Access to shelter appears to be a valued resource for most horses when kept individually on paddocks during summer, Swedish researchers report.
However, the jury remains out on precisely why they choose to use them. Is it shade from the sun, shelter from insect pests, or through some sense of security, particularly among horses that are used to stabling?
“Shelter use may not be primarily related to weather conditions but is most likely dependent upon individual preferences,” Kristina Dahlborn and her colleagues reported in the journal, Acta Veterinaria Scandinavica.
A shelter that was closed on three sides emerged as most likely to be preferred and had the best potential to give some relief from flying insects, they reported.
Dahlborn, joined by Elke Hartmann Richard Hopkins and Claudia von Brömssen, noted that the provision of shelter for horses kept on summer pasture was rarely considered in welfare guidelines, perhaps because the benefits of shelter in warm conditions were poorly documented scientifically.
“We found in a previous study that horses utilized shelters frequently in summer,” they reported.
“A shelter with a roof and closed on three sides (shelter A) was preferred and can reduce insect pressure, whereas a shelter with roof and open on three sides was not utilized.”
However, the shelter enclosed on three sides restricted the all-round view of a horse, which may be important for horses as flight animals.
“Therefore, we studied whether a shelter with roof, where only the upper half of the rear wall was closed (shelter B), would be utilized while maintaining insect protection properties and satisfying the horses’ sense for security.”
A third shelter was offered with walls but no roof (shelter C) to evaluate whether the roof itself was an important feature from the horse’s perspective.
Eight warmblood horses, all chestnut or bay, were tested, each for two days, kept individually for 24 hours in two turnout paddocks with access to shelters A and B, or shelters A and C, respectively.
Shelter use was recorded continuously during the night and the following day, and insect defensive behaviour, such as tail swishing, were noted in scan samples at 5-minute intervals during daytime.
Seven horses used both shelters A and B, but when given the choice between shelters A and C, shelter C was scarcely visited.
There was no significant difference in duration of shelter use between day and night.
Daytime shelter use had a significant effect on insect defensive behaviours, they found. “The probability of performing these behaviours was lowest when horses used shelter A compared to being outside.”
All eight horses were allowed to become familiar with the test paddocks and were familiarized with the shelters before the experiment began. No shade was available other than the shelters provided.
They described the 4m by 4m shelters as follows:
- Closed shelter A had a roof and a covered-in rear wall and transparent wind nets on two sides.
- Open shelter B had a roof and a covered-in read wall that only covered the upper half. It had no sides.
- Shelter C had no roof, but wind nets on three sides.
Seven of the eight horses used the shelters. They were observed inside the shelters during 35.4% of daytime observations during the study period.
The time spent inside the shelters A and B with roof did not differ significantly between night (105.8 minutes) and day (100.8 minutes).
Shelter A was visited less during nights compared to shelter B, but there was no difference in duration during daytime.
Horses were observed inside the shelters for longest between 6pm and 7pm and between 9am and 10am the following day.
“Individually kept horses used shelters with a roof during both the night and the day. The horses preferred shelters with a roof and partially closed on at least one side (shelter B) or three sides (shelter A) when these shelters were tested in combination.
“When given the choice between shelter A and a shelter closed on three sides but without a roof (shelter C), the shelter with a roof (A) was favoured.
“Noticeably,” they continued, “shelter use reflected individual preferences as some of the horses hardly used any of the provided shelters which were also the same individuals studied in the previous experiment.”
They observed: “Shelters were frequently used during nights and it seems that some feature of the shelter structure was appealing beside the possibility that horses sought shelter to find shade.
This may be due to an increased sense of security, as was suggested by other researchers.
“We propose that this may be relevant for singly kept horses that also have the experience of being stabled in boxes at night.
“During the cold season, horses seem to use shelters mostly during nights, and lying behaviour occurred almost exclusively inside the shelter which may support this security seeking hypothesis.
“Another plausible explanation of shelter use may be that horses seek to avoid insects. Under free-ranging conditions, horses often seek refuges at times of peak insect activity by moving to spots with maximum wind velocity, avoiding areas with dense vegetation.”
Blood-sucking insects usually found their hosts initially via smell.
“When getting closer, visual contact is made whereby the host will be more easily detected the greater the contrast is with the background and the larger the animal.
“Given these host-searching strategies, it is possible that horses staying inside shelters, where at least one side is partially covered, become less apparent and harder to detect relative to the background.
“This may be supported by the finding that insect defensive behaviours were exhibited less in horses using shelters A and B. Tail swishing, in particular, tended to be lower in horses observed in the shelter closed on three sides (A) compared to the shelter with only one side partially closed (B).”
Future research should establish whether horses kept in groups would seek shelter to a similar extent as when kept individually, they said.
The researchers are with the Swedish University of Agricultural Sciences in Uppsala.
24-h sheltering behaviour of individually kept horses during Swedish summer weather
Elke Hartmann, Richard Hopkins, Claudia von Brömssen and Kristina Dahlborn.
Acta Veterinaria Scandinavica 2015, 57:45 doi:10.1186/s13028-015-0135-x
The full study can be read here.