Congenital Hypothyroidism Devastates Western Canada Breeders

Veterinarians in western Canada report that 2004 has been a disappointing year for many breeders because of an increase in cases of fatal congenital hypothyroidism in foals. Newborns with the disease can exhibit clinical signs such as contracted

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Veterinarians in western Canada report that 2004 has been a disappointing year for many breeders because of an increase in cases of fatal congenital hypothyroidism in foals. Newborns with the disease can exhibit clinical signs such as contracted tendons, protruding lower jaws, and an inability to stand. While researchers haven’t been able to pinpoint the definite cause of congenital hypothyroidism, they suspect it might be linked to high levels of nitrate in feedstuffs or water consumed by broodmares, which interferes with iodine metabolism in the mares. It has been suggested that the source of these high levels of nitrate are feedstuffs derived from stressed or immature plants.


The report, which ran in the fall issue of the Western College of Veterinary Medicine’s (WCVM) Horse Health Lines, provided viewpoints from breeders who had been affected by the disease this year. In some cases, breeders had 100% of their foals show clinical signs of the disease, with up to 75% of the foals dying or requiring euthanasia within the first several days of their lives.


Background
Congenital hypothyroidism was first described by researchers at the WCVM in Saskatoon, Saskatchewan, in 1981, and it has been known to cause foal deaths in Western Canada and parts of the United States, mainly the Northwest. The disease is caused by decreased thyroid function in foals developing in their dams’ wombs.


Andy Allen, DVM, MVetSc, PhD, a veterinary pathologist at WCVM said, “This is one of the busiest foaling seasons I’ve had since I started researching this disease in 1990.” Allen said he received calls about cases as far east as Brandon, Manitoba, and as far West as the British Columbia interior. Some veterinarians have reported twice the amount of cases that they see in a typical year–some see three to four per year but are now seeing seven to eight affected foals. It is suspected there are more cases that horse owners do not report to veterinarians

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Written by:

Stephanie L. Church, Editorial Director, grew up riding and caring for her family’s horses in Central Virginia and received a B.A. in journalism and equestrian studies from Averett University. She joined The Horse in 1999 and has led the editorial team since 2010. A 4-H and Pony Club graduate, she enjoys dressage, eventing, and trail riding with her former graded-stakes-winning Thoroughbred gelding, It Happened Again (“Happy”). Stephanie and Happy are based in Lexington, Kentucky.

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