For many years, antibiotics have been used as growth promoters in poultry, after they were found to improve growth rates and gut health.

But regulators and consumers are keen to see their use reduced in the industry, as fears of antibiotic-resistant pathogens grow.

Many researchers have been looking at non-medicated feed additives as alternatives to antibiotic growth promoters.

Global animal nutrition business, Cargill, performed studies on a variety of different feed additives, including essential oils, probiotics, yeast derivatives and medium chain fatty acids (MCFA).

A combined total of 77 comprehensive in vitro and in vivo trials have been conducted since 2009, at facilities in the Netherlands, Jordan, France, Poland, India and the US.

For consistent performance improvement, essential oils turned out to be a major solution.

Essential oils are multifunctional in protecting gut health

Ms Ladirat explained that essential oils impact all four key aspects of gut health.

These areas include maintaining a well-balanced population of bacteria in the gut; immune function and response to pathogens; nutrient absorption, which is important for the conversion of feed into body weight; and the physical barrier against pathogens.

Essential oil compounds derived from thyme, cinnamon and oregano had the most comprehensive effect on overall gut health.

In particular, the studies showed that poultry fed these essential oils benefited from improved antimicrobial activity in the gut.

The essential oils also stimulated enzyme production, which helps birds to digest feed and improves body weight gain.

However, Ms Ladirat said that some of the ways in which these compounds work are still unknown.

For example, on immune function, the scientists have worked out that essential oils can stimulate the production of certain molecules that can be pro- or anti-inflammatory, but they do not yet know the real mode of action and at what stage essential oils are important.

In the fourth area of gut health, the physical barrier against pathogens, Cargill's research showed that the irritation caused by these essential oils stimulated the production of a thicker mucous lining in the gut.

Ms Ladirat explained that this physical barrier is important to prevent pathogens entering the bloodstream and affecting the bird. A strong physical barrier will allow pathogens to pass through the gut and be excreted instead of causing infection.

Dosing level of essential oils is very important

However, if the essential oils cause a thicker mucous layer to form on the gut lining, an unwanted side effect might be that it is harder for birds to absorb nutrients from feed.

That's why providing the correct dose of essential oils in the feed is so important, Ms Ladirat explained.

At too low a level of essential oils, gut health will not be improved at all.

As the dose gets higher, digestive enzyme production and the thickness of the mucous layer will both increase, and producers will see the benefits in their birds.

But at some point, feeding more essential oils will mean the mucous layer is too thick and no further improvement will be seen.

Complicating the matter further is the level of pathogens present in the environment.

If there are more pathogens around, the protective barrier needs to be thicker, and in this situation protection from dangerous microbes becomes a more important effect of essential oils than improving digestion and nutrition.

Ms Ladirat and other researchers have the job of working out now what is the most appropriate dose to use in different scenarios.

Do essential oils work well enough to replace antibiotic growth promoters?

Experiments at Cargill's facility in the Netherlands have compared poultry given different feed additives, with poultry fed none.

Groups of poultry raised with essential oils or with one type of antibiotic both performed substantially better than the group raised with neither.

However, there was very little difference between the performance of the antibiotic group and the essential oil group, suggesting that essential oils provide a good alternative to antibiotics.

Ms Ladirat cautioned, though, that conditions in the testing facility were very different to the real conditions poultry producers face every day.

Testing facilities form a very clean environment, and also commercial poultry might be given several different types of antibiotics all at once, depending on the circumstances.

"It is very difficult to replace antibiotics," Ms Ladirat said. "Actually nobody really knows how antibiotics are working, they just know they work. So it's not a one-to-one switch."

She said that Cargill recommends essential oils as part of the solution, but also recommends tailored nutrition programmes and specific farm management through the advice of local experts.

Other research findings support combining essential oils with organic acids to get maximum efficacy.

Benefits for producers and society

Combined study results from 12 trials demonstrated that birds given Cargill’s feed additive, containing a mixture of seven carefully selected essential oil compounds, in combination with an antibiotic-free diet, consistently improved body weight gain by 2 per cent and feed conversion by 1.5 per cent.

This gave a return on investment of 5:1 for producers.

For poultry producers this high return on investment would be a top benefit of intestinal health support, but it also helps address issues in food safety and animal welfare.

Healthy poultry intestines may result in a lower risk of bacterial food contamination and in healthier barn environments.

In addition, the improved feed efficiency contributes to efforts to meet increasing demand for global animal protein in an efficient way.