April 2013 - AFMA

Table 5: Effect of sodium diformate dosage on
Campylobacter inhibition (% positive samples)
Control NDF 0,3% NDF 0,6%
Crop (microbiol.) 60 0 0
Intestine (microbiol.) 80 20 0
Meat (serol.) 80 0 0
Table 6: Intestinal microbial counts (cfu/g) in broilers
Microbial group Control NDF 0,6%
Enterobacteria 107 105
Lactobacilli 107 108
Bifidobacteria 105 106
molecule and the pathogenic bacteria, which is easily representable
under in vitro conditions. This means that as much as possible of
the active ingredient of an organic acid has to reach the site where
pathogens are located.
Most pathogenic bacteria, such as E. coli and Salmonella, are located
in the small intestine. Under in vivo conditions and by using a
practical dosage of 5kg liquid formic acid per ton of compound feed,
Kirsch (2010) only found 5,5% of the active ingredient present in the
small intestine of pigs. In addition, Maribo et al. (2000) detected 4,4%
of the active ingredient in the small intestine by using a dietary dosage
of 0,7% liquid formic acid, whereas 85% of the active ingredient
of a diformate passed through the stomach and reached the duodenum
(Mroz et al., 2000).
This high bypass effect of diformates leads to a high efficacy in
reducing the incidence of E. coli-associated diarrhoea, even in comparison
with antibiotics and zinc oxide, as described by Portocarero-
Kahn (2006) in a trial on weaned piglets (Table 1). A total of 576 weaners
were assigned to four experimental groups and observed over a
period ranging from 28 to 60 days of age.
Overland (1998) observed a significant reduction in E. coli numbers
in the duodenum and the jejunum of piglets fed potassium
diformate (KDF). Jorgensen (2000) confirmed this E. coli-reducing effect
of KDF also in the porcine caecum.
This pronounced antibacterial effect was also particularly well
illustrated by data collected on eight farms in Ireland (Lynch et al.,
2007). The main objective of this investigation was to evaluate the
efficacy of Salmonella control measures on highly infected farms.
Salmonella control has been compulsory under Irish law since 2002,
and the farm status is categorised by the percentage of positive pigs
in a herd according to the Danish mix-ELISA test.
Category 3 (>50% positive) farrow-to-finish farms and their associated
fattening units were selected for the study. Five farms were
selected where diets supplemented with KDF (0,6%) alone were
tested. All but one farm, on which KDF was used, finished the trial
period with a significantly improved Salmonella status (serological
prevalence), whereas the bacteriological prevalence was low on
most farms.
As another treatment, a formic-propionic acid blend (0,5%) was
tested, but no effect on the reduction of Salmonella numbers was
detected, neither on bacteriological prevalence nor on serological
prevalence (Table 2). These findings were expected and can be
explained by the low proportion of such active ingredients passing
through the stomach into the intestine (Maribo et al., 2000; Kirsch,
2010).
However, this was not the first time that this effect was observed.
Studies by Dennis and Blanchard (2004) in the UK, as well as most recently
in France by Correge et al. (2010), concluded potassium diformate
to be an effective tool in Salmonella control strategies on commercial
farms (Table 3).
These antibacterial effects can also be observed in poultry. Lückstädt
and Theobald (2009) clearly showed the beneficial effects of
sodium diformate (NDF) against pathogenic bacteria in broilers. No
positive samples of Salmonella were found in meat from broilers fed
the additive. Furthermore, there were no Salmonella-positive samples
from the gastro-intestinal tract of diformate-fed groups (Table 4), and
no positive samples for Campylobacter in the diformate group if used
at 0,6% (Table 5).
Notably, lower enterobacteria counts and distinctly higher lactobacilli
and bifidobacteria numbers provided further evidence of the
beneficial impact of diformate on the intestinal microbiota in broilers
(Table 6).
The reduced impact of pathogenic bacteria on the broiler, as well
as the improved gut microflora, leading to a state of eubiosis in treated
chickens, implies that including diformate in broiler diets will also result
in improved bird performance (Lückstädt et al. 2010, Lückstädt &
Theobald, 2011).
Since only field data on infection rates under practical conditions
are available, Goodarzi et al. (2013, in press) performed a challenge
trial with laying hens to test the effects of 0,6% NDF on the Salmonella
colonisation of different organs. A total of 40 Lohmann birds, divided
equally into two groups, were inoculated orally with a single dose of
1 x 109 CFU/ml Salmonella enteritidis (SE).
Between day 26 and 28 post inoculation, the birds were euthanised,
and the SE concentration in liver and caeca samples determined. The
use of NDF led to a highly significant reduction of the frequency of colonisation
within the liver and caeca (P