Scientific Opinion on the safety and efficacy of L-cystine for all animal species

EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP)

L-cystine is a dispensable sulphur-containing amino acid, naturally occurring in proteins of plants and animals. L-cystine is safe for all animal species if the requirements for sulphur amino acids are respected. The maximum amount of L-cystine that can be safely added to the diet will depend on the levels of other sulphur-containing amino acids. Supplemental L-cystine will not be deposited in animal tissues as such: it will be incorporated in body proteins without causing any change in their natural composition or it will be metabolised and excreted. The product under application does not contain substances of toxicological concern. Thus, the use of L-cystine in animal nutrition does not raise any concerns for consumer safety. In the absence of any data, it would be prudent to consider L-cystine as irritant to skin, eyes and mucous membranes and as a potential dermal sensitiser. Therefore, it would be prudent to assume that exposure of skin, eyes and respiratory tract is hazardous. The use of the natural amino acid L-cystine as feed additive does not represent a risk to the environment. L-Cystine is considered efficacious in partially meeting the requirements for sulphur-containing amino acids in all animal species

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(FEEDAP), EFSA: Scientific Opinion on the safety and efficacy of L-cystine for all animal species. 2013.

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