How to formulate diets for nursery pigs with the newly established upper limits or safe levels for antinutritional factors

By Jessika van Leeuwen, Global Category Manager Swine at Hamlet Protein A/S

There is a global trend to reduce total energy and include a higher proportion of soy derived proteins in nursery diets to limit diet costs. Soy, being the protein source of excellence for pigs, because of its balanced amino acid profile, is also the most cost-effective choice.

However, raw unprocessed soy naturally contains so-called anti-nutritional factors (ANF’s) that serve the crop as protection against molds, bacteria and consumption by wild animals. The presence of certain ANF’s reduces the digestibility of protein. Undigested protein can be fermented by (harmful) bacteria when it reaches the hindgut. As a result of this process, toxins are produced that impair the integrity and functioning of the intestinal membrane and activate the immune system. Other ANF’s can trigger a direct inflammatory response in the gut leading to chronic inflammation. This reduces the absorption capacity and increases nutritional requirements for maintenance to sustain the inflammatory response. So less nutrients are available for growth and performance of the animals.

The ANF’s can be grouped according to their effect on nutritive values of feed ingredients and biological responses in animals. The three most important ANF’s for piglets from soy are trypsin inhibitors that limit the digestion of proteins (TIA), alpha-galacto-oligosaccharides that trigger gas formation and (osmotic) diarrhea (αGOS) and beta-conglycinin, an antigen that activates an inflammatory response in the gut (βcon). It is therefore common practice to avoid or limit the inclusion of soybean meal in nursery diets to minimize the exposure to high levels of ANF’s.

So, how do you determine which levels of exposure to ANF’s are too high? The best answer to that question is to regularly sample the purchased SBM and analyze for ANF’s. Most companies do every now and then check the level of TIA of the SBM they receive. But it is not common practice to analyze for αGOS, like raffinose and stachyose and there are only very few labs in the world that can analyze βcon which makes it difficult to incorporate in routine checks.

At Hamlet Protein we are equipped with two state-of-the-art analytical labs (1 in our factory in Horsens, Denmark and 1 in our factory in Findlay, OH, USA) where we can measure TIA, αGOS and βcon on a routine base. As we have analyzed thousands of samples of SBM from all over the globe we have learned that a large variation exists in the levels of TIA, αGOS and βcon between different samples of sbm, regardless of the region of origin (figure 1).

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Figure 1 variation in levels of 1: trypsin inhibitors (TIA), 2: alpha-galacto-oligosaccharides (αGOS) and 3:beta-conglycinin (βcon) in SBM samples analyzed at Hamlet Protein.

The average levels of ANF’s found in the analyzed SBM samples were: 2.7 mg/g TIA, 7.11 % of αGOS and 49430 ppm of βcon. These averages can be used to by nutritionists to make a prediction on how much sbm to include in the diets of nursery pigs. That is if they knew the upper tolerance levels of nursery pigs for ANF’s. Surprisingly, however, there are no clear guidelines on the upper limits of dietary ANF’s for nursery pigs. Therefore, we combined different findings in the literature with tolerance levels for TIA, αGOS and βcon for nursery pigs into one clear guidance for nutritionists.

The literature reveals that there is a clear dose effect on swine performance from exposure to TIA (figure 2. Zarkadas and Wiseman, 2000) and that with an exposure between 0.8 – 1.3 mg/g TIA in the diet the efficacy of protein digestion (N retention and N utilization) decreases significantly in nursery pigs (Jansman et al., 1998). Levels of over 1% of αGOS in nursery diets significantly reduce feed efficiency and N retention (Zhang et al., 2001) while levels of 4000 ppm of βcon negatively altered gut morphology in weaned pigs compared to no damage at 2000 ppm (figure 3 Ma et al., 2019).

Figure 2: effect of intake of trypsin inhibitor activity (mg/day) on growth performance of weaned pigs (adapted from Zarkadas and Wiseman, 2000)

Figure 3: A) average daily gain (ADG g/pig/d) and B) morphology (duodenal villi height, µm, and villus height to crypt depth ratio (VH:CD)) in pigs fed a diet with SBM (βcon = 4000 ppm) or a diet where SBM was partially replaced with an enzyme treated SBM (βcon = 2000 ppm) D0-14 or D0-28 post-weaning (HP300-1 and HP300-2, respectively). Adapted from Ma et al., 2019

Let‘s have a look at the three ANF’s individually to see which of them is most limiting for diet formulation (see Table 1).

Trypsin inhibitor activity

TIA content in SBM is quite frequently around 2.7 mg/g, therefore it is usually not limiting for the formulation of nursery diets (so as not to exceed the upper level in feed, 1.3 mg/g) as levels of 52% could be used and this is not common to include in nursery diets. Even if we assume the highest level of TIA content (5 mg/g) this still allows for an inclusion of 26% of SBM in the nursery diet.

We can therefore safely conclude that TIA is not a limiting ANF for diet formulation of weaned pigs using regular SBM.

Alpha galacto oligosaccharides

αGOS levels in SBM average 7.11% and respecting the level of 1% of αGOS in the nursery diet leads to a restriction in the usage of SBM to a maximum of 14%. For the highest level of αGOS found in SBM (10.12%) the maximum inclusion level of SBM is 10%.

Betaconglycinin

The highest variation in terms of ANF concentration undoubtedly comes from βcon. And there is no correlation with the other ANF’s. Both TIA and αGOS can be low while βcon is still to be found above the average of around 50000 ppm. Considering this average, it becomes clear that βcon is the most limiting ANF for the formulation of nursery diets. Respecting the safe level of 2000 ppm no higher inclusion than 4% of SBM is recommendable for nursery pigs with a range up to max 8% if one goes up to 4000 ppm. However, it becomes even more limiting when the SBM contains very high levels of βcon (150000 ppm), because then the maximum inclusion level is 1.4-2.8%% in order not to risk any damage to the gut epithelial.

So, from the three ANF’s described above βcon puts the strongest pressure on inclusion rates. Since only 2000 ppm is considered completely safe without altering gut morphology it is recommendable that if one does not know the exact βcon content of their raw material to refrain from using SBM in phase 1 diets for nursery pigs. Only then the risk of overexposure to βcon can be fully avoided.

However, it can be necessary to use SBM in nursery diets. In this case, make sure to respect the safe limit of 2000 ppm βcon and in any case never exceed 4000 ppm βcon during the first 4 weeks after weaning. The rest of the protein in the diet should then come from a low in ANF’s protein source.

ANF’s can be partly reduced by processing of the protein ingredient through heat treatment or fermentation, but the most effective way to eliminate ANF’s is through enzymatic treatment. The use of enzyme treated soybean meal in diets for young animals minimizes the activation of feed-induced immune reactions at an early age, avoiding negative effects on performance later in life.

In conclusion

With the clearly established upper limits for TIA, αGOS and βcon nutritionists now have a tool in their hands to be able to calculate the maximum safe inclusion of their SBM in nursery diets. However, it is therefore necessary to conduct periodic measurements of ANF levels of the raw materials. The most limiting ANF for the inclusion of SBM in nursery diets is betaconglycinin which has safe inclusion levels of around 2000 ppm only and therefore strongly limits the use of SBM in these diets.