These are live bacteria or micro-organisms that are either mixed in the feed or administered individually by mouth to produce a beneficial effect on the organism in the gut.

Under normal conditions the intestines of the pig contain a complex of 400 or more organisms which constantly protect against disease. Specific bacteria can also protect against specific pathogens.

Probiotics are believed to act in the following ways:

• Neutralise toxins in the intestinal tract.
• Prevent the adhesion of pathogens to the mucosal surface by competition.
• Stimulate local immune defences.
• Reduce the numbers of pathogens by competition.

The common organisms used include lactobacilli, yeasts, streptococci, enterococci and non pathogenic E. coli. Lactobacilli are the most common and at least seven have been identified as having a beneficial effect. They produce large amounts of lactic acid which creates an unfavourable environment for certain bacteria. In the piglet this creates high acid conditions in the stomach helping to prevent the establishment of pathogenic E. coli.

Probiotics have been available for use in pig feeds for a number of years and yet the results of their use are inconsistent and at times in the field remain unconvincing.

Oral preparations given to piglets and their response to E. coli diarrhoea can be difficult to assess on the farm because their use often starts with ongoing diarrhoea problems, most of which go away with better management and hygiene. A typical example was their use in a 1000 sow operation where 30% of all litters scoured. This was associated with a continual pig flow policy in the farrowing houses. This was changed to all-on all-out and at the same time probiotics were given to all piglets at birth. The problem gradually disappeared. Three months later due to costs, the probiotic use ceased. The scour problem did not return.

Probiotics appear to have little effect on piglet diarrhoea after five days of age.

Lactobacilli have been used for growth promotion but consistency of results in the field are poor and it is difficult to see large numbers of well controlled trials that give sufficient confidence for their continual use. Field experiences in the immediate post-weaning period have in a few herds shown a beneficial effect but in most an economic return could not be justified.