The use of dried distillers grains with solubles (DDGS) in swine diets has increased dramatically in recent years due to the increased availability and cost competitiveness of this corn co-product compared to corn and soybean meal. Due to high ingredient prices, pork producers are using DDGS at levels up to 40% in growing-finishing diets to minimize feed costs. However, when high inclusion rates of DDGS are included in the diet, pork fat quality is reduced. Dried distiller’s grains with solubles contains approximately 10% corn oil, and a large proportion of the fatty acids in corn oil are polyunsaturated, especially linoleic acid (C18:2). The fatty acid composition of grower-finisher swine diets has a significant effect on the fatty acid composition of pork fat. Therefore, feeding increasing levels of DDGS results in reduced pork fat firmness. Soft pork fat is a concern for pork processors because it may lead to challenges related to carcass handling and fabrication, processing yields, shelf-life, product attractiveness, and acceptability in certain export markets. Tallow is a readily available, relatively low cost feed fat source that is low in polyunsaturated fatty acids and high in saturated fatty acids relative to corn oil. We hypothesized that adding a saturated fat source (e.g. tallow) to grower-finisher diets containing a high level (30%) of DDGS may alleviate the negative effects of DDGS on pork fat firmness. Therefore, the objective of this study was to assess the effects of fat source (tallow and corn oil from DDGS) independently, and in combination, on growth performance, carcass quality, and pork fat quality and apparent ileal fatty acid digestibility.

Two separate experiments were conducted to meet the objectives. The first experiment utilized 315 mixed sex pigs 71.4 ± 1.5 lbs that were housed in one of 40 pens and were assigned to one of four dietary treatments throughout the 81day grower-finisher period. Dietary treatments consisted of: 1) a corn-soybean meal control (C); 2) a corn-soybean meal diet containing 5% supplemental beef tallow (T); 3) a corn-soybean meal diet containing 30% DDGS (D); and 4) a corn-soybean meal diet containing 5% tallow and 30% DDGS (DT). All diets were formulated to contain a constant SID Lys: ME ratio. A three-phase feeding program was utilized with phase changes occurring when the average body weight (BW) of the pigs within each pen was within 5 lbs of the target weight for the phase change. Diet phase changes were made at 130 and 200 lbs BW. All pigs were harvested in a single group at a commercial plant.

Final BW was not affected due to dietary treatment (Table 1). Likewise, ADG did not differ among treatments. However, pigs fed T and DT consumed less feed compared to pigs fed C and D (P < 0.01). The reduction in feed intake was due to the high caloric density of diets containing tallow (T and DT). Furthermore, feed intake was also slightly reduced when feeding pigs D or DT (P < 0.04). The addition of DDGS may decrease the palatability, and therefore, feed intake of the diet. Feed to gain ratio was reduced for pigs fed T and DT (P < 0.01).

Effects of dietary treatment on carcass characteristics are shown in Table 1. Hot carcass weight was greater for pigs fed T and DT compared to pigs fed C and D (P < 0.01). The addition of 30% DDGS to the diets did not alter carcass yield, but adding 5% tallow to diets increased carcass yield. Backfat depth was reduced in D and DT carcasses (P < 0.02) compared to carcasses of pigs that were not fed DDGS containing diets, and was increased for pigs fed T and DT (P < 0.01) compared to pigs not fed tallow. Loin depth did not differ among treatments. However, calculated carcass fat free lean percentage was greater for pigs fed 30% DDGS diets compared to no DDGS (P < 0.05), but less for pigs fed 5% tallow containing diets (P < 0.01) compared to diets not containing tallow.

Table 2 shows the effects of tallow and DDGS on pork fat quality. As expected, feeding diets containing 30% DDGS (D and DT) resulted in softer pork fat as indicated by a greater belly flop angle (P < 0.01), and these results are consistent with previous research results. More specifically, the iodine value (IV), which is the ratio of unsaturated to saturated fatty acids, was increased while feeding D or DT (P < 0.01) regardless of fat depot site. There was a DDGS × tallow interaction (P < 0.03) for the IV of the belly fat. This indicates that when tallow was included in the 30% DDGS diets, the IV of belly fat decreased; however, when diets contained no DDGS, and 5% tallow is added, the IV increased. Polyunsaturated fatty acids (PUFA) were significantly higher in belly and backfat for pigs fed D and DT compared to C and T (P < 0.01). Similarly, monounsaturated fatty acids (MUFA) were greater for pigs fed T and DT in both fat locations. However, in backfat, MUFA levels were significantly decreased for pigs consuming D and DT (P < 0.01) compared to those pigs not fed DDGS containing diets.

In summary, feeding a combination diet of 5% tallow and 30% DDGS did not negatively impact growth performance. However, pork fat quality is not improved with the addition of tallow (saturated fat source) to diets containing DDGS (unsaturated fat source). Furthermore, the addition of tallow to DDGS diets does not improve belly firmness, even though it does reduce IV in belly fat, but not in backfat.