Dear Christopher Cat: One of my cats is hyperthyroid, and I'm thinking of treating her disease without medication, by feeding Hill's y/d, a prescription low-iodine diet. It would be easiest for me to feed all my cats the same food. Is y/d safe for cats that are not hyperthyroid?

Christopher responds: Yes. Hill's y/d contains a reduced but adequate amount of iodine, an important component of thyroid hormone, so even healthy cats that eat y/d produce normal levels of the hormone.

When cats with hyperthyroidism eat a conventional diet, one with abundant iodine, they produce too much thyroid hormone. Treatment options include y/d, a single dose of radioactive iodine, surgery or a daily medication called methimazole, which can be given orally or applied to the skin.

A recent study evaluated thyroid function over a two-year period in 14 healthy cats fed the limited-iodine diet and 12 healthy cats fed a conventional diet. The cats were young and had normal thyroid function at the start of the study.

Every six months, researchers performed a full panel of blood work, urinalysis, thyroid hormone levels and thyroid ultrasound. They found that all the cats, including those eating the limited-iodine diet, maintained normal thyroid size and function.

So you can feel confident feeding y/d to your entire cat family.

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Dear Daisy Dog: A neighbor's dog brought influenza home from an out-of-state dog show. Should I have my dog vaccinated for influenza?

Daisy responds: Veterinary experts say dogs that travel to shows are at greatest risk of influenza, and pet dogs with little exposure to other dogs are at lowest risk. Discuss your dog's lifestyle with your veterinarian, who can advise you about whether to vaccinate.

Some veterinarians recommend vaccinating dogs at low risk to increase "herd immunity." The concept is that if most dogs are protected, the chance of an unvaccinated dog contracting and spreading the disease is low.

Keep in mind that the U.S. has two strains of influenza, H3N8 and H3N2, and three vaccine options: an H3N8 vaccine, an H3N2 vaccine and a new bivalent vaccine that incorporates both strains. Since neither single-strain vaccine confers immunity against the other strain, many veterinarians prefer the bivalent vaccine.

These vaccines reduce the severity of the disease, though they don't prevent infection or viral transmission from dog to dog. The virus is transmitted through contact with an infected dog's nasal secretions and saliva, both before clinical signs begin and during illness.

Clinical signs range from coughing, sneezing and nasal discharge to lethargy, fever and pneumonia. A small number of dogs have died of influenza.

Your best source of advice about your own dog is your veterinarian.

Ask the Vet's Pets appears Friday in the print edition of the Reading Eagle. The animal authors of the column live with Lee Pickett, V.M.D., who practices companion animal medicine. Contact them at www.askthevetspets.com.