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I recently came across a very interesting experimentation done in 2019 by Huting, MSc, X.Guan, MSc and F.Molist, DVM, PhD from Schothorst Feed Research. This publication was focusing on the importance of measuring the Acid Buffering Capacity (ABC value) of the diets in piglets to predict growth performance. ABC is a well know concept for animal nutritionists but it is too rarely calculated and taken into consideration when formulating piglet diets despite the fact that modern formulation software automates such calculation.

Young piglets have problems with the acidification of their stomach. In suckling piglets, the hydrochloric acid (HCl) secretion is low. The bacterial fermentation of lactose to lactic acid from sow’s milk acidifies the gastrointestinal contents but can suppress HCl production at the same time. Large and frequent intakes of solid feed can stimulate HCl production however creep feed consumption is low and variable between and within litter up to at least four weeks of age.

The combination of the low HCl secretion, lack of lactose in the diets, and the consumption of large meals at infrequent intervals at weaning can result in elevated stomach pH, often over 5.0 and remain high for several days. The latter, negatively influences stomach bactericidal properties and protein digestion. A low gastric pH is necessary for: 1) the conversion pepsinogen to pepsin, which occurs rapidly at a pH of 2.0 but only slowly at a pH of 4.0 and 2) protein hydrolysis by pepsin (at a pH of 2.0 to 4.0). A high gastric pH may also allow pathogens to survive and to colonise in the digestive tract. In addition, the high levels of undigested protein in the intestinal tract as a result of the reduced protein digestion in the stomach may increase protein fermentation leading to unfavourable by-products (biogenic amines, NH3) negatively influencing the permeability of the intestinal wall.

A high acid-binding/buffering capacity of the feed (i.e. its ability to neutralise acid) further raises the stomach pH. The concept of manipulating stomach acidity by adding acids to feeds or reducing ingredients with high acid-binding or buffering capacity (like animal proteins, carbonate and zinc oxide) has been around for a long time (Jasaitis et al., 1987; Bolduan et al., 1988; Lawlor et al., 2005). The addition of organic acids to piglet starter feeds to reduce the risk of post-weaning diarrhoea has become a common practice to mitigate the high ABC value of common piglets diets. Organic acids can act in three ways reducing the incidence of diarrhoea and improving piglet performance by: 1) their direct bacteriostatic effect; 2) a low stomach pH improving the onset of protein digestion; and 3) a low stomach pH increasing the retention time favouring protein hydrolysis in the stomach (Partanen and Mroz, 1999).

In their experiment, the Schothorst team of researchers included 16 different diets, 8 for the pre-starter stage (first 2 weeks) and 8 for the starter stage (weeks 3 to 5). They set 3 different levels of ABC-4 at 175, 225, and 275 mEq/kg of complete feed. As a reference, the recommended level of ABC-4 for weaned piglets is below 250 mEq/kg. To reach a level below 250 mEq/kg, the researchers incorporated organic acids, either as citric acid, formic acid, or a combination of both. Since citric acid has a lower ABC-4 value than formic acid (-6000 mEq/kg vs. -14,000 mEq/kg), the dose of citric was more than double the dose of formic acid to compensate for the difference in ABC-4 values.

The differences were confirmed through analysis. Once solubilized in water, the measured pH of the different diets ranged from 4.7 for the lowest up to 6.1 for the highest, which would definitely significantly affect stomach pH and digestion effectiveness.

Discussions and Conclusions

I encourage you to go through the publication in detail for more information – Validation and Evaluation of the ABC-4 Value in Post-Weaning Piglet Diets – A. Huting et al., 2019. In summary, the publication presents the following conclusions: 

  • There is indeed a positive correlation between a reduction in ABC-4 and piglet growth, feed intake, and FCR. Even a reduction of 50 mEq/kg of complete feed would have a significant positive effect on piglet performance.


  • The effect of low ABC-4 is more significant during the first 2 weeks after weaning when the piglet's production of HCl is at its lowest.


  • There is no source effect from organic acids. The main element is their effect on the reduction of the overall ABC-4 value of the diet rather than their respective modes of action. Other strategies aiming at reducing ABC-4 would have the same effect on performance as the incorporation of organic acids.


  • The ABC-4 reduction shows particular benefits when a piglet is facing gut health challenges – the growth effect may be less obvious when piglets do not have gut health issues.

This topic is particularly important in Southeast Asia. In these countries, it is quite common to see diets with an ABC-4 value between 350 and 450 mEq/kg of complete feed, far from the 250 mEq targeted in Europe. Given the epidemiological context, such high ABC-4, and consequently high stomach pH, creates a favorable environment for the development of pathogens in the stomach, leading to intestinal contamination.

There are several explanations for this high level of ABC-4 in the region.First, under the pressure of regulations and marketing practices, piglet diets are formulated with a high level of crude protein (22% against 18% in Europe). Moreover, it is quite common to see a significant contribution of animal protein, either fish meal or poultry meal. These ingredients have respective ABC-4 values of 1,380 and 1,007 mEq/kg, whereas soybean meal and fermented soybean meal have 600 and 200 mEq/kg. 

Second, for economic reasons, the most common source of calcium is calcium carbonate and dicalcium phosphate, which have extremely high ABC-4 values of 18,000 and 2,700 mEq. We must not forget to pay attention to the carrier used in premixes, which is also often composed of calcium carbonate. That could bring the total calcium carbonate up to 12-15kg per ton of diet, contributing for 220 to 270 mEq/kg of complete feed compared to the maximum target at 250!

 Third, there are still numerous feed manufacturers who are using 3kg of Zinc Oxide per ton of pre-starter diet. Zinc Oxide is the ingredient with the highest ABC-4 value between 18,000 and 22,000 mEq/kg, depending on the research centers. At such a level, Zinc Oxide will contribute between 55 to 70 mEq/kg of complete feed to the diet. In Europe, they do not have similar issues as the regulations set lower limits for the use of Zinc Oxide in piglets. 

Fourth, given the points raised above, we can estimate that a standard pre-starter diet in the Southeast Asian context, including animal protein, high levels of zinc oxide, and carbonate, will reach an ABC-4 value between 400 to 500 (before taking into account the acidifiers). One of the easier ways to bring the ABC-4 level closer to 250 mEq/kg, without having to make significant changes to the diet formulation, would be to incorporate organic acids. But, for cost reasons again, the common practice in our region, the dosage of organic acids (60% concentrated) does not exceed 3 to 5kg of a mix of organic acids that would reduce the diet's ABC-4 value only by 18 to 30 mEq/kg. To obtain the reduction of 100 to 150 mEq/kg that we would need, we should increase the dosage to 12 to 15kg of organic acid mix (considering that these mixes contain a maximum of 60% of organic acids and 40% of carrier).

In conclusion, to create a better environment for piglets during the weaning phase, we need to pay more attention to the stomach pH and therefore start paying attention to the ABC-4 level of our pre-starter and starter diets. In most diets, we have a deficit of at least 100 mEq/kg that we need to regain. Below I have listed the four most obvious strategies to improve the ABC-4 value. The first strategy to consider is the reduction of high doses of zinc oxide. That strategy is five times cheaper than the use of acidifiers.

If the ambition is to achieve a reduction of more than 100 mEq/kg, we will need to work on several strategies simultaneously, starting from the most economical to the most expensive. An alternative strategy that I could add to the table is to replace powdered organic acids with liquid organic acids, as it is a cheaper source of ABC-4 reduction.

If you would like me to send you the complete publication of Schothorst and the list of ABC-4 values for all ingredients, please let me know by email.


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