Apparently the dog is losing blood somewhere as it could be losing blood through its stool, or have a bleeding ulcer. See your local vet as soon as possible. The dog may require surgery and probably be given vitamin K to help with the anemia.
Its been found in all female breeds than in male. The main cause can be due to the change in their immune system regulation. One other cause is abnormalities in their blood cell.
This could be a couple of things. The most likely is the dog is not getting enough Vitamin B 12. Vitamin B 12 is essential for blood cell formation and often dogs don't get enough.
Anemia can be caused by a bad diet. Cancer can cause anemia in any age of a dog. Liver disease can be the culprit. Your vet should be the one to ask. He can do diagnostic tests.
The two biggest or most common causes for that especially in an older dog are worms and fleas over populating on the dog. The other thing that can cause it and it will happen quickly is if the dog has ticks on it they are a nightmer to find and even harder to remove the vet can do it best.
There are many causes for anemia in dogs. Blood loss, intestinal parasites, gastric or intestinal ulcers, liver failure, kidney failure, chronic illness, and several cancers just name a few of the possibilities.
