the use of acidifiers in piglet diets

Forum: An update on the use of acidifiers in piglet diets

Published on: 06/16/2009
Author/s : Mathieu Cortyl
For several years already "acids" have been used in swine nutrition - and especially in piglet diets - as they have shown their ability to reduce some of the negative consequences of weaning. One of these acids, butyric acid, possesses interesting characteristics that make it "not just an acid". Besides the well documented anti bacterial effect, butyric acid stimulates the production of pancreatic...
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June 16, 2009

This is an excellent article about the use of organic acids in fish nutrition.

However, I wish to point out to the author that he may have made a mistake. First, he stated that formic acid appears to be primarily effective against yeasts and some bacteria such as E. coli and Salmonella.

He then quotes acetic acid as an example, stating that it inhibits the growth of several species of bacteria but is less effective on yeasts and moulds. As for propionic acid, he states that it is usually targeted at moulds but has a reduced efficacy against bacteria and none against yeasts.

So how then can the Minimum Inhibitory Concentration (MIC) of formic acid against E. coli be five times higher than that of acetic and propionic acid, if formic acid is supposed to be primarily effective against E. coli, while propionic acid is supposed to have reduced efficacy against bacteria?

MIC is supposed to be the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. So the higher the MIC, the less efficacious the substance is as an antimicrobial.

So to me, this is a contradiction and a paradox.

I hope the author will explain this in greater detail.

June 16, 2009
Dear Dr Tan

Thank you for your positive comments and thank you for pointing out the mistake in my article. Indeed you are right that there is a contradiction in what was written.

The correct sentence should have been: As a comparison, the MIC of formic acid against E. coli is five times lower than of acetic and propionic acid.

This is just a typing mistake and I cannot blame the secretary since I wrote this article myself... Let me just apologize for that mistake.

Regarding the five times lower we could also discuss the validity of this statement. As you certainly know MIC will depend on the protocol that is used, and especially on the original pH of the environment. The pH will affect the rate of dissociation of each acid (depending on their pKa value) and therefore will also have an impact on their MIC. This is why antibacterial effect of the organic acids can be variable depending on the buffer capacity of the feed.

Thanks again for spending some time to read carefully this article.

Best regards

Mathieu Cortyl
July 6, 2009

Nice article about the use of organic acids in fish nutrition.. Just to know, what are the chances of resistance development against these acids, in due course of time, particularly wrt E. coli and Salmonella?

July 21, 2009
Dear Dr. Puneet Agrawal

Thanks for your question and sorry for the time taken to reply, but I was enjoying my summer vacation!

Some researchers have demonstrated the existence of an adaptive response to acidity for some pathogenic bacteria. This phenomenom is called acid tolerance response (ATR). However, this is not a resistance to the acids, but an adaptation to the acidic environment. For this ATR to happen, the bacteria must first encounter mildly acidic conditions for a certain time, after which it will be able to produced the so-called acid shock proteins (ASP). The ASP will help the bacteria to better survive acidic conditions.

To summarize, the bacteria needs to adapt itself to mild acidic conditions before it can survive under acidic conditions. This means we should avoid using acidifiers at low dose, with for instance the objective to reduce the cost of the feed additive.

Ding Li Ding Li
Marketing Manager
May 4, 2011
One question: which is the active of sodium butyrate in the intestinal : Butyrate or butyric acid?
Sergio Velez Sergio Velez
Animal Nutritionist
June 19, 2012

Over the years many organic and even inorganic acids and combinations of these have been offered to be included in pre starter and starter feeds.

Frequently we - feed manufacturers- are offered simple, "straight" organic acids that range from formic to citric ( C number) and less common ones as benzoic.

Acidification is known not only to affect microbial ecosytems and intestinal architecture of the gut but also feed intake.

Given that the antibiotic effect of organic acids depends on the pH of the intestines it would be nice to know what are these values for each section and how they relate to teh acids Pk

Could you please help us with this data?


June 19, 2012

Dear Sir,

Thanks for your interest in the article and your question.

As you already know, pH values vary in each part of the intestinal tract. The stomach pH of an adult pig is usually around 2.5 to 4.0, because of the secretion of hydrochloric acid. In the piglet after weaning, the pH of the stomach can sometimes be as high as 4.5 to 7.0. We want to avoid a too high pH as a low stomach pH is required to ensure good protein digestion and to prevent bacterial growth. The pH of the small intestine is usually between 4.5 and 6.5, as it increases after the addition of bile salts and pancreatic enzymes. In the large intestine, we can expect pH values from 6.0 to 8.0. This higher pH favors the growth of the bacterial population and undigested feed substrate reaching this point will be fermented by the bacteria into lactic, acetic, propionic and butyric acids.

Now, to answer your question regarding the effect of acids in the gut: when looking at published research, we can see that gastric pH reduction has been observed when using acids with relatively low pKa, such as citric, formic, lactic and orthophosphoric acids. Based on reports available, we can say that pH reduction in stomach is most likely to be observed in piglets just after weaning, and rarely after 2 weeks post weaning.

An interesting review of the literature by Tung and Pettigrew (2006) has shown that acidifiers have a clear ability to reduce the pH of the diet. However, they did not significantly influence pH in the digestive tract as explained below:
- Out of 59 trials, acids reduced the pH of the diet in 58 cases (average reduction 21%, highly significant)
- Out of 22 trials, acids reduced the pH of the stomach in 11 cases, resulted in increased pH in 9 trials and had no clear effect in 2 trials (small average reduction)
- Out of 12 trials, acids reduced the pH of the small intestine in 6 cases, and resulted in increased pH in the other 6 trials (small average increase, not significant)
- Out of 11 trials, acids reduced the pH of the cecum in 4 cases, and resulted in increased pH in the other 7 trials (no difference when looking at averages)
- Finally, in the 11 trials studying the pH effect of acids at the colon level, pH was reduced in 8 cases, and was increased pH in the other 3 trials (no difference when looking at averages)

However, it has to be noted that in all the published data, diet characteristics (pH, buffer capacity) are not always reported which makes interpretation quite difficult.

So to summarize, pH is not going to be much affected in the gut, especially after the stomach. The antibacterial effect of the acids is dependent on their pKa as you know, which means that acids with a high pKa value (for instance butyric) have more chances to be effective against the pathogens.

As an additional comment, you have to remember that homeostasis (the tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes) is there to ensure that pH does not go outside the values required for a good digestion process and optimum activity of the intestinal enzymes. For instance, secretin (a polypeptide hormone produced by S cells in the duodenum, especially on contact with acid, will stimulate secretion of pancreatic juice which is alkaline due to the high concentration of bicarbonate ions. So there is little way to change dramatically the pH of the intestines with the addition of acids. This is not what we want anyway.

I hope that helps.

Dan L. McDermott Dan L. McDermott
Bachelor of Science ANIMAL SCIENCE
August 6, 2012

Mathieu Cortyl
and others,

There is no mention of using hydrochloric acid, the piglet's natural in vivo acid, as an option.
Any thoughts?

August 7, 2012
Dear Sir,

Personally I don't have experience of using HCl in pig diets. So may I quote the literature review made by Tung and Pettigrew (2006) and already mentioned above:

" It was found that growth performance was retarded with hydrochloric acid and sulfuric acid, but not with phosphoric acid (Giesting, 1986). However, Straw et al. (1991) indicated that supplementation of hydrochloric acid to the diet improved average daily gain during the first 3 weeks after weaning. Apart from the acidifying effect, hydrochloric acid is also utilized as a source of chloride to pig diets. Mahan et al. (1996 and 1999) showed that the improved performance and nitrogen retention, due to hydrochloric acid addition to the diet, resulted in more pronounced responses during the initial weeks postweaning than during the subsequent period. This suggests that hydrochloric acid secretion may be initially inadequate in weanling pigs. Thus, the addition of dietary hydrochloric acid would supply a needed source of chloride for pepsinogen activation, which could improve protein digestion. "

I hope this helps.
Best regards
Vasileios Papatsiros Vasileios Papatsiros
Assist. Professor of Poscine Medicine
September 29, 2012
Arunachalam Ravi Arunachalam Ravi
Animal Nutritionist
May 5, 2014
Very nice discussion so far. What about the age at weaning. In our place weaning is done at 42 or 56 days. Will these acids be effective at this age and how to account for the buffering ability of the feed in neutralizing the acids. Are there any dose related response to the antimicrobial effect of these acids.

April 5, 2019

Hi, did the breed have effect on the assimilation of feed nutrition value? Thanks.

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