Utilization of Soya Pulp: a by-product of soymilk in livestock feeding

Green fodder, dry fodder and concentrate mixture for our livestock is deficient and so as the major and minor nutrients. This deficit is expected to increase in upcoming years as productive livestock population as well as the demand for foods of animal origin is showing an increasing trend. Concentrates is the costly component in livestock raring, not only due to costly feed ingredients used, but also due to food- feed competition between humans and livestock. Keeping these in mind, farmers and researchers have been trying to incorporate new and unconventional feed resources as livestock feed. Soya pulp is one such product, which has not yet been explored fully. India produced 11.86 million tons of soybean in 2013-14 (Department of Agriculture and Cooperation, Government of India, 2015) mostly from Madhya Pradesh (also known as soybean bowl of India), Maharashtra, Rajasthan, Andhra Pradesh, Karnataka, Uttar Pradesh and Chhattisgarh. Soybean is used in various forms such as feed for livestock, source of protein and oil by human beings and also it is processed into various products such as soya milk powder, soya milk, tofu, soya sauce, soya flour, soybean oil, tempeh etc. The popularity of soya products are demand driven and soya processing is slowly picking up in India due to the availability of newer technologies.
Soya pulp is a by-product of soybean during the production of soya milk or tofu. Soya pulp is beige in colour and has a light, crumbly, fine grained texture, which makes it look like moist sawdust or grated coconut and tastes similar to almond. About 1.1 kg of fresh soya pulp is produced from every kilogram of soybeans processed into soya milk or tofu. Soya pulp is mostly discarded as waste by industries, which is a major environmental concern also, due to its susceptibility to putrefaction. Also, the high moisture (85%) present in soya pulp makes it difficult to handle and it decays quickly. This paper reviews the composition and scope for utilisation of soya pulp in animal feeding.
The composition of soya pulp will depend on the variety of the crop used, harvesting time, processing methods and probably drying method. The fibre is of good quality and it has been reported that it can reduce cholesterol level, regulate blood sugar in diabetic individuals and cure irritable bowl in human being. Rahman et al. (2015) observed that the soya pulp contain 96.59% OM, 27.81% NDF and 21.99% CP. Soya pulp is also found to contain isoflavones, but in comparatively lower amounts than in soybean. The processing method employed for soybean governs amount of isoflavones left in soya pulp.
Application in animal feeding
Soya pulp is a good source of protein and fibre and it is also palatable to animals. Therefore, it can replace part of soybean in cattle, pig, goat, chicken and fish feeding. There is an immense potential of utilising soya pulp in cattle feeding as a replacement of soybean and other conventional protein sources to reduce the cost of feeding. Wang et al. (2003) in China have tried to replace 50% of soybean with soya pulp in HF cows, which maintained milk yield and milk fat percentage without affecting nutrient intake. Under Indian conditions, Thakur et al. (2015) replaced soya pulp with other soya by-products viz., soybean meal and full fat soya in the concentrate mixture up to 30% without any adverse effect on DM intake, milk yield and milk composition of dairy cows which indicates the importance of this product in livestock feeding.
Organic livestock production prohibits the use of antibiotics, growth promotors and animal byproducts in the ration. Satisfying the high protein requirements of swine with less production cost is a big challenge to organic pork producers. Alternative protein sources could increase the availability of organic feedstuffs and augment organic production demands. Dietary supplementation of soya pulp in organic pig diet has also been tried. Hermann and Honeymann (2004) reported that up to 25% inclusion levels of dietary soya pulp had no effect on average daily gain, DMI and FCR.
India has the largest goat population in world. Most of the goats are not offered with concentrate mixture at all, due to high cost of cakes and also due to lack of awareness. Soya pulp as a cheaper source of protein can be fed to goats. Supplying soya pulp in adult goats feeding @ 2% of BW/day on a dry matter basis resulted in higher intakes of DM, crude protein (CP) and metabolisable energy (ME) and improved the digestibility of DM, organic matter, CP and neutral detergent fibre than low levels of soya waste
(Rahman et al., 2015).
Constraints to the use of soya pulp in animal feeding
Moisture: The moisture content of fresh soya pulp is around 80-85% which makes it difficult to preserve. Consequently, soya pulp will decompose rapidly once produced. To overcome these limitations fresh soya pulp must be dried as early as possible under appropriate drying conditions. Drying process requires specialized equipment and is energy intensive. The resultant costs can be extremely high relative to the value of the product. This is the major factor limiting the commercial use of soya pulp worldwide. However, for economising the feeding sun drying is the method of choice and old drying methods improvised with recent technologies for the purpose.
Anti-nutritional factors: Raw soybeans contain variety of anti-nutritional factors, especially trypsin inhibitors which are partially inactivated during the solvent extraction and toasting process. Trypsin inhibitor is one of the most important factors that will probably limit the application of soya pulp in animal feed. But the processing method employed viz., soaking and grinding of soybeans, reduces the amount of trypsin inhibitor to a level which can be safely used in livestock feeding.
Soya pulp is a cheaper source of protein and fibre to animal feeding. Different workers have tried feeding soya pulp to various classes of animals. It can be used as a replacement to conventional concentrates for economic feeding without any effect on growth performance, FCR and milk yield. More studies need to be done regarding suitable drying methods and its health implications in animal feeding.
References are available upon request

by Manjula Thakur, Sanjay D. Howel, A. Majumder, Sahil and G. Mondal
Department of Animal Nutrition, ICAR-NDRI