Beneficial claims from dietary inclusions of acidifiers include control of bacterial growth in feed, increased growth performance, improvement in nutrient digestibility, and control of harmful bacteria in the gut.

What are acidifiers?

Acidifiers are compounds that have acidic properties: they may be organic or inorganic acids. Organic acids that have shown positive effects on growth performance in weaned pigs include citric, formic, fumaric, and propionic acids. In studies involving inorganic acids,^1-3 positive growth responses have been reported with the use of phosphoric acid. However, research evaluating other inorganic acids, such as sulfuric acid, reported negative growth performance.⁴ Thus, phosphoric acid is the most commonly utilized inorganic acid in swine diets.

Inorganic acids are usually less costly than organic acids. Organic and inorganic acid combinations are often used in commercially available acidifiers. The response to mixed acids is generally better than to single acids,⁵ apparently due to dissociation properties of these acids at various locations in the pig’s digestive tract.

What are the benefits of using acidifiers?

A recent report² summarizing several studies on acidifiers indicated that, in general, they appear to improve pig growth performance. However, the magnitude and consistency of the response may vary, depending on inclusion rate and other dietary factors. The exact mode of action of acidifiers has not been fully elucidated. However, acidifiers are commonly marketed as growth-promoting products and as alternatives for in-feed antibiotics. Unfortunately, due to the lack of consistent results, use of acidifiers to replace antibiotic growth promoters is still not justified. Acidifiers are believed to enhance growth by improving gut health through reduction of pH and buffering capacity of diets, improvement of pancreatic secretions that increase nutrient digestibility, or promotion of beneficial bacterial growth while inhibiting growth of pathogenic microbes.^2,6 There is limited data indicating that acidifiers can act synergistically with phytase to improve phosphorus and magnesium digestibility.^7,8

What factors affect the response to acidifiers?

Research suggests that age of pigs can affect the response to acidifiers, with newly weaned pigs showing the greatest response.^4,9 Acidifiers are most beneficial during the first few days after weaning. The stomach of a weaned pig is not yet physiologically mature and may not be able to secrete a sufficient amount of acid to aid in digestion of solid food or inhibit proliferation of detrimental bacteria. However, the exact mechanism of the response to acidifiers is not clear.

Diet composition also may affect the response to acidifiers. It appears that greater responses are seen when simple diets are fed rather than complex diets containing milk products.¹⁰ This is presumably due to conversion of lactose from the milk products to lactic acid by Lactobacillus species in the stomach, thus creating an acidic environment and reducing the need for dietary supplementation with acidifiers.

Disadvantages of acidifiers

Corrosiveness, one disadvantage of using some acidifiers, may pose handling and equipment issues to the feed manufacturer. Salts of organic acids are generally odourless and less corrosive than their acid forms, making them easier to handle in the feed manufacturing process. Acidifiers may negatively affect diet palatability when added at excessive levels, resulting in lower feed intake. There may also be legal restrictions with the use of some acids. For example, pure formic acid is not legal for use in the United States, but salts of formic acid are available for use in feeds.

Summary

Acidifiers added to pig diets may potentially help improve growth performance by improving digestive processes through several mechanisms. However, a clear mode of action has yet to be described. The use of acidifiers appears to be most beneficial in the early period after weaning. Thus, acidifier use is typically limited to diets for pigs weighing less than 6.75 kg (15 lb).

References

1. Walsh MC, Sholly DM, Hinson RB, Saddoris KL, Sutton AL, Radcliffe JS, Odgaard R. Murphy J, Richert BT. Effects of water and diet acidification with and without antibiotics on weanling pig growth and microbial shedding.
J Anim Sci. 2007;85:1799–1808.

2. Tung CM, Pettigrew JE. Critical review of acidifiers. National Pork Board. 2006. Available at: http://www.pork.org/Documents/PorkScience/ReviewOfAcidifiers.pdf Accessed 10 April 2009.

*3. Stein H. Feeding the pig’s immune system and alternatives to antibiotics. Proc London Swine Conf. London, Ontario, Canada. 2007;65–82.

4. Ravindran V, Kornegay ET. Acidification of weaner pig diets: A review. J Sci Food Agric. 1993;62:313–322.

5. Hardy B. The issue of antibiotic use in the livestock industry. What have we learned? Anim Biotechnol. 2002;13:129–147.

6. Partanen KH, Mroz Z. Organic acids for performance enhancement in pig diets. Nutr Res Rev. 1999;12:117–145.

7. Omogbenigun FO, Nyachoti CM, Slominski BA. The effect of supplementing microbial phytase and organic acids to a corn-soybean based diet fed to early-weaned pigs. J Anim Sci. 2003;81:1806–1813.

8. Jongbloed AW, Mroz Z, van der Weij-Jongbloed R, Kemme PA. The effects of microbial phytase, organic acids and their interaction in diets for growing pigs. Livest Prod Sci. 2000;67:113–122.

9. Bergstrom JR, Nelssen JL, Tokach MD, Goodband RD, Loughmiller JA, Musser RE, Nessmith WB Jr. An evaluation of several diet acidifiers commonly used in pig starter diets to improve growth performance. Kansas Agricultural Experiment Station Progress Report 772. 1996;772:74–78. Available at: www.oznet.ksu.edu/library/lvstk2/srp772.pdf. Accessed 15 July 2009.

10. Weeden TL, Nelssen JL, Hansen JA, Richardson KL. Effect of acidification on starter pig performance and nutrient digestibility. Kansas Agricultural Experiment Station Progress Report 610. 1990;610:62–65. Available at: www.oznet.ksu.edu/library/lvstk2/srp610.pdf. Accessed 15 July 2009.

* Non-refereed reference.