Because of the rapid increase in ingredient prices in recent years, swine producers have explored alternative ingredients and alternative formulation strategies in attempts to minimize feed costs. A strategy that makes sense for some producers is to lower the energy density of the diet, either by removing dietary fat or by using lower energy ingredients. In this paper and presentation, the authors explore the impact of using lower energy diets and help provide guidelines to make sure that all potential ramifications are considered.

For many of us, feeding a low-energy diet used to mean feeding a grain-soybean meal based diet without added fat. When we talk about low-energy diets now, not only is the energy level of the diet reduced, but the fibre content is often greatly increased as corn and soybean meal are displaced with ingredients, such as wheat byproducts (middlings, shorts, bran, etc), canola meal, soybean hulls, corn byproducts (distillers grains, germ, bran, etc) or other high fibre ingredients. The impact of the fibre components are often difficult to separate from the impacts of the energy level itself when assessing the influence of lower energy diets on pig performance.

What happens when pigs are fed lower energy, higher fibre diets?

• ADG is usually reduced; however, the magnitude depends on genetics, energy level and environment
• Feed efficiency is always worse
• Carcass yield is reduced (again magnitude varies, but yield will go down due to increase in large intestine content and weight)
• Bulk density of the diet is reduced, thus, transportation cost can increase if more loads of feed are required and a lower quantity (weight) of feed can be stored at the production site.
• Although relatively minor compared to other impacts, iodine value, which is an indicator carcass fat softness, has increased in some trials indicating carcass fat is softer for pigs fed lower energy, higher fibre diets. The reason for this response may be because fat usually becomes a higher percentage of dietary energy in high fibre diets and because pigs fed diets with higher fibre levels usually have less backfat, which leads to higher iodine values.
• Manure systems are influenced by an increased volume of manure production and manure that may result in more retained solids in storage facilities.

The key to understanding whether low-energy diets are economically justified is to understand whether the costs of these negative impacts are offset by the diet cost savings from using the low energy ingredients. So how do you go about estimating these impacts?

Assigning Nutrient Values for an Ingredient

First, we need to know the nutrient values for the low energy ingredient to understand how much dietary energy will be reduced with the inclusion. Assigning nutrient values is not as easy as it sounds. Nutrient values can be obtained from published sources, calculated from laboratory assays, estimated from nutrient values of other ingredients, or a combination of all of the above. All of these approaches have their own issues and none is perfect. Often, lower energy ingredients are more variable in composition than corn and soybean meal and the variability must be considered in formulation to avoid over-valuing the ingredient.

The nutrient that is most difficult to estimate because it cannot be measured directly in a laboratory is metabolisable or net energy. Energy values can be estimated from chemical analysis for other nutrients, such as moisture, neutral detergent fibre (NDF), acid detergent fibre (ADF), crude fibre, starch, fat and crude protein; however, the equations used for the estimates were, most often, not developed with the ingredient for which you want to estimate an energy value.

There are several sources of equations that can be used to estimate the energy value of an ingredient including NRC (1998); INRA (2004); or Rostagno (2011).

If using a standard equation to estimate energy value, the value being estimated should be related to the energy value of a known ingredient, such as corn, and the percentage change in energy relative to the value for corn with the same equation should be used to estimate the energy value for the ingredient in your formulation matrix.

For example, corn has a ME content of 3,420kcal per kg in NRC (1998). Using a standard equation, you may calculate that the ME of wheat midds as 2,706kcal per kg from chemical analysis of your source of wheat midds. This is 79 per cent of the energy value of corn. However, if you obtain a chemical analysis of your corn from the same lab that analysed your wheat midds and used the same equation that you used to estimate the energy value of wheat midds, you may estimate the energy value of corn at 3,300kcal per kg. Thus, the wheat midds would have 82 per cent (2,706/3,300) of the energy value of corn. Thus, you would want to multiply the 82 per cent times 3,420 to put the wheat midds energy value on a NRC equivalence to compare to the energy value of corn from NRC (1998). Thus, the energy value for this wheat midds source would be estimated at 2,804 (82 per cent × 3420) instead of 2,706kcal per kg.

The important point here is to not use a standard equation to estimate the energy value for one ingredient and use a book value to estimate the energy value for another ingredient. It is also important to use the same lab and same estimation equation for the known ingredient as the unknown ingredient. They need to be compared on the same basis.

Impact of Dietary Energy on ADG, ADFI and F/G

As the energy density of the diet increases for pigs under field conditions, most pigs have linear improvements in average daily gain (ADG) through the highest energy level that can be fed. The only time that this does not occur is when pigs consume feed beyond their needs for maximal protein deposition. This can occur with sick pigs that have lowered levels of protein deposition or for healthy pigs with very high levels of feed intake. The rate of improvement in ADG with each change in energy density can vary. However, for calculations, a simple rule of thumb is that ADG increases by about three per cent for every 100kcal per kg increase in ME content of the diet. Conversely, ADG decreases by three per cent for every 100kcal per kg decrease in ME content of the diet.

Another part of the reason that there is variability in the impact of dietary energy on ADG is that some low energy ingredients have more negative impact on ADFI than others. As dietary energy is decreased, pigs often increase feed intake, such that energy consumption is not reduced as much as the diet energy was reduced. However, as energy density decreases further and certain fibre components increase in the diet, the pigs cannot continue to consume more feed. Thus, feed intake and energy intake eventually decrease. This is one of the reasons that moderate fibre levels can have a smaller negative impact on growth performance relative to the large negative effect of higher levels.

The most consistent response to decreasing dietary energy is poorer feed efficiency. If the diet energy is valued correctly, feed efficiency will worsen linearly as dietary energy decreases.

Estimating Cost of Decreased Growth Rate

The cost of the poorer feed to gain ratio (F/G) with lower energy diets is easy to determine because feed cost per pig must still be lower with the higher feed usage to make the lower energy diet economical. Assigning the economic value on growth rate on the other hand is a bit more difficult. The key question that must be answered is whether pigs can achieve the same ideal market weight when low or high energy diets are fed. If excess space is available, such as in the winter time, the cost of the reduced ADG may be low and only a factor on the last pigs removed from the barn. If however, space is limited, such as during the summer months, the decreased ADG must be valued on a margin over feed basis and can quickly nullify any advantage of reduced diet cost from using a lower energy diet, especially when market prices are considerably higher than feed costs.

What about Value and level of Impact on Other Variables?

As mentioned above, reductions in dietary energy are accompanied by increases in dietary fibre components. The increases in dietary fibre lead to increases in large intestine weight at market. Thus, yield is reduced. Pigs fed high fibre, lower energy diets usually have reduced backfat, which further reduces yield. The impact of dietary energy on yield can be variable but a value of 0.25 per cent reduction in yield for every 100kcal per kg reduction in dietary energy can provide an estimate for base economic calculations. If increasing the lean percentage will further increase lean premium, the positive impact of lowering energy density on lean percentage should be included in the economic equation.

The cost of decreasing the bulk density of the diet will vary greatly depending on how feed is processed and delivered. Low energy diets will increase the volume required to transport and store the same quantity (tons) of feed. For example, most feed mills have found that three tons of a diet containing 30 to 40 per cent by-products (DDGS and wheat middlings for example) cannot fit into a three-ton mixer. Feed trucks often cannot maximise the legal weight capacity of the truck because the feed simply will not fit into the compartments. Thus, some mills have purchased mixers with a larger volume and other mills are mixing a smaller quantity with each batch. Both of these solutions add cost to the system.

Currently, considerable research is being conducted to determine whether further processing of the high-fibre ingredients, such as reducing particle size, will increase their feeding value. These costs will also need to be accounted for in estimating the value of high fibre ingredients.

The softness of the fat, which is often measured as the iodine value of the fat, is more closely related to dietary fat content and composition than fibre level. However, it does appear that feeding low energy diets can increase the unsaturation of the body fat stores, which results in higher iodine value readings. This impact can be small at only 1 or 2mg per gramme, which is similar or smaller than the difference between barrows and gilts, but should be considered if iodine values are close to the processors maximal permissible value.

Another potential downside of feeding higher fibre diets that needs to be considered is variability. The low-energy ingredient itself can often be much more variable in composition than the grain and soybean meal that it is replacing in the diet. Also, some trials indicate that lowering the energy density of the diet can increase the variability in growth rate of pigs in the barn. Again, this is a minor consideration compared to the impacts on pig performance and carcass yield; however, it should be considered.

Can Negative Effects be Reduced through Management Strategies?

Considerable research is currently being done to minimise the negative impact of feeding lower energy, high fibre diets. While all the negative effects cannot be eliminated, it does appear that we can reduce the impact by switching pigs to higher energy diets for three or more weeks before market.

For example, in a recent trial, the authors found (Asmus et al., 2011; Table 1) that withdrawing pigs from a high NDF diet containing DDGS and midds before market can improve F/G, carcass yield, iodine value and reduce large intestine weight. However, the optimal length of withdrawal depends on the response criteria targeted. Shorter withdrawal was sufficient to recover the yield response but longer withdrawal was needed to make greater changes in overall feed efficiency or iodine value.

Table 1. Effect of dietary Neutral Detergent fibre (NDF) level prior to marketing on finishing pig performance and carcass characteristics¹
1 A total of 264 pigs (PIC 327 × 1050, initial BW=40.9kg) were used in this 90-d trial.
2 Low = corn-soybean meal diet with 0 per cent DDGS and 0 per cent midds with NDF of 9.3 per cent.
3 High = corn-soybean meal diet with 30 per cent DDGS and 19 per cent midds with NDF of 19 per cent.
4 Medium = corn-soybean meal diet with 15 per cent DDGS and 9.5 per cent midds with NDF of 14.2 per cent.
5 Percentage yield was calculated by dividing HCW by live weight obtained at the farm before transport to the packing plant.
6 Carcass characteristics other than yield and iodine value were adjusted by using HCW as a covariate.
a Linear effect of withdrawal time P<0.01.
b Fibre level fed during withdrawal P<0.05.

Do Enzymes Provide More Benefit in Low-energy Diets?

In theory, pigs fed lower energy, higher fibre diets should benefit more from added enzymes than pigs fed grain-soybean meal based diets because the higher fibre diets provide more substrate for the enzymes. Unfortunately, most of the data to this point indicates that although certain enzymes can improve the digestibility of certain fibre components, the benefit is not great enough or consistent enough to provide a general recommendation to include particular enzymes in low energy diets.

Summary

Because of the high cost of grain, it appears that use of lower energy, higher fibre diets will continue to increase. With increased use, we will become more accurate with our estimates of the energy content and other nutrient values for these ingredients.

We may change our systems to allow more time to achieve the same market weight achieved with higher energy diets. Owning more space and feeding lower energy diets may be more economical than feeding higher energy diets.

We will also increase our understanding of the impact of their use on pig performance and carcass composition. Most importantly, we will become increasingly adept at developing feeding strategies that maximize the use of these ingredients while minimizing their negative impacts.

References

Asmus, M.D., J.M. DeRouchey, J.L. Nelssen, M.D. Tokach, S.S. Dritz, R.D. Goodband and T.A. Houser. 2011. Effects of Lowering Dietary Neutral Detergent fibre Levels Prior to Marketing on Finishing Pig Growth Performance, Carcass Characteristics, Carcass Fat Quality and Intestinal Weights. KSU Swine Day Report. access via www.KSUswine.org

INRA. 2004. Tables of Composition and Nutritional Value of Feed Materials. 2004. Eds. Daufant, D., J.M. Perez and G. Tran. Wageningen Academic Publishers, The Netherlands.

NRC. 1998. Nutrient Requirements of Swine, 10th ed. Natl. Acad. Press, Washington, DC.

Rostagno, H.S. 2011. Brazilian Tables for Poultry and Swine. Universidade Federal de Vicosa-Departmanto de Zootecnia.

Further Reading You can view the full proceedings by clicking here.