Reports from the world of equine research.
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A natural lifestyle - freedom to roam, and the ability to choose what to eat - does not necessarily result in ideal foot conformation.
The feet of feral horses, such as the North American mustang and the Australian brumby, have been held up as examples of ideal conformation. However, not all feral horses are the same, as work carried out in New Zealand demonstrates.
A report published in the Australian Veterinary Journal documents the shape and abnormalities of the feet of Kaimanawa feral horse population.
Lead researcher was Brian Hampson of the Australian Brumby Research Unit, at the University of Queensland’s School of Veterinary Science.
"The aim of the study was, for the first time, to investigate empirically both the morphometric characteristics and the incidence of foot abnormalities in a group of adult feral horses and to determine the effect of a free-roaming feral lifestyle and lack of human intervention on foot morphology and health of the population."
Kaimanawa horses are small (133 -151cm at the withers), being descended from Welsh and Exmoor-type ponies that have been feral since the 1880's. Other bloodlines were added as the result of escapes from farms and cavalry units so that present day horses are more closely related to the Thoroughbred.
About 1500 animals live in a land of upland plateaux, with steep hills, river basins and valleys, covering an area of about 700sqkm.
The research team took standardised photographs of all four feet and lateromedial radiographs of the left fore foot of 20 adult horses from the Kaimanawa horse population.
They found a wide variation between horses. There was no consistent foot type. Foot abnormalities were surprisingly common. For example, 35% had long toe conformation, 15% had medio-lateral imbalance, and 85% of horses had lateral wall flares.
Other common abnormalities included large hoof wall defects, frog abnormalities and contracted and under-run heels.
The most surprising finding was the radiographic and visual evidence of chronic laminitis. Laminar rings were present on 80% of horses.
In contrast to the more standardised conformation of the feral horses of North Australia, the Kaimanawa horses had a wide range of foot shapes. According to Hampson, this is most likely explained by differences in substrate hardness and distances travelled, and the effect of these two variables on hoof wear.
"The large range in the morphometric variables and the high incidence of abnormalities in the feet of Kaimanawa feral horses may be related to dietary or environmental influences, or a combination of both" he writes.
"There may be insufficient environmental pressure driving natural selection of foot type. Perhaps their environment, consisting of a soft substrate and with easy access to pasture and water, tolerates a broad range of foot conformation in Kaimanawa horses."
"Clearly this group of feral horses should not be used to guide the direction of foot care practice."
In a further study, Hampson looked for microscopic evidence of chronic laminitis in hoof samples.
Histopathologic examination revealed a high incidence of changes in the laminae. Many samples had changes in the laminae. The features were similar to those found in domestic horses with chronic laminitis.
This seems to be the first study to confirm microscopically that chronic laminitis occurs in feral horses, Hampson points out. It supports the hypothesis that the horse is vulnerable to laminitis irrespective of its state of domestication.
Maybe the physiological and bioengineering adaptations of the foot, that give horses such speed and agility, have been achieved at the cost of vulnerability.
He suggests nutrition is likely to be a major contributing factor. "Long day lengths at high altitude in the Kaimanawa Ranges coupled with temperatures below freezing produce the ideal scenario for pasture-induced laminitis."
For more details see:
Morphometry and abnormalities of the feet of Kaimanawa feral horse in New Zealand.
BA Hampson, G Ramsey, AM Macintosh, PC Mills, MA de Laat, CC Pollitt.
Aust Vet J (2010) 88, 124-131
For more about the Brumby Research Unit of the University of Queensland, see
Report by Mark Andrews. Published online 19.11.10