Cows do not die for No Reason.
A Good vet should be able to give a rough diagnosis from a description of symptoms.
Given the symptoms you have listed I would run tests for Anaplasmosis, and also Jone's, and Bovine Leucosis, that is three tests, all run off one blood tube sample, cost under $35.00. I would certainly seek out a new Large animal vet, and call your State Vet Teaching hosppital, I don't know what state you live in.
You could also send it to TVMDL, Texas Veterinary Medical Diagnostic Lab, that's who I use.
Blood in stool, can be caused by coccidia, (coccidiosis). Worms, in a heavy enough parasite load can cuase the ssymptoms you have mentioned if enough damage has been caused, and at that point there is too much damage to save the animal. A simple fecal float will be able to determine the parasite load. Get fresh feces and store in a refrigerator till you can get it to the lab.
I do not think it is Anthrax, it is common in Texas, but rarely diagnosed in the live animal. Black Leg is also common, and the only good prevention is vaccination. Blackleg does not cause the symptoms you mentioned.
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