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Effects of Dietary Ingredients On Carcass Quality Measures

Three separate Kansas State University (KSU) research trials confirm that adding fat to swine diets increases carcass iodine values. The exact impact on the carcass depends on the fat source

Three separate Kansas State University (KSU) research trials confirm that adding fat to swine diets increases carcass iodine values. The exact impact on the carcass depends on the fat source.

In the first experiment, researchers found that adding ingredients high in unsaturated fats, such as dried distiller's grain with solubles (DDGS) or extruded expelled soybean meal (EESM), have a greater effect on iodine value of the carcass fat than choice white grease (CWG), even when the calculated dietary iodine values were similar.

When comparing corn-based vs. sorghum-based diets in a second research trial, KSU researchers concluded that feeding sorghum reduces iodine value when compared to feeding corn. They say sorghum could potentially be used to replace corn when iodine values approach the maximum level.

Results of the third research trial suggested for each 10% increase in DDGS added to the diet, iodine value increases by 1.5 to 3 g./100g., depending on where the fat is stored in the body.

The research trials were based on the knowledge that feeding ingredients containing unsaturated fats can have a large impact on carcass iodine values. Iodine value is a measure of the level of unsaturation of fats, and therefore a measure of fat firmness. Calculating a diet's iodine value appears to underestimate the impact of unsaturated fat sources on carcass fat iodine value as compared to saturated fat sources. This indicates dietary iodine values may not be an accurate predictor of carcass iodine value.

For processors targeting the Japanese market or the fresh belly market, fat softness is becoming a major issue. These processors have measured iodine value of carcass fat and, to date, have asked producers to alter diets to be below a maximum iodine value target. Production costs could further increase if lower-cost ingredients, such as bakery products, DDGS or EESM, must be limited or eliminated from the diets.

In the first research trial, researchers took a look at the impact on finishing pig growth performance and fat quality if choice white grease was added to corn and sorghum-based diets. Sorghum is often an economical replacement for corn in some swine diets. The researchers noted that Triumph Foods, St. Joseph, MO, has set a maximum jowl iodine value of 73.

Previous research showed that adding an unsaturated fat source during any portion of the finishing phase can result in iodine values above 73. Researchers speculated that because sorghum has a lower oil content than corn, a lower carcass iodine value may result.

Researchers used 120 crossbred barrows and gilts with an initial weight of 119.9 lb. in an 83-day experiment. Experimental treatments were arranged based on whether the diet included corn or sorghum, if fat was added and the gender of test animals. The fat options included 0, 2.5 or 5% CWG.

Pigs fed sorghum-based diets had increased average daily gain (ADG) compared to pigs fed corn-based diets. The higher ADG was due to an increase in average daily feed intake (ADFI) for pigs fed sorghum-based diets.

Typically, the researchers say they would expect similar ADG and slightly poorer F/G for pigs fed sorghum-based diets compared to corn-based diets. Pigs fed increasing levels of CWG improved ADG, too.

The results shown in Tables 1 and 2 confirm that added dietary fat improves pig growth. Pigs fed corn-based diets had improved dressing percentage, reduced 10th-rib backfat and improved lean percentage compared with pigs fed sorghum-based diets. The results also confirmed barrows had lower lean percentages than gilts.

The researchers found substituting sorghum for corn in diets for finishing pigs can be an effective way to reduce iodine value without affecting growth.

In the second trial, KSU researchers found that DDGS and EESM can be economical to feed to growing and finishing pigs. However, using these ingredients increases the dietary fat level when they are substituted for corn or soybean meal.

When dietary fat level increases, the result is softer carcass fat. The trial to study the effects of DDGS and EESM on growth performance and fat quality included 120 barrows with an initial weight of 105.7 lb.

Diets included: a corn-soybean meal control diet with no added fat; corn-EESM diet with no added fat; corn-EESM diet with 15% DDGS; corn-soybean meal diet with 15% DDGS and 1.55% CWG; corn-soybean meal diet with 3.25% CWG; and corn-soybean meal diet with 4.7% CWG. Diets were formulated to have three dietary iodine value levels of 42, 55 and 62, to compare the impact of the fat source within dietary iodine levels.

Jowl and backfat samples were collected after 83 days. The results indicated pigs fed the control diet, EESM or 4.7% CWG had increased ADG compared with pigs fed either diet containing 15% DDGS (Tables 3 and 4).

Pigs fed the control diet had increased ADFI compared with all other treatments. Pigs fed the EESM with 15% DDGS and the diets with 4.7% CWG had improved feed/gain compared with pigs fed the control diet and pigs fed DDGS with CWG. Pigs fed high CWG diets had greater loin depth compared with pigs fed low-CWG diets.

Pigs fed either of the diets with 15% DDGS had increased backfat iodine values when compared with pigs fed diets without DDGS. Pigs fed EESM had increased backfat iodine values when compared with the control diet or diets with 3.25 or 4.7% CWG.

Adding DDGS, using EESM or adding CWG to the control diet increased iodine value of jowl fat. Feeding ingredients with higher levels of unsaturated fat, such as EESM and DDGS, had a greater impact on fat iodine value than CWG, even when diets were formulated to similar iodine value levels.

The results confirm that adding fat to finishing diets improves growth performance. Feeding DDGS in this trial resulted in decreased ADG and ADFI. Adding DDGS, EESM or CWG increased iodine value and reduced the percentage of saturated fatty acid.

Feeding ingredients with higher levels of unsaturated fat, such as EESM and DDGS, had a greater impact on fat iodine value than CWG, even when dietary iodine values were similar. Feeding pigs a diet with more unsaturated fat may lead to jowl fat and backfat with more similar iodine values.

In the third trial, KSU researchers used 1,112 pigs in a 78-day trial to evaluate the effects of including DDGS at 0, 5, 10, 15 or 20% of the grow-finish diet.

Previous research has shown that DDGS levels could be fed at up to 30% of the diet before growth performance was reduced. The impact of DDGS on growth performance is blamed on product variability between batches. Variations in palatability are suspected to influence performance.

As noted earlier, DDGS has been shown to impact carcass characteristics by reducing percent yield and carcass weight, while making carcass fat softer and bellies less firm.

The research barn was topped at Day 57 to simulate normal pig marketing under commercial production practices. The three heaviest pigs from all pens were removed and marketed. Six barrows from among the tops were randomly chosen from each treatment to collect data for analysis. The remaining pigs were shipped at the end of the experiment for collection of standard carcass data. Samples were collected and frozen for further processing and analysis.

Overall, ADG and ADFI decreased with increasing DDGS (Table 5). However, the greatest difference in ADG occurred when DDGS was increased from 15 to 20% of the diet. Pigs fed 5% DDGS tended to have improved F/G compared with pigs fed other dietary treatments. There were no differences in live slaughter weight or loin depth. Carcass weight and percent yield decreased with increasing DDGS in the diet. Increasing DDGS tended to decrease backfat and fat free lean index (FFLI).

Backfat, jowl fat and belly fat iodine values and percentage of C 18:2 fatty acid (the major unsaturated fatty acid) increased with increasing the DDGS in both topped pigs (Table 6), and pigs marketed at trial completion (Table 7). Percentage saturated fatty acid in backfat and belly fat decreased with increasing DDGS in both sets of pigs.

Increasing DDGS reduced ADG, carcass weights and percent yield. The reduction in ADG was driven by a reduction in ADFI as DDGS level increased in the diet. The reduced carcass weights equated to a reduction of 4 lb./pig fed the 20% DDGS. Iodine values increased as DDGS levels were increased. For each 10% of DDGS added to the diet iodine value increased by 1.6, 2.4 and 3.0 g./100g. in the jowl fat, backfat and belly fat respectively.

The researchers concluded, based on these results and previously conducted research trials, the linear reduction in yield and increase in iodine value must be considered when determining the economic value of DDGS.

Researchers: Justin M. Benz; Sara K. Lineen; Joel M. DeRouchey; Mike Tokach; Steve Dritz, DVM; Jim Nelssen; and Robert Goodband, Kansas State University. Contact Benz at (785) 532-1270.

Click below to view the accompanying tables

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