Monday, February 27, 2012

How the zebra got its stripes

Why does the zebra have stripes? Perhaps they provide camouflage in the African savannah; perhaps they break up the animal's outline making it more difficult for predators such as lions.

However, research published recently in the Journal of Experimental Biology suggests that the stripes may confer protection against a different sort of predator.

An international team of scientists, led by Gábor Horváth of the Eötvös University, Hungary, found that the zebra's stripes help ward off biting flies.

Such flies are widespread in Africa, and, as well as spreading disease, they cause annoyance and disrupt grazing.

According to Horváth, these insects are guided to a wet habitat suitable for breeding by homing in on horizontally polarized light, which results when light is reflected off water. However, blood-sucking female flies also locate their victims by following polarized light reflected from their skin.

The research, carried out in Hungary, showed that a horse model with zebra stripes attracted far fewer horseflies (tabanids) than did homogeneous black, brown, grey or white equivalents.

The research team found that as the width of the stripes decreased the horseflies were less attracted. They also found that the width of the stripes on zebras coats fell within the range that was most disruptive to these biting flies.

Tabanids have been shown to respond strongly to linearly polarized light,” they explain “and we demonstrate here that the light and dark stripes of a zebra’s coat reflect very different polarizations of light in a way that disrupts the attractiveness to tabanids.”

It appears to be the polarisation of the reflected light, rather than the colour , that is significant. The research team found that even on homogeneous grey surfaces the attractiveness to tabanids was reduced if the surface had bands of alternating polarisation.

We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies”, says the team. They add, “The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]”.

Welfare implications of restrictive nosebands

Horse welfare at the Olympic Games is threatened if current trends are allowed to continue, according to the International Society for Equitation Science (ISES). The Society maintains that the practice of over tightening nosebands to avoid penalties in competition is covering up poor training at the expense of horse welfare.
ISES notes that, in the last few decades, there has been a steady increase in the design of nosebands that effectively mask evidence of a horse’s discomfort.
The incentives for athletes to over-tighten nosebands arise from the rules of dressage that penalize displays of discomfort such as open mouths and lolling tongues. These rules were written by the sport’s governing bodies to promote excellent training and the demonstration of qualities such as freedom, harmony, lightness and acceptance of the bit without tension. Restrictive tight nosebands can prevent the horse from displaying unwanted behaviours such as opening, gaping or crossing the jaw, and are enabling competitors to mask signs of tension which judges should penalise as evidence of inferior training. Thus nosebands may hinder effective judging.
Recent research*, by Professor Paul McGreevy and others, suggests that horses wearing tight nosebands undergo a physiological stress response, are sensitized to bit pressure and may have reduced blood flow with potential to cause injuries and tissue damage including nasal bone deformities, even when padding accompanies the noseband such as in the case of so-called crank nosebands.

ISES recommends:
  • a return to the established practice of placing “two fingers” under the noseband to demonstrate that it has not been over-tightened. This amount of space under the noseband allows horses to express tension or seek relief from the pressure of the bit and so aligns with the principles of ethical equitation.
  • that, for fairness and objectivity, a standard taper gauge should be used by stewards at competition. The taper gauge should be placed without force at the nasal midline and be clearly marked to show the desired stop, which, in alignment with established industry guidance, should be the dimensions of two average adult fingers.

Help sought for Cushing's disease research

Cushing's disease (equine pituitary pars intermedia dysfunction - PPID) appears to be becoming more common as horses live longer. While the true incidence of this disease is unknown, a recent survey of horse owners showed that signs of Cushing's disease were reported in 20 to 30 per cent of horses.

Researchers at the Western College of Veterinary Medicine (WCVM), University of Saskatchewan, are starting to explore a possible new treatment for the condition.To learn more about the incidence and prevalence of Cushing's disease, WCVM equine specialist Dr. James Carmalt has designed an online survey that will be distributed to equine practitioners around the world. Dr. Carmalt and his colleagues at the western Canadian veterinary college will use practitioners' responses from this short, 16-question survey to:

  • determine the incidence of disease

  • determine the most common treatment protocols being used by practitioners

  • evaluate the need for developing new treatment methodologies.

Owners whose horses have been diagnosed with Cushing's disease are urged to bring the survey to the attention of their veterinarian.

Many horses still too fat after winter


In the past, horses would lose condition over the winter, start the year in lean condition and gradually recover over the grazing season.

However, a recent survey of groups of horses spending at least six hours out at pasture has shown that more than a quarter were obese at the end of the winter months. 

This alarming trend may suggest that well-meaning winter management strategies such as rugging and a reduction in exercise could be having a detrimental impact on the welfare of horses in the United Kingdom.

The research was conducted by Sarah Giles, Dr Sean Rands and Professor Christine Nicol of the University of Bristol's Animal Welfare and Behaviour Research Group, in collaboration with the WALTHAM® Equine Studies Group, headed by Professsor Pat Harris. They examined the variations in body condition in small groups of horses during the month of February 2011.

A cross sectional study of 127 horses and ponies was carried out in Somerset . Horses were kept in herds of three or more, and were at grass for at least six hours a day. Their condition was assessed using the nine point body condition score (BCS) system and the five point cresty neck score (CNS). The prevalence of obesity (BCS of 7 or above) was 27.6% with a slightly higher incidence in horses, while the prevalence of cresty neck (CNS of 3 or above) was 48.8% with a higher number of ponies affected.