This is the third article in a series about the use of organic acids in feed. The first two article dealt with the concepts of pH and pKa and buffering which is important to understand the rest of the series.
In the same way you don’t use a saw to hammer in a nail, its important to pick the right tool for the job when it comes to your acid toolbox. Not all acids are created equal and different acids have different effects, whether it be in the feed or in the animal.
The first thing a good acid needs to do is lower the pH in the stomach. This is particularly important in young animals like weaning piglets that have a low natural acid secretion. The acid that is present – lactic acid – comes mainly from the fermentation of the sugar lactose in the sows’ milk. To add to the problem the lactate in the milk reduces the levels of HCl in the stomach.
Why is the level of HCl in the stomach important? Because one of the key enzymes that are produced in the stomach, pepsin is pH dependent. Its pretty much stops working above pH 2 – 3,5. More importantly pepsin levels are themselves determined by pH because pepsin is formed from a precursor molecule called pepsinogen. This conversion is also pH dependent, where again the magic happens at pH 2 and at pH 5 or 6 pretty much nothing happens.
As the animal goes from milk to solid feed the levels of lactic acid fall, which stimulates the production of HCl. However, since the animal is so young and still developing this process isn’t quite ready yet. Add a low intake of creep feed and it can take up to 4 weeks before things are working like they should.
All this combined leads to a recipe for disaster with gastric pH caused by a combination of low acid secretion, lack of lactose to ferment to lactic acid, and eating fewer and bigger meals at infrequent intervals, all give a higher gastric pH.
So, if you are looking to use acids to help your piglets you need to look for acids that are capable of lowering pH around the period of weaning. By the way just lowering pH using inorganic acids like phosphoric or hydrochloric acid doesn’t seem to work well either. It is important that it is an organic acid.
Picking the right tool for the job
It is important that you pick an acid or blend of acids that can reasonably be expected to do the job you want them to do. Having illustrated that one thing you want your acid to do is lower gastric pH, the next thing you want to look for are acids that bring you added value. One key added value of organic acids is their antimicrobial effects.
For example Formic acid is well known as an excellent anti-bacterial shown to have effects against a number of gram negative bacteria, like E.coli, Salmonella sp., and others. It is also really good at lowering gastric pH. Whilst propionic acid is much more powerful against yeasts and moulds than against bacteria.
Other acids exert their effects in the animal directly, like butyric acid, that is a source of energy for intestinal cells or have an antimicrobial effect in the intestine like benzoic acid.
So, the question you need to ask yourself is, what problem am I trying to solve by using organic acids?
The most commonly used antibacterial acid is formic acid, either alone or in a blend. Being the smallest of the organic acid molecules, it can easily penetrate bacteria and disturb their internal pH balance. As such formic acid has excellent antibacterial properties with effects shown against gram negative bacteria E.coli, Salmonella, Listeria and others. Formic acid is often used in liquid feed and evidence points towards that addition of formic acid can help preserve nutrients like amino acids in the feed.
Lactic acid is often used in blends for swine very effectively, in fact a mix of formic and lactic acid in swine feed has been shown to improve the production index by 5 points and was not statistically different to benzoic acid. While in this trial no significant effect was seen of the blend against Salmonella, other data seem to suggest that lactic acid at relatively high doses (2,8%) has an effect against Salmonella. In a trial comparing single acids lactic acid seems to have the strongest effect against post-weaning diarrhea. Lactic acid alone does not appear to offer the same production benefits compared to formic acid alone or in combination with formic acid.
Propionic acid is the probably the organic acid most commonly used in feed. That is because its primary effects are the ability to inhibit both yeasts and moulds. As such it is an excellent product for feed preservation. Despite its widespread use the mechanisms of exactly how propionic acid exerts its effects are still resulting in new discoveries. The net result is that it disturbs moulds structure and results in cell death. While this acid does have antibacterial effects, it requires higher doses and relative to cost, formic acid does a better antibacterial job.
Benzoic acid is by many considered to be one of the most effective acids to use in swine. One of the key differences compared to the acids mentioned above is that this product is a powder in its natural state. This often makes it easier to add directly to the feed without the need of specialized liquid dosing equipment. Benzoic acid offers another advantage in that it is effective along the entire intestinal tract and may in fact benefit the growth of the intestine. This is mainly due to benzoic acids low solubility and high pKa. It can exert its antimicrobial effects in the intestine to a higher degree than other acids that tend to mainly exert their effects in the stomach. However, keep in mind that if you have an effective antimicrobial barrier in the stomach using other acids the benefit relative to cost may not be as high as you might think.
Another acid that offers significant benefits over and above those mentioned above is butyric acid. This is one of the most studied acids out there. That is because it has a whole host of proven effects ranging from being an energy source for intestinal cells, to immunostimulation, strengthening intestinal wall integrity and more and it is in fact one of the acids produced naturally by intestinal fermentation in the pig. Historically the problem with this acid has been the smell and that it is most effective in the intestine. There are a number of different product variations available out there, the most common of which is as a coated butyrate salt that is able to pass the stomach and the latest iteration, tributyrin, in which the acid is turned into a triglyceride that is broken down by enzymes in the small intestine thereby releasing the effective molecule where it is needed.
There are several other acids that are commonly used mainly to increase the effect of the acids mentioned above, as there is some evidence that combinations of acids work better than single acids alone. Citric and fumaric acid are often used to help increase the pH lowering effect in the stomach and in the case of fumaric acid may serve as an energy source for intestinal cells. While sorbic acid is often used due to similar effects as benzoic acid, however, is in general cost prohibitive.
Hopefully now you can see taht not all acids are created equal and that you can use them effectively depending on the challenges you are facing.
As a general rule of thumb formic and lactic acid are very useful in young animals where you need to help with the lowering of pH and can help with post-weaning diarrhea caused by gram negative bacteria like E. Coli, Salmonella and others.
If you also have problems with yeast and moulds in your feed a blend that includes propionic acid will be more effective. Whilst benzoic and butyric acid derivatives will do more to support intestinal function, immunity and intestinal integrity.
In the next article in our series we will look more closely at the differences between dry and liquid acids, where acid salts, buffered acids and non-buffered acids all play a role.