Processing grains and oil seeds for animal feeding
Simple processing of grains such as grinding facilitates the digestion particularly in cattle and buffaloes. Fine grinding of sorghum and barley increases their feeding value compared to coarse grinding. However, for sheep and goats, particularly for young ones, processing of grains is considered unnecessary because of their chewing habits. Dry heat roasting of grains has not gained wide acceptance. However, it could become a practical method of processing grains because of its relatively low processing cost. Despite the small improvement on animal performance by grain processing, there is considerable evidence to show that various processes and degree of processing alter the site and extent of their nutrient digestion. Among oil meals, soybean meal is produced only by the solvent extraction method and its toasting is necessary to inactivate trypsin inhibitor, haemoglutinins, saponins and isoflavones, which adversely affect the health and productivity of monogastric animals. Rapeseed meal contains glucosinolates which are hydrolysed by endogenous myrosinase during the crushing of seeds, however under the optimum conditions of moisture and temperature, glucosinolates hydrolysis can be minimized with optimum quality of residual oil. Though mustard and rapeseed oil cakes, have low palatability due to their glucosinolate content, yet their feeding value has been reported at par with groundnut cake, as far as growth of young crossbred calves is concerned. Reduction of glucosinolate content has been attempted by the use of heat, microorganisms or chemicals but these methods either have been proved uneconomical or have resulted in a reduced protein quality. Low glucosinolates containing varieties of rapeseed have been developed in Canada and registered as Canola. Meals from such varieties can be added in the diet of pigs at higher levels than those containing high glucosinolates. Similarly, cottonseed cake, having low protein degradability, contains gossypol (free and bound forms) which is toxic mainly to pigs. Meals produced by screw press method are low in free gossypol but have poor protein quality, because of binding the lysine. Processing of certain unconventional protein supplements improves their utilization e.g. solvent extraction of karanj cake, ammonia treatment or water washing of mahua cake, toasting of guar meal or degumming of babul seeds.
The major benefits of processing of protein supplements for ruminants differ frommonogastric animals as these processes affect the degradability of the protein within the rumen. In general, the protein supplements of vegetable origin have higher rumen degradability, which causes improper utilization of nitrogen by rumen microbes, therefore, attempts have been made to reduce their protein degradability by simple physical (heat) or chemical (formaldehyde) treatments