Due to inevitable price fluctuations of feed ingredients, pork producers and nutritionists are frequently seeking low cost feed ingredients capable of reducing overall feed expense without compromising pig performance and carcass quality. DDGS is commonly added to swine diets at minimal levels (10-20 per cent inclusion) to decrease diet cost without diminishing pig performance.

Currently, there is a tremendous economic advantage for feeding diets containing even greater levels (40 to 50 per cent) of DDGS. No data have been published regarding the effects of feeding grower-finisher diets containing 40 per cent or more DDGS on growth performance and carcass quality. Whitney et al. (2006) showed that growth performance and carcass characteristics of growing-finishing pigs are reduced when feeding diets containing 30 per cent DDGS compared to diets containing 10 or 20 per cent DDGS when diets were formulated on a total lysine basis. However, Xu et al. (2010) demonstrated that if diets are formulated on a digestible amino acid basis, DDGS may be added to growing-finishing swine diets at levels up to 30 per cent without compromising growth performance and carcass quality.

The addition of DDGS to grower-finisher diets may only be economical intermittently throughout the grower-finisher phase depending on the market price and availability of DDGS. An earlier study conducted in the University of Minnesota lab showed that the rapid inclusion and removal of 20 per cent DDGS in diets for growing-finishing pigs does not affect pig performance or carcass characteristics; however, rapid inclusion and removal of 40 per cent DDGS in diets may reduce daily feed intake and hot carcass weight (Hilbrands et al., 2008). These results provided the first evidence in the feasibility of capturing increased economic returns by rapidly introducing or removing DDGS (at or below 20 per cent inclusion) from grower-finisher diets without compromising pig performance. However, dietary cost-savings achieved from intermittently feeding a 40 per cent DDGS-based diet may be diminished due to the negative effects on performance and carcass characteristics associated with feeding a high level of DDGS.

Variability in nutrient content and digestibility among DDGS sources is well known. The physical appearance, chemical composition and nutrient digestibility of DDGS can vary considerably depending on the source due to differences in processing and drying procedures (Cromwell et al., 1993). Modern ethanol plants generally produce DDGS that has greater concentrations of fat, lysine and metabolisable energy (Spiehs et al., 2002) and improved digestibility of phosphorus (Whitney and Shurson, 2001) compared to values published in NRC (1998).

Drescher et al. (2009) demonstrated that DDGS sources of low digestible crude protein and lysine may reduce pig performance, while higher digestible amino acid (AA) DDGS sources can support performance similar to a corn-soybean meal diet. Therefore, it appears that some of the inconsistent growth and carcass quality responses from feeding DDGS diets may be due to quality and amino acid digestibility differences in the DDGS sources used.

The effects of switching diets that contain DDGS with low or high amino acid digestibility throughout the grower-finisher phase have not been documented. If it is possible to rapidly introduce and remove DDGS of differing amino acid digestibility without compromising pig performance, pork producers would be more likely to include DDGS at high levels in commercial grower-finisher swine diets. Therefore, the University of Minnesota research group conducted an experiment to determine whether relatively high dietary levels of high digestible amino acid DDGS can be fed throughout the grower-finisher phase to achieve acceptable performance and carcass quality. Additionally, they sought to determine if intermittent inclusion of DDGS of different estimated amino acid digestibilities into diets can be achieved without affecting feed intake and carcass composition.

A total of 324 pigs were housed in one of 36 pens and assigned to one of six dietary treatments. Dietary treatments consisted of:

1. a corn-soybean meal control (CON)
2. a corn-soybean meal diet containing 40 per cent low AA digestibility DDGS (Lo)
3. a corn-soybean meal diet containing 40 per cent high AA digestibility DDGS (Hi)
4. Lo and CON diets alternated throughout the trial (Lo-CON)
5. Hi and CON diets alternated throughout the trial (Hi-CON) and
6. a diet alternating between Hi and Lo (Hi-Lo).

Feed switches between DDGS and non-DDGS based diets (Lo-CON and Hi-CON), as well as, between high amino acid digestibility DDGS diets and low amino acid digestibility diets (Hi-Lo) were implemented at phase changes. All phase changes were made on a pen basis when the average body weight (BW) of pigs in the pen was within 5lb. of the target weight for the phase change.

Final bodyweight was affected by both the addition and amino acid digestibility of DDGS being fed with the final bodyweight of pigs continuously consuming a DDGS based diet lower than those pigs consuming a corn-soybean meal diet. However, the continuous consumption of a low amino acid digestible DDGS diet resulted in lower growth rates than the continuous consumption of a high amino acid digestible DDGS diet when compared to corn-soybean meal fed pigs.

Final bodyweight was lower (P<0.05) for Lo and Hi-Lo pigs than CON pigs while Hi pigs only tended to have lower (P<0.10) final bodyweight than CON pigs.

Considering the differences in final bodyweight, it is not surprising that gain followed the same trend. Average daily gains were reduced (P<0.05) for Lo and Hi-Lo pigs when compared to the CON pigs while Hi pigs only tended to gain less (P<0.10) than the CON pigs.

Pigs continuously fed the Lo diet exhibited lower average daily feed intake than the CON pigs (P<0.10). This suggests possible palatability issues with the low amino acid digestibility DDGS diet.

Hasted et al. (2004) demonstrated that when given a choice pigs prefer a corn soybean-meal diet over a diet containing DDGS, and that as the level of DDGS in the diet increases average daily feed intake decreases.

Feed efficiency was not affected by treatments.

Carcass traits were also negatively affected by the amount of DDGS fed as well as the amino acid digestibility of the DDGS being used, with Lo and Hi-Lo pigs possessing smaller loin muscle area than the CON pigs (P<0.05). Hot carcass weights were also reduced (P<0.05) for Lo and Hi-Lo pigs, while there was only a tendency for lighter (P<0.10) hot carcass weight in Hi pigs when compared to CON pigs. Percentage carcass lean was not affected by dietary treatment whereas dressing percentage was lower for those pigs continuously consuming the Lo diet (P<0.05). The intermittent consumption of DDGS did not affect growth performance or carcass quality with Lo-CON and Hi-CON pigs performing similarly to the CON pigs.

Results from this study suggest that pigs continuously fed a 40 per cent low digestible amino acid DDGS based diet formulated on a Standardized Ileal Digestible (SID) amino acid basis, experience lower average daily gain, reduced average daily feed intake, lighter hot carcass weight and smaller loin musce area than pigs continuously consuming a corn-soybean meal based diet.

These results are consistent with previous findings (Whitney et al., 2006) where diets containing 30 per cent DDGS resulted in reduced growth performance and carcass characteristics in growing-finishing pigs when compared to pigs consuming 0, 10 or 20 per cent DDGS diets.

This suggests that the estimated SID amino acid value and/or calculated ME content of the Lo diets was overestimated when formulating diets.

It appears that the use of a high digestible amino acid DDGS source may be able to diminish the negative responses incurred in growth performance and carcass characteristics when feeding DDGS at a 40 per cent level, suggesting that estimated SID amino acid values and metabolisable energy content of the Hi diets was more accurate than values obtained for the Lo diet formulations.

The periodic inclusion and removal of 40 per cent DDGS from the diets of finishing pigs did not adversely affect growth performance or carcass characteristics regardless of the amino acid digestibility of DDGS being fed.

May 2013