Shetland Sheepdog nutrition: coat, thyroid and the MDR1 gene

The American Shetland Sheepdog Association lists hip dysplasia, thyroid disease, eye diseases, dermatomyositis, von Willebrand's disease and epilepsy as known health problems in Shelties, and in the same statement stresses that none of them is common. Diet neither causes nor reverses any of these. What food decides is whether a small dog with a big coat stays at the right weight, and whether its skin and coat have what they need. The American Kennel Club gives a height of 13 to 16 inches, a weight of 15 to 25 pounds (6.8 to 11.3 kg) and a life expectancy of 12 to 14 years.

Daily calories

The Merck Veterinary Manual's formulas give a starting point. Resting energy requirement is 70 × (body weight in kg) raised to the power 0.75, multiplied by a factor for age and neuter status.

A Sheltie's coat hides both fat and weight loss. Feel for the ribs under a thin layer of fat and for a waist behind them rather than judging by eye, and weigh the dog every month. A dog that keeps gaining on a measured ration, or that slows down and loses coat at the same time, should have its thyroid checked before its food is cut again.

Dermatomyositis

Familial dermatomyositis damages small blood vessels in the skin and sometimes the muscles. A review of these ischemic skin diseases notes that the familial form occurs most often in young Collies and Shetland Sheepdogs. Lesions appear where skin is thin or rubbed: the face, ear tips, tail tip, toes and bony points. They show as hair loss, scaling, crusts, sores and color changes. In more severe cases the muscles become inflamed and waste. A reaction to rabies vaccination can look the same and can happen in any breed.

The same review names pentoxifylline combined with vitamin E as the most reliable treatment for the signs of these conditions, rather than a cure. Both are prescribed and dosed by a vet. Fish oil is sometimes added, though evidence for it alone is limited, and diet is not a treatment. Muscle loss in a severely affected dog is a reason to make sure the food is complete and eaten in full, not a reason to raise protein beyond that. The breed association lists a DMS DNA test among its elective health tests for breeding dogs.

The MDR1 mutation and medicines

The MDR1 mutation affects a pump that normally keeps many drugs out of the brain. Washington State University's veterinary diagnostic laboratory puts the frequency of the MDR1 mutation in Shetland Sheepdogs at about 15%, against about 70% in Collies. The problem is medicines, not food.

• Loperamide (Imodium), at doses used for diarrhea, causes neurological toxicity in dogs with the mutation and should be avoided in all of them. Never give a Sheltie a human antidiarrheal without asking the vet.
• Ivermectin in heartworm prevention at label doses has been tested and judged safe in dogs with the mutation. Other ivermectin products and doses need specific dosing advice from the vet.
• A cheek-swab DNA test settles the question once, and the result belongs in the dog's medical record.

Thyroid disease

Hypothyroidism slows metabolism. Typical signs are weight gain without eating more, lethargy, a dull or thinning coat and recurrent skin problems, and they are easy to mistake for age or overfeeding. The breed association's health statement lists autoimmune thyroiditis testing through an OFA-approved laboratory among its elective tests, alongside DNA tests for dermatomyositis, von Willebrand's disease, MDR1 and Collie eye anomaly.

Commercial complete foods contain enough iodine and selenium for thyroid hormone production. Kelp and other iodine supplements can add risk rather than benefit on top of a complete diet, because too much iodine also disrupts the thyroid. After a hypothyroid dog starts levothyroxine its energy use rises, so a ration that was causing weight gain may start to cause weight loss. Recheck weight a few weeks after treatment starts.

Collie eye anomaly

Collie eye anomaly (CEA) is an inherited underdevelopment of the layer of blood vessels behind the retina. Mild cases barely affect sight. Severe ones can involve the optic nerve or cause retinal detachment. The mutation is a deletion in the NHEJ1 gene, and a DNA test identifies clear, carrier and affected dogs. In Italian genetic testing records, half of the 74 Shelties tested were carriers and about 11% had two copies. Dogs sent for testing are not a random sample of the breed, so figures for the whole breed may differ, but the numbers show why breeders test.

Diet has no effect on CEA. A dog with poor vision copes better with food and water bowls that stay in the same place.

Teeth

Small dogs tend to build tartar quickly, and crowded teeth trap more of it. Daily brushing with a dog toothpaste is the most effective home care. Dental chews and diets carrying the Veterinary Oral Health Council seal have been tested for plaque or tartar reduction, and their calories belong in the daily total. Cooked bones splinter and hard chews break teeth. Bad breath, red gums or dropping food needs a dental exam, often with cleaning under anesthesia.

Coat and diet

Coat quality reflects diet mainly when something is missing. The Merck Veterinary Manual lists a dull, unkempt coat among the signs of protein deficiency or protein out of balance with calories. A Sheltie on a complete and balanced food in the right amount should not run short. Heavy seasonal shedding is normal for a double coat. A thin, dull coat outside the shedding season points to thyroid disease, skin disease or an unbalanced home-made diet, and supplements such as biotin will not fix any of those.

Sources

1. Shetland Sheepdog dog breed information. American Kennel Club.
2. Health statement. American Shetland Sheepdog Association, via the American Kennel Club, 2017.
3. Ischemic dermatopathies. Veterinary Clinics of North America: Small Animal Practice, 2013.
4. MDR1 in dogs. Washington Animal Disease Diagnostic Laboratory, Washington State University.
5. Genotypic and allelic frequency of a mutation in the NHEJ1 gene associated with collie eye anomaly in dogs in Italy. Veterinary Record Open, 2022.
6. Nutritional requirements of small animals. Merck Veterinary Manual.