The use of blood products for treating sick and injured pets has increased so dramatically that there is a growing shortage of canine and feline blood.

The donated blood is used in the same way that blood is used in human medical facilities: as whole blood, plasma and packed red cells. The blood is collected in sterile plastic bags and is handled and stored in the same way as human blood.

Although most stored blood comes from "professionalÓ donors -- typically dogs living in a veterinary hospital or, more recently, retired racing greyhounds kept in colonies as blood donors -- in some areas, canine blood drives are held. The blood is donated (you can't earn money from your dog's donation), but it's certainly for a worthy cause.

Most dogs kept as blood donors are adopted out after a relatively short period of service. Since they're chosen for their size (bigger dog equals more blood) and temperament (must be easygoing), these dogs make wonderful pets.

Feline donors are also a mellow lot. They normally are given a mild sedative for the blood draw, and they can donate every three months.