Salmonella in pigs

Salmonella control has a high priority in European pork production. It is a significant cause of human salmonellosis and causes major economic losses in the pork production chain, through reduced productivity, increased veterinary and hygiene control costs. Preventing the spread of salmonella to the consumer requires special control measures during slaughter and processing. The extra cost of these controls is increasingly being transferred back to the producer in the form of financial penalties or the loss of the market for contaminated pigs.

A study undertaken by Teagasc, University College, Dublin and the Department of Agriculture and Food in Co. Kildare (Lynch et al., 2007) tested some on-farm control measures to reduce salmonella contamination in infected slaughter pigs. Data was collected from 12 farms in Ireland, classified as category 3 (> 50% positive) according to the national salmonella control programme in effect in Ireland since 2002. The effects of including the organic acid additive FORMI over the 24 months of the study are given in Table 1. All the farms that were treated with the additive alone; or a combination of FORMI with improved hygiene and biosecurity measures (farms J and L) had notable improvements in both bacteriological and serological prevalence of Salmonella spp. All but one farm in which FORMI was used ended the trial with a much improved Salmonella status, with bacteriological prevalence also low on most farms. Improving hygiene and biosecurity alone improved Salmonella status to a much lesser extent.

A commercial trial in a grower/finisher pig unit in the UK (Dennis and Blanchard, 2004), also concluded potassium diformate (FORMI) to be an effective tool in salmonella control. In this study, the percentage of salmonella positive pigs was reduced by 50% and in pork meat juice ELISA scores by 46%, respectively in grower finisher pigs. Herds in which the additive was included also had an improvement in daily gain of 7.7%, reduced mortality and a reduction in medicinal intervention compared to the rolling average for that unit before the study. The authors estimated that, excluding reductions in veterinary bills and culling rates, FORMI addition to grower/finisher diets with improved hygiene management practices could deliver a net benefit of GB£5850 in the average herd.

As these findings demonstrate, protection from recontamination is an important salmonella control measure and should continue within the feed during transport, storage and subsequent outfeeding and in the animal´s intestinal tract, where warmth, moisture and pH are optimal for bacterial growth. Creating and maintaining a healthy intestinal environment that inhibits pathogen survival and growth has been demonstrated an effective strategy in protecting productivity and in food safety programmes. Acidification with organic acids like FORMI, which is based on potassium diformate, works against Salmonella both within the feed and within the pig, where it exerts possibly its biggest benefit. A study performed by the Danish feed company KFK (Olesen,1999), demonstrated a sustained effect of potassium diformate use, even after removal of the additive from the feed (Figure 1), although Blanchard and Burch (2004) concluded that continuing additive use will prevent further cross contamination in the unit.