Life in the wild for horses has its stresses, research shows

Levels of the stress hormone cortisol were higher in free-living horses than their stabled counterparts, including those who did police work.
A free-living horse in Italy. File image by davdenic

Healthy free-ranging horses in a mountainous area of Italy showed much higher levels of the stress hormone cortisol in their hair than their stabled counterparts, research has shown. Their levels were even higher than horses involved in police work.

Francesco Cerasoli and his fellow researchers, writing in the journal Animals, said horses have been used for companionship, work, transportation, and performance purposes over the centuries.

There are different ways of managing horses, but studies on how horse welfare is influenced by different activities and management practices are scant.

The study team set out to assess welfare in three groups of horses kept in three different ways, based on levels of cortisol in their hair. In recent years, cortisol has proven to be a reliable indicator of stress in animals.

Levels in horse hair have been used as an indicator of chronic stress. Horse hair, they said, is a matrix where cortisol can accumulate over time, forming a stress “archive”.

In all, 47 clinically healthy horses were enrolled in the study, comprising 18 females and 29 males. They were aged 5 to 15.

The horses were made up of three groups. The first, comprising 16 horses of various breeds, were stabled individually in boxes with daily paddock access. They were fed with hay and hard feed (a ration balanced by a veterinarian). Their bedding was dust-free wood shavings. The horses, under the care of the Italian State Police, carried out training activities and flatwork 3 to 4 times a week.

The second group, also comprising 16 horses of various breeds, were individually stabled and had no paddock access. They had a similar diet and bedding to the first group. They all worked daily helping to maintain public order in service to the Italian State Police in Rome. On days off, the horses were walked.

The third group comprised 15 free-ranging horses who lived in the mountains of central Italy at an altitude of about 600 metres. They had access to natural food and hay without supplements, while drinking water was available via tanks. The horses were not limited by fences and only natural shelter was present. The area is also inhabited by wild animals such as deer, wolves, and bears. The horses live together and have no direct contact with humans. While they were gathered in a fenced area for sampling, this acute stress would not have altered cortisol horsehair concentrations.

Cortisol analysis was carried out using liquid chromatography coupled to hybrid Orbitrap high-resolution mass spectrometry – a laboratory technique used for the first time to quantify horse-hair cortisol.

Horses were included in the three groups only if they had received a positive welfare assessment in accordance with the European Animal Welfare Indicators (AWIN) protocol.

The free-ranging group of animals displayed much higher levels of cortisol than the stabled horses who had daily paddock access and did flatwork. Levels in the free-ranging group were also noticeably higher than the stabled horses who did daily police work.

“Though it is usually assumed that outdoor animals kept under ‘naturalistic’ conditions can experience a better degree of welfare, this assumption indeed depends on the presence of several stress-related variables that have to be considered,” they said.

The free-ranging horses recorded higher levels of cortisol over time, even though they could express social behavior, and despite showing, at least apparently, very good health.

The authors, with the Experimental Zooprophylactic Institute of Abruzzo and Molise, noted that other researchers have delivered a range of results in stress studies in horses. One 2020 study found no significant differences in horsehair cortisol concentrations between management regimes. Another noted that, even if animals are living under natural conditions, they may be exposed to constraints, such as climate challenges or feeding problems.

Others have shown that confining horses in individual boxes could reduce opportunities for the expression of natural social behaviours, while other research has pointed to reduced stress levels in horses that spend the night stabled.

“The higher cortisol levels found in free-ranging horses might be due to the fear of being predated during the night,” the study team wrote. “The area where the study was conducted is mountainous with the regular presence of wolves and bears during the whole year.”

The results, they said, show that horses living in the wild can be more subject to stress, the study team. “Although further studies on this matter are desirable, this research adds an important piece to the stress associated with the management of horses.

“This study also reveals how good human management of horses, even those subjected to work and training, can provide lower cortisol levels than horses in the wild that live in more natural and less stressful conditions. Further research is also needed in this regard.”

The study team comprised Cerasoli, Michele Podaliri Vulpiani, Giorgio Saluti, Annamaria Conte, Matteo Ricci, Giovanni Savini and Nicola D’Alterio.

Cerasoli, F.; Podaliri Vulpiani, M.; Saluti, G.; Conte, A.; Ricci, M.; Savini, G.; D’Alterio, N. Assessment of Welfare in Groups of Horses with Different Management, Environments and Activities by Measuring Cortisol in Horsehair, Using Liquid Chromatography Coupled to Hybrid Orbitrap High-Resolution Mass Spectrometry. Animals 2022, 12, 1739.

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

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