In Canada and the United States there's been ongoing pressure to reduce the amount of antimicrobials used in livestock feed, particularly for growth promotion but even for prevention of disease driven by concerns over antibiotic resistance that can spill over into human therapies.

Dr Alan Mathew, the Head of Purdue University's Animal Science Department, says the use of essential oils is a new and emerging field because there are so many of these compounds that are being studied right now.

Dr Alan Mathew-Purdue University

Typically they're plant based.

The have some subtle effects on the gut microbiota, they may help with palatability and intake, which is very important in getting young pigs off to a good start.

Some seem to have beneficial effects.

Some are certainly bacteria killers, at least in the lab but how that plays out in the gut we don't quite understand yet.

There does seem to be some research that indicates they do change the gut microbiota slightly towards the beneficial organisms so they have a place in the strategy and they may help reduce some of the E. coli overgrowth that seems to be occurring when those pigs are troubled nutritionally.

Dr Mathew says where we need to do better is understanding the complexity of this mass microbiome and vast array of bacteria of the gut so we can fully understand what the effects are when we apply these strategies and, what are they impacting.

He says we need to understand what species we want to facilitate and promote and suggests our newer molecular technologies where we can identify hundreds of species in the gut are helpful in advancing our knowledge and the efficacy of the different strategies.