Brahman bull losing weight, severely, yet eating, also laying around most of the time. Vet took blood tests, no worms, nothing showing up. Is there a form of Cushing's Syndrome in cattle? Or, what other possibilities?
have you tested for Jonnes, or bovine leucosis, these are two key DX I would test for, pull red tops and submit to state labs
Could also have hardware DX, such as bailing twine in digestive tract preventing proper absorpion of nutrients, or a prior parasite overload may have caused such damage to Digestive tract that it is irreparable
Unfortunately, it does sound like Johnes. Not a good prognosis.. the bull will possibly seem to get better for a period of time, but continually relapse. If it is Johnes, you also have to worry about the rest of your herd being infected.