Encouraging “friendly” bacteria in the intestines of poultry has been widely lauded as the alternative to routine antibiotics use.

But as Juha Apajalahti from Finnish research company Alimetrics told the meeting, it can compromise feed conversion rates, and if antibiotics are then introduced, could leave birds’ intestines defenceless.

Microbiota populations found in the intestines of poultry are made up of both commensal bacteria and pathogenic bacterium, he explained. The latter are “gram negative” and have the potential to infect and cause illness in the bird, or humans that consume its products.

Commensal bacteria, on the other hand, are “gram positive” and many of these perform a number of roles in promoting healthy guts.

The problem is that most antibiotics target gram-positive bacteria, and are less effective against pathogenic gram-negative ones.

“Commensal microbiota can be very well adapted to the environment and intestinal habitat,” said Mr Apajalahti. “It simply doesn’t let in any pathogens as they don’t have any chance to compete.”

He explained that intestines have attachment sites for bacteria, which commensal bacteria can totally dominate, preventing pathogens from establishing. “That’s typical of competitive exclusion theory.”

Introducing antibiotics to this environment appeared to dramatically reduce the number of both commensal gram-positive bacteria, while controlling the presence of pathogenic gram-negative bacteria. “Sudden withdrawal of antibiotic would then leave the intestine defenceless for the period of time that it takes for the natural commensal microbiota to recolonise the habitat.”

Mr Apajahti pointed to a study, which showed antibiotics reduced bacterial numbers, freeing-up more energy for the bird, while maintaining the protection from pathogens that commensal bacteria provided through displacement.

The small intestine size also shrunk, further reducing potential for bacterial concentration.

“It’s very important to understand here that we have to let this commensal bacteria work, otherwise they don’t protect from pathogens. They must be relatively active and they must be at relatively high numbers to be protective. It’s difficult for them to work if you use antimicrobials at the same time.”

Mr Apajahti added that, by their nature, gut promoters were not an alternative to antibiotics, as they worked in completely opposite ways: antibiotics suppressed gut activity, saving energy as well as preventing illness.

A healthy gut containing commensal bacteria could perform the same role, but used more energy, adversely affecting FCR.