MISSISSIPPI STATE -- Guinea pigs, chinchillas, rats, mice, hamsters and gerbils are popular in pet stores, but taking home and caring for some of these animals can be difficult.

Dr. John Harkness, laboratory animal veterinarian at Mississippi State University's College of Veterinary Medicine, said packaged pet foods do not always meet pet rodents' dietary needs.

"Owners of small rodents, especially of guinea pigs, usually buy feed from the colorful and often overpriced array of boxes and bags available in retail pet stores," Harkness said.

Some of these feeds include seed mixtures, vitamin and mineral additives, hay cubes, food pellets, salt blocks, chewable wood and treats.

"A variety of treat foods lure unsuspecting buyers because of those treats' resemblance to the snack foods preferred by the animals' owners," Harkness said.

Labeling is a serious problem with some pet foods, especially for guinea pigs, Harkness said. Many food labels claim to be for all rodents, but diet requirements actually vary greatly. Recommending diet supplements often can lead to nutritional imbalances.

"Conventional pet animal products made by reputable companies usually offer adequate, balanced nutrition, but even those diets can be altered by damp, heat, oxidation and vermin contamination," Harkness said.

Many owners supplement pet diets with fruit, vegetables, hay or other treats. These should not replace more than 10 percent of the regular diet. Older animals can have 25 percent of their diet in supplements, as the additional fiber can limit obesity and other problems.

A recommended rodent diet is a reasonably fresh pellet containing essential nutrients and at least 16 percent crude protein. The package label should state that it meets National Research Council requirements. Except for occasional hay or treats, this should be the only food provided.

"The standard pelleted, complete diets may be fed to hamsters, gerbils, mice and rats," Harkness said. "Guinea pigs and chinchillas should be fed special diets labeled for those species."

The following are general tips for the diet of specific rodents:

Guinea pigs -- Specially formulated diets should contain 18 to 20 percent crude protein and 9 to 18 percent fiber. Eating table scraps can lead to serious health problems. Provide water in sipper tubes with a metal end. Vitamin C can be added to their diets through small quantities of washed fresh greens, fresh fruit or a vitamin supplement. Guinea pigs are picky eaters and may not be able or willing to change types of food.

Hamsters -- Diets should include 16 to 22 percent crude protein and 8 percent fiber. They are susceptible to vitamin E deficiency problems, so food should be a quality pelleted variety.

Gerbils -- Feed standard rodent diets containing 16 percent protein. Moisten hard food pellets for young. Sunflower seeds are a favorite, but the low calcium and high fat content of these can lead to bone deformities if proper diet is not maintained.

Rats -- Diets should include about 20 percent crude protein for normal growth and reproduction. Carbohydrates are needed, as is a fiber level of at least 5 percent.

Mice -- Despite widespread use in laboratories, mice nutritional requirements are not accurately known. Diets should contain 20 to 25 percent crude protein, but less may actually be required. About 2.5 percent of the diet should be fiber.

Harkness recommended not changing a pet rodent's diet once it is set.

"Whenever you change the nature of the diet, there is the probability you will change the internal microorganisms, and this can be very hard on the animal," Harkness said.

Contact: Dr. John Harkness, (601) 325-1131