Acidifiers in piglet diets
An update on the use of acidifiers in piglet diets
Published: June 9, 2009
By: 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 secretions, including enzymes. It also improves the absorption of electrolytes and reduces the incidence of diarrhoea, providing the ileal and the hindgut mucosa with a preferred energy source. By combining inorganic and organic acids, together with sodium butyrate, it is possible to ensure a smoother transition during the post weaning phase.
Challenges at weaning
We all have heard about the ban of antibiotic growth promoters in the European Union, or more recently, in South Korea where the use of seven types of antibiotics in animal feed (penicillin, neomycin, chlortetracycline, colistin, oxytetracycline, lincomycin and bacitracin zinc) is now prohibited. The main concern when antibiotics are no longer on the list of available tools is how to manage critical periods like feed changes, especially at weaning. As shown in figure 1, without low dose anti-microbials, the main trend is an increase in mortality and a reduction in weight gain.
Even with antibiotics weaning of the piglet is a high-risk phase because it is an accumulation of stress: first, there is an abrupt separation from the sow; piglets are mixed and usually transferred to a new environment; their diet is changed from milk to a less digestible, more complex and dry feed. The first consequence is generally under-nutrition. Feed (and also water) intake is low and highly variable, which turns into a low and variable growth performance. As shown by Le Dividich (see figure 2), the most marked effect of weaning between 21 and 28 days of age is the temporary drastic reduction in energy intake. Subsequently, digestive disorders are often observed and may have negative consequences on the architecture and functions of the small intestine, on the gut micro flora, and even on the local immune system.
One of the consequences of weaning of piglets is the reduction in length size of intestinal villi, which obviously reduces their growth performance. Indeed, it is accepted that a large luminal surface area with optimal enterocyte functional maturity is important to young, growing animals, so they may attain maximum digestive and absorptive capability. Cera et al. demonstrated that during the suckling period there is a moderate decrease in the size of the villi, which is compensated by the increase in size of the digestive tract itself. However, once piglets are weaned, there is a dramatic drop in the height of the intestinal villi, which is much less obvious in piglets of the same age that are still suckling the sow (see figure 3). The shortened villi surface area of the small intestine could predispose the weanling pig to reduced absorption of nutrients, possible dehydration, diarrhoea and enteric infection-conditions that are frequently encountered on swine farms.
Benefits of acids
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. Their mode of action relies on the reduction of pH that limits the development of pathogens - and helps in the digestion of proteins at stomach level - and the ability that some organic acids have to enter inside the cytoplasm of bacteria and disrupt their metabolism.
Low pH is necessary at the stomach level: it helps limit the entry of pathogens in the digestive tract, and it also aids in the digestion process. For instance, pepsinogen activation is rapid at pH 2.0, but very slow at pH 4.0 while pepsin activity is optimal at pH 2.0 or pH 3.5, but reduced when pH is above 3.5. Young piglets have a limited capacity to produce hydrochloric acid (HCl) in the stomach; during suckling, this is partly compensated with lactic acid synthesis from the lactose in milk by Lactobacillus. After weaning, the insufficient production of gastric HCl leads to an increase in the pH value. Whereas in mature pigs gastric pH is in the range of 2.0 to 2.5, it is not rare to observe pH values from 3.9 to 4.7 (or even higher!) at the time of weaning. Due to their usually high levels of calcium (as carbonate) and protein, weaning diets make the situation even more challenging because of their high buffer capacity. A higher than required pH value in the stomach will result in undigested protein reaching the small intestine, where they can serve as substrates for the proliferation of coliforms and lead to diarrhoea. In order to reduce pH, acids with a low pKa value (such as phosphoric acid) are preferable.
The other reason why acids are used is their antibacterial effect. Most of pathogenic bacteria, for instance Salmonella, can live under a pH range from 4 to 9, but the optimum range for their growth is between 6 and 8. Therefore low - or high - pH values in the environment will inhibit the growth of the bacteria. At very low pH values (e.g., pH 3) protons (H+) leak across the membrane faster than the homeostasis system can remove them; this results is an intracellularacidification to levels that damage or disrupt key biochemicalprocesses. However, lowering the pH to extreme values is not practical because acids are corrosive and dangerous for human and animals, as well as equipment, moreover, it is almost impossible to significantly modify the pH value of the digestive tract of animals because the homeostasis system, combined with the buffer capacity of feed, reduces pH variations.
Organic acids (belonging to the group of weak acids) have a different mode of action against pathogenic bacteria. In solution, organic acids exist in pH-dependant equilibrium between uncharged, acid molecules and their respective charged anions (for example propionic acid / propionate). The key basic principle of their mode of action is that when non-dissociated (non-ionized, more lipophilic) they can penetrate the bacteria cell wall and disrupt the normal physiology of certain types of bacteria. Organic acids will traverse the membrane in the non-dissociated form. Since the proportion of dissociated acid increases as pH increases, once inside the cell they will be exposed to the near neutral intracellular pH of the bacteria and dissociate thus liberating an anion (A-) and a proton (H+) in the cytoplasm; the internal pH will decrease and because pH sensitive bacteria do not tolerate big differences between the internal and external pH, a specific mechanism (H+ -ATPase pump) will act to bring the pH inside the bacteria to a normal level (Figure 4). This phenomenon consumes energy and eventually can stop the growth of the bacteria or even kill it.
The anionic (A-) part of the acid is trapped inside the bacteria because it will diffuse freely through the cell wall only in its non-dissociated form. The accumulation of (A-) becomes toxic to the bacteria by complex mechanisms resulting in inhibition of metabolic reactions, reduction the synthesis of macromolecules, or disruption of membranes. Conversely, the non-pH sensitive bacteria (such as lactic acid bacteria) will tolerate a larger differential between the internal and the external pH, if the internal pH becomes low enough, organic acids will re-appear in a non-dissociated form and exit the bacteria by the same route they went in. Another explanation for this may be that Gram-positive bacteria have a high concentration of intracellular potassium, which provides a counter cation for the acid anions.
An important parameter to take into account is, therefore, the constant of dissociation of the acid (pKa), which is the pH value for which the concentrations of dissociated and undissociated species are equal. This means for example that formic acid (pKa = 3.75) will be 50% dissociated and 50% undissociated at a pH value of 3.75. The anti-bacterial activity of organic acids will therefore depend on their pKa and on the pH of the intestinal tract. For instance, the level of undissociated lactic or formic acid is about 5% at pH5 while that of butyric acid is 40%. This means the specific antimicrobial effect is 8 times quicker for butyric acid when compared to lactic or formic acids at pH5.
Butyric acid - not just an acid
Butyric acid, sometimes called butanoic acid, is a carboxylic acid with the chemical formula CH3CH2CH2-COOH. Butyric acid is a natural product of the bacterial fermentation of the carbohydrates in the intestine of monogastrics, or in the rumen of ruminants. With acetic and propionic acid, butyric acid belongs to the group of VFAs (Volatile Fatty Acids). It is usually applied in feed as a salt of sodium (sodium butyrate) which makes its handling easier since it is solid, stable and much less odorous. In the large intestine, sodium butyrate is rapidly absorbed to provide energy to the epithelial cells and promote sodium and water assimilation. Over many years, different researchers have shown positive effects of sodium butyrate on the intestinal epithelium, such as increase in the villi length and crypt depth, which result in a better absorption of nutrients. More recent research demonstrates an anti-inflammatory effect of sodium butyrate on gastric and intestinal mucosal cells. The immune system seems less challenged, which results in a better overall use of the nutrients absorbed. This explains the positive influence of sodium butyrate on the body weight gain and feed conversion of pigs.
Another benefit of sodium butyrate is its positive effect on the composition of the intestinal micro flora in pigs. It is known that VFAs can inhibit the growth of bacteria of the group of Enterobacteriaceae (Salmonella, Escherichia coli, ...). The reason for volatile fatty acid toxicity is that the undissociated form of these acids can diffuse freely across the bacterial membrane into the cell of the microbe. Once inside the bacterial cell, the acid dissociates, thereby reducing the internal pH, which causes internal cell damage. Butyric acid is easily soluble in water, ethanol, and ether. Also, butyric acid has a higher diffusion coefficient than other acids with a shorter chain, which enables it to pass through the bacterial membrane more easily. Experimental data indicate that the concentrations of butyrate required to reduce the growth of E. coli by 50% are much lower than the concentrations of the other volatile fatty acids, acetate and propionate. In poultry, it has been shown that butyric acid is more efficient than for example acetic, formic or propionic acids in controlling the development of Salmonellaenteritidis.
Recently a trial was conducted at the Putra University in Malaysia, to observe the effects of feeding sodium butyrate (Gustor B 92, NOREL & NATURE) on the growth performance, faecal pH, Enterobateriaceae and lactic acid bacteria counts in piglets after weaning. No significant differences were observed for weight gain, feed intake or FCR, probably due to the small number of piglets (16 per group), even if sodium butyrate at 500 g/MT gave the best results as far as weight gain and FCR are concerned. Levels of Enterobateriaceae were significantly reduced when using either antibiotics or Gustor B-92 while counts of lactic acid bacteria were not different among treatments. The lowest faecal pH value was observed with sodium butyrate (see figure 5).
What is a good acidifier?
Ideally, acidifiers should be active already in the feed (sanitizing), but also in the stomach to ensure the pH is low enough, and finally in the intestine where they can help in controlling pathogens. Unfortunately there is not such an acid which can guarantee an action at all three levels simultaneously, therefore different acids must be combined in order to achieve the desired effect.
The combination of strong acids (acids with low pKa value, having a strong pH effect) and weak acids (of higher pKa value, having an anti-microbial effect) will form an effective barrier against pathogens, and increase feed safety. Acids that have mainly a pH effect are inorganic acids such as phosphoric acid, together with some organic acids (fumaric, citric... ). On the other hand, it is necessary to use some organic acids such as butyric acid, formic or lactic acids, for their anti-microbial properties; these latter of course will also have an effect on pH.
t is beneficial to combine different organic acids together, which makes the overall spectrum broader and combines the good qualities of the different acids: e.g. formic acid appears to be primarily effective against yeasts and some bacteria such as E. coli and Salmonella, whereas lactic acid bacteria and moulds are relatively resistant to its effects.
Further examples are acetic acid, which is reported to inhibit the growth of several species of bacteria - but is less effective on yeasts and moulds - and propionic acid, which is preferred when targeting moulds: it has a reduced efficacy against bacteria and none against yeasts, since the latter can metabolize it. As a comparison, the MIC of formic acid against E. coli is five times higher than of acetic and propionic acid. Another organic acid, lactic acid, is principally effective against bacteria, as many moulds and yeasts can metabolize it.
The right combination of acids with different pKa values, a specific efficacy against different types of pathogens, will result in a synergistic product that will provide the best efficacy at reduced dosages.
GUSTOR, the third generation acidifier
Taking into account all the parameters discussed above, NOREL&NATURE designed Gustor, a range of different products combining volatile fatty acids together with organic and inorganic acids, in the form of free acids and salts, to reduce the corrosiveness of the product.
The combination ensures that Gustor is a gastric acidifier, having a pH effect that will increase digestibility of nutrients and help to control pathogens at the stomach level. Also, Gustor will play the role of intestinal acidifier, by controlling pathogens and maintaining the balance in favour of Lactobacilli and beneficial bacteria in general. Last but not least, thanks to the presence of sodium butyrate in the formula of Gustor, the growth of intestinal villi is promoted resulting in a greater surface for nutrient absorption and hence better growth of the animal. Different formulas of Gustor have been designed to satisfy the specific requirements of the different animal species. Available are Gustor Monogastrics, specially formulated for swine, but also Gustor Poultry or Gustor Aqua. All are designed for application in feed, while Gustor Liquid can be applied via the drinking water. Several trials have been - and continue to be - conducted demonstrating the efficacy of this product range.
In one such trial, set up under the supervision of Prof. Du'o'ng Thanh Liem (Nutrition Department, Nong Lam University, Vietnam), the effects of supplementing the feed with Gustor Monogastrics, chlortetracycline or a combination of both, on performance of piglets after weaning were compared. There were 3 groups of piglets, one positive control (with chlortetracycline), one supplemented with Gustor Monogastrics at 2 kg/MT, and the last group was combining chlortetracycline and Gustor Monogastrics. Performance data indicates significantly better growth and FCR for Gustor Monogastrics or the combination Gustor Monogastrics + chlortetracycline whereas feed intake was not different among the groups. Using Gustor Monogastrics resulted in a decreased incidence of diarrhoea when compared to the control (with antibiotics) but the best results were seen for the combination: Gustor Monogastrics + chlortetracycline; also this combination gave best performance in the economical analysis.
These results, as well as other trials, demonstrate that when using the right combination of inorganic and organic acids, together with sodium butyrate, such as in Gustor Monogastrics, it is possible to reduce the negative consequences of weaning, and ensure a smoother transition during the post weaning phase.
Figure 1: Effects of removing low-dose antibiotics in Denmark (Source: Callesen, 2002)
Figure 2: Energy intake of piglets around weaning (Source: Le Dividich)
Figure 3: Effect of weaning on the height of intestinal villi (Adapted from Cera et al., 1988)
Figure 4: Control of cytoplasmic proton-level by the membrane-bound H+-ATPase pump (Adapted from Lambert and Stratford, 1998)
Figure 5: Effect of supplementation with antibiotics or sodium butyrate (Gustor B-92 at 500 g/MT) on faecal bacteria count and faecal pH of piglets, adapted from Lee et al., 2008
Table 1: Effect of supplementation with chlortetracycline and / or Gustor Monogastrics (2 kg/MT) on the performance of piglets post weaning
Figure 1: Effects of removing low-dose antibiotics in Denmark (Source: Callesen, 2002)
Figure 2: Energy intake of piglets around weaning (Source: Le Dividich)
Figure 3: Effect of weaning on the height of intestinal villi (Adapted from Cera et al., 1988)
Figure 4: Control of cytoplasmic proton-level by the membrane-bound H+-ATPase pump (Adapted from Lambert and Stratford, 1998)
Figure 5: Effect of supplementation with antibiotics or sodium butyrate (Gustor B-92 at 500 g/MT) on faecal bacteria count and faecal pH of piglets, adapted from Lee et al., 2008
Table 1: Effect of supplementation with chlortetracycline and / or Gustor Monogastrics (2 kg/MT) on the performance of piglets post weaning
Group | Chlortetracycline | Gustor 2 kg/MT | Gustor 2 kg/MT + Chlortetracycline |
Initial body weight (kg) | 6.14 | 6.09 | 6.17 |
Final body weight (kg) | 17.83 | 18.19 | 18.36 |
Daily weight gain (g) | 278 a | 288 b | 290 b |
Daily feed intake (g) | 513 a | 493 a | 494 a |
FCR | 1.84 a | 1.71 b | 1.70 b |
Incidence of diarrhoea (%) | 18.6 | 12.5 | 8.3 |
a, b: different letters indicate significant differences (p<0.05)
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Tonisity
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29 de septiembre de 2012
You can read my article The Prophylactic Use of Acidifiers as Antibacterial Agents in Swine
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Tonisity
7 de agosto de 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
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Tonisity
19 de junio de 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.
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Tonisity
21 de julio de 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.
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Tonisity
16 de junio de 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
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5 de abril de 2019
Hi, did the breed have effect on the assimilation of feed nutrition value? Thanks.
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5 de mayo de 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.
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6 de agosto de 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?
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Alimentos CCR
19 de junio de 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?
Thanks.
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4 de mayo de 2011
One question: which is the active of sodium butyrate in the intestinal : Butyrate or butyric acid?
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