an important ingredient, appropriate feeding strategies must be used to optimize both feed cost and carcass quality.

Corn-derived DDGS contains approximately 10 per cent oil, which is rich in linoleic acid (C18:2), a polyunsaturated fatty acid that is primarily responsible for soft pork fat. Numerous studies have shown that when the content of DDGS is increased to 20 or 30 per cent of the diet, pork belly firmness declines, which makes further processing more difficult and can lead to poor product quality. Recent research has demonstrated that the linoleic acid content of belly fat is significantly higher in pigs that were fed diets containing just 10 per cent DDGS.

Some US pork processors are so concerned with the potential for reduced belly firmness and decreased carcass quality when pigs are fed DDGS that they have instituted a minimum iodine value (a measure of the degree of unsaturation of fat) for pork carcasses coming into their plants.

Withdrawing DDGS from the diet for a period of time prior to slaughter is one alternative strategy for improving pork fat quality when feeding diets containing DDGS. Several researchers have shown that the fatty acid profile of belly fat can be manipulated by changing the diet. One such study found that when researchers changed the diet to a more saturated fat source, the C18:2 content of belly fat was reduced by 60 to 70 per cent in the first two weeks after the diet change and by more than 90 per cent in six to eight weeks. Another positive impact of withdrawing DDGS from the diet is improved dressing percentage. Research by Gaines et al. (2007) showed that carcass dressing percentage was improved in pigs fed 30 per cent DDGS with a three- or six-week withdrawal period in the grower-finisher.

A comprehensive study evaluating different DDGS feeding strategies was recently completed by Xu et al. (2010). In this study, they looked at various DDGS feeding levels (0, 15 or 20 per cent DDGS) and withdrawal periods (0, three, six or nine weeks before slaughter) and the effects on pig growth performance, carcass quality and the fatty acid profile of pork fat.

In terms of growth performance, the overall average daily gain (ADG), gain to feed (G:F) and average daily feed intake (ADFI) were not affected by dietary content of DDGS or withdrawal period (Figure 1). The growth performance of the 30 per cent DDGS diets with no withdrawal (D30-0wk) however, was significantly different than the control diet (D0). This was inconsistent from other studies and the researchers hypothesised that it may have been due to variation in DDGS quality. As with the growth performance data, the carcass weights and meat quality measurements taken (longissimus muscle firmness, marbling and visual colour score) were not affected by either dietary DDGS content or withdrawal period.

Figure 1. Effect of DDGS level and withdrawal period on ADG, G:F and ADFI.

As summarised by Shurson and Stein (2009), the effect of increasing dietary DDGS content on carcass dressing percentage is inconsistent. Some studies have shown no change in dressing percentage, while others showed a reduction in dressing percentage when increasing amounts of DDGS are fed. In this study, dressing percentage was similar for pigs fed 0, 15 or 30 per cent DDGS and there was no effect of withdrawal period.

Increasing the content of DDGS in the diet increased the total polyunsaturated fatty acid content of belly fat. Linoleic acid (C18:2) content increased from 1.74 to 2.74 per cent for diets containing 0 to 30 per cent DDGS, respectively. As a result, pigs in the study had greater belly fat iodine values when fed increasing dietary DDGS (Figure 2). By increasing dietary DDGS withdrawal period from 0 to nine weeks before slaughter, the iodine value and C18:2 content of belly fat were significantly reduced (Figure 2).

Figure 2. Effect of DDGS inclusion and withdrawal period on fat quality

When compared with bellies from pigs in the control group (D0), those pigs assigned to either the 15 or 30 per cent DDGS inclusion and nine-week withdrawal (D15-9wk, D30-9wk) achieved a similar iodine value. However, the belly fat iodine values in pigs assigned to the other dietary treatments were greater than in pigs fed the control diet. According to the US Pork Composition and Quality Assessment Procedures, created by the National Pork Producers Council (2000), acceptable pork fat quality has an iodine value of less that 70. In this study, only the 30 per cent DDGS inclusion and zero week withdrawal treatment exceeded this value. As a result, it was also the only treatment to have significantly lower belly firmness.

The results of this study and others demonstrate that while DDGS is a valuable ingredient, inclusion needs to be managed in a feeding programme to avoid carcass quality issues. With any new or alternative ingredient, producers should consult with their feed consultant or nutritionist to optimize feed cost and economic return.

Sources

Gaines, A.M., Spencer, J.S., Petersen, G.I. and N.R. Augspurger. 2007. Effect of corn distillers dried grains with solubles (DDGS) withdrawal programme on growth performance and carcass yield in grow-finish pigs. J. Anim. Sci. 85(Suppl. 1):438 (Abstr).

National Pork Producers Council. 2000. Pork Composition and Quality Assessment Procedures. Natl. Pork Producers Counc., Des Moines, IA.

Shurson, G.C. and H.S. Stein. 2009. Boardinvited review: The use and application of distillers dried grains with solubles (DDGS) in swine diets. J. Anim. Sci. 87:1292-1303.

Xu, G., Baidoo, S.K., Johnston, L.J., Bibus, D., Cannon, J.E. and G.C. Shurson. 2010. The effects of feeding diets containing corn distillers dried grains with solubles, and withdrawal period of distillers dried grains with solubles, on growth performance and pork quality in grower-finisher pigs. J. Anim. Sci. 88:1388-1397.