In this weeks Horse and Hound, the veterinary section looked on six topics which are new in the equine veterinary world :
Pasture myopathy – how do latest findings affect UK-based horses?
Pasture myopathy is a disease in horses, more common in Europe in the Autumn, and can kill horses who are living out. Affected horses have such severe muscle cramps and breakdown that they collapse, often leading to death. Last year, Horse and Hound reported that risk factors for severe acute myopathy included grazing fields overhung by trees and with accumulations of fallen autumn leaves.
Scientists in the US have discovered that seasonal pasture myopathy is similar to a human disease cause by poisoning with an amino acid called hypoglycin, which is found in unripe Jamaican ackee fruit. When they looked for traces of the toxic metabolites of hypoglycin in the blood and urine of seven affected horses, the scientists found them in all seven. They then searched the pastures where the horses had been grazing for plants, leaves or seeds that had significant hypoglycin levels. They found that some American box elder trees (Acer negundo) produced seeds stuffed with hypoglycin.
This tree was present wherever their clinical cases had gone down with the disease. What was interesting was that the hypoglycin levels in boy elder seeds varied greatly. Seeds from some pastures had 50 times more of the poison than identical looking seeds from the same plant elsewhere. This tree is a member of the sycamore family and produces the typical helicopter like seeds that spin as they fall to the ground.
Box elders are not widespread in Europe, although they have been introduced here, Ornamental varieties with yellow leaves are planted as specimen trees in parks and gardens, where they are more commonly known in the UK as the ash-leafed maple. The English sycamore is, however, very common. Hypoglycin occurs in sycamore seeds too.
Horses and donkeys are different species of equid. Horses were domesticated from an Asian horse sometimes called the Tarpan, whereas donkeys were domesticated from the African wild ass. Despite the fact that these two species are so different, there is a tendency to think of donkeys as ‘almost or horse’ or to treat them as ‘odd looking’ ponies. This fallacy has been highlighted recently by the publication of reference values for thyroid hormones in the two species.
Spanish vets studied 38 healthy Andalusian donkeys and 19 healthy Andalusian horses kept exactly under the same conditions and fed the same diets. They took blood samples from them at the same time and measured their thyroid hormone levels. The normal, resting and fasting thyroid levels in the donkeys were significantly higher than the corresponding levels in the horses. This means that if the well-publicised horse levels of thyroid activity were applied to donkeys, misdiagnosis could easily occur. A normal healthy donkey would appear to have an overactive thyroid and be misdiagnosed as a hyperthyroid case. A sick donkey with an under-active thyroid suffering clinical hypothyroidism could similarly be blood sampled and declared normal,
The results indicate that the vets must treat donkeys as a separate species with unique metabolic and physiological profiles – a message the Donkey Sanctuary has been preaching for years.
We’re so familiar with flu and tetanus jabs that it seems unthinkable to live in a country where they are unnecessary because the virus does not occur.
Equine influenza is endemic in Europe and much of the US. It occurs at a continual low level and bubbles up here and there in pockets of infection. The normal flu vaccination programme consists of two primary injections, which the manufacturers recommends should be four to six weeks apart, followed by a third after about five months. Full protective immunity is not achieved until after the second of the two primary jabs. The minimum time between the first two injections under FEI rules is 21 days.
What can the authorities do when an epidemic of the proportion seen in South African in 2003-4 and Australia in 2007 is ripping through the equine population?
In both outbreaks, horses were administered a rapid course of vaccines, the first two given just 14 days apart and the third at about 105 days. Many double this would give sufficient immunity, but it was worth the risk. After a full investigation of this technique, Australian scientists recently revealed that the accelerated course gave the equivalent long-term protection to the recommended course.
This does not mean that we can shorten the interval between our vaccines – this particular one was the most up-to-date product available and not all vaccines would work so quickly. So for the moment, we must stick to FEI and racing rules, but these may change as a result of this research.
Collected vs extended trot – which is worse?
The received wisdom about building up young dressage horses has collects suggested that the collected trot is hard on the joints, especially the hocks. But recent research from Newmarket scientists has shown surprising results.
In contrast to what was predicted, it was found that the extended trot placed more strain on the hocks than the collected gait. IN extension, the fetlocks were overextended and therefore dropped more. These are the two factors that are known to contribute to upper suspensory ligament strain – an injury far more common in dressage horses than in other sport horses.
Surface and stress fractures – a link?
Vets have long suspected that the incidence of certain injuries in racing varied according to the type of surface on the track. Horses racing on American dirt tracks appeared to suffer a different spectrum on injuries from those on England’s turf courses. But such hunches have been difficult to measure objectively because there are so many other possible factors.
Vets in California have had the perfect opportunity to test their theories on three courses that switched from dirt to synthetic surfaces in 2006-7. The study concentrated on one specific injury, the stress injury and fracture of the humerus (the chunky bone between the shoulder and the elbow). Vets studied the cases of 841 racehorses who had sustained such injuries in the two years before and after the track surface switchover. With bone-scans, radio graphs and post-mortem findings on record, they could see if surface changes had altered the nature of stress on the bone.
They already knew that the bone could be stressed and fracture either near the top beside the shoulder, or near the bottom beside the elbow. Stress changes near the top were more likely to give rise to catastrophic fractures and the loss of the horse. Those near the bottom commonly caused lameness that resolved with rest.
The study results revealed a clear trend. Horses that raced on dirt tracks were far more prone to stress problems near the top of the bone and therefore to disastrous fractures. Horses that raced on synthetic tracks suffered a higher incidence of injury at the bottom of the bone, but fewer life-ending fractures. The softer and more forgiving synthetic surfaces do cause stress effects on the humerus of young racing thoroughbreds. Stresses are less severe and with less drastic effects, however, than when dirt tracks were used.
Together for donkey’s years
More interesting research on donkeys. It seems they may form close and long-term bonds with other donkeys, irrespective of age, sex or biological relationship. This has been observed anecdotally for years, but recently published research now proves it.
Scientists in Edinburgh studied a group of 55 donkeys consisting of 38 geldings and 15 females. By observing them in their social groups and herds, they worked out that 44 of these donkeys had special close friends. This friendship was usually reciprocal – in other words, there were about 22 pairs of closely bonded friends.
They then took 12 of the companion pairs and separated them. One donkey was put in a pen at the end of a menage, next to a pen containing a random donkey. The other member of the best friend pair was able to enter the menage at the far end, where it could see, hear and eventually smell both penned animals.
The scientists observed that the loose donkeys could – and did – recognise their special friends and sought out their company. Regardless of whether the other donkey was a complete stranger or another donkey from their small social group, the behaviour clearly showed that the donkey pals were bonded and wanted to be together.
Such pair bonding is unusual in domestic animals. The research suggests that donkey keepers should take care when groups are split to make sure that best friends are not separated.
I found it particularly interesting looking and writing up these articles this week.I previously knew about none of these topics, other than having my own hunches about surfaces in any sport, not just racing. More next week!