Soybean meal is not the only protein source that has anti-nutritional factors for young birds

By Alfred Blanch, Hamlet Protein

According to the scientific bibliography on the subject and based on the findings obtained in our recent investigations, we have allowed ourselves to establish maximum thresholds for each of the main soy ANFs with relevance in the feeding of young chicks:

  • Trypsin inhibition activity: <1.4 mg/g feed
  • Stachyose + raffinose: <1.8%
  • Β-conglycinin: <25,000 ppm

In order not to exceed these thresholds in (pre-) starter feed, our recommendation is that the inclusion levels of total soybean meals (e.g. toasted soybean meal, full fat meal) be less than 30 %. However, the high amino acid requirements of young birds force us to include other protein sources in feed for early ages, if the soybean meals’ content is less than 30%. We cannot fill the gap between the amino acid contributions of soybean meals and the amino acid requirements of the young bird with only synthetic amino acids. The question is: can we use any type of protein source without any limit to fill this gap? I'm afraid the answer is that we can't.

Obviously, there are various protein sources available on the market for poultry feed. All of them have their advantages but also their drawbacks. It is imperative to take these drawbacks into account when trying to formulate diets for young birds, which are physiologically, immunologically and microbiologically immature. Limiting the level of inclusion of protein sources will allow to overcome their possible negative effects on chicks and poults. The main sources of protein used in feeding young birds vary according to the market. In any case, in this article we are going to expose the main ones as well as enumerate those ANFs or risk elements that each one of them presents.

Fishmeal: the freshness of this raw material, as well as the characteristics of its processing and storage conditions affect the worsening of fishmeal and, consequently, its content of peroxides, volatile nitrogen and toxic biogenic amines, all of which are elements that compromise the nutritional value of this ingredient and can induce inflammation in the young bird that ingests them. On the other hand, it is well known that fishmeal is a predisposing factor to necrotic enteritis in chickens (Moore, 2016). This predisposition is related to the high non-protein nitrogen (NPN) content in fishmeal, which can be more than three times higher than the content in soybean meal (Figure 1), being a good substrate for proteolytic bacteria such as Clostridium species.

Figure 1. NPN and amino acid protein content in soybean meal and fish meal (Hamlet Protein unpublished data

Another element to consider with fishmeal is that, even though its amino acids are highly digestible, the digestion kinetics of this protein source is quite slow and, in any case, slower than the kinetics of soybean meal (Figure 2). It is well known that it is not enough to have a high protein digestibility but also a fast protein digestion, since the speed of the protein digestion is correlated with the productive performance of the birds (Selle et al., 2016).

Another element to consider with fishmeal is that, even though its amino acids are highly digestible, the digestion kinetics of this protein source is quite slow and, in any case, slower than the kinetics of soybean meal (Figure 2). It is well known that it is not enough to have a high protein digestibility but also a fast protein digestion, since the speed of the protein digestion is correlated with the productive performance of the birds (Selle et al., 2016).

Figure 2. Soybean meal shows faster protein digestion speed (protein kinetics) compared to fish meal (Hamlet Protein unpublished data).

Meat and bone meal and poultry byproduct meal: these slaughterhouse by-products, although they are protein sources with an acceptable quality : price ratio, have the disadvantage of showing a high variability, a high risk of microbiological contamination as well as rancidity of their lipid fraction -rich in unsaturated fatty acids-, which can lead to feed-induced inflammation in the immature intestine of young birds. In addition, as with fishmeal, the NPN content in this type of animal protein can be tremendously high (Figure 3), favoring the proliferation of certain pathogenic bacteria in the intestines of chicks and poults, such as Clostridium perfringens. Furthermore, increased gizzard pH, stimulated by dietary animal proteins, also encourages C. perfringens proliferation (Williams, 2005).

Figure 3. NPN and amino acid protein content in soybean meal and poultry byproduct meal (Hamlet Protein unpublished data)

Corn gluten meal: although this protein source has high digestibility coefficients in poultry, it is often the cause of wet litter problems when included in diets for young birds. It has been described that zein, a type of prolamine that is a main component in corn gluten, may damage the integrity of the intestinal epithelium (Sandhu and Fraser, 1983), which could be behind the problems of wet litter that we have observed many times on farms. Another disadvantage of corn gluten is its slow protein digestion, which can impair the productive performance of chickens. Berrocoso et al. (2020) fed chickens with diets with fast protein kinetics and diets with slow protein kinetics, the latter containing corn gluten as a "slow protein" source. The authors observed that diets with corn gluten, despite having the same ileal digestibility as diets with fast protein, resulted in poorer productive performance of young chicks.

DDGs: they undergo heating during their industrial process, which may affect the digestibility of amino acids. In addition, the risk of contamination by alpha toxins and other mycotoxins is much higher than in the original grain. Besides the risk of presence of mycotoxins, microbial contaminations (e.g., Salmonella) in DDGs is another risk factor to consider (FEDNA, 2021).

Rapeseed meal: the main antinutritional factor of rapeseed are glugosinolates (GLS), which are a large group of sulfur-containing secondary plant metabolites. The major GLS present in rapeseed meal are gluconapin (3-butenyl), glucobrassicanapin (4-pentenyl), progoitrin (2-hydroxy-3-butenyl), gluconapoleiferin (2-hydroxy-4-pentenyl), glucobrassicin (3-indolylmethyl), and 4-hydroxyglucobrassicin (4-hydroxy-3-indolylmethyl). It is generally held that GLS, per se, are harmless. However, they are always going together with by the enzyme myrosinase in the seed. In the presence of moisture and following break of the seed, the GLS are hydrolyzed to yield a range of compounds, including isothiocyanates, goitrin, nitriles, and thiocyanates, that adversely affect growth performance in birds. In the 1970s, double-zero rapeseed or canola was developed to reduce its glucosinolate content below 15 micromol/g. In broiler chickens, feeding a high level of dietary GLS results in reduced feed intake, growth rate, and increased mortality.

Erucic acid and tannins are other ANFs present in rapeseed meal. Erucic acid has been shown to cause cardiovascular problems as it is deposited in heart muscle whereas tannins may form complexes with protein and proteolytic enzymes in the gastrointestinal tract, thus affecting protein digestion and bird growth. Khajali and Slominski (2012) carried out an excellent review on the importance of the different ANFs in rapeseed that can compromise the productive performance of meat birds.

Sunflower meal: The content of sunflower antinutritive factors is quite low. Only chlorogenic acid has been detected as such, a polyphenolic compound present in concentrations of 1-3%, which could reduce the activity of some digestive enzymes. The activity of two important intestinal disaccharidases (maltase and sucrase) and body weight gain is reduced in broiler chicks when fed high levels of sunflower meal (Horvatovic et al., 2015). However, the main limitation for the use of sunflower is its high fiber and lignin content (FEDNA, 2021).

Peas meal: peas contain ANFs, which can be classified in proteinaceous ANFs, including antigenic proteins, trypsin inhibitors, α-amylase inhibitors, and lectins, as well as in non-proteinaceous ANFs, such as alkaloids, tannins, and saponins. While trypsin and α-amylase inhibitors are known to reduce the nutrient digestibility of feed associated with reduced animal performance, antigenic proteins and lectins interact with the intestinal mucosa and thus may initiate immune reactions (Röhe et al, 2017).

Potato protein: High contents of aromatic amino acids in potato protein may be metabolized by intestinal microbiota resulting in phenolic compounds which are toxic for the gut epithelium, impairing the intestinal integrity. Furthermore, potato protein may contain high content of trypsin inhibitors, which will compromise protein digestibility and therefore performance when it is fed to chickens. All in all, Palliyeguru et al. (2010) saw that the inclusion of potato protein in diets for broilers may be a predisposing factor for intestinal clostridiosis and increase the incidence of necrotic enteritis lesions in the intestine more than the inclusion of fish meal or soybean meal (Table 1).

Table 1. Incidence of necrotic lesions of duodenum and proximal jejunum in broiler chickens fed different protein sources (Palliyeguru et al., 2010). *Number of lesion-positive birds out of 48 birds sampled per treatment.

The negative effect of high levels of potato protein in broiler chickens has been corroborated by Fernando et al (2011). The birds fed on a potato protein-supplemented diet had a significantly lower feed intake and a significantly lower growth rate compared with the birds fed on a soya-based diet. There were no significant. The apparent crude protein digestibility of the potato protein-supplemented diet was significantly lower. Furthermore, a significantly higher alpha toxin antibody titer and a significantly increased incidence of hepatic lesions were found in the birds fed on the potato protein-supplemented diet compared with those fed on the soya protein diet.

The content of ANFs in each of the above-referred alternative protein sources greatly limits their inclusion, especially in diets for young ages. In short, no alternative protein source alone can fill the gap between the amino acid intake from soybean meal when included at less than 30% in the (pre-) starter and the high amino acid requirements of young birds. At Hamlet Protein, we can help you reduce soy ANFs in your (pre-) starter feed, without having to risk introducing other raw materials’ ANFs that could compromise intestinal health and the growth of your chicks. Do not wait any longer, contact our delegates in your area and we will help you together.


Providing the right nutrition in the first life stage determines the overall lifetime performance of the animal. Our soy-based specialty ingredients improve health, welfare and performance of young animals. That is how we deliver a strong return on investment to producers around the world.