IT IS CHEAPER IF IT IS LIQUID
At weaning, commonly between 17 and 21 d, piglets still have a relatively underdeveloped GIT. Pigs’ hydrochloric acid production is limited until the pig reaches 7 to 8 weeks of age. Switching pigs to a solid diet at weaning may lead to an increase in gastric pH as high as 5.0 for several days postweaning. Low stomach pH is important for protein digestion and when stomach pH increases above 3.5, pepsin activity rapidly declines. Increased gastric pH allows opportunistic pathogens to survive and compromise the digestive tract leading to clinical infection and growth impairment.
Organic acids have been used for decades as a solution to reduce the pH stomach in Swine and Poultry nutrition. To be effective, organics acids need to supply as many H+ as possible. The more H+ they will release and the faster they will reduce the pH.
In addition of pH reduction, the H+ will have an antibacterial effect in the stomach. The H+ cannot enter the bacteria when it is dissociated. But it can when it is associated as an organic acid (R-COOH), they gain a lipophilic nature that enables them to penetrate bacteria walls. Once inside the bacteria cell, the H+ will dissociate and disturb bacteria activity.
The most effective organic acid is the Formic acid. It is indeed the smallest (HCOOH) in the family of organic acids with only one carbon compared to acetic acid (2 carbons), Lactic acid (3 carbons), Propionic acid (3 carbons) or Fumaric acid acid (4 carbons). Because of its small size, in one kilogram of pure acid can bring more molecule of formic acid than we can obtain with any other organic acids. As every molecule of organic acid come with an H+, one kilogram of pure formic acid will bring 21g of pure H+ whereas acetic, propionic, lactic and fumaric will contribute respectively to 16g, 13g, 11g and 16g of H+ only.
The second element to consider is the capacity of an organic acid to dissociate and release its H+. The easier it will dissociate and the more it will contribute to a reduction of pH. The level of dissociation is measured by the pKa. Organic acids with low pKa will tend to dissociate easily and are called strong acids. Formic acid is there again the stronger acid among the commonly used organic acids. As reference, very strong acids like Phosphoric acids have a pKa of 2.
The best way to measure organic acids effectiveness is done experimentally by calculating the quantity of acids required to bring the pH of one kg of Feed from 4 to 3. This measurement is called Acid Binding Capacity or ABC (ABC4 to bring the feed pH from 4 to 3 and ABC3 to bring the feed pH from 3 to 2). That in-vitro test is directly measuring the quantity of H+ that each acid supplies and it is measured in meq / kg. The table below compares the results for each organic acid.
It is not a surprise to see here that Formic acid appears as the most effective organic acids. Given its small molecular mass and its low pKa, Formic acid supplies indeed 10 times more H+ than propionic acid and more than double than lactic acid.
Another aspect to take into consideration when selecting the organic acids to use is their presentation. Most of these organic acids are indeed in a liquid state at normal temperature. The table below is showing the melting point confirming the temperature above which products are liquid.
To get a powder based on formic, lactic, propionic acids, a reprocessing is required. We need indeed to spray these liquid acids onto a support. Most of the time, the support used is silica. But there is a limit to the quantity of organic acids that silica can absorb. Normally, the limit is around 60% of organic acids against 40% of carrier. The important part that silica takes into the composition have an impact in term of cost.
As you may have noticed on the table above, Fumaric acid have a melting point far above normal temperature. That means that they appear under solid form under ambient temperature and can simply be obtained in a very concentrated powder form. It may be more convenient, but it would be less effective and often more expensive.
Another option is to select organic salts (R-COO-) as formate, propionate, lactate, etc…These products are in a solid form at normal temperature with a high melting point. When combined with cations like Sodium or Calcium, these salts can be used in powder in concentrated formula (66% of formate in Sodium formate). But these salts have been depleted from their H+ and will therefore not contribute to the reduction of pH in the stomach (ABC4 formate is 2,900 meq against -13,550 meq for Formic acid). Technically, they are not acidifiers. At the opposite, when they will arrive in the stomach, a part of them will combine with H+ present to reform a formic acid. These salts will indirectly have an antibacterial effect as once recombined into formic acid, it will regain the ability to pass the bacteria cell walls.
In conclusion, when feed manufacturers are looking for a strong acidifier together with antibacterial effect, the most economical strategy is to go for the highly concentrated liquid solution of formic acid. It will save the cost of reprocessing it onto silica and it will reduce the shipping fees by half as carrier is not required anymore. Being under a liquid form, that strategy may bring more complexity to its application as it needs to equip the production line with specific applicators to spray the formic acid directly on the pellets. It is essential to select a supplier that can provide the formic acid but as well provide safe solutions regarding applicators adapted to corrosive solutions. The selection of the applicator is actually as important as the selection of the formic acid itself.