Speaking at the International Production and Processing Expo in Atlanta, Dr Charles Hofacre from the University of Georgia said that the most common transmission of salmonella on broiler farms was from mother to chick.

Dr Hofacre said that salmonella and birds have happily existed together in an almost perfect host and parasite relationship.

And in a study that sampled 55 flocks46 per cent of the birds going into the processing plant tested positive for salmonella.

However, he added that the processing plants are “doing quite a good job” at getting the numbers down, with a gradual reduction of salmonella in the rehang, pre-chill and post-chill stages.

Dr Hofacre said that the campylobacter load on the birds is also being reduced through interventions within the processing plant although the contamination with campylobacter starts at a very much higher level.

“Eighty per cent of salmonella on broiler farms is from vertical transmission from mother to chick,” said Dr Hofacre.

However, Dr Hofacre showed that there are also other potential sources for salmonella contamination on the farm, including the water, wildlife, insects and rodents, fee, contaminated litter and mites – all of which also have to be addressed.

Within the processing plant interventions such as the use of organic acids can help to reduce contamination along with rigorous cleaning and disinfecting.

But on the farm, once the broiler flock is found to be positive with salmonella, it is virtually impossible to reverse the situation as the whole flock becomes colonised.

While use of competitive exclusion methods including the use of active flora and probiotics, antibiotics and organic acids in the water can help the situation vaccination of the breeders is the ideal way to control salmonella, although it will not make it go away once the chicks are infected.

Vaccination helps to give an early protection and by vaccinating the breeders studies have shown that it can reduce salmonella in the broiler flock by as much as 50 per cent