Don’t Pay For Energy Lost During Digestion, Swine Nutritionists Say

Most swine diets are formulated based on metabolizable energy, but some experts say it’s time for a different approach to swine diet formulation. Hans Stein, professor of swine nutrition at the University of Illinois, encourages producers to formulate diets based on net energy.

In order to use the most accurate energy value in feed formulation, Stein says producers should formulate diets based on net energy. Not only could it lower the cost of production, but it may also help reduce waste and conserve resources.

Russell Fent, director of the swine technical group at Ralco Nutrition, explains the concept of net energy as the reverse of the high-protein/low-carb Atkins Diet. 

“Efficient weight gain, not weight loss, is the focus of a net energy formulation,” Fent says. “Putting lean gain on hogs requires energy and easy-to-digest amino acids and avoiding excess protein. Net energy values the use of energy for productive purposes rather than being inefficient in energy usage.”

Why Net Energy? 
“Net energy is the energy an animal obtains from a specific feed ingredient after the energy that is lost in feces, urine, and heat has been subtracted,” Stein says. “The net energy will typically be between 30% and 90% of the gross energy in a feed ingredient – so there are large differences among feed ingredients in terms of the net energy they provide.”

The net energy can then be used for maintenance of the animal and for production of meat or milk (in lactating sows), he adds. 

Comparatively, metabolizable energy values are calculated by subtracting the energy in feces and urine from the ingested gross energy in a feed ingredient. However, Stein says metabolizable energy values do not take into account the heat that is lost during digestion like net energy does. 

“The difference between net energy and metabolizable energy is that net energy values only contain the energy that can be used by the animal, whereas metabolizable energy values also contain the energy that will be lost in the form of heat during digestion,” Stein says.

Don’t Waste Your Energy
Because the energy lost in heat during digestion is different among different feed ingredients, Stein says formulating diets based on net energy values rather than metabolizable energy values makes sure that the correct energy value is assigned to each feed ingredient. In other words, the producer does not “pay” for the energy that is lost during digestion.  

Soybean meal contains as many as 20 amino acids. Jim Hedges, senior swine technical advisor for Ralco Nutrition, says most of these are in excess of what the pig needs. Because of this, pigs will waste energy breaking down the excess amino acids and consume more water to excrete the excess nitrogen.

“Purified amino acids, like lysine, provide pigs with an essential amino acid that is quickly absorbed and can more readily meet their daily nutritional requirements,” Hedges says. “The more we understand the relationship between purified amino acids and energy absorption, the further we can push net energy diets.”

Is a Net Energy Diet More Sustainable?
Decreasing protein may or may not reduce waste and preserve resources, Stein says. It all depends on how the amino acids are balanced. 

“If the protein can be reduced without providing amino acids below the requirement, the amount of nitrogen that is excreted in the urine from the animals may be reduced resulting in less nitrogen in the manure. But if amino acids do not meet requirements, this will not be the case,” Stein adds. 

Research by Ajinomoto Animal Nutrition shows for every 1% reduction of crude protein (provided all amino acids are at the requirement) in a feed ration, the result is 5% less manure, 10% less nitrogen in manure, 10% less ammonia, and 12% less water consumed per pig.

In addition to reducing production waste, feeding a low-protein diet reduces body heat generated as a pig’s body works to digest soybean meal. During summer, this can have a big impact on feed intake, Hedges says.

“By rethinking nutrient conversion and reducing energy waste, net energy diets not only save producers through lower feed costs, but they save in manure management and play a role in conserving resources as well. Net energy formulation holds the promise of a nutrition approach that is truly built to drive and fine-tune efficient performance,” Hedges says.

What’s Ahead?
Stein and his team at the University of Illinois have recently invested in equipment to measure net energy in diets and feed ingredients fed to pigs. The equipment, which is based on an approach called “indirect calorimetry,” allows for determining energy losses in feces, urine and heat from pigs. This facility, therefore, allows for determining net energy of ingredients and diets fed to pigs, Stein explains. 

“There are only a few research institutions in the world that can do that,” Stein says. “But the really unique thing about the facility is that it allows pigs to be housed in groups and fed on an ad libitum basis.”

Over the next few years, his team plans to conduct a number of experiments to determine net energy in all the commonly used feed ingredients and based on that, they will be able to better guide formulations of diets for pigs, he says.

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