May_153_Vet_Forum_Owner Breeder 21/04/2017 14:19 Page 86
VET FORUM: THE EXPERT VIEW By SIMON CURTIS
The development of the hoof Hailed as a miracle of biological engineering, the horse’s hoof changes significantly in the first few months of life and can often require intervention from the farrier
T
he foal stands upon its feet within minutes of birth. Although this may seem remarkable to us, this is not unusual in large herbivores which need to follow their herd to escape predators. The unique feature of the horse is that it does this on the tip of a single hoofed toe. The earliest equid (member of the horse family) was Hyracotherium, perhaps better known as Eohippus the Dawn Horse, which stood at 3060 centimetres and lived 50 million years ago. Hyracotherium had four toes in front and three behind; by the Pleistocene epoch, 2.5 million years ago, equus arrived in a form all of us would recognise as a horse with a single digit, encased in horn, supporting each limb. The single-toed hoof is a marvel of nature that has served the horse well, allowing it to become the mammal with the greatest stamina of all and ranked in the top ten for speed. When the foal is born the hoof is ready to fulfil its role of providing grip, resistance to wear, purchase over ground and protection for the sensitive tissues within. Unlike all other hoofed mammals the horse’s hoof wraps around the digit, apart from the back where the heel bulbs allow movement and anti-concussive mechanism. The hoof of a foal grows at twice the speed of its mother and the hoof is renewed in 145 days, compared to mature horse renewal which is about 330 days. The speed of renewal is to allow the rapid development of the bones within the hoof capsule. While the foal is doubling its weight in a month and trebling it in two months, with the bones growing proportionately, it is still walking on the hoof with which it was born. This is one reason that foals need to be trimmed from one month of age. Trimming the hoof extends the base of foot back so that even foals with a slight flexural laxity gain support. All horses produce hoof growth rings at times of change in their lives. Illness, alteration of diet and environment all give rise to visible growth rings at the same distance from the coronary band on all four feet. There is no greater change in any foal’s life than the day that it is born. The foal hoof crease becomes visible at about one month of age and marks the boundary between the fetal hoof, below it which developed in the uterus and the foal hoof above, which has grown since birth. The junction between these two is an area of weakness where the hoof can
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Figure 1: The foal hoof crease (arrow) records the time of birth in the hoof wall; below the line is hoof developed in utero and above is the foal hoof grown since birth
drastically change angle in cases of a flexural deformity and is often the site of hoof breaking at the toe (Figure 1). Trimming should be immediate to round off the hoof wall to reduce breakage, and hoof hardener should be applied. The colour of the hoof wall is not fixed at birth but often changes immediately afterwards, revealing its permanent pigmentation as the fetal hoof is replaced by the foal hoof. The colour of the hair above the coronary band is often an indicator of its future hue. In some cases the colour change is quite striking and the foal, for a short time, has two-tone hooves (Figure 2).
The hoof wall is thickening from the coronary band downwards as the wall grows. This is sometimes a cause of concern to breeders as it takes on an inverted cone shape which is more pronounced in some foals than others (Figure 3). The inverted cone resolves itself at four to six months of age, when it begins to expand at the ground bearing surface and takes on the recognised truncated oblique cone shape seen in mature horses. Foals are born with hooves that are individually symmetrical to an imaginary line through the frog and also paired left to right.
Figure 2: Sometimes the colour of hoof changes after birth; this two-month-old foal was born with light coloured hooves which changed to dark post partum
THOROUGHBRED OWNER & BREEDER INC PACEMAKER