Not eating is bad for sheep as the gut bacteria, on whihc they rely, die and it's hard to get them back. I always found ivy to be a good appetite stimulant. One year I had a ewe that was unwell after lambing - I made her green shakes with grass, dandelion, ivy, pureed and drenched it into her. She survived.
If he was n otherwise good health, maybe try that for a couple of days?
But sheep are funny buggers.