What is the likelihood of injury in horses kept in groups?

What is the likelihood of injury in horses kept in groups?
25 Jul 2017

Competition horses are sometimes not turned out for fear of injury.

Horses naturally like to live in herds, but in modern times competition horses are sometimes not turned out with other horses for fear they will get injured. Nordic researchers set out to quantify the incidence and severity of injuries in horses kept in groups.

Study Methods
In total, 61 groups (233 individual horses) were involved in the study which was carried out between September 2007 and November 2008. During the study horses who lived out 24/7 and were studied for 6 week periods at time. The researchers assinged the horses into one of several kinds of groups to see if this would have any effect on injuries. The types of groups were: same sex groups, mixed sex groups, similarly aged groups, mixed aged groups, stable groups (group remained the same throughout the study period) and dynamic groups (one horse was removed and a new horse added each week).

Reactiveness of horses kept in groups
As well as recording incidences of injury, the researchers also decided to record how reactive horses in different groups types were, with the hypothesis that older horses may have a calming effect on younger horses and groups made up purely of younger horses may be more reactive. To test this, the researchers put a string of plastic bottles in the field while the horses were being fed. The plastic bottles were then dragged across the ground 5 meters in front of the horses and individuals’ reactions were recorded. This was done once for each group.

Inspection and scoring of injuries
The horses involved in the study were inspected three times for their injuries: before they entered their groups for the study, the day after being put in their group and at least four weeks after the group was formed. The injuries were scored from 0-5, with 0 and the scores were defined as follows:

  • 0 – no injury
  • 1 – hair missing
  • 2 – lesion involving a moderatley swollen area and/or superficial wound, but the skin is not cut through
  • 3 – lesion involving a minor cut to the skin
  • 4 – lesion of a size that would normally be stiched by a vet
  • 5 – extensive and severe injury possibly leading to the loss of long term function

Results
Injury occurrence was recorded in all 233 horses. A total of 1088 injuries were recorded of which 597 were present on day 0, before the horses were put into their groups for the study. 188 new injuries were recorded after grouping day 1 and 303 new injuries were recorded after 4 weeks. The majority of injuries were minor (80% category 1, 18% category 2). Throughout the whole study, a total of 3 injuries were recorded as category 3 and 2 injuries were recorded as category 4. The two category 4 injuries occurred to young warmblood horses.

There was no difference between mixed age and similar age groups, mixed sex and same sex groups or the stable and dynamic groups in the mean number of new injuries recorded. The main predictor of injury actually turned out to be breed, with Warmblood horses significantly more likely to get injured than Icelandic horses. The researchers hypothesise this could be because the Icelandic horses have been bred for a calmer temperament, and they also tend to have more body fat and thicker coats which better protect them from kicks and bites.

Reactiveness Results
The main predictor of reactiveness was breed, with Warmbloods being the most reactive breed and Icelandic horses being the least reactive. Mixing older horses with younger horses or just having groups of older or younger horses did not have any significant effect on reactiveness.

This study suggests that horses are unlikely to get severely injured from being turned out in groups and their welfare is more likely to be compromised if they are not allowed to socialise with other equines and exhibit normal herd behaviour. One thing to note that could affect rates of injury is competition for resources. In this study, all horses were in paddocks of at least 0.5 hectares and at feed time each horse was given its own pile of feed.

Reference
Keeling, L.J., Bøe, K.E., Christensen, J.W., Hyyppä, S., Jansson, H., Jørgensen, G.H.M., Ladewig, J., Mejdell, C.M., Särkijärvi, S., Søndergaard, E. and Hartmann, E., 2016. Injury incidence, reactivity and ease of handling of horses kept in groups: A matched case control study in four Nordic countries. Applied Animal Behaviour Science, 185, pp.59-65.

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