by Dr. Henrique Cemin, Senior Swine Nutritionist, Hubbard Feeds

In North America and many other pork-producing regions, pigs are weaned at a young age (approximately 21 days).

Economically, this is a sensical decision on the producer’s part to help optimize all farm sow productivity and throughput.

Physiologically, however, this can be a challenging time for piglets.

We know that young pigs have poor stomach-acid production up to seven to eight weeks of age (Pluske, 2016), and many of the ingredients commonly used in nursery diets have a high acid-binding capacity (ABC-4; Stas et al., 2022), which can further raise the stomach’s pH.

A high stomach pH is concerning because it can lead to a myriad of issues, ranging from poor nutrient digestibility to increased pathogen proliferation, diarrhea, and mortality. Considering all the other stressors involved during the weaning period, it’s the last thing a piglet needs.

The use of acidifiers is a widespread practice that attempts to overcome this issue and promote growth and health benefits for piglets.

The proposed mode of action includes reducing the pH in the GI tract, improvements in nutrient digestibility, promoting the growth of beneficial bacteria, and pathogen inhibition (Jacela et al., 2009).

Ultimately, the objective is to reduce the diet’s ABC-4 (Acid-Binding Capacity-4 is the amount of acid needed to lower the pH of a feed ingredient or diet to 4, which is important for maintaining a healthy stomach environment in young pigs, especially after weaning).

Unfortunately, most ingredients used in swine diets have a high ABC-4.

For example, in a compilation of the most commonly used ingredients, Stas et al. (2022) reported that soybean meal, whey permeate, and spray-dried plasma have ABC-4 values of 602, 520, and 713 mEq/kg (milliequivalents per kilogram), respectively.

Other key ingredients, like limestone and zinc oxide, have extremely high ABC-4s of 18,384 and 21,863 mEq/kg, respectively.

Acidifiers, on the other hand, have negative ABC-4 values and can help partially counteract the negative effects of a high-ABC-4 diet.

ABC-4 management can be achieved by avoiding ingredients known to have a high ABC-4 or by using more ingredients with a low or negative ABC-4. Stas et al. (2025) observed performance improvements when complete nursery diets had an ABC-4 of around 200 to 250 mEq/kg.

The acidification of swine diets can be achieved by using an individual acid or blends of organic (such as fumaric, lactic, benzoic, or citric) and inorganic (hydrochloric or phosphoric) acids.

Thanks to their potentially synergistic activities, blends of acidifiers could provide the most optimal responses. In a recent meta-analysis of 52 publications, Wang et al. (2022) concluded that blends of acids are superior to individual acids and consistently improve the average daily gains (ADG) and feed efficiency (F/G) of nursery pigs.

Recently, the Alltech pork technical team conducted a series of four commercial-scale research trials to evaluate the effects of a blend of organic and inorganic acids (in the form of Alltech’s Acid-Aid) on the growth performance and health outcomes of nursery pigs. The results of these four studies were recently presented at the 2025 ASAS Midwest Section Meeting (Faccin et al., 2025; Hart et al., 2025).

In trial 1 (Table 1), 2,529 nursery pigs were studied to evaluate the effects of increasing levels of the acidifier blend included in their diets, ranging from 0% to 0.47% (9.4 lbs./ton) for 16 days after weaning. The results of this pilot study showed a tendency for linear improvements in F/G as well as numerical improvements in ADG when the acidifier blend was included in the diet.

Trial 2 (Table 2) was conducted to further elucidate the responses and included two levels of the acidifier: 0% or 0.235% (4.7 lbs./ton). In this trial - which also featured a total of 2,592 pigs and lasted through 16 days after weaning - pigs fed diets with the acidifier blend recorded a 4.7% improvement in their ADG and a 2.7% improvement in their F/G.

Trial 3 (Table 3) compared the impacts of a control diet (with no acidifiers), the acidifier blend (0.265%), and pure benzoic acid (0.50%) on 1,081 pigs for the first 18 days after weaning. The inclusion levels of the acids were adjusted to achieve the same ABC-4 as in the complete diet. Consistent with the results of the previous trials, a significant improvement in ADG was observed in correlation with the acidification strategies. In contrast to the previous trials, however, the driver of that response was feed intake and not F/G.

Finally, trial 4 (Table 4) studied 973 pigs to evaluate the effects of the acidifier blend or benzoic acid, similar to trial 3, with the exception that these pigs were fed the acidifiers throughout the entire 41-day nursery period. Furthermore, the pigs used in trial 4 were by far the youngest, smallest, and most health-challenged group of pigs in this series of trials. Those facts may help explain the magnitude of the response observed in trial 4: The pigs that received the acidification strategies displayed an 11% higher ADG. Similarly to trial 3, this gain response was driven by feed intake, with no differences observed in F/G. As this group presented a more challenging start due to their health status and lower weaning age, a significant reduction in mortality and removal rate was also observed (Figure 1). That finding translated to almost 3% more full-value pigs out of the nursery in correlation with the acidification strategies.

Figure 1. The mortality and removal rate and the number of full-value pigs were observed in trial 4. A total of 973 pigs were used in this 42-day trial to evaluate the effects of including 0.50% benzoic acid or 0.265% Acid-Aid in the pigs’ diets.

When considered altogether, these results demonstrate a consistent improvement in the growth performance of nursery pigs fed the acidifier blend, as illustrated through their increased intake levels and/or improvements in efficiency. Furthermore, in a situation where a health challenge is present or pigs are weaned at a very young age, acidification can prove to be even more valuable.

It was determined that these results indicate that diet acidification is an effective strategy for nutritionists looking to maximize their nursery performance, throughput, and, ultimately, the economic performance of their operations.

References:

Faccin, J.E.G., H.S. Cemin, S.A. Hansen, M.D. Hart, E.L. Hansen, J.L. Pietig, and J.A. Soto. 2025. Effects of the inclusion of benzoic or a blend of organic and inorganic acids to nursery diets on pig performance and survivability. Journal of Animal Science (Abs.). Published: March 2025. Link: https://asasmidwest2025.eventscribe.net/ajaxcalls/PresentationInfo.asp?PresentationID=1549990 Note: Link is from the conference website.

Hart, M.D., H.S. Cemin, J.A. Soto, J.E.G. Faccin, S.A. Hansen, and E.L. Hansen. 2025. The effects of Acid–Aid in-feed acidifier on nursery pig growth performance. Journal of Animal Science (Abs.). Published: March 2025. Link: https://asasmidwest2025.eventscribe.net/ajaxcalls/PresentationInfo.asp?PresentationID=1550031 Note: Link is from the conference website.

Jacela, J. Y., J. M. DeRouchey, M. D. Tokach, R. D. Goodband, J. L. Nielssen, D. G. Renter, and S. S. Dritz. 2009. Feed additives for swine: Fact sheet – acidifiers and antibiotics. Journal of Swine Health and Production. 17:270-275. Published: September 2009. Link: https://www.aasv.org/shap/issues/v17n5/v17n5p270.pdf

Pluske, J.R. 2016. Invited review: Aspects of gastrointestinal tract growth and maturation in the pre- and postweaning period of pigs. Journal of Animal Science. 94:399-411. Published: September 1, 2016. Link: https://academic.oup.com/jas/article-abstract/94/suppl_3/399/4731486?redirectedFrom=fulltext

2022. Evaluation of the acid-binding capacity of ingredients and complete diets commonly used for weanling pigs. Translational Animal Science. 6:1-9. Published: August 17, 2022. Link: https://academic.oup.com/tas/article/6/3/txac104/6670570

Stas, E.B., M.D. Tokach, J.C. Woodworth, J.M. DeRouchey, R.D. Goodband, and J.T. Gebhardt. 2025. Evaluation of dietary acid-binding capacity level on nursery pig growth performance and fecal dry matter. Journal of Animal Science. Published: February 12, 2025. Link: https://academic.oup.com/jas/article-abstract/doi/10.1093/jas/skaf039/8010094?redirectedFrom=fulltext

W. Long, D. Chadwick, X. Zhang, S. Zhang, X. Piao, and Y. Hou. 2022. Dietary acidifiers as an alternative to antibiotics for promoting pig growth performance: A systematic review and meta-analysis. Animal Feed Science and Technology. 289:115320. Published: July 2022. Link: https://www.sciencedirect.com/science/article/abs/pii/S0377840122001183

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Dr. Henrique Cemin
Dr. Henrique Cemin is a Senior Swine Nutritionist at Hubbard Feeds, where he provides technical services and manages the company's swine research and development projects.

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