Each donation takes between three to four minutes. (AFP/Getty Images)

Shortages at blood banks are not just a problem for people but for dogs too, and as with human blood shortages, the canine supply waxes and wanes, with late summer being the most critical time.

W. Jean Dodds, a veterinarian and president of the Hemopet blood bank and rescue center in Garden Grove, Calif., said summer was a particularly dangerous time for dogs because they can be susceptible to heatstroke, snakebite and other summer ailments and accidents.

"There's never enough blood to supply the needs of the nation," said Dodds. "Especially during holiday weekends, people's animals get into accidents."

In July, the Baltimore Humane Society hosted a canine blood drive with the Blue Ridge Veterinary Blood Bank after determining there was a "serious" shortage of canine blood available in the state of Maryland.

Although canine blood banks have existed for more than 20 years, there are only five commercial blood banks operating in the U.S.

Large veterinary schools have their own blood banks for teaching purposes, but the labor intensive practice can be prohibitively expensive for smaller operations.

Dodds said Hemopet and other canine blood banks keep repositories of blood all over the country, and veterinarians can have blood delivered to their offices in emergencies. Dogs, like people, have different blood types, and only universal donor blood can be used in transfusions, since even the most dedicated dog owners probably don't know their dog's blood type.

Different blood products, from red blood cells to plasma have expiration dates that range from slightly more than a month to five years. But Dodds said the canine blood demand is so great that there are almost never any leftover products.

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While some of the commercial canine blood banks allow owners to volunteer their dogs for blood donations, in California, where Hemopet is located, only a closed colony of dogs can be used to give blood.

Since Hemopet is a rescue center, the donor population can quickly change from between 250 to 500 dogs, which changes the amount of blood available.

Hemopet's rescued dogs that are deemed healthy end up giving blood twice a month for up to 18 months. But Dodds said her center's goal was to have the rescued dogs adopted, and it doesn't want to keep the animals at the shelter just so they can donate blood.

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"We want them to [end up as] companions [after] they were 'volunteers' to be blood donors," said Dodds.