Did you know that high levels of soy β-conglycinin in (pre-) starter feed induces intestinal inflammation in your chicks and impairs their performance?

By Hamlet Protein

Soybean has proven to be, without a doubt, an extraordinary source of plant protein for feed in intensive poultry production systems. However, high levels of soybean protein (e.g., toasted soybean meal, full fat soybean meal) in poultry (pre-) starter diets cause poor growth and feed efficiency in young birds. These negative influences are due to the antinutritional-factors (ANFs) present in the different types of soybean meal (SBM), as we have previously reported (Blanch, 2022). Among these ANFs, the storage protein β-conglycinin has been well-known for a long time as an immunogenic and allergy-causing factor in piglets, rabbits, dogs and fish, showing a big influence in the immune response of the small intestine (Zhao et al., 2008; Taliercio et al., 2014).

However, it has only been a few years that new research has revealed the effect that β-conglycinin from SBM can have on the immune response of birds. Lately, Taliercio and Loveless (2020) have demonstrated that chickens mount an immunogenic response to soy β-conglycinin since they observed that some epitopes of β-conglycinin bind all three classes of chicken immunoglobulins (IgA, IgM and IgY) while other bind only one or two Ig classes (Figure 1). In other words, it has been clearly shown that the bird's immune system reacts to soy β-conglycinin as does the immune system of other animal species.

Figure 1. Chicken immunoglobulins bind β-conglycinin epitopes

Almost at the same time as the aforementioned study, Kang et al. (2020) investigated the effects of β-conglycinin-induced allergic sensitization on chicks’ small intestine by feeding 60 mg of pure soy β-conglycinin to 7-day-old chicks and colleting small intestine samples before feeding or 1 h, 6 h or 12 h after feeding. These authors observed that β-conglycinin-induced allergic sensitization marginally damages the epithelium lining of the duodenum villi and, in addition, significantly increases the accumulation of mast cells in the lamina propria and crypt of the duodenum (Figure 2). Mast cells are a type of white immune cell that is found all through the body, including in the intestine. They play a key role in the inflammatory process, releasing "mediators" or compounds that induce inflammation.

Figure 2. Dietary soy β-conglycinin increases mast cell number in the duodenum of 7-d-old chicks (Kang et al., 2020). Columns with different superscripts differ (p<0.05).

Moreover, the proinflammatory TNF-α level always increased after feeding β-conglycinin. The proinflammatory cytokines IL-8 and IL-2 were significantly downregulated 1 h after feeding; however, there were significant increases 6 h and 12 h after feeding. All in all, it was shown that soy β-conglycinin also causes inflammation in the small intestine of young chicks.
However, until very recently, the negative effect of soy beta-conglycinin on the productive performance of young chicks has not been demonstrated. Hamlet Protein, always at the forefront of knowledge on protein in young animal nutrition, has funded novel research on the effect of soy β-conglycinin on the productive performance of young broilers. Thus, Teague et al. (2023) investigated the effects of dietary soy β-conglycinin on feed intake (FI), body weight gain (BWG) and feed conversion ratio (FCR) in 7-day-old chicks through a dose response study. Purified β-conglycinin was added to soy-protein isolate-based diets to achieve 0, 25,000 or 50,000 mg β-conglycinin / kg of mash feed or pelleted feed. No interactive effects were observed between β-conglycinin level and feed form from 0 to 7 days of life, so the effects of β-conglycinin are the same both in mash feed and in pelleted feed. FI and BWG were significantly reduced by 50,000 mg β-conglycinin / kg feed compared to 0 and 25,000 mg β-conglycinin / kg feed. Likewise, FCR was significantly increased by 50,000 mg β-conglycinin / kg feed compared to the other two experimental treatments (Table 1). It should be said that, although there were no significant differences between 0 and 25,000 mg β-conglycinin / kg feed, chickens without β-conglycinin in their diet did show a numerically better productive performance than chickens that were fed the diet with 25,000 mg β-conglycinin / kg. All things considered, these findings allow us to conclude that soy β-conglycinin does indeed have a dose-dependent negative effect on the performance of young chicks and that the threshold for this anti-nutritional factor in early-age feed is less than 25,000 ppm.

Table 1. Dietary soy β-conglycinin affects performance of 7-day-old broiler chickens (Teague et al., 2023). Columns with different superscripts differ (p<0.01).

At Hamlet Protein, we can help you reduce the β-conglycinin content in your broiler or turkey (pre-) starter feeds without adding other ANFs and without damaging the amino acids with overheating. Contact our delegates or distributor in your market.
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