Isolated sheep were calmed down by photos of other animals.© Alamy

Exposing isolated sheep to photos of other sheep lowers their stress levels, shows a recent study. Researchers suggest the practice could be used to soothe solitary and sick animals and hope the work will help elucidate the brain mechanisms behind the ability to link faces with emotion.

Like many of us, sheep do not like being alone. They are also excellent at recognizing individual faces, and can remember the features of up to 50 sheep and 10 humans over a two-year period¹.

So Keith Kendrick and colleagues from the Babraham Institute in Cambridge, UK, wondered if photos of sheep faces could be used to appease lonely bleaters. Their findings are reported in the Proceedings of the Royal Society of London B².

Telling the sheep from the goats

The team took 40 sheep of a Welsh lowland breed called Clun Forest, and isolated them one at a time in a funnel-shaped enclosure. For the first 15 minutes, four identical pictures of a white inverted triangle were projected on to the rear wall. For the next 15 minutes, the animals were shown either four photos of an unfamiliar sheep face or four photos of an unknown goat face.

As soon as the animals were left alone, their heart rates began to soar. At the end of the first 15 minutes, adrenalin and stress hormone levels had increased, indicating clear signs of stress.

Like many of us, sheep do not like being alone.© Keith Kendrick

But after 15 minutes of simulated sheep company, the animals became calmer. Heart rates fell to pre-isolation levels. Stress hormone and adrenaline levels more than halved, and the number of unhappy bleating noises dropped by 20-fold.

The animals seemed to ignore the triangle pictures, but they actively spent time looking at the sheep photos and even moved to be close to them. "The face pictures affected every single measure of fear and stress that we took," says Kendrick.

Goat pictures produced intermediate effects, suggesting that sheep find photographs of their own species more comforting than those of other animals.

Because sheep are so good at recognising flock members, the effect might also be boosted by showing the animals pictures of buddies, says Kendrick. But it's unlikely that this will always be possible, so the team instead chose to focus on unfamiliar, same-species faces.

The timing and type of isolation mimics that seen during normal animal husbandry practices. Vets also tend to house sick creatures on their own while monitoring them, and wild animals are sometimes shipped long distances alone.

Kendrick speculates that the effect is likely to apply to other species too, and suggests that a photo of a friendly face could alleviate unnecessary stress when animals are placed in holding pens. 

• References

  1. Kendrick K. M., et al. Nature, 414. 165 - 166 (2001). | Article | PubMed | ISI | ChemPort |
  2. da Costa A. P., Leigh A. E., Man M. S. & Kendrick K. M. Proc. R. Soc. Lond. B, (2004).