The inclusion of soya meal into the poultry diet is relevant, as a source of high quality protein. However, as soya is planted for both human and animal consumption, the cost is high.
The production of tofu and soymilk generates okara as a waste product which can be added fresh or dried, to poultry rations, reducing both soya meal inclusion and costs. Due to its high fibre content, the amount of okara in the diet should be limited to avoid a decrease in feed intake.
• Due to its chemical and amino acid composition (Table 1 and 2), Okara can be used in different ways in the poultry diet. A possible use is to include okara in the starting and growing phases (from the 1st to 21st day). Another possibility is to feed okara from week 1 to slaughtering time. Okara inclusion replacing soyameal quantity from 25 to 75 % in the diet, will not affect feed intake or mortality, and it will reduce ration cost and achieve comparable daily body weight gains, to 100 % soya diets. However, due to the high fibre content, overfeeding Okara, could decrease feed intake and performance (Motawe et al., 2012).
• The composition of Okara ranges between 20 % and 47.3 % protein and 9.3 % and 22.3 % fats. It contains high amounts of isoflavones and the polyunsaturated fatty acids, linolenic acid, and linoleic acid (O’Toole 1999; Bowles and Demiate 2006). The energy content is also important to ensure weight gain from day 1 to 21 (Table 3).
• According to Rostagno et al. (2011), the okara digestibility of crude protein (CP), amino acids (AA) and lipids is higher than that of soya. In particular, okara CP has a higher digestibility of around 99.6% instead of 91%. Protein content, protein efficiency coefficient, and essential AAs of okara are usually higher than those of other soybean-based products, due to the heat process that soybean undergoes during processing of the soybean aqueous extract. This makes certain AAs better available, which in turn increases the digestibility of proteins and fats (O’Toole 1999)
• It should be noted that according to Diaz-Vargas (2016), okara CP content was 21 % lower than that of soy (45%). However, the biggest difference between okara and soybean meal was in regard to tryptophan, with 55.5 % less found in okara. The contents of lysine, methionine, and threonine varied by 7.5 %, 13.3 %, and 16.5 %, respectively (Table 3).
• The economic viability of including okara in the diets was determined according to the equation described by Bellaver et al. (1985), which calculates the average cost of feed per kilogram of body weight.