L-isoleucine

Branched amino acids and their sources:

• Whey protein
• Maize

Branched amino acids can be used as energy sources by complex organisms. This is limited in equine metabolism because it is linked to a more complex mechanism. Indeed, during long and average distance efforts, fatigue appears when the glycogen reserves are empty. But whenever this glycogen drop is associated with a decrease of the ratio branched amino acids/L-tryptophan, fatigue occurs sooner. That is why it seems worthwhile to supplement horses with branched amino acids.  

Valine has a specific role in DNA production and is essential for cell development.

If we consider the needs of leucine, isoleucine and valine together, they are estimated at 1.6 g/kg of metabolic weight per day.
 
The metabolic weight corresponds to the horse weight to the power 0.75: for example a horse of 450 kg : 450 ^0.75 = 98 kg of metabolic weight; its needs will be 156 g of these 3 branched amino acids per day. A normal ration usually contains a sufficient quantity of these amino acids, except if a horse suffers from a muscular problem or during an endurance effort.