08/01/2023
INDIVIDUAL STABLING FOUND TO ALTER IMMUNE RESPONSE
A recent study has found that horses moved from group housing to individual stabling showed changes in their white blood cell counts and plasma cortisol levels. These changes could mean they are at a higher risk of infectious disease.
Equine scientist Sonja Schmucker and her colleagues at the University of Hohenheim in Germany studied 12 warmblood geldings aged 2-3 years old during several management changes, monitoring their behaviour and immune response.
The horses used were all living in a group, turned out at pasture. For the first part of the study the group was then split into two, each kept in a separate paddock so that the horses in one group could not see the others. After a trial period of eight days all the horses were returned to their original group, living together. They were then were left out at pasture for eight weeks.
For the second part of the study the horses were all moved into individual stables, where they could see and touch their neighbours through bars. During the first week of being stabled, the horses were given 30 minutes of turnout in an indoor area. From the second week onwards, the horses were lunged.
Throughout the study the research team collected blood samples from the horses to analyse their immune cell numbers and cortisol concentrations.
The results showed that moving the horses to individual stabling led to acute stress-induced immune changes. However, dividing the larger group into two smaller groups at pasture did not.
“The number of eosinophils, monocytes and T cells declined, whereas the number of neutrophils increased resulting in an increased N:L ratio. This pattern of change resembles the well-known picture of an immunomodulation induced by acute social stress.”
The plasma cortisol concentrations didn’t change after dividing the group into the two smaller groups at pasture, but there was an increase in cortisol concentrations one day after stabling which then returned to the previous levels eight days later. However, the researchers said “Although cortisol concentrations returned to baseline level after 8 days, the alterations in most immune cell numbers persisted, pointing to a longer-lasting effect on the immune system of the horses."
The team also found, unsurprisingly, that some of the horses started to perform stereotypical behaviours as soon as one week after stabling.
The team reported that the results “strongly indicate that social isolation is a chronic stressor with negative impact on welfare and health of horses and highlight the advantage of group housing systems in view of immunocompetence."
The researchers concluded that “relocation to individual stabling represented an intense stressor for the horses of the present study, leading to acute and lasting alterations in blood counts of various leukocyte types. In contrast, fission of the stable group did not result in behavioural, endocrine or immunological stress responses by the horses."
This sudden change from group turnout to individual stabling with training being introduced is a very common scenario for horses being started for the first time. Again this study gives us yet more evidence that stabling horses individually is stressful and detrimental to their physical and psychological wellbeing. The majority of the horses I see are stabled for the bulk of the day. I do wonder how much evidence is needed before horse owners and professionals act on this information and change their management to increase turnout and group living...
The research is free to access and is a very interesting read: Schmucker S, Preisler V, Marr I, Krüger K, Stefanski V (2022) Single housing but not changes in group composition causes stress-related immunomodulations in horses. PLoS ONE 17(8): e0272445.
