Another liability of cottonseed meal is its content of free gossypol, which is moderately toxic to monogastric animals. Approximately 0.03% free gossypol will suppress growth rate in rainbow trout (Herman 1970). Levels of ≥ 20% prepress solvent-extrated cottonseed meal in channel catfish diets cause gossypol toxicity, but lower levels processing (Lovell 1981). Generally, free gossypol contents of three types of cottonseed meal are as follows: direct solvent meal, 0.2% to 0.4% ; screwpress meal, 0.02%; prepress solvent, 0.05%. The addition of 0.85 to 1.0 part ferrous sulfate to each part free gossypol in diets of swine and poultry has proven successful in blocking the toxic effects of gossypol.