The Europeans are eons ahead of U.S. producers in managing the energy portion of a pig's diet.

Defining an ingredient's true energy value requires a system much more rigorous than digestible energy (DE) or metabolizable energy (ME),” says John Patience, president and CEO of Prairie Swine Centre, Inc., a non-profit research and technology center affiliated with the University of Saskatchewan in Saskatoon. “Without question, net energy (NE) places a more accurate relative value on ingredients.”

European producers have been using net energy in ration formulation for decades. Since many of them utilize imported feedstuffs, they focus on feed costs, which explains the more rapid adoption of a NE system, Patience told participants of the recent Minnesota Nutrition Conference. “Without doubt, the net energy system is superior for this purpose. In North America, the focus tends to be on performance.”

Patience admits net energy formulation offers less advantage over DE or ME when simple diets are fed. And that means there is little incentive to adopt NE for corn and soybean meal-based rations.

But the industry is changing, he contends. Increased use of synthetic amino acids and the resulting lowering of dietary crude protein and increased use of by-product feeds, such as distiller's grains and fat, are prompting reviews of the most appropriate energy system to use.

In western Canada, even conventional diets are based on wheat, barley, field peas, canola meal and soybean meal, with substantial use of synthetic amino acids. With these complex diets, the NE system comes into its own and offers substantial benefits to the producer, states Patience.

Areas feeding complex diets can benefit by a minimum of $2/pig sold, he says. U.S. producers feeding less complex diets could benefit by at least $1/pig by using NE systems.

The long-term benefit of $2/pig is less at the present time due to the low cost of feed and a relatively narrow range in price between cereal grains and protein sources, notes Patience. However, the current pricing of ingredients is not reflective of the 10-year average.

Three Energy Systems

Of the three energy systems, DE is the simplest.

Metabolizable energy is about 96% of DE in typical commercial diets used in North America — the difference being urinary and gaseous energy losses.

Net energy is defined as ME, less the heat increment associated with the use of ME for maintenance and productive purposes. Fundamentally, NE is estimated by summing fasting heat production plus retained energy.

Variation in any of the components related to maintenance, digestion, growth, lactation, or reproduction brings into play a fluctuation in performance that will not be predicted by either DE or ME, says Patience. The NE system was developed to address this issue. Digestible energy and ME ignore a critical aspect of energy utilization in the pig. As such, the relative value of ingredients rich in protein and/or fiber will be overestimated, while those rich in fat, or low in protein and fiber, will be under estimated (Table 1).

The feed ingredients commonly used by the pork industry vary much more in energy content than most of us wish to admit, continues Patience. The challenge is in finding a solution to this problem. Bushel weight, the ubiquitous trading standard in the grains industry, must be discarded. Other than for extreme highs and lows, bushel weight is a poor indicator of actual value to the pig.

In a study at the Prairie Swine Centre, ingredient variability was compared using formulated DE vs. determined DE. “It clearly showed that we tend to overestimate energy in weanling diets, but do not achieve the level of precision in growing and finishing diet formulation we would like. If we have difficulty estimating DE of ingredients, we will have no greater precision in this regard with NE, since digestibility of dietary components is integral to the NE system,” explains Patience.

Animal Factors Play Bigger Role

“Perhaps the biggest challenge of all is that NE will force us to understand composition of pig gain,” continues Patience. “An increased focus on carcass and meat quality will drive adoption. The NE system does a better job of describing the amount of energy available to the pig for maintenance and for lean gain and for fat gain. Commercial nutritionists rarely know the composition of gain of their pigs, so adjustments in energy supply are difficult. This is changing, however, as we develop an increased understanding of commercial genotypes.”

Unlike the research community in Europe, few laboratories in North America are conducting research on energy metabolism in the pig. That will further delay adoption of NE on this side of the Atlantic.

Prairie Swine Centre does not have its own NE values, so they use Dutch and French numbers, at least for the time being, explains Patience. There are differences between the Dutch (CVB) NE system and the French (INRA) NE system, but differences are modest (see Table 2). The most troublesome disagreement between the two is in estimated NE value of fat sources.

The Centre is evaluating adoption of the European NE systems under North American conditions by collaborating with the University of Illinois, South Dakota State University, the University of Missouri and Iowa State University on developing new initiatives focusing on energy metabolism in the pig.

“I suspect we can plug in their values,” Patience assures. “Nutritionists might also consider shadow formulation. Enter NE values for all ingredients into the feed formulation matrix, excluding specific individual diets. An ME or DE system is still used as the basis for formulation, but resulting NE values of the diets are concurrently watched to see how they move in relation to each reformulation process. This use of NE in the ‘background’ is continued until the nutritionist feels comfortable and familiar with NE before making the switch.”

Minnesota swine nutritionist Gregg Sample agrees that NE is more accurate than the ME system most use, but there's little reason to switch when corn and soybean meal are cheap.

That could change, however, he says. Sample does the nutrition work for Next Generation Pork, a LeRoy, MN, operation that markets over 100,000 pigs annually. According to Sample, “if you believe the forecasters, the landscape surrounding the world supply and demand of our commodities is changing. As more co-products like DDGS (distiller's dried grain with solubles) become available, the industry may endorse the net energy concept out of necessity. The environmental drive to reduce nitrogen and phosphorus excretion also favors the use of NE.”

In Canada, the NE system is being used with increasing frequency, but like the United States, most pigs are still fed diets based on DE or ME, says Patience. “But I've never seen a downside to switching from ME to NE, and given the financial advantage, we believe the trend will continue.”

Table 1. Energy Supplied by Various Dietary Constituents
Constituent Crude Protein Crude Fat Starch Dietary Sugars Fiber
kcal/g.
Gross energy 5.40 9.27 4.18 3.99 4.45
Digestible energy 5.38 7.60 4.37 3.85 0.12
Metabolizable energy 4.71 7.70 4.35 3.80 0.12
Net energy 2.82 6.91 3.54 2.75 -0.21
Source: Noblet and van Milgen, 2004
Table 2. Comparison of Net Energy Values (kcal/kg) for Common Ingredients According to Either the CVB or INRA Systems
Ingredient CVB INRA
Barley 2.510 2.613
Corn 2.934 3.055
Field peas 2.570 2.601
Rapeseed meal 1.725 1.837
Soybean meal - 48% 2.197 2.173
Soy hulls 1.176 1.143
Sugar beet pulp 1.814 1.560
Sunflower meal 1.280 1.325
Wheat 2.696 2.878
Wheat bran 1.621 1.690
Animal fat 7.671 7.107
Vegetable fat 8.197 7.115
Calculated values according to CVB and INRA systems, assuming identical nutrient profile of each ingredient.
Source: Rijnen et al., 2004

Danish System Revised

The Danes recently revised their energy evaluation system. It is based on their well-known feed units (FU) system, which is now going to be based on the physiological energy value of an ingredient, says John Patience, president and CEO of Prairie Swine Centre, Inc., Saskatoon, Saskatchewan.

In this respect, the Danes have rejected the net energy system and any system based on bomb calorimetry. The new system, first introduced in 2002, now has separate energy values for gestating sows, as distinct from lactating sows, and growing pigs.

The new system has increased the energy value of barley, wheat and oats, but lowered the energy value of soybean meal, fishmeal and rapeseed meal, as compared to the previous Danish energy system, explains Patience. This means the new Danish system has had the same impact as net energy; or, in other words, it has decreased the relative value of protein sources and increased the relative value of low-protein ingredients.