What is it?
Isoleucine (Ile or I) is essential branched-chain amino acids (BCAAs) that required by cats and dogs for protein biosynthesis among other functions. Other BCAAs are leucine and valine.
This branched aliphatic amino acid has four isomers, the L-, D-, L-allo– and D-allo-isoleucine. Its side chain is hydrophobic, and it is both gluconeogenic and ketogenic (can undergo a metabolic pathway to produce glucose and can be converted to ketones to produce energy).
Its absorption occurs in the small intestine by neutral amino acid transporters. On the other hand, renal reabsorption occurs in the proximal tubule actively.
Foods rich in isoleucine include eggs, turkey, chicken, pork, veal, cheese, fish, seaweed, lamb, soy protein, wheat germ, and legumes.
Requirement in cats
As the AAFCO 2014 notes, cats require a minimum of 0.56% for growth and in reproduction while the minimum requirement for the case of adult maintenance is 0.52% on dry matter basis. Basing on 1000 kcal of cat food, these amounts are 1.40g and 1.30g respectively.
One of the known function is being a structural unit of protein, i.e., the “hydrophobic side chains this BCAA induce inward folding of protein structures,” notes WikiVet.
Also, it is part of muscle proteins and Veterinary Practice recommends an increased amount of these amino acids in senior cats. Diets such as Royal Canin’s range of Senior Consult diets have higher levels of BCAAs, especially leucine to help in muscle maintenance.
Finally, the BCAAs are part of the sarcopaenia in cats nutritional management.
Kittens whose diets are isoleucine deficient experience poor growth and they will experience weight loss if their diets lack this amino acid completely.
According to NRC, within a few days of inadequate isoleucine, kittens “developed porphyrin-type crusty material around the eyes, nose, and mouth, a rough hair coat with desquamation of the outer layer of the epidermis on the pads of the paws with cracking and occasional lesion, lethargy, and incoordination.”
Upon supplementation of isoleucine, the above symptoms resolved including staphylococcal bacteria noted on conjunctiva meaning that a deficiency affects kittens ability to resist some of the common dermal bacteria.
No cases of deficiency have been noted in adult cats. Therefore, you do not need to worry about it.
Most commercial cat foods have enough amount of isoleucine. Similarly, most of the sources we mentioned have adequate amounts. There is no need for supplementation unless your vet advises you to do so.
No toxicity cases have been reported in cats including adverse clinical signs or growth problem as a result of felines having large amounts of isoleucine in their diets.
Finally, its dietary sources do not affect the concentration of other branched amino acids in feline’s blood plasma.