In the last two years, Hamlet Protein has developed scientific studies aimed at determining the maximum levels of soybean meal (SBM) antinutritional factors (ANFs) that should be in broiler starter diets, leading to interesting findings, published in "The Poultry Site" in various articles. The most relevant SBM ANFs in poultry farming are trypsin inhibitor activity (TIA), the indigestible oligosaccharides stachyose and raffinose and the antigen beta-conglycinin.

The content of these ANFs is highly variable in SBM as observed by Garcia-Rebollar et al (2016) and is shown in table 1. Thus, we can see SBM samples with high content of trypsin inhibitor activity (e.g. > 5 mg/g) but low in stachyose + raffinose (e.g. < 5%) but also vice versa (e.g. >1.5 mg TIA/g and up to 10% stachyose + raffinose). Likewise, the content of the antigen beta-conglycinin in SBM can range between 15,000 and 150,000 ppm (Hamlet Protein internal data).

The variable content of each one of these ANFs in poultry starter feed will affect the intestinal health of young birds and consequently their productive performance throughout their lives. We cannot focus on eliminating just one of these ANFs in broiler and turkey starter diets, but rather we must ensure that the content of each one of them is reduced below their maximum tolerance thresholds.

Table 1. Content of trypsin inhibitor activity (TIA) and stachyose and raffinose in different SBM sources.

	USA (n=180)			BRA (n=165)			ARG (n=170)			S.E.M.
	Average	Range	CV (%)	Average	Range	CV (%)	Average	Range	CV (%)
TIA (mg/g DM)	3.5a	1.4-5.5	22.1	2.9b	1.8-4.7	18.9	2.8b	1.4-4.6	20.2	0.053
Stachyose (g/kg)	63.9a	4.3-8.3	8.4	52.5c	3.7-7.3	10.1	56.5b	3.7-7.1	9.5	0.440
Raffinose (g/kg)	10.9c	0.6-1.9	25.9	15.8a	0.9-2.6	17.2	13.5b	0.9-2.0	14.2	0.230

Rada et al. 2017 observed by reducing the level of TIA in the diet by approximately 15%, it was possible to increase the weight of broilers by more than 100 g at 38 days of age and decrease the FCR by 4 points. Although the heating process in manufacturing SBM significantly reduces the TIA content, there is substantial variability in the TIA content in SBM, as reported by García-Rebollar et al. (2016). In starter feeds formulated with more than 30% of SBM, TIA concentrations can exceed 1.4 mg/g, compromising the growth of chickens. In addition, high TIA content in feed impairs the digestion of the protein which directly affects the intestinal health of chickens. Palliyeguru et al. (2011) demonstrated dietary soy TIA elicited an increased severity of sub-clinical necrotic enteritis. When amino acid digestibility is compromised, the ileal digesta will have a relatively high content of undigested amino acids that pass into the large intestine and cecal tonsils, where it can be used by pathogenic bacteria such as C. perfringens. Thus, reducing SBM content below 30% in starter feed can be used strategically to diminish adverse performance attributed to high TIA in finished feed.

Stachyose and raffinose, soy galacto-oligosaccharides, are not digested in the monogastric intestinal tract due to the absence of endogenous α-1,6-galactosidase activity in the intestinal mucosa (Gitzelmann and Auricchio, 1965). The poorly digested carbohydrates exert an osmotic effect in the duodenum and jejunum portion of the intestinal tract until they are fermented in the cecal tonsils (Marteau and Boutron-Ruault, 2002). Higher osmotic pressure caused by consumption of noxious quantities of soy oligosaccharides creates abnormally aqueous digesta that increases the feed passage rate in broilers (Coussement, 1999; David and Peter, 2001), which leads to lower digestibility, absorption and live performance (Ravindran and Abdollahi, 2021). According to our recent research (Brown et al., 2022), young chicks can ferment up to 1.25-1.8% soy galacto-oligosaccharides in feed. Any level higher than this threshold will trigger intestinal disorders.

Beta-conglycinin is a storage glycoprotein which plays a large part in its immunogenicity (Amigo-Benevent et al. 2009). Beta-conglycinin is comprised of three subunits (α, α’ and β) all of which display immune-reactivity (Ogawa et al, 1995; Krishan et al. 2009; Zheng et al. 2014). Kang et al. (2020) indicated that the oral administration of beta-conglycinin induces intestinal damage in 7 day old chicks, which consequently may also affect live performance due to reduced digestion and absorption capacity.

Conclusion

The content of soy ANF’s in poultry feed has been demonstrated to elicit a negative effect on the digestibility of the diet and the intestinal health of birds, which impact live performance. Frequent, effective monitoring of the ANF content in SBM and procedures to reduce levels of soy ANFs through the minimization of conventional SBM inclusion serve as a pertinent strategy to minimize live performance losses. It is not a good tactic to focus only on the reduction or elimination of only one of these ANFs while neglecting the level of the other two.

Literature references

Garcia-Rebollar P. et al (2016). Influence of the origin of the beans on the chemical composition and nutritive value of commercial soybean meals. Anim. Feed Sci. Technol. 221: 245-261

Rada V. et al (2017). The effect of soybean meal replacement with raw full-fat soybean in diets for broiler chickens. J. App. Anim. Res. doi: 10.1080/09712119.2015.1124337

Palliyeguru M.W.C.D. (2011). Effect of trypsin inhibitor activity in soya bean on growth performance, protein digestibility and incidence of sub-clinical necrotic enteritis in broiler chicken flocks Br. Poult. Sci. 52: 359-367

Gitzelmann R. and Auricchio S. (1965) The handling of soy alpha-galactosidase by a normal and galactosemic child. Pediatrics, 36: 231–232

Marteau P. and Boutron-Ruault M.C. (2002). Nutritional advantages of probiotics and prebiotics. Br. J. Nutr. 87: S153–S157

Coussement P.A.A. (1999). Inulin and oligofructose: safe intakes and legal status. J. Nutr. 129: 1412–1417

David L.T. and Peter M.C. (2001). Short-chain fatty acids and human colonic function: roles of resistant starch and non-starch polysaccharides. Physiol. Rev. 81: 1031–1064

Velmurugu Ravindran and M. R. Abdollahi (2021). Nutrition and digestive physiology of the broiler chick: State of the art and outlook. Animals (Basel). 2021 Oct; 11(10): 2795. Published online 2021 Sep 25. doi: 10.3390/ani11102795

Brown, K. et al. (2022). Is soybean meal bad for broiler gut health? The Poultry Site, September 2022. https://www.thepoultrysite.com...

Amigo-Benavent M. et al. (2009). Carbohydrate moieties on the in vitro immunoreactivity of soy β-conglycinin. Food Res. Int. 42: 819-825

Ogawa T.et al. (1995). Alpha-subunit of betaconglycinin, an allergenic protein recognized by IgE antibodies of soybean-sensitive patients with atopic dermatitis. Biosci. Biotechnol. Biochem. 59: 831-813

Krishan H.B. et al (2009). All three subunits of soybean beta-conglycinin are potential food allergens. J. Agric. Food Chem. 57: 938-943

Zheng S. et al (2014). Role of soybean β-conglycinin subunits as potential dietary allergens in piglets. Vet. J. 199: 434-438

Kang, D.R. et al. (2020). Soybean beta-conglycinin induces intestinal immune responses in chicks. Brazilian Journal of Poultry Science, vol. 22, nº 2: 1-10