Racehorse success may depend on their gut microbiome in early life

Racehorses seem to perform better and have a lower risk of health complications if they had diverse gut bacteria as foals.

The findings suggest that, as suspected in humans, the gut microbiome of horses has a critical window for establishing a bacterial composition that may contribute to an individual’s long-term health and fitness.

Christopher Proudman at the University of Surrey in the UK and his colleagues performed DNA sequencing on faecal samples from 52 Thoroughbred foals born on five stud farms in 2018.

They collected samples nine times over the first year of life – at ages 2, 8, 14 and 28 days, and at 2, 3, 6, 9 and 12 months. When a year old, the animals were moved to 29 different race training centres in the UK.

The researchers then measured the horses’ athletic performances when aged 2 and 3 years old during races, including gathering data on finishing positions and total prize money. They also kept records of the horses’ respiratory and orthopaedic health, as well as that of their soft tissues.

The team found that greater bacterial diversity at 28 days of age was linked to better racing performances. The researchers also detected two families of bacteria, Anaeroplasmataceae and Bacillaceae, that were associated with having a competitive edge.

By contrast, low bacterial diversity at 1, 2 and 9 months of age was associated with an increased risk of orthopaedic issues and other problems, such as muscle strains or “hairline” fractures. The team also found specific bacterial families that when abundant at around 1 or 2 weeks old were linked to greater risks of respiratory or musculoskeletal disease later in life.

The foals that had been treated with antibiotics – which can affect the gut microbiome – in the first few weeks of life had significantly less bacterial diversity at day 28 than their untreated counterparts, says Proudman. These animals later earned less prize money and developed respiratory diseases at 10 times the rate of the non-treated foals after the age of 6 months.

It is possible that the early health issues that prompted antibiotic treatment may have been what actually affected later performance and health, says Simon Daniels at the Royal Agricultural University in Gloucestershire, UK. But it is also realistic to think that the antibiotics themselves led to a lack of bacterial diversity that is associated with poorer health and performance, he says.

“While we need more evidence before drawing strong conclusions, it would appear that the way we manage young horses is particularly important for their athletic ability later in life,” says Daniels.