Gossypol
Gossypol (see the Cotton (general) datasheet for more information) is a toxic polyphenolic compound found mostly in glands localized in the cotton seeds. It exists in a free toxic form and in a bound, non-toxic form (Morgan, 1989). Free gossypol is the more important form in unprocessed cotton seeds. In Gossypium hirsutum seeds, total gossypol concentrations ranging from 0.6 to 1.15% DM and free gossypol concentrations from 0.05 to 0.7% DM have been reported (OGTR, 2008). Gossypol content depends on species, cultivars, fertilizer rates, growing conditions and insect pressure (Blasi et al., 2002; Randel et al., 1992; Carter et al., 1966). "Glandless" cotton varieties without gossypol have been developed but these varieties are more sensitive to pests, less productive, and have thus been found less economically viable, though investigations are still ongoing (Rodman, 2006; Bourzac, 2006). The free gossypol content of cotton products may depend on processing: heating, for instance, increases gossypol binding and reduces toxicity, whereas fine grinding breaks the gossypol glands, releasing gossypol in the product (EFSA, 2008). Extrusion was shown to reduce free gossypol by 71 to 78% in cotton seeds (Buser et al., 2001).
Free gossypol causes moderate acute toxicity in animals. Signs of acute gossypol toxicity include constipation, dyspnoea, anorexia and loss of weight while repeated exposure to lower doses of gossypol (in rats and humans) mainly affects the testis in males (reduced sperm motility, inhibited spermatogenesis and depressed sperm counts), and reproductive organs and embryo development in females (EFSA, 2008).
The effects of gossypol on animal health and performance depend on the type of animal. The rumen of mature ruminants detoxifies cotton seeds by exposing gossypol to rumen microorganisms, causing its deactivation, binding, and degradation. Young ruminants with an immature rumen as well as monogastric animals do not benefit from this protection and are thus more sensitive to gossypol (Blasi et al., 2002; Poore et al., 1998). In these species, the use of unprocessed cotton seeds is not recommended, though it is possible to alleviate gossypol toxicity through the addition of iron salts to the diet, which are able to bind gossypol (EFSA, 2008).
Tannins
Whole cotton seeds contain condensed tannins that are located in the hulls where they are mainly bound to proteins and fibres (Yu et al., 1996).
Cyclopropenoid fatty acids
The oil of cotton seeds, particularly those of Gossypium hirsutum, contain about 0.5-1% of cyclopropenoid fatty acids such as malvalic, sterculic and dihydrosterculic acids. These fatty acids have been found to have deleterious effects on animal performance and various harmful effects on health (reproductive disorders, growth retardation and altered fat metabolism) in rainbow trout, rodents and poultry (OGTR, 2008; Sebedio et al., 1989; Phelps et al., 1964).
Aflatoxins
Cotton seeds can be contaminated by the fungus Aspergillus niger, which produces aflatoxins, a group of mycotoxins deleterious to animal and human health. Aflatoxin levels in cotton seeds should not be higher than 0.02 mg/kg and 0.03 mg/kg in the EU and in the USA respectively (Jouany et al., 2009). Inadequate storage conditions tend to increase aflatoxin contamination and it is recommended that cotton seeds are stored at moisture contents lower than 10% (O'Brien et al., 2005). Aflatoxin contamination can be reduced by processing: for example aflatoxin content was reduced by 50% when the cotton seeds were processed by two stages of extrusion at a temperature of 132°C (Buser et al., 2001).