Dealing with an ordinarily 100% healthy, spunky, fit, 9 yr old intact male Australian shepherd. About 65 lbs. As of Sept 16th, a major problem. Paper-white gums and sudden lethargy. Immediate not eating. Took him to vet, no abdomen tenderness. Blood work showed low platelets. Put him on antibiotic. That evening dog seemed near death. Isolated him in room with his food bowl and water overnight. He has eaten same high-quality dry dog food his whole life (he normally eats 1 to 1-1/2 cups twice a day). However, by morning, he had eaten entire bowl of food and was up and happy and seemed at least 80% better. Gums still pale. Within next few days gums back more pink. Activity/eating normal. At exactly 1 week later, same dramatic turn to white/lethargic/not eating. Weight at vet's showed dog had lost 2 lbs. Started him on vitamin K, Prednisone twice a day dosage and different antibiotic, amoxicillan. Blood tests later showed not D-con so stopped vitamin K. Within a day or so, dog again dramatically better. Eating like a horse on the prednisone, peeing a river. Increased his food to 2 cups per serving twice a day to try to regain some weight. Added a spoonful of high-quality canned dog food and some water to make gravy of dry food to encourage him to eat. Vet thinking an autoimmume problem, though the dramatic back and forth does not quite fit. Finished antibiotic, following weeks took him to vet for re-check and platelets dramtically better all blood work that of normal levels but dog still had lost another pound of weight. Otherwise seemed energetic, happy, same dog he'd been before all this. Gums pink. In next 2 weeks, dropped prednisone to only once a day. As of 5 days ago, stareted prednisone every other day dosage. Today at 3pm he was happy and begging for a dog biscuit. By 6pm he was suddenly dramatically lethargic, white gums, not wanting his supper.
He is pooping normally, I see no blood, normal color. No tapeworms. Volume of poop has increased as you'd expect w/ food volume but he's not putting on any weight, may have even lost more weight. He doesn't eat/have access to other animals or snakes or livestock. Except do have his sister dog right with him who is not sick and their friend our cat who is also not sick and never has been. Cat also catches/eats no vermin. None of pets foods have changed. Dogs do eat cat poop and steal some cat food but have done that their whole lives.
Anybody out there know a possible diagnosis?

Only other infor that may or may not be important: On Sept 15 he was stung by multiple bees. We put sting kill (benzocaine) on his nose which he may have klicked off. The following day (Sept 16) he was fine and we also applied his K-9 Advantix that day. (He's had it applied at least 4 times before ths application--last year and in the spring of this year) Don't know if any of that matters or not, just happened to be the only other 'unusual' things that happened about same time he's gotten sick. It was evening of the Sept 16 that he first got sick.

My hound had something similar two years ago to the point where we thought we would lose her, however, very good vet but she was at a loss to know what the trouble was. Taffy had white gums, would fall asleep and her bladder would go and she would wake up in a puddle. She was on prednisone as well (seems to be a catchall drug for big dogs). Blood work showed she was anemic. She was a very sick dog for a long time.

My diagnosis was that while out walking she had eaten some grass that had been treated with pesticides and the pesticides had attacked her kidneys.

She is well and happy now but close call but I think I came the closest to figuring it out.

My input, maybe something for you to think about.

However, she is eleven now and in excellent health.