An example of Salmonella typhimurium
penetrating gut epithelium.
vigilant in terms of producing Salmonella-
free feedstuffs for their pigs.
Before looking at the options for
controlling Salmonella in feed, it is
important to remember the aim should be to
expose the pig to as few viable Salmonella
organisms as possible and not to rely on
that pig’s ability (or otherwise) to protect
itself from the Salmonella it consumes.
Pigs are capable of killing some of
the Salmonella they ingest. However,
the more they consume, especially if
concentrated in micro-colonies within the
feed, the higher the risk that their innate
enteric defense mechanisms are unable to
cope and they become infected.
Producing clean feed
Heating feed during the steam-conditioning process is often relied upon to
produce Salmonella-free feed. However,
to be confident of eliminating 100% of
the Salmonella in feed (including heat-tolerant strains), the meal must be heated
to more than 85°C for at least four minutes
and have a moisture content of between
14.5% and 15%. The vast majority of
animal feed mills come nowhere close to
achieving these conditions.
Importantly, even when meeting these
standards, the “clean” feed still has to be
January/February 2012 | www.WATTAgNet.com
A high proportion of infected
pigs become carriers and
intermittent excretors of
Salmonella in their feces.
cooled, stored and distributed. It is easy
for Salmonella contamination to occur at
these stages and for pigs to be exposed to
Organic acids and their salts are also
popular Salmonella-control products in
pig feed. There are, however, significant
limitations to their effectiveness in-feed.
To kill Salmonella they need to penetrate
the bacteria. This requires the molecule
to be dissociated; generally requiring low
pH – conditions typically not found in feed.
But pigs’ stomach acid exert their greatest
anti-Salmonella effects; arguably too
little and too late for some pigs.
A recent study found that organic
acid-treated samples often show up as
Preventing the contamination of
farms with viable and persistent
Salmonella burdens from outwardly
‘healthy’ pigs is difficult to achieve.
Salmonella-negative, despite containing
viable Salmonella. (Carrique-Mas et al.,
2006). Such masking of Salmonella is
potentially catastrophic for both feed
manufacturer and pig producer. The feed
manufacturer risks contaminating their
mill and all the feed it produces, while the
pig producer risks infecting his pigs with
For many organic acids and blends,
high inclusion levels are required to
provide effective in-feed Salmonella
the poultry industry