Alternative sources of soy protein in pigs' feed

Food costs vary according to the ingredients used in the ration, representing approximately 70% of production costs. The constant fluctuation of prices on the market, due to the increasing demand of grains and legumes as raw material for human consumption, bio-fuels and bio-industrial products, as well as the climate change, to name but a few, call for the search for cheaper alternative ingredients that can be added to the feed without affecting the animals' performance.

There are a variety of pulses and legumes, as well as by-products, that can partially or completely replace soy. One of the major limitations to their use is the presence of anti-nutritional factors and variations in their nutritional composition, which directly affect the availability and digestibility of nutrients.

However, at the time of seeking alternatives, it is necessary to consider, including but not limited to: their origin, nutritional composition, digestibility and availability of nutrients, anti-nutritional factors, practical levels and production stage of the animal. Importantly, it is still also necessary to add industrial amino acids to meet the demands of the animals, and this may increase the price of feed compared to the use of soy.

Green peas

The increase in production and by-products for human consumption generates a certain amount of discarded product that does not meet quality indices, but that are still suitable for use in swine feed. Peas have high levels of lysine and energy, but low levels of sulfur amino acids and tryptophan (Stein et al., 2006.) Its use is recommended only from two weeks post-weaning, so as to not affect performance due to immaturity of the piglets' gastrointestinal tract (Stein et al., 2004.) It is possible, in growing-finishing pigs, to completely replace soy with peas without affecting performance, carcass composition (Newman et al., 2011) or palatability (Stein et al., 2006.) Since tolerance of low levels of anti-nutritional factors increases in the animals from the age of 63 days, their feed intake is higher and replacing soy can lower production costs, thus justifying their use in this phase, where feed costs amount to 60-70% of the total feed costs.

Rapeseed cake

The main problem associated with its inclusion in the feed is the reduction in feed intake due to the presence of anti-nutritional factors. From a production point of view, the most important anti-nutritional factors are glucosinolates, which are not toxic themselves, but the action of the enzyme myrosinase present in the grain, or of enzymes present in the microorganisms in the gastrintestinal tract, lead to the formation of hydrolysis products (isothiocyanates, oxazolidintiona and nitriles), that affect consumption (Fedna, 2011). Plant breeding has significantly reduced the presence of glucosinolates; however,  it is recommended to limit their use in piglets in the initial phase due to the decrease in performance, probably associated with the presence of fibre, tannins, sinapine and probably glycosinolates. In growing-finishing pigs, studies have shown an inclusion of up to 25% does not affect animal performance (Beltranena E, 2014.)

Cottonseed meal

One of the major factors limiting its use in feed formulations is its variation in chemical composition, associated with the different seed processing methods for oil extraction (Paiano et al., 2006), and the presence of gossypol, a free polyphenolic pigment which is toxic for monogastrics, causing, including but not limited to: loss of appetite, pulmonary oedema, enlarged liver, cardiac muscle necrosis, reproductive problems and fragile erythrocytes. During the oil extraction process, gossypol binds to lysine and proteins, thus reducing its availability (Ezekiel, 2002.)

Table 1 shows the average chemical composition and digestibility coefficients of amino acids from some protein ingredients that can partially or completely replace soybean meal, from different literature sources.

Table 1. Average values ​​of chemical composition and digestibility coefficients of amino acids in rapeseed, rapeseed meal, peas and cotton cake for pigs, based on data from different authors.

To sum up, the addition of alternative ingredients to the ration will depend mainly on how their variation in nutritional composition compares to soybeans and on their price, which will determine the inclusion rate and the actual inclusion.