Lowering dietary fibre in finishing diets can improve performance
Monday, August 4, 2014
Research suggests that lowering the level of dietary fibre before marketing can improve feed efficiency, carcass yield and carcass IV, and reduce large intestine weight
by JANICE MURPHY
The use of cereal byproducts in finishing feeds is common. Researchers have extensively investigated the potential for distillers dried grains with solubles (DDGS) and wheat middlings (midds) as alternatives to traditional corn-based diets.
Research has shown that 30 per cent DDGS is the upper limit for feeding to finisher pigs without affecting pig performance. Feeding higher levels of DDGS reduces carcass yield and the unsaturated fat inherent in DDGS compromises carcass fat quality. Since packers associate soft and off-colour fat with discounts on processed products, such as bacon, some have begun devaluing pigs that have a high iodine value of carcass fat. Iodine value (IV) is an indirect measure of carcass fat firmness and is directly affected by the level of unsaturated fat in the diet. Since unsaturated fatty acids are softer or less firm, iodine value is often used as an indicator of the firmness of carcass fat.
Adding 20 per cent dietary wheat midds to finishing diets has also been associated with poorer performance – decreased weight gains and feed efficiency – and lower percentage carcass yield, hot carcass weight and backfat depth. Although midds are lower in fat than DDGS, they are higher in fat than corn, so increases in IV have also been reported with the addition of midds to finishing diets.
Reducing the level of DDGS in the diet prior to market has been successful in lowering IV and improving carcass yield. However, no research has yet revealed the length of time required and the level of reduction needed to achieve optimum carcass yield and fat quality when pigs are fed DDGS and midds in combination.
Researchers at Kansas State University recently performed a 90-day trial to determine the effects on growth performance and carcass characteristics of decreasing or completely removing fibre before market on pigs fed high dietary fibre, provided by wheat midds and DDGS.
Starting at an initial weight of 41 kilograms, 264 pigs were randomly allotted to one of six treatments. A positive control (corn-soybean meal-based) diet containing no DDGS or midds and a negative control diet with 30 per cent DDGS and 19 per cent midds were fed throughout the experiment. The other four treatments were arranged in a two-by-two factorial design (an experimental model where there are two separate variants, each having two levels) to test the main effects of length of fibre reduction (23 or 47 days before marketing) and fibre level fed during the reduction period (low or medium). Pigs on these treatments were fed the negative control before the reduction treatment. The low-fibre diet was the positive control diet, while the medium-fibre diet contained 15 per cent DDGS and 9.5 per cent midds.
Adding dietary fibre from wheat midds and DDGS decreased the bulk density of the dietary treatments (Table 1). From day 0 to 43, growth performance was no different between treatments when pigs were fed either the control or only the high-fibre diet (Table 2).
For the duration of the trial, however, as length of dietary fibre reduction increased, the data showed a significant decrease in average daily feed intake (ADFI) and improvement in feed efficiency, with no change in average daily gain (ADG). This dip in ADFI seems to have been driven by lowered feed intake in phases three and four of the experiment (days 43-67 and 67-90, respectively) as the level of dietary fibre was reduced.
An interesting observation was uncovered in the intake data. When pigs were switched from the high-fibre (low-energy) diet to the control (high-energy) diet, ADFI increased numerically during that time period. The researchers suggested that this increase in feed intake could be driven by the differences in bulk density. So, even though the pigs were switched to the low-fibre diet, they continued to consume the same volume of feed for a period of time; however the actual intake in kilograms was greater.
Increasing the amount of time that the control diet was fed by increasing the reduction time from 23 to 47 days resulted in a significant increase in backfat depth and, although it was not significant, a numerical reduction in lean percentage.
Lowering the fibre level in the diet significantly improved carcass yield, with an even greater response when the low-fibre diet was fed for 23 days and the medium-fibre diet came out in the middle (Table 3). Reducing the fibre level also significantly decreased full large intestine weight, with an even greater response when the low-fibre diet was fed during the reduction period, compared to the medium-fibre diet.
The IV measured in jowl fat significantly decreased as fibre reduction time increased and was significantly lower in pigs fed the low-fibre diet during the reduction period, compared to pigs fed the medium fibre diet. The 47-day reduction period improved IV by 78 and 27 per cent when pigs were moved to the low- and medium-fibre diets, respectively. These results indicate that IV is improved by approximately 0.35 grams per week for every 10 per cent DDGS removed from the diet.
The greatest impact of the fibre reduction strategy was on large intestine weights, with the response similar to that observed in carcass yield. Increasing the duration of fibre reduction significantly decreased both full and stripped large intestine weights. As fibre level increased in the diet from day 43-67 or 67-90, full and stripped large intestine weights also increased significantly. Pigs fed the low-fibre diet during the reduction period had significantly lower full large intestine weight than those fed the medium-fibre diet.
Previous research has suggested that feeding diets high in dietary fibre may indirectly cause increases to the animals' maintenance requirement by repartitioning nutrients away from the carcass into the visceral organs.
Based on these results, the researchers confirmed that lowering the level of dietary fibre before marketing can improve feed efficiency, carcass yield and carcass IV, and reduce large intestine weight. However, in order to determine the optimal duration of fibre reduction, the producer must first decide on the targeted response criteria. If the goal is to have an impact on carcass yield, shorter reductions are effective, while longer reductions would be necessary to improve carcass fat quality.
These decisions would need to be made with full knowledge of specific market demands. BP
Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.
Sources:
M. D. Asmus, J. M. DeRouchey, M. D. Tokach, S. S. Dritz, T. A. Houser, J. L. Nelssen, and R. D. Goodband. 2014. Effects of lowering dietary fibre before marketing on finishing pig growth performance, carcass characteristics, carcass fat quality, and intestinal weights. J. Anim. Sci. 2013.92:119–128
J.M. DeRouchey, M.D. Tokach, S.S. Dritz, R.D. Goodband and J.L. Nelssen. 2010. Iodine Value and Impact on Pork Quality: What is Iodine Value and Why Should We Be Concerned. Swine Profitability Conference, Manhattan, Kansas.
