2007 Volume 44 Issue 2 Pages 119-134
The residue of cottonseed oil extraction industry popularly known as cottonseed meal (CSM) is a fairly good source of protein (222.0 to 560.2gkg-1) and metabolizable energy (7.4 to 11.99MJkg-1). The use of CSM in poultry diet is limited due to the presence of gossypol, cyclopropenoid fatty acids (CPFA), high fibre and poor protein quality. The most critical amino acid in CSM is lysine. During the oil extraction from cotton- seeds, a portion of free gossypol (FG) binds with the epsilon amino group of lysine, thereby reducing the availability of lysine to the chicken. The concentration of nutrients, FG, CPFA in CSM depends on the variety of cultivars, methods of oil extraction, proportion of kernel to husk, lint and seed coat. The concentration of FG in various varieties of CSM ranges from 200 and 5300mgkg-1. In glandless variety, the FG concentration is less (>130mgkg-1). Gossypol inhibits the activity of pepsin and trypsin in gastro-intestinal tract, thereby reducing the digestibility of protein. The reported toxic effects of gossypol are growth depression, lameness, decreased egg size and hatchability. Gossypol and CPFA also deteriorates the internal egg quality by causing yolk mottling and pinkish discoloration of albumen, respectively. The tolerance levels of FG in birds vary widely depending on the age and strain of birds, protein content and quality, duration of feeding, presence of minerals especially the iron content in the diet. The tolerance of FG in chicks varies widely (90 to 1000mgkg-1 diets), however performance of layer chicks could be affected even at a lower FG intake of 2.02mg day-1 bird-1. Though, growth was not affected in broilers at FG concentration in diet below 150mgkg-1, feed efficiency was reduced at lower levels i.e. 60-100mgkg-1. The depression in egg production in layers fed diets containing more than 100mgkg-1 was mainly due to lowered feed intake. The egg weight and egg quality was not affected at FG levels upto 200mgkg-1 diet. Iron treatment (4 : 1; Fe : FG) proved to be effective in alleviating the negative effects on egg quality, but could not alleviate the depression in laying performance. Lysine supplementation to CSM containing diets is also effective in counteracting the ill effects of FG in chicken, especially chicks and broilers. Other processing methods like solid substrate fermentation, production of glandless cotton seed and use of organic solvents were though effective in improving the nutritive value of CSM and reducing the FG content in CSM, these methods are of little practical relevance and uneconomical. Production of glandless variety of cottonseed through genetic modification (Bacillus thuringiensis cotton) is one of the recent trends of reducing the FG content. Some other methods like pelleting, extrusion, cooking and Ca (OH)2 treatment of CSM could be tried for improving the feeding value of CSM in poultry.