Formic acid in feed for pigs and poultry

Formic acid - strongest bactericidal/ bacteriostatic effect

The performance benefits of including formic acid in feed for pigs and poultry that have been reported widely under farm conditions stem from its strong antimicrobial activity; as seen in numerous in vitro tests.

Contaminated feedstuffs, recontamination during storage, transport and outfeed result in significant losses in productivity, if not severe outbreaks of disease, as a result of pathogen growth. Feed is an excellent source of nutrients for animals and pathogens alike and the intestinal environment provides excellent growth conditions for bacteria, so adding bactericidal or bacteriostatic agents prevent disease and allow livestock to utilise feed efficiently. Mould growth also reduces the nutritive value of feed and can result in mycotoxin contamination, which can cause disease and mortality and render livestock more susceptible to bacterial diseases. Bacterial contamination in drinking lines and drinkers should also be prevented.

One way in which feed additives can be compared is in their ability to combat bacterial growth. The minimal inhibitory concentration (MIC) has long been a useful tool in establishing how effective an agent is at inhibiting growth of microoorganisms. The lower the MIC for a particular agent and microbe, the less is needed and the more effective it can be considered.

Formic acid has been shown effective against a number of pathogens under practical conditions, in tests with both poultry and pigs as well as other livestock species. Organic acids exert their bactericidal and bacteriostatic activity within the cell of the target organism, where the hydrogen ions disrupt the ionic balance, forcing the cell to expend energy in actively expelling the ions. However, not all acids are equally effective. Inorganic acids might be considered extremely effective in decreasing pathogen load in the stomach of piglets, indirectly through pH reduction (since they do not have direct antimicrobial properties); but their use in feed is limited by their tendency to cause irritation during handling, feed refusal by animals and corrosion of equipment used in transport, at the feed mill and on the farm.

The strongest bactericidal and bacteriostatic effects have been reported for formic acid, which is effective against the most serious bacterial threats to poultry and pig productivity, as shown in Table 1. The MIC for formic acid against these pathogens lies in the range of 0.1 to 0.2 percent, i.e. the lowest dose of the acid at which bacterial growth is prevented.

Table 2 compares the effect of formic acid against that of two other widely used organic acids - propionic and lactic acids. The MIC of formic acid to inhibit growth of all pathogens tested is noticeably lower than the other two acids. Between 0.05 and 0.25 % less formic acid solution is needed than each of the other two acids for a given pathogen. Given the intense pressure on feed manufacturers to mobilise every fraction of a percent of feed available to maximise productivity, this comes as good news to all those who strive to produce high quality, safe feed.

In practice, formic acid salts, with their improved handling characteristics and better palatability to livestock, have been found to be a more user-friendly method of applying formic acid to feed and water, without compromising their efficacy.

Table 1: Antimicrobial effect of formic acid against different bacterial (after Strauss and Hayler, 2001) - Minimal Inhibition Concentration MIC in %