Benefits of a holiday break on pasture seen in sport horses

Stabled competition horses appear to benefit from a holiday on pasture, according to researchers, whose just-published study identified links between the composition of microorganisms in the gut and poor welfare.

Nuria Mach and her fellow researchers, writing in the journal Scientific Reports, said elite sport horses that live in individual boxes and train and compete for hours can experience long-term physical and mental stress capable of compromising welfare and altering the gut microbiota.

Mach and her colleagues set out to discover if a temporary period on pasture with other horses could improve animal welfare and, in turn, favorably affect intestinal microbiota composition.

A total of 27 sport horses were monitored before and after a six-week break on pasture a few kilometers away from their home, and their fecal microbiota and behavior profiles were compared to 18 sport horses kept in individual boxes during the 21-month study period.

All 45 horses lived at the same riding school in France and generally shared a similar environment. When stabled at the facility, all were typically trained at high intensity six days a week.

The pasture group horses were monitored three times before being turned out on pasture, and one and three months after their return to the stables. The horses in the stable control group were monitored at the same five time points.

The overall diversity and microbiota composition of pasture and control individuals were similar over time, suggesting resilience to environmental challenges. Resilience describes the amount of stress that a system can tolerate before its state shifts towards a new equilibrium that potentially has different functions.

However, pasture exposure induced an increase in Ruminococcus and Coprococcus that lasted for a month after their return to individual boxes, which may have promoted beneficial effects on health and welfare.

When returned to individual boxes, the authors noted a strong occurrence of stereotypies, periods of withdrawn posture, and spells of hypervigilance during the first five days compared to the control horses.

“Furthermore, the pasture horses tended to express more alert postures than the control group up to three months after the return to the individual boxes.”

Because of this, the researchers sought to determine whether the increased occurrence of these behaviors, all of which are linked to compromised welfare, were associated with their gut microbiota profiles.

The study team confirmed associations between gut microbiota composition and behavior indicating poor welfare.

Horses tended to show less withdrawn behavior when their relative abundances of Lachnospiraceae AC2044 group and Clostridiales family XIII were higher. Both accommodate a large part of butyrate-producing bacteria, they noted.

“While we cannot infer causality within this study, arguably, these findings suggest that management practices maintained over a longer period of time may moderate the behavior link to the gut ecosystem beyond its resilience potential.”

The authors said repeated exposures to pasture with other horses may be required to ensure a bloom of butyrate-producing bacteria such as Ruminococcus and Coprococcus, which in turn, may drive long-lasting positive immune, metabolic and psychological changes in sport horses.

The study team comprised Mach and Sophie Dhorne-Pollet, with the University of Paris-Saclay in France; Léa Lansade and Alice Ruet, with the University of Tours in France; David Bars-Cortina, with the University of Lleida in Spain; and Aline Foury and Marie-Pierre Moisan, with the University of Bordeaux in France.

Mach, N., Lansade, L., Bars-Cortina, D. et al. Gut microbiota resilience in horse athletes following holidays out to pasture. Sci Rep 11, 5007 (2021). https://doi.org/10.1038/s41598-021-84497-y

The study, published under a Creative Commons License, can be read here.