Why do zebras have stripes?

It has been a topic of debate for many years. Suggestions have included camouflage, confusing predators, thermoregulation… 

There is increasing evidence that the black and white stripes help limit attack by blood-sucking flies, although how that happens is not yet clear. Recent work from the University of Bristol, GB and UC Davis, California, USA, has provided a possible explanation.

Professor Tim Caro, Dr Martin How and colleagues have been investigating the behaviours of tabanid horse flies around captive zebras and domestic horses on a farm in North Somerset, using video analysis techniques.

Their new study has shown that stripes don't deter horse flies from a distance, with both zebras and domestic horses experiencing the same rate of circling from the flies. However, video analyses revealed differences in approach speed, with horse flies failing to slow down on approach to zebras, which is essential for a successful landing.

Professor Tim Caro, Honorary Research Fellow from the University of Bristol's School of Biological Sciences, said: "Horse flies just seem to fly over zebra stripes or bump into them, but this didn’t happen with horses. Consequently, far fewer successful landings were experienced by zebras compared to horses."

Dr Martin How, Royal Society University Research Fellow in the School of Biological Sciences, added: "This reduced ability to land on the zebra’s coat may be due to stripes disrupting the visual system of the horse flies during their final moments of approach.

"Stripes may dazzle flies in some way once they are close enough to see them with their low-resolution eyes."

(C) T Caro et al. PlosONE

Their second experiment was to observe horse fly behaviour around the same horses wearing different coloured cloth coats: black, white or zebra striped livery. This excluded any differences in behaviour or smell between horses and zebras. Just as before, when horses wore coats with striped patterns, they experienced fewer horse fly landings compared to when they wore single-colour coats.

Horse flies are a widespread problem for domestic animals so mitigating techniques, such as the development of anti-fly wear designed to resemble zebra stripes, may, from this research, be an interesting outcome for animal health and wellbeing.

The research also observed zebra and horse behaviour in response to biting flies. Zebras exhibited preventative behaviour, such as running away and tail swishing at a far higher rate than horses. Consequently, any horse flies that did successfully land on zebras spent less time there compared to those landing on horses, with few staying long enough to probe for a blood meal.

In Africa where zebras are native, horse flies carry dangerous debilitating diseases such as trypanosomiasis and African horse sickness which cause wasting and often death. Therefore, it is unsurprising that zebras utilise both behavioural defences and morphological striping to avoid horse flies.

This research provides new evidence for the theory that zebras evolved dichromatic striped coats to evade biting flies and has considerable implications for the horse industry.

For more details see:

Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses

T. Caro, Y. Argueta, E.S. Briolat, J. Bruggink, M. Kasprowsky, J. Lake, M.J. Mitchell, S. Richardson, M. How.

PLoS ONE 14(2): e0210831

https://doi.org/10.1371/journal.pone.0210831

Survey: who take part in horse activities?

University of Kentucky researchers Karin Pekarchik and Kimberly Tumlin are seeking participation for an online survey to better understand who participates in horse activities and sports.

Anyone dealing with horses, for work or pleasure, is encouraged to take part in the survey: “Portrait of a Rider: Characterizing Active Participants in Horse Activities and Horse Sports."

The researchers hope to receive completed surveys from at least 1,000 people so they can create a statistically valid portrait of participants in horse activities.

The survey will be open until March 31. To participate, click here:
 https://uky.az1.qualtrics.com/jfe/form/SV_6qTJQ6H7CT5jMtn.

Environmental poisons may contribute to equine metabolic syndrome

Endocrine-disrupting chemicals (EDCs) in a horse's environment may play a role in the development of equine metabolic syndrome (EMS). 

This finding, made by researchers at The University of Minnesota, could explain some of the variability in EMS severity that can't be explained by other commonly measured factors, such as diet, exercise and season. The study, funded by the Morris Animal Foundation, was published in Chemosphere.

"This is a pivotal piece of a very complicated jigsaw puzzle. There are a lot of horse owners out there who are very diligent about providing their horses fantastic care, but the horse is still diagnosed (with EMS)," said Dr. Molly McCue, Professor and interim Associate Dean of Research in the College of Veterinary Medicine, University of Minnesota. "It's important to be aware that these chemicals contribute to the problem, so we can look for ways to reduce horses' exposure to them."

The research team studied more than 300 horses from 32 farms in the United States and Canada. They focused on Welsh ponies and Morgan horses, as these breeds are more likely to develop EMS than others. The team collected data on the horses' lifestyles, including diet, exercise and past illnesses, as well as their farm location.

Researchers also examined plasma from the horses and looked for EDCs that have effects on estrogen (EEQ) and aryl hydrocarbon (TEQ) receptors in the horse. Simultaneously, they determined whether an individual horse had blood test results consistent with an EMS profile (including insulin and glucose at rest and following a sugar challenge). The team then analysed the results to look for correlations between plasma EDC concentration and these variables.

They found that serum glucose and insulin, both baseline and after oral sugar challenge, and leptin concentrations were associated with EEQ, and serum triglyceride concentration was associated with TEQ.

The team concluded that accumulation of EDCs may explain some environmental variance seen in horses with EMS, but the precise role and dose response to EDCs in horses with EMS is not clear at this time.

Endocrine-disrupting chemicals are usually man-made substances, found in products such as pesticides, plastics and personal care products. They are common in the environment and can mimic a body's hormones, blocking real ones from doing their jobs. Because of this, they are known to produce harmful effects in humans and wildlife. Horses likely encounter EDCs in their food.

Equine metabolic syndrome is characterized by endocrine abnormalities in horses and ponies. Affected horses and ponies tend to develop pockets of fat and/or become obese, and they have altered insulin dynamics. EMS also is one of the most common causes of laminitis.

"The more we know about a disease, especially a devastating and incurable disease like EMS, the more we can find innovative ways to prevent it," said Dr. Kelly Diehl, Morris Animal Foundation Interim Vice President of Scientific Programs. "While EDCs are difficult to avoid at the moment, the information from this study will greatly improve veterinarians' ability to predict the disease and provide opportunities to prevent it."

This is the first study to examine associations between EDCs and disease in domestic animals. Dr. McCue said it remains to be seen how significant the association is but hopes future studies will further scientific understanding and help advance veterinary care for horses.

For more details, see:

Associations between endocrine disrupting chemicals and equine metabolic syndrome phenotypes

S.A. Durward-Akhurst, N.E.Schultz, E.M.Norton, A.K.Rendahl, H.Besselink, P.A.Behnisch, A.Brouwer, R.J.Geor, J.R.Mickelson, M.E.McCue.

Chemosphere (2018) Vol 218, pp 652-661

https://doi.org/10.1016/j.chemosphere.2018.11.136