WHAT’S NEW in the veterinary world?
Peter Green MRCVS reviews research into the use of blue light with broodmares, and with Cushing’s cases
BLUE EYE THINKING
WE’VE known for some time that the oestrus cycle and breeding season of mares can be manipulated by using artificial light. This is common in thoroughbred stud practice, where mares need to conceive early in the year so that their foals arrive as early as possible after 1 January. Early foals are more mature when they come to race as two and three-year-olds.
Artificially long hours of daylight trick the mare into thinking that spring has arrived early and she comes into oestrus earlier than normal in the year.
Recent experiments have revealed some even more interesting effects of light.
Stud vets in Germany took 20 warmblood mares and fitted them with special hoods that shone low-intensity blue light into one eye in late pregnancy, starting in December. The mares were due to foal between February and May. The blue light was generated by small LEDs and was only 50 lux in brightness. As a comparison, most retail and office spaces have lighting of about 500 lux.
The blue light was switched on for 16 hours daily, from 8.00am until 11.00pm. All the mares were used twice in the study, over two pregnancies, so that some had the blue light treatment in year one, but only natural light in year two, while others had normal light for the first pregnancy and blue light therapy during the second. Each mare therefore acted as her own control in the experiment.
All the mares had uneventful pregnancies and delivered healthy foals, but when the various careful measurements of their gestations and their foals were compared, there were some surprising results.
To start with, mares given the blue light therapy had shorter gestations, by an average of about eight days. Foals from mares treated with blue light stood up sooner than those from mares under natural light, although time to first suckling was the same. Foals from bluelight treated mares were shorter at the withers by an average of over 1cm, but there was no difference in weights between the two foal groups.
Most bizarrely, foals from blue-light treated mares had significantly shorter hair coats than foals from mares under natural light.
All the mares and foals were at the same stud in Brandenburg and experienced the same weather, temperatures and ambient conditions. The mares had a small patch of coat close-clipped in December and the regrowth was measured on the day after foaling. Blue light treated mares had shorter hair regrowth compared with those under natural light.
WHY THE SHORT HAIR?
THE effect of blue light on hair growth got scientists thinking. Many elderly horses and ponies suffer from pars pituitary intermedia dysfunction, known as PPID or Cushing’s disease, and one of the most common signs is excessive hair growth and failure to shed long winter coats. Would low-intensity blue light therapy affect this abnormal hair growth?
Eighteen PPID horses and ponies from a university herd were split into two groups: ten were kept under natural light and eight received the blue light therapy in one eye for four months from summer through autumn. All were kept out at pasture. Over this period hair growth and weight was carefully measured.
Sure enough, the bluelight treated PPID patients had significantly less hair growth than their untreated counterparts. But when the scientists looked at pituitary hormone levels and stimulation tests, there were no differences.
So the blue light works, but not by altering the hormones that are abnormal in PPID horses. Just how does it work? More investigation is needed.