Shared stressful experiences lead to close knit bonds in sheep

Sheep which share stressful experiences together develop closer bonds, according to CSIRO research.

A CSIRO study published in Biology Letters investigated the closeness of interactions between Merino ewes. The authors say understanding how stress influences social dynamics in animal populations has implications for adaptation and resilience in the face of habitat clearing, natural disasters and other interventions.

“We know that in humans, there’s a lot of evidence that if you experience something traumatic together, then you are more likely to become friends, so we were wondering, does a similar sort of thing happen in animals?” study author and CSIRO Senior Research Scientist, Dr Dana Campbell tells Cosmos.

So, how did they put sheep under pressure and record the outcome?

For the experiment, 70 non-pregnant Merino ewes aged 3 to 6 years were selected from five established flocks and moved to separate holding paddocks. The sheep were then tested sequentially in groups of 10, two from each paddock.

On day one of each experiment two sheep were randomly chosen from each of the five paddocks. Half of the randomly selected group (five sheep, one from each flock) were sent for a day of induced stress, while the other half (five sheep, the control) spent the day in a paddock.

The day of induced stress involved intermittent activities every 45 minutes, including trailer transport, being physically restrained, and moving through yards with a dog.

Day in the life of a stressed sheep
A stressful day for a sheep. Summary of stress-inducing activities / Credit: CSIRO

After their day of stress or paddock time, the ten sheep were brought back together. Their location and proximity to one another was tracked in real time using special ‘real time kinetics’ devices fitted to a harness.

Sheep which had undergone the stressful day initially preferred to hang closer to familiar sheep from their original flock. “And then over time, they were starting to go closer to those sheep that they had shared the stress with,” Campbell says.

She says the results help understand the complexities of social relationships in these animals.

“When they were in that stress, and they had that other sheep with them, it was helping to make them feel better during that stressful experience. And then they remembered that once they went back in the paddock.”

The study notes that while no sheep were harmed physically, physiological stress wasn’t measured.

Campbell says the activities selected for the stressful experiences are experienced by sheep as part of standard animal management practices, the key difference was compressing them into one day.

“We didn’t anticipate that any sheep would be harmed by it, it was just maintaining a heightened stress level, through things that they would normally go through, they were just probably not going to go through them all compressed in time. We didn’t expect any long-term negative effects.”

A follow up study will look at whether sheep form bonds after going through a shared positive experience.

Campbell says there’s evidence humans form social bonds after shared happy experiences, like singing together in a choir.

“So we thought maybe if there’s some kind of very highly preferred feed, and they share that experience, all eating that feed together, will that have a similar sort of effect.”

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