About a month ago I had a bottle baby doe kid die on me at two weeks old. Perfectly healthy kid.
I went into the house to get the afternoon bottle, I was coming out the back door and I saw her walking along in the backyard, she just sort of pitched forward onto her face and fell over. I thought she tripped or something, anyway she didnt really try to get up. I picked her up, she was disorientated, and didnt appear to be able to control her front legs. She kept falling over, so I picked her up, she was convulsing (just sort of jerks in the limbs and head, not paddling or anything) and didnt settle down.
I raced her into the vet, she convulsed all the way in (45 min) and her temperature was below normal and her heart had slowed right down. My vet put her on a drip and heat pad, the convulsions stopped and heart rate and temp came back up to normal. A couple hours later she started convulsing again, her temp crashed and though they gave her valium to calm her she died.
My vet hadnt seen anything like it, his theory was perhaps an infection which had got to the brain, possibly through the navel - but she hadnt had navel ill or been sick at all. As far as the autopsy goes - we considered it but my vet said a visual autopsy on a case like this probably wouldnt yield much info, we would need to do lots of tests and it would push us up around $500 at least. But we did make the decision that if another one came down with it we would do the tests.
Just the other day I was talking to an old friend who said she had a lamb that did exactly the same thing. She took it to the vet, long story short they saved the lamb. Her vet said it was an accumulation of toxins in the brain from something in the feed/pasture. My friend couldnt remember what it was exactly and we are trying to find out. Also trying to find what the vet gave the lamb. Apparently 90% of cases are fatal.
It does sound similar to what you experienced with your calf. Here's hoping you can save the next one.
I know the awful, sinking feeling of watching an animal die while you have no idea what is wrong with it or how to help it. That kid I lost was the first time I didnt know what to do. I have been around plenty of sick and dying animals, and always had an inkling of what was wrong and how to try to help. This kid ... I had nothing. Couldnt do a thing. Thats why I rushed her into the vet. I couldnt just stand there and watch her die without doing something. Its an awful awful feeling, being inadequate. I feel for you having to go through that, I really do. I know how confusing and painful it can be.
God bless, take care.
Sorry for the novel lol