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Emerging issues in swine nutrition

Using alternative ingredients in order to lower feed cost is now common practice in swine diets. However, now the challenge is to strike a balance between cost and quality.


Formulating swine diets over the past few years has increased considerably in complexity for nutritionists and producers. In order to help offset increased traditional cereal grain and protein ingredient costs, an increased use of alternative ingredients is now a common practice.

However, this change does not come without challenges. Most alternatives have increased nutrient variation, fiber and levels of unsaturated fatty acids. Therefore, balancing the economics of using alternatives so growth rate and carcass quality are not jeopardized is a juggling act now more than ever in formulating optimal swine diets.

Lower energy pig diets

One of the largest changes that swine nutritionists and producers are facing involves formulating diets to a lower energy level than in the past. This is due to the increased price for energy ingredients, such as added fat. This strategy has been a logical one for some producers economically, but does not come without some negative consequences.

One of the indirect decisions to lower diet energy is the increased dietary fiber that is often associated with this change. When corn and soybean meal are partially substituted with ingredients, such as wheat byproducts (middlings, shorts and bran), soybean hulls, corn byproducts (distillers grains and germ), canola meal or other high-fiber ingredients, we have to account for the negative aspects from the fiber they contain. The impact of the fiber 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.

There are many effects for feeding a diet lower in energy and higher in fiber. These effects include:

  • Average daily gain is usually reduced
  • Feed efficiency is always worse as diet energy decreases
  • Bulk density of the diet is reduced
  • Manure systems are influenced by an increased volume of manure production
  • Carcass yield is reduced

Use of byproducts

Since alternative ingredients in a typical corn-soybean meal diet are now a standard in the swine industry, the use of the term “alternative” is really no longer valid. Bakery byproducts, DDGS and wheat middlings are commonly found in swine diets and have become relied upon to economically supply dietary nutrients. However, all nutritionists and producers know that the variability of these ingredients is often greater than that of cereal grains and soybean meal they are replacing. Not only is there higher nutrient variability from load to load, often the digestibility of amino acids is less understood.

While these negatives cause less confidence in feed quality, they have not prevented the widespread use of these ingredients. Assigning an accurate nutrient value for some ingredients can be quite difficult. Nutrient values can be obtained from published sources, calculated from laboratory assays, estimated from nutrient values of other ingredients or a combination of these. All of these approaches have their own issues and none are perfect.

Energy values

Unfortunately, the nutrient that is most difficult to estimate because it cannot be measured directly in a laboratory is energy (metabolizable or net energy). Energy values can be estimated from chemical analysis, such as analyzed moisture, neutral detergent fiber, acid detergent fiber, crude fiber, starch, fat and crude protein. However, the equations used for the estimates were, most often, not developed with the ingredient for which you wanted an energy estimate.

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. It is also important to use the same lab and same estimation equation for the known ingredient as the unknown ingredient.

Impact of lower energy diets

Feeding pigs lower energy diets from a milling perspective can greatly impact the throughput in two main ways. First, lower energy diets worsen feed conversion, or the amount of feed required for each pig to reach a desired market weight. Thus, entire mill tonnage must be increased to feed the same number of pigs. Secondly, lower energy diets decrease the bulk density of the diet, and this magnitude 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 percent to 40 percent byproducts (DDGS and wheat middlings, for example) cannot fit into a three-ton mixer.

Feed trucks often cannot maximize the legal weight capacity of the truck because the feed simply won’t fit into the compartments. Also, bulk density affects feed handling characteristics (flow ability) that may lead to a higher number of feed outages once delivered to the farm.

Research is underway to determine whether further processing of the high fiber 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 fiber ingredients.

Avoiding negative impacts on carcass quality

Carcass yield.  Previously, we discussed the fact that as dietary energy decreases, dietary fiber often increases from various ingredients such as wheat middlings or DDGS. One clear negative from this is a reduction in carcass yield percentage (carcass weight/live weight X 100). This is important as the vast majority of swine producers are paid on a carcass-weight basis. There are a couple direct reasons lower energy diets and higher fiber ingredients can have an effect on carcass yield.

First, dietary fiber leads to increased large intestine weight and the amount of digesta present in the large intestine at market. Since this weight is lost at time of evisceration, the weight of the carcass relative to its live weight is negatively impacted. Secondly, pigs fed lower energy diets usually have reduced backfat, which causes yield to be lower.

Practically, this challenge can be managed by reducing the level of dietary fiber in the last diet(s) prior to market. Research has shown that removing fibrous containing ingredients for as little as two to three weeks prior to slaughter can fully restore yield, with partial fiber reductions having intermediate improvements. This is one reason that generally DDGS and/or wheat middlings is reduced in the final diet prior to marketing compared to higher inclusion levels in growing and finishing diets.

Carcass fat quality.  While several of the common ingredients used to partially replace corn and soybean meal contain higher levels of fiber, they also can contain higher concentrations of unsaturated fat, which in turn gets deposited in the pig’s body in that form. Examples of this are bakery byproducts, DDGS and even wheat middlings. Carcass fat composition is very predictable in that fatty acid profiles and fat firmness are altered as the fat type (unsaturated or saturated) is added to the diet. The impact of this carcass fat change on product value varies by customer. Thus, processors with strong Japanese export business and fresh-belly customers are quite concerned with fat firmness. However, other processors that predominantly market fresh pork to domestic markets or bellies for microwavable bacon are less concerned with fat firmness.

The ethanol industry is currently adopting technologies to remove between 2-5 percent of the oil from traditional DDGS (normally 10-11 percent crude fat). One argument for the use of reduced oil DDGS in swine finishing diets is to lessen this negative effect on carcass fat quality. In fact, feeding any ingredient that has reduced levels of unsaturated fat helps mitigate the softening of carcass fat. However, by removing a portion of the oil from DDGS, the energy value decreases and fiber level increases, exacerbating the problems already discussed with lower energy ingredients.

Producers have learned to manage carcass fat composition requirements of their processor by reducing levels of certain ingredients fed throughout the growing and finishing period, or by reducing or withdrawing unsaturated fat ingredient sources for the last portion of the finishing period. However, a reduction or removal of these ingredients takes a longer period of time than that to recover carcass yield. This area is and will continue to be a major challenge for both nutritionists and producers to optimize low cost diets while meeting processor specifications for fat quality in the future.

The future of low energy diets

Because of the high cost of grain, it appears that use of lower energy, higher fiber diets will continue to increase. With increased use, more accurate nutrient values will need to be established. Pig producers may change their systems to allow more time to achieve the same market weight as that achieved with higher energy diets. Owning more space and feeding lower energy diets may be more economical than feeding higher energy diets. Most importantly, the industry will become increasingly adept at developing feeding strategies that maximize the use of these ingredients while minimizing their negative impacts.

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