Pig International - January/February 2012

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 Salmonella-contaminated feed.

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 Salmonella.