Potential blood donor Prelude, a 5-year-old golden retriever lab mix, bounded up to a table, snatched a squeaky toy and dog biscuit from a veterinary technician and settled down to help his fellow dog. Prelude took part Wednesday in a canine blood drive at Bailey Veterinary Clinic in Roseburg, which aspires to establish a stock of blood for dogs. “There are a lot of reasons dogs need blood,” said veterinary technician Sara Morrow. “If we had it on hand, we would use it a lot more.” The clinic currently buys blood from a Portland canine blood bank, DoveLewis. The blood …