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There are many differences in protein nutrition in animal production. Why are nutritionists more focused now on amino acids in animal feed formulation and what do they consider with amino acids in meal decisions? This three-part series breaks down why focusing on amino acid balance will allow for a more cost- and time-efficient animal. 

What Are Amino Acids?

Proteins are made up of several different combinations of approximately 20 amino acids. During the process of digestion, animals break down proteins into individual amino acids that are absorbed into the bloodstream. 

Amino acids in meal are the key element for proper growth and development of animals. Soybeans are considered a complete protein because they contain all five key amino acids needed for proper nutrition. These five amino acids are lysine, threonine, methionine and tryptophan. Animals such as pigs do not have a specific requirement for crude protein, but rather for amino acids, the individual components or sub-units that make up protein.1

Limiting Amino Acids in Feed

Although soybean meal provides a complete protein source and with desirable nutrient density, during feed formulation different meal products are often blended together. Factors such as price and availability impact formulation of an animal feed. 

Nutritionists consider amino acid balance in the blending process. Protein complementation, often practiced by animal nutritionists, combines protein sources to ensure all the amino acid needs are met. The limiting amino acids — lysine, threonine, methionine and tryptophan — are required in all formulations. If a diet has inadequate amounts of any of these essential amino acids, protein synthesis cannot proceed beyond the rate at which that amino acid is available. Therefore, digestible and metabolizable amino acid calculations must be a consideration with different protein sources.

For example, methionine is the first limiting amino acid in soybean meal, but tryptophan is the first limiting in cornmeal. By creating a blend of these two meals together, nutritionists work to ensure both needs will be met by the other protein source. This means that if soybean meal does not provide an adequate amount of methionine, cornmeal will supplement the rest of the needs to move on to the next amino acid. 

Yet, it is still even more complex. In a corn-soybean meal blend, lysine is the first limiting amino acid. Also important to the formulator: threonine, which is more limiting than tryptophan in a corn-soybean meal diet in young pigs, while tryptophan is more limiting in older finishing pigs. These protein sources and animal specific facts compound the complexities of meeting amino acid needs correctly and demonstrate the importance of understanding how amino acids interact under different conditions. 

Protein quality depends on meeting the needs of the most limiting amino acid relative to an animal’s requirement. An incorrectly balanced diet with a shortage of one of the essential amino acids will reduce growth rate and performance. An amino acid imbalance may occur when a second limiting amino acid is added to a diet while the first limiting amino acid is still deficient. This results in a reduction in feed intake and reduced performance.1

“If we fed a bird only soybean meal, and the amino acids aren’t balanced for what the bird needs, some of that protein will go to waste,” says Dr. Scott Carter, an animal nutritionist who has spent his career focused on formulating animal feed.

Dr. Craig Coon, poultry nutritionist at University of Arkansas, echoed this principle at a recent USSEC meeting. “Essential amino acids in soybean meal are very important. Be it a Ross or a Cobb [breed], there are certain specs you must have based on digestible amino acids,” Coon says. 

“If you’ve got a soybean providing the major part of those digestible amino acids, that’s a really nice thing to have,” Coon continues. “Otherwise, your birds are going to underperform. You’ll have poor feed conversions — you’re going to really pay.”

The Cost of Different Diets

Animal nutrient requirements vary from species to species, by age and production phase of the animal.3 Although nutrient needs vary, digestible amino acids, metabolizable energy and available phosphorus are three of the most expensive nutrients making up animal diets.3 Formulators can include these nutrients from several sources, but the cost adds up quickly when the nutrients come via different sources and with additional supplements.

Coon explains certain amino acids, especially those found in soybeans, are crucial and the important starting place for formulating feeds. “One of the key things that [U.S. soybean meal] has is a very important amino acid, and that is lysine,” he says. “It is really high in lysine on a protein basis and on a percent basis. And it’s better than what you’ll find in any of the other countries, and people know that.”

“The reason it’s important is because of the way we feed broilers, called the ideal profile method,” Coon continues. “We tag everything to lysine. So, whatever the lysine is, I automatically know what the other percentages are going to be. That lysine is the lead going into these diets. So, if you have a really nice digestible lysine level, all the other amino acids work in with that, and you have a nice profile.”

Providing nutrients naturally through ingredients such as soybean meal also helps with the cost. For example, lysine and methionine in soybean meal produce higher density diets even at a lower inclusion rate, allowing cheaper cost per kilogram of feed.4 However, market conditions and availability of product sometimes make it necessary to supplement, often with synthetic materials.

According to the Food and Agricultural Organization, the industrial application of amino acids for feed has an almost 40-year history. In the late 1950s and 1960s, DL-Methionine, produced by chemical synthesis, began finding its way into poultry feed. Production of L-Lysine by fermentation started in Japan during the 1960s. In addition to DL-Methionine and L-Lysine, HCl, L-Threonine and L-Tryptophan were introduced in the late 1980s.4 

With progress in biotechnology, the cost of production of each amino acid has significantly reduced, which has been a key factor in the expansion of amino acids in animal feed.4

The general assumption is that protein can be reduced 2% in a corn-soybean meal diet if 0.15% lysine is added (0.192% lysine-HCL) for grow-finish pigs. 

When formulating diets with commonly available grains and protein sources, the level of crude protein typically used to describe the diet will usually contain adequate amounts of amino acids to meet the animal’s requirement. However, when using synthetic amino acids and alternative or by-product feed ingredients, that this is not always true. The dietary levels of synthetic amino acids should always be checked.4 Protein quality can be defined as how closely the essential amino acids in the protein source come to meeting the animal’s estimated requirement for those amino acids. Carter states, “Synthetic amino acids should still be included in feeds to maintain efficiency and cost-effectiveness.”

When determining protein options, consider the entire economic value of incorporating U.S. soybean meal in feeds aside from cost alone. A recent USSEC-funded project covering an eight-year series of 27 feeding studies in Asia, South America and Europe of more than 234,000 broilers, layers and swine, demonstrates a superior economic value of U.S. dehulled soybean meal with higher protein, amino acids and digestibility. The studies examined the performance of animals fed various lots of soybean meal from the U.S., Argentina, Brazil, India, China, Thailand and Malaysia. Using normalized feed ingredient prices in all studies, the U.S. dehulled soybean meal provided an economic advantage of U.S. $33.60 more than non dehulled soybean meal from India, Brazil, Argentina and China. The studies also show U.S. dehulled soybean meal had an economic advantage of U.S. $8.74 more per metric ton than similar dehulled soybean meal produced in Argentina, Brazil, Paraguay and China. The results show continued use of U.S. dehulled soybean meal gives an economic advantage, even when priced higher than soybean meal from other origins.2

“You’re much better off by having a soybean that has all the nutrients in there without having to go out and add extra vegetable oil, extra DL-methionine, extra lysine,” adds Coon. “You’ll have to add that one way or another if you want the performance. That’s why we must look at all of these when we are evaluating soybean meal.”