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On the quest to find a high quality soy protein for piglets
Young animals like piglets need special care in feeding. At weaning stage, piglets need to cope with the change from suckling milk to eating solid feeds while their digestive system is not fully developed. This is also the reason why piglets are very sensitive with anti-nutritional factors (ANFs) in feed ingredients. Thus, piglets easily get stressed, reduce feed intake, decrease growth performance and have diarrhea. Providing high digestible and high quality feed becomes a "must" to support piglets overcome this tough time.
Traditionally, soybean meal was not ranked as a "safe" feed for piglets due to its high content of ANFs:
- Trypsin inhibitor - a heat labile ANFs that can be destroyed by heat: inactivate protein-degrading enzymes and reduce protein digestion, which of course results in lower growth performance.
- Antigens: large molecular proteins that escape digestion and become immunogenic in piglets.
- Soy oligosaccharides: a factor cause gas production (flatulence) and diarrhea in piglets
However, soybean is the most available vegetable protein source (284 million tons produced in 2015) with a balanced amino acid profile and good digestibility. This fact attracts interests of many researchers to transform soy protein into an alternative protein to replace expensive protein sources like fishmeal, skim milk powder and potato protein in diets for piglets. Several processes involve in removing ANFs in soybean, and give birth to three main soy protein product ranges that have more than 50% crude protein (CP) content: fermented soy, enzyme-treated soy and soy protein concentrate. Thanks to this, soy protein has its own position in piglet's diets; however, it also makes farmers get lost on the quest to find a high quality soy protein for piglets. In this article, we aim to make an outlook of soy protein utilization in piglets.
Historically, the process is originated from the production of tofu, soya sauce and soybean paste in Asia. Fermented soy is made from the fermentation of soybean meal by fungal and bacterial strains such as Aspergillus oryzae and Lactobacillus subtilis. The fermentation process is supposed to reduce or even eliminate the ANFs in soybean, and the final product would be more digestible and have a better nutritive value compared to conventional soybean. Indeed, the level of trypsin inhibitor, antigens and soy oligosaccharides was much lower in fermented soy compared with conventional soybean. This ranked fermented soy in the second place in term of low ANFs among other soy products, just after soy protein concentrate. However, one problem with fermented soy is that during the fermentation process, microbes convert soy protein and amino acids into their own protein profile.
Talking about enzyme-treated soy, as the name told us, it is a soy protein that is treated by enzyme (mostly a mixture of enzymes) to remove ANFs in soybean. Enzyme-treated soy is often being classified in the same group with fermented soy, which gives the wrong impression that the nutritive value of these two is the same. Using just the enzyme to remove ANF, will not interfere with the protein and amino acid profile of soy, and will also guarantee the quality of enzyme-treated soy between each batch much more stable in comparison with fermented soy. For example, AlphaSoy 530 (Agro Korn A/S, Denmark) is one of the leading enzyme-treated soy products. AlphaSoy 530 is produced from the well-selected soybean meal, gone through the strictly-controlled high thermal short time process (extrusion) with the fortification of enzymes to reduce ANFs and disrupt the complex structure of the seed matrix. The final product, AlphaSoy 530, is a gentle and balance protein source (53% protein) that is high digestible, suitable and very safe for the piglet's digestive system.
Soy protein concentrate
Soy protein concentrate is ranked as a premium soy protein source with a higher price tag than fermented soy and enzyme-treated soy. To achieve this high level of crude protein, the production of soy protein concentrate removes all the water- or alcohol-soluble non-protein components, and even the soluble carbohydrates through the extraction of dehulled and defatted soybean meal. This extraction process also removes most of ANFs, especially oligosaccharides.
Nutritive value and utilization of soy protein in piglets
Among soy products, enzyme–treated soy (AlphaSoy 530) and soy protein concentrate have higher metabolizable energy value than soybean meal (Figure 1). AlphaSoy 530 (3937 kcal/kg) is also far superior in term of ME value to fermented soys (3305 – 3635 kcal/kg). This is because of the extrusion process, and the enzyme treatment of AlphaSoy 530 that disrupt the rigid structure of the seed matrix and transform the fiber part as well as oligosaccharides to more digestible form and consequently provide more energy to the animals. However, in fermented soy, microbes may consume all starch, sugar (sucrose) and oligosaccharides and even partly protein of soybean meal as energy sources for their growth during fermentation. This may explain why Rojas and Stein (2014) even observed a lower ME value in fermented soy compared to soybean meal fed to weanling pigs. In case of soy protein concentrate, its high crude protein content also contributes to the diets as an energy source;
Figure 1. Metabolizable energy of various soy protein vs. soybean meal (Danish Pig Research Centre, 2014). Means with different letter are significant different (P<0.05)
In term of growth performance, a study in weanling pigs proved that enzyme-treated soy (AlphaSoy 530) is an outstanding protein source that can replace fishmeal completely while keeping up the increase in weight gain and an efficient feed conversion ratio (Figure 1) as well as a good gastrointestinal health (Sørensen and Nørgaard, 2016). The positive effect of enzyme-treated soy on growth performance and diarrhea after weaning is rather consistent in piglets in many studies; however, it is not the same in the case of fermented soy and soy protein concentrate. A new study of Harper Adams University observed that using 10% of enzyme-treated soy (AlphaSoy 530) in the diets for weaned pigs led to the highest daily weight gain compared to other soy products while the lowest one was in pigs fed soy protein concentrate (Figure 3). As the results, the higher benefit margin over feed by 1-2 € per pig was achieved in enzyme-treated soy compared with other soy products.
In general, further studies are required to clarify the effect of various soy products on growth performance and gut health in piglets. However, at this point in time, enzyme-treated soy seems to be an alternative protein source that is more consistent in quality and more economical to replace conventional high protein sources in comparison with fermented soy and soy protein concentrate.
Figure 2. Gain:Feed in newly weaned pigs fed enzyme-treated soy (AlphaSoy 530) vs. fishmeal (Sørensen and Nørgaard, 2016).
Figure 3. Average daily gain of weaned pigs fed various soy protein. Means with different letter are significant different (P<0.05) (Harper Adams University 2016).
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Article made possible through the contribution of Agrokorn
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