Leucine

Mechanism

Leucine is an essential, branched-chain amino acid (BCAA) and acts beyond its pure building-block function as a signalling molecule: it activates the mTORC1 signalling pathway and thereby stimulates the initiation of muscle protein synthesis. In horses it has been shown that feed or amino-acid intake switches on mTOR-dependent signalling pathways in skeletal muscle; the specific, isolated role of leucine is, however, less extensively studied in the horse than in rodents and humans, from whose data much is transferred. Leucine is discussed in the field of muscle maintenance and recovery, particularly in the growing, in-training or older horse. NRC 2007 and GfE 2014 primarily quantify lysine as the balanced, first-limiting amino acid (in part additionally threonine/methionine); a specific leucine requirement is not defined, which is why dosages are derived from analogy and individual studies.

Cautions

• · Mind the amino-acid balance - isolated BCAA supplementation can trigger an antagonism with isoleucine/valine.
• · No substitute for sufficiently high-quality total protein and a covered lysine requirement.
• · Evidence for isolated performance/muscle effects in the horse is limited; much is extrapolated from rodent/human data.

Sources