Researchers at Scotland’s Rural College (SRUC) have identified a high number of antimicrobial resistance (AMR) genes in pig feces at a commercial farm, following the first longitudinal study of its kind.

SRUC said while antimicrobial agents have been used in agricultural systems to improve the health, welfare and productivity of livestock, little is known about how this affects AMR gene dynamics — the ability of a microbe to resist the effects of medication.

In partnership with the University of Edinburgh's Roslin Institute, the study was carried out during a single production cycle on a commercial pig unit with high historic and current antimicrobial usage, SRUC said.

SRUC reported that a total of 144 different genes were identified on the farm, with individual genes present in the tens, hundreds and thousands of millions per gram of pig feces.

The study, published by Scientific Reports, highlights the extent of AMR gene "pollution" in livestock production and the environment, SRUC said.

The study found that AMR gene counts were relatively stable over time, suggesting that the genes had become integrated into the fecal microbial community, SRUC noted, adding that the administered antimicrobials were still effective in controlling production-limiting diseases on the farm.

“At the start of the study, we hoped to find two or three genes to follow their numbers through the pig production cycle. The richness of AMR genes and their numbers were unexpected,” said professor Michael Hutchings, head of Animal & Veterinary Sciences at SRUC.

The study was funded by the Natural Environment Research Council and the government of Scotland.