The Biology of the Goat

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The Case of the Polydactyl Kid
Polydactyl kidIn the spring of 2009 a kid was born in my herd with an extra toe on the left front leg. When he was born a white cap was covering what looked like an enlarged dew claw on the inside of the left front leg.

It wasn't long before it was obvious that that dewclaw looked instead like a small hoof. A close up view of the front feet of this kid is shown below.

closeup

The following three photos show the extra hoof from the back.
extra hoof view

extra hoof view

extra hoof view


When the kid was about 4 months old I had the veterinarian take an xray of the leg. The radiographs revealed that the bones of the extra toe were complete all the way up to the knee. Unfortunately, the view did not include the carpal bones of the knee. xray of polydactyl leg

The illustration below helps explain what is seen in the xray. The bones of human hand are compared with the bones of the normal front leg of a goat and the bones of this polydactyl goat. The carpal bones which make up the human wrist are located in the area that we call the knee in the goat. The large bone just below the carpals is the fused third and fourth metacarpal bone. Goats do not have metacarpals 1, 2 and 5. The extra toe in the polydactyl goat is actually the second metacarpal bone with the additional phalanges 1, 2 and 3. The dewclaw is missing.

metacarpal bones

While polydactyly in ruminants is rare, this type of polydactyly -- appearance of the second metacarpal plus phalanges and the missing dewclaw -- is the most common type. It has been reported in cattle, sheep, camels, pigs and rarely in horses. Usually this condition is seen on both forelimbs or both hind limbs. It is only rarely seen in only one limb like this kid, or in all four limbs. The reasons for this type of polydactyly is unknown. The polydactyl kid has a full brother who has the normal number of toes, and the kid's dam has had a total of 6 kids in this and two other pregnancies. With this exception, all of the other kids had the normal number of toes.

At almost a year of age, as of this writing, the wether shows no sign of discomfort or lameness. The small hoof requires reqular trimming.