What is isoleucine?
Isoleucine is one of the three branched-chain amino acids, together with leucine and valine. It is an isomer of leucine: both have the same formula, C₆H₁₃NO₂, but a different arrangement of the side chain. Animals cannot synthesise isoleucine, so it is an essential amino acid.
Besides being built into proteins, isoleucine can be broken down in muscle for energy and contributes carbon both to glucose and to ketone bodies.
What does it do in animal feed?
- Growth: an insufficient isoleucine supply reduces feed intake, daily gain and feed efficiency in pigs and poultry.
- Low-protein diets: supplementing isoleucine can allow crude protein to be reduced further while keeping the amino acid balance, which can lower nitrogen excretion.
- Piglets: relevant in diets that use spray-dried blood cells or other blood products, which are rich in protein but low in isoleucine.
- Tissue maintenance and immune function: as an essential amino acid it supports protein turnover in all tissues.
Balance with leucine and valine
The branched-chain amino acids share the enzymes that break them down. A large excess of leucine, which is common in diets rich in corn and corn by-products or in blood products, can increase the breakdown of isoleucine and valine and so raise their effective requirement. Nutritionists therefore evaluate isoleucine together with valine and leucine rather than alone, especially in very low-protein diets.
Sources and forms
Soybean meal and most animal proteins are reasonable isoleucine sources, while corn and blood cell products are relatively poor in it. Feed-grade isoleucine is L-isoleucine produced by bacterial fermentation and supplied as a crystalline powder; its guaranteed content is given in the product specification and certificate of analysis. Some fermentation-based amino acid products also supply isoleucine together with other amino acids, in which case the declared content of each should be used.
How is the requirement assessed?
Isoleucine is formulated on a digestible basis, usually as a ratio to digestible lysine within the ideal protein concept. The appropriate ratio depends on species, age, the crude protein level and the leucine content of the diet. Synthetic L-isoleucine is added only once the earlier limiting amino acids are balanced and isoleucine has become the factor that limits further reduction of crude protein.
Quality criteria
- Guaranteed L-isoleucine content and purity.
- Moisture, ash, heavy metals and microbiological quality.
- Particle size and flowability for even distribution in premixes and feed.
- Certificate of analysis (CoA) and lot traceability.
CTF Premix and isoleucine
Isoleucine can be included in CTF Premix's vitamin, mineral and custom premixes according to the customer's formulation, alongside other amino acids, vitamins and trace minerals. Our premixes are produced at our Ankara facility under ISO 9001:2015 and GMP, and every lot is supplied with a certificate of analysis and full lot traceability.
This page is for general information. Inclusion rates and product choice should be decided with a nutritionist, taking into account the species, the feed formulation and the applicable regulations.