During the late 1980s, it was discovered that pharmacological concentrations (1,500 to 3,000ppm) of zinc oxide (ZnO) resulted in reduced post weaning diarrhoea (PWD) and increased growth in weanling pigs. It had been widely used at such dosages to control E. coli F4 infections. Several researchers have concluded however that one cannot assume a widespread antibacterial effect of ZnO as MIC values differ greatly both among and within bacterial species. This has been very recently confirmed by Neath and colleagues who found minimum inhibitory concentrations of ZnO for E. coli, but also for S. typhimurium, S. suis or S. aureus to be above 31 mg×ml-1, thus proving no efficacy. Its impact against certain E. coli strains for instance is understood rather as a stabilizer of the intestinal microbiota and preventing attachment of pathogenic bacteria to the intestinal villi, which can prevent many problems associated with weaning diarrhoea. Unfortunately, as Zn is poorly absorbed, it becomes highly concentrated in manure. In order to minimize the risk of environmental pollution, European authorities have reduced the maximal Zn concentration authorized in pig diets. From June 2022 onwards, pharmacological doses of ZnO will be no longer authorized in the EU. Therefore, alternative strategies and/or additives to manage PWD are immediately needed. Many authors have directed their R&D effort towards the use of acidifiers – as this group of commonly used feed additives proved rather successful after the ban on antibiotic growth promoters in the EU back in 2006. Some authors even claimed, that "…Dietary acidifiers can actually become the most common and efficacious alternative solution to antibiotics, in order to improve health status and performance in pigs". One of those acidifiers, potassium diformate (Formi, KDF, ADDCON), was even approved by the EU as a non-antibiotic growth promoter for use in pig diets – the first product to receive such approval. It was therefore no surprise, that diformates had been tested in diets containing low levels of ZnO. The current article aims to give an overview on the usage of potassium diformate or sodium diformate (Formi NDF, both substances produced and registered by ADDCON, Germany) in zinc-oxide reduced piglet diets.
One of the first results on the usage of KDF in low zinc oxide diets was published in 2001. The authors used diets with 150 ppm zinc oxide in the control, while the treatment diet contained an additional 1.2% KDF. In three successive trials in Spain, with 56 piglets per trial, the effect of potassium diformate on the performance and health status of weaned piglets (Pietrain x Dalland) was observed (Table 1). Data showed the significant performance enhancing impact of the dietary diformate, as well as a clear impact on PWD.
Table 1. Daily gain and feed efficiency of weaned piglets (weaning age 24 days) fed low ZnO-diets with or without FORMI
Another report from Spain in weaners (432 post-weaning piglets in 3 groups, with 8 replicates per treatment) compared a pharmacological dosage of ZnO (2500 ppm) with 1.2% dietary KDF (Table 2). Both additives improved weight gain against a negative control significantly, while only the diformate had a significant impact on feed efficiency against the control. It was concluded by the authors that an improved gut health by using KDF in the critical period after weaning, was the cause of the improved production performance achieved.
Table 2. Performance parameters of weaned piglets (weaning age 28 days) until 40 days of age
The trial was continued till 60 days of age (Table 3), however the ZnO-dosage was reduced to 150 ppm. Performance parameter as well as the impact on diarrhoea rate were monitored. Like in the first part of the study, the significant performance enhancing impact of KDF and its suppressive effect on diarrhoea were noticed.
Table 3. Performance parameters and impact on diarrhoea of weaned piglets until 60 days of age
A Chinese study also proved the growth promoting impact of potassium diformate (FORMI) in piglet diets containing only 150 ppm ZnO (Table 4). This time, the authors used 1.0% KDF in the diet of weaned piglets (weaning age 28 days with 5.91 kg initial weight) over a period of 35 days. Final bodyweight increased significantly (P=0.009) by 9.9%, while the FCR was also significantly (P=0.022) enhanced by more than 5.9%. Furthermore, due to a highly significant (P<0.001) improvement of the crude protein (CP) digestibility, less chances for PWD will occur. Thus, it can be assumed that dietary diformate can improve performance post-weaning and keeps diarrhoea rates low, also in the absence of pharmacological dosages of ZnO.
Table 4. Growth performance and apparent protein digestibility in weaning piglets
A similar experience was reported by authors from the Kansas State University. The researchers were running a trial to assess alternatives to replace the use of zinc oxide in nursery pig diets. The inclusion of 1.2% Formi NDF alone resulted in a similar feed per gain ratio and faecal dry matter as the positive control containing pharmacological levels of ZnO until day 25. Furthermore, the use of a combination of the three tested alternatives (1.2% NDF, 4% coarse ground wheat bran, and 18% CP), as a replacement to ZnO, improved the appearance of faeces and resulted in similar faecal DM content and faecal score to pigs fed diets containing ZnO. A similar experiment was published by the same research institute just recently. This time ZnO was added till day 7 at 3000 ppm and till three weeks post-weaning at 2000 ppm. From day 0 to 21, pigs fed added ZnO had an improved (P<0.05) average daily gain (ADG), average daily feed intake (ADFI), feed efficiency (FCR), and increased day 21 bodyweight (BW) compared to those fed the negative control with only 110 ppm Zn (Table 5). Adding sodium diformate (1.2%) significantly (P<0.05) improved ADG, FCR, and BW. In summary, dietary addition of ZnO or sodium diformate independently improved nursery pig performance. The authors concluded that the addition of an acidifier with or without ZnO could be a useful practice to improve nursery pig growth performance.
Table 5. Effects of pharmacological levels of zinc oxide and sodium diformate on growth performance of nursery pigs till day 21
More research was recommended by the studies listed above. This is currently carried out: unpublished data from the same university suggest that an agglomerate of sodium diformate and monolaurate (Formi 3G, ADDCON) fed to weaned piglets at 1% can reach similar performance parameters at day 28 post weaning to high dosages of zinc oxide and has at the same time a beneficial impact on the gut microbiome.
In the context of the above listed data, it can be summarized that the acidifier Formi (potassium diformate), Formi NDF (sodium diformate) or Formi 3G (agglomerate of sodium diformate and monolaurate) can play a vital part in zinc oxide reduction strategies and may further help in improving the feed efficiency in post weaning piglet production – thus playing an important part in world-wide sustainable pig production approaches.
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Article made possible through the contribution of Christian Lückstädt and ADDCON GmbH, Bitterfeld-Wolfen, Germany