The Fundamentals of Amino Acids in Animal Nutrition:
10 Practical Tips

The digestible content of each amino acid in an animal feed is a predictive criteria for performance. Since the usual criterion for crude protein is only the nitrogen quantity multiplied by the coefficient 6.25, it is not a good indicator for risk management.

Thanks to advances in amino acid nutrition research, we are able to go further than the crude protein criterion and create formulas using minimal standardized digestible values for each amino acid. The formulas thus obtained offer a technical-economical optimum between the supply in feed-use amino acids and those coming from raw materials.

Good amino acid nutrition occurs by taking into account the dietary intakes in essential amino acids. The latter can vary according to the species as well as the animal’s physiological stage.

In feed formulas that contain a variety of raw materials, the essential amino acid profile is generally imbalanced. Certain amino acids appear in deficit, while others are in excess, causing variations in dietary digestion and animal growth. However, it is possible to get closer to nutritional balance through:

• Decreasing the levels of dietary crude proteins,
• Identifying the most limiting amino acids and their interactions,
• Monitoring the proportion of certain raw materials,
• Providing an accurate and precise supply of feed-use amino acids.

If one of the essential amino acids is not provided in an optimal quantity, it then becomes the limiting factor in the feed formula. Identifying the most limiting amino acid in a feed is equivalent to detecting the progress targets in feed and animal performance. Any incremental change in the limiting amino acid nutritional level will make it possible to obtain better performances. Moreover, by choosing an adequate amino acid level, one limits the risks of deficiency linked with the variability in feed manufacturing and the variability of feedstuffs used in the formula. The limiting amino acid depends on the animal’s needs and the type of raw materials used. Defining the limiting amino acid is therefore contextual and must be studied on a case-by-case basis.

At the R&D level, evaluating the response to an amino acid requires respecting certain model protocols in order to avoid too much variability in the results, which would then be difficult to transpose into practice. Since intakes in amino acids are studied in relation to Lysine, it is important that in the dose response experiments the first limiting factor is the studied amino acid followed by Lysine. If this is respected, this method makes it possible to estimate the response to an amino acid and find the balance point between an amino acid and the referent one (Lysine). One can then construct reliable response rules and make choices in accordance with each criterion and each application context.

The results from our amino acid nutritional research make it possible to establish rules regarding responses and standards. However, this is not enough to establish the correct levels that must be used in feed formulas. Indeed, it is important to integrate farming contexts (raw materials, performance and economics) as well as clearly identifying the objective to which one must respond.

the following criteria are to be taken into consideration when making a decision regarding amino acid levels:

• Performance objectives,
• The raw materials used and their variability,
• The analytical control plan,
• The dietary protein levels,
• And the digestibility coefficients used.

Employing feed-use amino acids combined with response rules are concrete tools in the risk management of feed production or concentrates for on-farm manufacturing.

Lysine is the first limiting amino acid in pigs and the second in poultry. The direct correlation between the intake of Lysine and muscle mass turns it into a crucial element in amino acid nutrition. Since other amino acids are expressed as a ratio of Lysine, it is essential to choose the Lysine level that best corresponds to the need of the animal without being limiting. Consequently, the growing use of feed-use amino acids (L-Lys, L-Thr, L-Trp, L-Val, etc.) makes it possible to get as close as possible to animals’ needs without increasing the levels of dietary proteins.

In order to do this, it is necessary to take two factors into consideration: the ingestion level and the performance objective. Since ingestion itself depends on genetic and farming contextual factors, the level of Lysine can thus be variable within a species.

To make these choices, one generally uses mathematic models that incorporate equations on the use of Lysine and other amino acids. Tests are regularly conducted in order to validate the levels of Lysine and readjust them, if necessary.

Although standardized through the concept of the ideal protein, requirements in amino acids also depend on their functional roles and the desired objectives. It is then necessary to study the interactions between all of the amino acids and their functional roles.

A few examples on the multiple roles of amino acids:

• Since Threonine plays a dominant role in intestinal integrity, monitoring its level is essential in difficult health-related contexts.
• As for Tryptophan, it is known for its multiple effects on the animal’s dietary ingestion, health and behavior. Its level will also need to be adjusted according to the objectives.
• Responses to and requirements in Valine, Isoleucine and Leucine vary, depending on two factors: on the one hand, the interactions within their amino acid family (branched chain amino acids) and, on the other hand, the intakes in other amino acids sharing the same transporters.
• Arginine is an important nutrient which requirement varies in accordance with the animal’s physiological stages and its specific impacts (on blood circulation, as a precursor to key metabolites, etc.).
• Glycine, implicated in numerous metabolic pathways, must be considered in terms of its interactions and in accordance with the intake of its precursors.

Using amino acids makes it possible to correctly respond to animals’ needs while reducing the levels of dietary proteins. The benefits go beyond animal performance and are essential in terms of sustainable development:

• Measurable decrease in greenhouse gas emissions (N2O) related to climate change,
• Reduction in the acidification and eutrophication of environments,
• Improvement in animal health and welfare (fewer outbreaks of poultry footpad dermatitis, contribution to better intestinal health in piglets, etc.),
• Reduction in the dependence on imported protein-based raw materials,
• Optimization of animal life cycles.

A genuine nutritional strategy based on amino acids is capital for the sustainability of these industries.

A nutritional imbalance between energy and amino acids intakes can have numerous consequences on the animal and its environment: increase in the animals’ fat ratio or nitrogen excretion accompanied with economic losses and negative environmental impacts.

Just like one uses the ileal digestibility system for amino acids, it is important to employ the net energy system in order to better track and predict animal performance. In pigs, for example, one observes that the animal regulates its dietary ingestion according to the net energy level. Furthermore, by using the net energy system and adequate amino acid levels, a reduction in proteins does not affect lean meat and fat ratios.

Net energy as the best predictor of animal response is a powerful optimization tool in formula costs. Combined with feed-use amino acids, it encourages the use of local resources (grains, byproducts, etc.). Lastly, it makes it possible to set up nutritional techniques that improve the sustainability of livestock farming and the life cycle of animal products.