My great uncle used to say it was caused by eating too much too green alfalfa(I think). He’d stick an ice pick in the cow’s belly to let the air out. you had to know exactly where to poke the hole. Stinky air and green goop would shoot out. Then the cow would get up and walk away.
You sure have to know the exact spot. I was told to put a straw or something in the hole for a few minutes...Never tried it as I figured I’d just kill the goat. But I have been scratching a goats ears when they brought up the cud with a burp....sure is stinky..but you get good at seeing the cud come up from the stomach before the burp and quickly walk away.....:O)