Is soybean meal bad for broiler gut health?

Do anti-nutritional galacto-oligosaccharides from soybean meal have a negative effect on broiler gut health?
calendar icon 16 September 2022
clock icon 4 minute read

What do we mean by 'gut health'?

Gut health can be an extremely broad topic with different meanings to different individuals. There is not a clear definition of what factors are included in “gut health”, but it is some combination of different physiological and functional features that affect the development, growth and maintenance, and immune status of an animal (Kogut and Arsenault, 2016). Furthermore, most would agree that the microbial community found within the gastrointestinal tract of poultry plays an important role in the “gut health” of the host through benefiting nutrient digestion and absorption, development of gut barrier function, and preventing colonization of pathogenic bacteria.

Animals lacking a diverse gut microbial community tend to have a lesser developed immune system and are more susceptible to disease challenges (Bailey, 2019). As it is a very complex environment, many poultry researchers have tried to define what a typical gut microbe community looks like. It has been determined that multiple factors (sampling technique and site, diet, geographical location, genetics) play a significant role in what different bacterial species and what proportion they exist within the gastrointestinal tract of broilers, with diet being the most influential factor (Richards et al., 2005, Lumpkins et al., 2010).

Nutritional value of soybean meal

Soybean meal (SBM), the primary choice of vegetable-based protein ingredients, has a favorable nutrient profile and global availability that can account for up to a third of a complete broiler diet. However, even with the ideal protein profile of SBM, there are variable levels of unwanted anti-nutritional factors that can negatively effect broiler growth and performance (Blanch, 2020 a,b). More specifically, indigestible galacto-oligosaccharides (GOS: stachyose and raffinose) can be present at levels of 5-10% (Garcia-Rebollar et al., 2016), reducing the nutritional value of SBM as an ingredient. Previous research indicates that some oligosaccharides may elicit a prebiotic effect promoting beneficial bacteria and improving growth performance (Richards et al., 2020). However, it has also been concluded that the prebiotic effect is observed at lower levels and soy GOS content above a specific threshold will start to negatively influence energy and protein utilization of the complete feed (Blanch and Brown, 2022).

How does the changing rate of GOS affect gut health?

Recently, we have investigated the effect of increasing levels of the soy GOS, stachyose and raffinose, on the ceca microbial composition of broilers at 21 days of age as a potential indicator of “gut health” (Brown et al., 2022). Broilers were fed 1 of 5 experimental diets. A basal diet based on soy protein isolate (SPI) to be devoid of soy GOS, or the SPI diet with the addition of 0.9, 1.8, 2.7, or 3.6% total GOS as a mixture of stachyose and raffinose at a ratio of 4:1, similar to SBM. Inclusion rates used were to be consistent with typical GOS ranges observed in commercial broiler diets with variable SBM quality.

Significant decreases were observed in alpha diversity with increasing level of stachyose and raffinose (P < 0.05). Shannon Index, an indicator for how diverse the species in a given community are, was significantly lower for SPI+1.8% GOS, SPI+2.7% GOS and SPI+3.6% GOS groups than that of the SPI and SPI+0.9% GOS groups, while SPI+2.7% GOS and SPI+3.6% GOS showed a lower Shannon Index compared to SPI+1.8% GOS (Figure 1. A).

Figure 1. Alpha diversity of cecal microbiota in broilers fed different levels of the soy galacto-oligosaccharides (GOS) - (A, B): Shannon Index and the number of Observed ASVs in the gut microbial community. Different letters over bars represent significance at P < 0.05.

With regards to Observed Amplicon Sequence Variants (ASVs), or single DNA sequences recovered, the SPI group had the highest value, followed by a step-wise decrease with SPI+0.9% GOS, SPI+1.8% GOS, SPI+2.7% GOS and SPI+3.6% GOS groups (Figure 1. B). It is well-known that decreased diversity of the gut microbiota is linked to a declined health status (Larsen and Claasen, 2018), which would explain the negative effect of high levels of soy GOS, stachyose and raffinose, on the gut health of young chicks, as previously reported on this website (Blanch, 2020b).

Overall, ceca microbial diversity is reduced with increasing levels of soy GOS, stachyose and raffinose, in starter broiler diets. These data indicate that soy GOS do influence ceca microbial community and consequently the intestinal health of young chicks.

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(2019) Gut Health in Poultry-The World Within: Update.. The Poultry Site
Blanch, A.
(2020a) Soy trypsin inhibitors do affect the growth and gut health of chickens.. The Poultry Site
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(2020b) Soy oligosaccharides and beta-conglycinin, behind gut inflammations, wet droppings and footpad dermatitis in chickens. The Poultry Site
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(2022) The antinutritional galacto-oligosaccharides from soybean meal in broiler starter feed also impair metabolizable energy and dietary N retention.. The Poultry Site
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(2022) Effect of dietary soy galacto oligosaccharides on AMEn, nitrogen retention and ceca microbiome of broiler chickens. In Proceedings of PSA Annual Meeting, July 11-14, 2022, San Antonio, Texas (USA).
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Kyle Brown

Nutritionist at Hamlet Protein

Alfred Blanch

Poultry Category Manager at Hamlet Protein A/S (Horsens, Denmark).

Simone Husballe Rasmussen

Hamlet Protein
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