Even short trips can alter the immune response of older horses, study shows

Older horses being transported for only short distances may have altered immune responses, which could increase their susceptibility to transport-related illnesses, according to researchers.
Photo by Shelly Busby on Unsplash

Older horses being transported for only short distances may have altered immune responses, which could increase their susceptibility to transport-related illnesses, according to researchers.

“Although further work is needed to confirm this, additional caution should be taken in the meantime when transporting these horses, such as by ensuring adherence to general biosecurity precautions and including increased monitoring for any potential adverse effects,” Ashton Miller and his fellow researchers wrote in the journal PLOS ONE.

Long-distance transport is associated with stress-related changes in equine immune function, and shipping-associated illnesses are often reported.

However, horses are frequently transported for only short distances. Yet the effects of these short trips on immune function remain largely unknown.

In their study, 12 horses aged 15 to 30 were assigned to either the control or treatment groups. The six treatment horses received a daily antioxidant supplement three weeks before and after transport.

All horses were transported for 1.5 to 2 hours, with blood collected for analysis 21 days before the trip, and on days 1, 3, 7, 14, and 21 after the trips.

Body temperature, heart rate, body weight, and concentrations of the stress hormone cortisol were assessed, as were the effects on a range of cytokines and proteins which play a role in the activation of immune cells.

Transport and supplementation did not appear to affect body weight, heart rate, nor four of the cytokines for which they tested, but it did have an influence on the expression of others, in particular IL-1β and the protein coding gene Serum amyloid A, which were consistent with the anti-inflammatory properties of the supplement used.

Transport increased total cortisol concentrations and body temperature, and exerted an effect on several of the cytokines and proteins for which they tested.

“Short-term transportation affected physiological, endocrine, and immune responses,” they said, noting that antioxidant supplementation may ease inflammation in aged horses.

“Immune responses were most altered at 15 minutes post-transport and typically recovered by Day 1, suggesting that horses may be vulnerable to disease during and almost immediately after short-term transport.”

Discussing their findings, the study team said that because immune responses have the potential to be both protective and destructive, they are highly regulated in healthy individuals.

“A strong pro-inflammatory response is generally considered protective during acute illness or stress, but an extended pro-inflammatory response can be damaging and must cease when no longer needed.”

“Overall,” they said, “the results of this study demonstrate that short-term transport significantly affects numerous aspects of equine immune function, particularly within the first 24 hours of transport, and may reflect altered activation of the acute phase and pro-inflammatory responses to transport stress.

“This is potentially concerning given both the frequency with which horses are transported across short distances as well as the consistency of the results with other research findings that have demonstrated that immune function is affected by long-term transportation.”

The findings show that antioxidant supplementation can successfully alter inflammation in horses and could potentially be used to modulate the immune response, they said.

“Considering the findings in this study and in other published work, further research into the immunological effects of transport stress in horses is warranted, especially for shorter transport durations and distances.

“Future work should focus on the first 24 hours after transport initiation to determine how immune function responds during this window.

“Additionally, investigations of the effects of age and trip frequency are also necessary to better understand the potential risks that may accompany transport,” they said.

The study team comprised Miller, Virginia Barker and Amanda Adams, all with the M.H. Gluck Equine Research Center at the University of Kentucky; and Patricia Harris, with the Waltham Petcare Science Institute in England.

Miller AB, Harris PA, Barker VD, Adams AA (2021) Short-term transport stress and supplementation alter immune function in aged horses. PLoS ONE 16(8): e0254139. https://doi.org/10.1371/journal.pone.0254139

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


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