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CARA HETLAND: Summer is a dreaded time of year at the nation's blood banks. Donors are busy. And the most common need, human hemoglobin, which is the blood's oxygen source, is in short supply. Human red blood cells can be stored in the refrigerator for only 42 days.

Biomedical companies are developing a blood substitute with a two-year shelf life that can be stored at room temperature. That makes it readily available for emergency treatment and replaces the need for crossmatching donors. The new product comes from cow blood and, in theory, could alleviate chronic blood shortages.

Sioux Valley Hospital Blood Bank Director Keith Anderson says it's a nice theory. But he wants more guarantees.

KEITH ANDERSON: If you could have a product that could be prepared in such a way that there was no risk of any contamination by any viruses or bacteria or any sort of infectious risks, that would be great. If I could know ahead of time that if I gave this product to anybody off the street, there would be no immunologic risks because of blood type incompatibilities, that would be wonderful. At this point in time, it's also pie in the sky.

CARA HETLAND: Anderson says donated blood is safer now than it's ever been. But there's still a risk of transmitting viruses through a transfusion. He says a blood substitute could cut that risk by as much as 80%. He's also concerned the body could develop a natural resistance to processed hemoglobin.

At least two companies are in final clinical trials with the experimental hemoglobin. Anderson says until those results are made public, he'll be critical of blood substitutes. One company is developing a substitute using donated human hemoglobin, and the other uses cow hemoglobin. In one of the only such cases, this new product is being sold first for use by veterinarians.

Marcie Ulrich talks about her boys like a new mother brags about her kids, even breaking out the photo album.

MARCIE ULRICH: And here he is, out here. I got one right down here. Here's his puppies. These are the two guys, and they're younger. But he was a sweetie.

CARA HETLAND: He was a 7-and-1/2-year-old black Cocker Spaniel named Ebony. In the backyard kennel, Ulrich plays with Ebony's puppies Cody and Cole and adopted lab Zach. About eight months ago, she noticed Ebony was listless and having difficulty walking.

MARCIE ULRICH: The whites of his eyes were yellow. And I started looking at his gums. And his gums weren't pink, they were yellow. So I called the vet. First thing I thought of was liver. Something's wrong with his liver. So I called Montrose. We got him in right away.

CARA HETLAND: The rural clinic in Montrose, South Dakota, was just 10 minutes from her house in Salem. Ebony was diagnosed with autoimmune hemolytic anemia by veterinarian Russell Daly.

RUSSELL DALY: His immune system decided, all of a sudden, that his own red blood cells were foreign attackers. So his body was destroying his own red blood cells.

CARA HETLAND: Normally, veterinarians would try a blood transfusion, a procedure that's difficult under any circumstance because of the limited supply of canine blood. Usually, a vet uses his own dog as a donor. Daly felt Ebony needed more oxygen in his blood to support the organs and allow the large dose of medicine to work. He decided to try a new product, Oxyglobin, derived from the hemoglobin of cow blood. Daly says the transfusion was helpful. But Ebony died later that same day.

RUSSELL DALY: But unfortunately, the damage to his internal organs from lack of oxygen probably was there already.

CARA HETLAND: None of the companies developing blood substitutes would comment for this story. The competition is intense. Even articles published in professional journals can make or break a company's research efforts.

Right now, the biggest question is whether the successful blood substitute will use human or cow hemoglobin. Some medical journals say the source of hemoglobin doesn't matter. Rather, the way it's processed is what's important.

The process currently in final clinical trials controls the amount of oxygen transfused to the organs. The processing of the hemoglobin also removes viruses. Still, Keith Anderson at the Sioux Falls Blood Bank is not convinced cow and human hemoglobin are interchangeable.

KEITH ANDERSON: Hemoglobin is not the same from species to species. And most proteins that circulate in a person's blood have analogous proteins in a cow, for instance. Many, many of those proteins, though, are slightly different. The DNA is somewhat different.

And so there may be 1,000 different amino acids that make up this particular protein. And in the human versus the cow-- and I'm just-- I don't know, pull a number out of the air. There might be 5 or 10 or 20 amino acids different from one to the other. They'll have the same function. But immunologically, they're not the same.

CARA HETLAND: Anderson says a blood substitute could be widely used for humans within five years. But he doesn't expect it would really replace the need for donated blood. He says heart and cancer patients still need the real thing. And, he adds, if human hemoglobin is used as a source for the substitute, that increases the need for human donations.

The need for blood substitutes is not disputed. But perfecting them and developing a new product that will save lives has already taken nearly 60 years. The research on blood substitutes began as a way to treat soldiers fighting in World War II. In Sioux Falls, I'm Cara Hetland, Minnesota Public Radio.