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FEATURE

by Tom Wedegaertner Cotton Incorporated

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very year, 11 million metric tons (mmt) of protein are produced as a byproduct of worldwide cotton production. This is an equivalent amount of protein to 16 mmt of fish meal. Unfortunately, this massive protein resource is underutilised due to the presence of a toxin which almost totally restricts feeding of cottonseed protein to

ruminant species. Cotton, like many other plants, has evolved a chemical defense mechanism that greatly reduces predation by a wide variety of animals and insects. Cotton contains the anti-nutritional factor “gossypol,” which is a cumulative toxin that is toxic to most animals, when consumed over an extended period of time. There is a renewed interest in cottonseed protein due to a recent biotechnology breakthrough that offers promise that gossypol can be genetically eliminated from the seed. This biotechnology derived “proof of concept” will eventually eliminate gossypol as a concern when using cottonseed protein in animal feeds. It will also allow widespread use of ultra-low gossypol cottonseed (ULGCS) in aquaculture feeds, where it is a highly digestible protein, widely available and cost effective. As a bonus, cottonseed protein appears to contain a feeding stimulant for several aquaculture species.

Highly variable processing conditions

In the meantime, cottonseed products that currently are available to the feed trade can be used in aquaculture feeds as long as strict usage guidelines are followed. The biggest issues when studying the literature on this subject are the highly variable processing conditions and product composition of cottonseed protein products used by the researchers, as well as their failure to not only accurately characterise the cottonseed product used in their research, but also to accurately analyse and report the compositional values for gossypol, iron and lysine. The single biggest factor limiting the use of cottonseed protein in animal feeds is the presence of gossypol; however, the level of iron and lysine in the diet also has a direct effect on gossypol toxicity and animal performance. These two compounds are two of the favorites of gossypol for irreversible chemical bonding. The bonding of gossypol to lysine reduces lysine availability. Gossypol binding to iron reduces toxicity, but also offers astute nutritionists the opportunity to double the usage of cottonseed protein in the diet without experiencing reduced performance. For example, typical CSM might contain .07 percent gossypol (10 pounds per ton). By adding iron at a 1:1 weight ratio to gossypol, the tolerance for many animal species can be doubled. An animal that can be safely fed a diet containing 100 ppm gossypol can consume a diet with 200 ppm gossypol when iron is added to the diet. Ferrous sulfate is the preferred form of iron for

34 | September | October 2016 - International Aquafeed

SEP | OCT 2016 - International Aquafeed