Rethinking the Measures Of Dietary Efficiency

The livestock industry has always competed with other sectors of the economy for corn and other feed ingredients. The most common example is the broad use of corn in the human food sector, where the grain is used for everything from breakfast cereals to sweeteners. Generally, growth in the human food and livestock sectors occurred at a balanced pace. But, more recently, the very rapid growth of another

The livestock industry has always competed with other sectors of the economy for corn and other feed ingredients. The most common example is the broad use of corn in the human food sector, where the grain is used for everything from breakfast cereals to sweeteners.

Generally, growth in the human food and livestock sectors occurred at a balanced pace. But, more recently, the very rapid growth of another competitor — the biofuels sector — has disrupted this balance. Consequently, as oil prices rose, the price and availability of corn followed, and the brunt of the escalating demand was felt by everyone associated with livestock feeding.

And, as human food and biofuel manufacturers tapped into more and more of the corn supply, the creation of new coproducts was a natural result. The human food sector generated bakery byproducts, corn gluten meal, corn gluten feed, distillers' grains and distillers' solubles, to name a few. The biofuels sector has dramatically increased the availability of corn distillers' dried grains, with or without solubles added. The increased use of corn for fuel has therefore focused more attention on feeding these by-products to pigs.

As swine feeding programs began adding more coproducts to traditional corn-soybean meal blends, new questions on how to evaluate their nutrient value surfaced. The fact that coproducts typically are less consistent in their composition and nutrient availability makes this task even more difficult.

European producers have a long history of using coproducts in pig diets. Table 1 offers some perspective on how the composition of U.S. swine diets differs from those in the European Union and The Netherlands.

Whereas typical U.S. swine diets have contained about 65% cereal grains (corn, milo, wheat, barley — depending on the region) and 20% coproducts of oilseed processing, namely soybean meal, the Europeans have used much smaller quantities of cereal grains and much higher quantities of coproducts from both the oilseed and human food industries.

While corn and soybean meal will likely remain the staple ingredients in practical U.S. swine diets in the foreseeable future, there is no denying that coproducts will play a bigger role. The survival of the pig industry demands it.

When corn reached the unimaginable price of $8/bu. last year, the volatility on the market was clearly demonstrated. Even though grain prices have settled back to more historically typical levels, we must be prepared for such dramatic changes in the future.

Adaptability in feed markets is important for another reason. The use of alternative feed ingredients gives pork producers more options in their feeding programs; more options generally translate into greater success.

Evaluating New Ingredients

As the market conditions change and producers consider new ingredients, they must understand their chemical composition, including energy, amino acids, vitamins and minerals. Not all nutrients in an ingredient are biologically available, so studies are required to measure the availability of energy, amino acids and phosphorus. Although other nutrients may be of interest, these are the most critical in basal ingredients.

Evaluating energy values is complicated by at least two unique issues. First, energy is not a single entity, but rather a compilation of four energy sources — starch, fats, fiber and protein. Each energy source is used by the pig in different ways.

For example, most starch is digested fairly easily and absorbed from the intestinal tract as glucose, an efficient energy source. However, some starch is resistant to digestion and passes through the small intestine and becomes fermented into volatile fatty acids in the lower gut. Volatile fatty acids are not used as an energy source as efficiently as glucose.

Nutritionists are just beginning to understand the portion of starch in a raw feedstuff that is resistant to digestion. Unfortunately, very little is known about how processing, such as drying, affects the portion of starch that is resistant.

Determining the availability of amino acids and phosphorus also presents technical challenges, but generally accepted procedures are useful and fairly accurate in providing this information.

Amino acids are used less efficiently for energy than starch because amino acids have to be broken down by the pig to remove the nitrogen molecule. There is a metabolic cost to this process, and the issue is further complicated by the fact that amino acids used to create proteins, such as lean tissue or enzymes, are not available as an energy source. Thus, we can see that amino acids used as energy are less efficient than starch, and the exact quantity available to be used as energy is uncertain.

On average, about 60-65% of the amino acids in a pig's diet are not used to build protein, so those are potentially available as an energy source.

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Likewise, fiber is not as readily available as an energy source as starch. First, pigs do not digest fiber well because it must be fermented in the gut, then absorbed by the pig as volatile fatty acids. As noted above, this process is less efficient as an energy source than glucose.

In addition, fiber levels vary among feed ingredients, so it is quite difficult to accurately estimate the quantity of energy provided by fiber in coproduct ingredients.

Fat, on the other hand, is used very efficiently as an energy source by the pig, particularly when it is transferred to backfat and other fat stores in the body. Even if fat must be broken down, it is still used for energy with greater efficiency than glucose.

Table 2 shows the efficiency of various energy sources. How efficiently they will be utilized by the pig will depend on whether they are used for maintenance or growth.

Rethinking Energy Systems

Digestible energy (DE) and metabolizable energy (ME) systems are most commonly used in formulating North American pig diets. Both approaches have served us well because the composition of our diets has traditionally been simple — most containing just two or three main ingredients.

However, as we begin to use more coproducts in our swine diets, the composition of diets will become more complex. It is, therefore, likely that we will see greater adoption of the net energy (NE) system.

The net energy system has an advantage over DE and ME in that it takes into account the differential efficiency of energy sources explained earlier, whereas DE and ME do not.

The differences between the three energy systems are illustrated in Figure 1. DE accounts for energy lost in the feces and ME further accounts for energy lost in the urine and in gases. Neither adjusts for the differential efficiency of energy, depending on the source.

NE does this by adjusting for what is called “heat increment,” which is the term applied to the metabolic cost of converting absorbed energy into a form that can be used by the pig for maintenance (NEm) and growth (NEg). Growth comes in two forms — fat and muscle — or as expressed in Figure 1, net energy (lipid) refers to the portion of net energy directed to drive lipid gain in the carcass, and net energy (protein) refers to that portion of net energy that drives protein or lean gain in the carcass.

New Measures of Efficiency

Feed conversion is both a simple and a complex measure. Technically, it is a simple calculation — feed used divided by pig growth or, if you prefer, the pounds of feed required to produce a pound of gain.

Practically, however, feed conversion is challenging to measure under farm conditions because accurate feed manufacturing and/or feed delivery records are critical.

A challenge, for example, is multiple barns on a single site, a very common situation. Feed delivered to one barn can easily be charged to another. If this happens, the result is an inaccurate calculation for both barns.

Additionally, feed conversion is calculated on a live hog basis, but many producers are paid on a dressed carcass weight basis. Since some diets can increase the size of the pig's gut, traditional feed conversion of a live hog will overstate the value of a diet. Calculating feed conversion on a dressed weight basis would remove this potential for error and provide information that is more closely linked to the payment received by the producer. In this case, feed conversion would be calculated as pounds of feed/lb. of dressed weight gain.

Feed conversion is also problematic because it can be easily changed by the nutritionist simply by adjusting the energy content of the diet. As Table 2 illustrated earlier, a diet containing less energy will generally result in a poorer feed conversion, while a diet containing more energy will generally improve it. Thus, a feeding program with 3% added fat will result in better feed conversion than one containing 1.5% added fat. Yet, this higher feed conversion may not be more profitable.

Adding to the complexity, supplemental fat in a diet may increase barn throughput, which has a high economic value in most systems. In this instance, the addition of fat to the diet is undertaken to improve growth rate and not feed conversion.

Both of these situations point out the limitations of feed conversion as a useful measure when it is taken in isolation of other very important considerations in the production system.

An alternative measure of feed efficiency that I believe will increase in value in the future is kilocalories of dietary energy/lb. of gain, which tells us how much energy is required to produce a pound of gain. Because energy is the most expensive component of the diet, this measure of efficiency helps us understand if we are using energy as efficiently as possible.

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It therefore becomes increasingly apparent that a financial component must be considered in the evaluation of diet efficiency. Too much focus on non-economic outcomes, like feed conversion, can mislead us into thinking that one diet is better than another, when it may not be.

For this reason, we are seeing evolving measures of efficiency that link pig performance to financial indicators, such as feed cost/pig, feed cost/lb. of gain, net return over feed cost, net return/pig and net return/pig place.

If we begin by looking at feed cost/pig — an important measurement because it defines the total cost of feeding a pig to market — it transforms feed conversion from a performance measure into something with a financial component. And it's easy to calculate — simply divide total feed cost by the number of pigs sold.

While feed cost/pig is a valuable number, it has one important flaw — it does not consider growth rate. Again, a nutritionist can develop a diet that minimizes feed cost/pig, but if growth rate suffers, then barn throughput declines and the number of pigs sold/year diminishes.

Some producers prefer to measure efficiency by calculating feed cost/pig place. If grow-out capacity is a limiting factor, which is often the case, then growth rate and, thus, barn throughput is important. Income/pig place minus expenses/pig place expresses the potential for profit from a given barn on an annual basis.

Taking a look at feed cost/lb. of gain, the most accurate calculation is to divide the total cost of feed used by the total pounds of gain produced. As explained above, using the dressed weight rather than live weight is even better.

Margin over feed cost is the difference between the value of the pig and the total feed cost. Adding in the cost of the feeder pig, either purchased or raised, provides another valuable number — return over feed and feeder pig. Since these are the three largest components of a cost of production budget, it allows producers to determine how much money is available to cover barn expenses, fixed costs and labor and how much is likely to be left over for profit. When observed in the context of the value of the market hog, the producer can see two major components of the budget — income and feed.

Of course, the total cost of feed for a given turn is a useful number as well, because it can be used to express net income over feed cost for the whole barn. While this is a very useful financial number, it is less useful as a measure of feed efficiency because too many variables, including mortality, can influence it.

More Challenges Ahead

In conclusion, as our industry moves forward into a world of greater uncertainty in feed markets, we are challenged with the need to identify the best way to feed our pigs and to achieve both performance and financial objectives. This will require us to rethink what we feed our pigs, how we feed them and how we measure success.

The goal remains the same — to produce high-quality pork that is desired by the consumer, and to do so in a manner that is both profitable and sustainable. How we measure feed efficiency will be an increasingly important topic in the coming years, because it must keep our focus on achieving the right outcomes.