Treatment of feedstuffs with formic acid or formaldehyde - things to consider
For many customers thinking about using a chemical preservative in feed, their first thought is formaldehyde. Particularly if they are looking for something to assist in their control of Salmonella spp. Formaldehyde has been approved for use as a Salmonella control agent by the FDA since 1998, and can be quite effective. However, in 2017 the use of formaldehyde in poultry feed has been banned by the EU member states, which led feed millers to formic acid containing products to improve feed hygiene. As of January 2018, formic acid was classified as the feed hygiene enhancer in EU. Overall, formaldehyde has been an effective means of reducing Salmonella contamination in feed, but the application has come with some drawbacks. Drawbacks that formic acid does not share.
One major drawback to formaldehyde has been worker health and safety. While formic acid and formaldehyde are both classified as hazardous substances, formic acid is not classified as a carcinogen. Formaldehyde, however, was classified as:
• a probable human carcinogen by the US EPA in 1987
• carcinogenic to humans (Group 1) by the IARC in 2006
• a "Known human carcinogen" by the US Department of Health and Human Services National Toxicology Program in 2011
Now, the classification of formaldehyde as a carcinogen, as with any hazard classification, does not mean that the material cannot be used safely. But it does mean that additional care and consideration are necessary for safe use, and that these additional precautions may come with additional costs in use.
3. Export Market Acceptance
Another topic outside of technical effect that needs to be considered, at least for companies that export feed or feed ingredients such as fishmeal or meat and bone meal, is the regulatory situation. Until recently, most major jurisdictions accepted the presence of formaldehyde in feed and feed ingredients as part of a Salmonella spp control or Salmonella-free certificate. However, the EU commission has chosen not to reauthorize formaldehyde for use as a feed additive. This change is in effect a ban on formaldehyde and leaves formic acid as the lone remaining ingredient in the recently added "feed hygiene enhancer" functional category in Europe as of January 2018.
Producers continuing to use formaldehyde are essentially locked out of one of the largest feed markets in the world. It is also possible that many other countries will follow the example set by the EU.
4. Protein and Formaldehyde
Both formic acid and formaldehyde have been shown repeatedly to inhibit Salmonella spp. But a growing body of evidence suggests that while effective for controlling Salmonella, formaldehyde does negatively impact protein availability in treated feed and feedstuffs when treated. Formic acid, however, appears to enhance protein availability in treated feed and feedstuffs. The reason for this difference likely comes down to how the two chemicals inhibit bacterial growth.
Formaldehyde works largely by denaturing protein and the formation of cross linkages between proteins (Figure 1). These cross linkages, like the cross linkages in complex dietary fiber, or the disulfide bridges in high cysteine feedstuffs like feather meal, interfere with normal enzymatic digestion. This is part of how formaldehyde kills Salmonella and is why producers of high protein rendered products expect to lose a point or two of protein value after treating with formaldehyde.
Figure 1. (Gustafsson et al., 2015)
The consequences of this cross-linking are illustrated beautifully by Campbell et al., (2018 a,b) in a pair of studies looked at the interaction between formaldehyde treatment and point of application on nursery pig performance. First, they applied formaldehyde directly to spray-dried animal-plasma before diet formulation. They reported no difference in proximate analyses (DM, N, ash), but did report a 3%-point drop in IgG in the animal plasma (relative reduction of 24%). This translated into a 10% reduction in average daily gain (ADG) and an 11% reduction in feed intake (ADFI). In the second study, they applied the formaldehyde to the complete diet instead of the isolated raw material. In that trial they reported a 3% drop in 14d body weight, a 14% drop in ADG, and a 4% drop in ADFI. Despite being of comparable magnitude, the differences in the feed treatment study were not statistically significant. This is likely due to their use of a slightly less powerful design in the second study (10 reps/treatment in the feed treatment trial vs. 12 reps/treatment in the ingredient treatment trial). Greiner et al. (2017) reported that over formulation of amino acids (AA) by 15% was necessary to overcome the negative effect of formaldehyde treatment of feed on nursery pig ADG and that ADG was maximized only if AA, phytase and vitamins were all over formulated by 15%.
To be clear, the interaction between formaldehyde and dietary protein is not unique to swine nutrition, but is the result of direct chemical interaction on the feedstuffs themselves. For example, Schmidt et al. conducted a series of trials in the early 1970 which report a consistent negative effect of formaldehyde treatment on the digestibility of protein from SBM fed to steers, rats and sheep (1973a,b; 1974). Spears et al. (1980) reported negative linear and quadratic effects of formaldehyde on total gain, feed intake, and gain:feed ratio of chicks fed graded levels of formaldehyde. This is likely due to reduced protein availability. Even the data originally used to register formaldehyde in Europe (EC, 2002) showed consistent negative effect of formaldehyde on performance of swine (Figure 2) and poultry (Figure 3). Again, the most plausible explanation being that performance was reduced largely because of formaldehyde-protein interactions.
Figure 2. Experiment 1 (blue), Experiment 2 (red) and experiment 3 (green) on the use of formaldehyde in swine feed (EC, 2002).
Figure 3. Experiment 2 (blue) and experiment 3 (red) on the use of formaldehyde in broiler feed (EC, 2002).
5. Protein and Formic Acid
Whereas formaldehyde delivers microbial control at the expense of protein availability in feed, formic acid has been shown to consistently improve performance, efficiency and availability of nutrients. This is because formic acid works by making the feed a more hostile environment for bacteria, and not by directly altering the structure of protein. Formic acid works by reducing the pH below the level that bacteria like Salmonella can grow. Reduced pH in feed can lead better acidification of the gut, greater activity of endogenous and exogenous enzymes (Blanke et al., 2012 & 2013), and an overall improvement in feed efficiency and nutrient availability.
A review on acidification of swine feed by Tung and Pettigrew (2006) reported that acidifiers as a class improved digestibility of DM by 0.82%-points and of crude protein by 1.33%-points (Table 1). When broken down by acid type, they found that formic acid improved digestibility of crude protein by 1.64%-points on average. Jendza et al. (2016) reported improved feed efficiency in lactating sows/piglets of 2.9%-points in response to 9 g/kg of Amasil NA.
Table 1. Summary of effects of acids on dry matter and crude protein digestibility. Adapted from Tung and Pettigrew (2006).
Figure 4. Effect of Amasil NA on cecal Salmonella typhimurium 9 days post oral challenge (Adhikari et al., 2017).
Figure 5. Feed conversion ratio of broilers fed Amasil NA and c hallenged with Salmonella typhimurium (Adhikari et al., 2017).
6. Inhibition of bacteria in feed
In feed decontamination trials, both products have been shown to be quite effective. In 2015 we conducted a feed decontamination comparison trial with a customer in which we collected feed samples and treated them with 0.3% formaldehyde containing product or 0.3 and 0.5% Amasil NA without any artificial contamination with bacteria. No Salmonella was detected in this trial, but we did see reductions in both E. coli and total coliform counts with feed treatment (Figure 6). When focusing on interaction with feed form, we found that 0.5% Amasil NA achieved reductions in total coliforms that was comparable to 0.3% formaldehyde, but in pellets, the reduction was identical for both products at the 0.3% level, with 0.5% Amasil NA achieving a further reduction (Figure 7).
Figure 6. Main effect of formaldehyde containing product and Amasil NA on microbial contamination of broiler feed.
Figure 7. Interaction between chemical treatment (formaldehyde containing product vs. Amasil NA) and feed form (Mash vs. Pellet) on total coliform counts in naturally contaminated broiler feed.
In another customer trial, we manufactured broiler pellets containing 0.4% formaldehyde containing product and 0.11% Amasil NA. The pellets were then inoculated with Salmonella to compare their ability to resist contamination of feed. On day of inoculation, there were no differences in Salmonella counts between treatments, but on day later we found that formaldehyde and formic acid had reduced Salmonella by 1.7 and 0.9 log10 cfu/g, respectively (Figure 8), or by roughly half as much (on a log scale) with one quarter the inclusion level.
In a feed decontamination trial, we looked at the interaction between dose and time (Jendza et al., 2018) and found that 1.0% Amasil NA reduced Salmonella counts by over 0.7 log10 cfu/g on the day of challenge, and as much as 3.7 log10 cfu/g within the first week (rendering the feed Salmonella negative; Figure 9).
Figure 9. Salmonellarecovery over time from broiler mash feed containing increasing concentrations of Amasil NA. (Jendza et al., 2018)
Both formic acid and formaldehyde based products have been shown to be highly efficacious at inhibiting the growth of bacteria such as Salmonella. However, since they both effect bacteria via different chemistry, they offer subtly different value propositions to potential users. Formaldehyde poses some relatively unique worker safety risks that require additional care to mitigate, raises regulatory acceptability questions for material intended for international export, and exerts an additional cost on the nutritional value of feedstuffs to which it is applied. Formic acid is potentially slower to act on bacteria, but evidence suggests it can actually enhance the feeding value of feedstuffs to which it is applied, thus delivering value that might not be accounted for in the initial comparison.
For more of the article, please click here.
Article made possible through the contribution of Dr. Joshua Jendza, Dr. Lily Li and BASF Animal Nutrition