William is always very sorry for himself for about 24 hours after anaesthetic, regardless of what it's for. So that might be part of Murphy's problem today. I think the after effects of anaesthetic can take several days to fully wear off.
When William was castrated he had quite a lot of internal and external stitches because his surgery involved the vet finding and removing a retained testicle that was eventually located near one of his kidneys
. He was very sore afterwards and I had to persevere with the cone of shame for several days. I took it off him at mealtimes, when we were out lead walking and when he settled on the sofa next to me and I could watch him like a hawk. Despite that he still had a sneaky pull at the stitches and the wound bled slightly and became infected. So even if you think Murphy isn't licking the wound please be very careful.
Have you tried tempting him with something nice like cooked chicken breast or cooked white fish? He won't come to any harm if he doesn't eat for a day or so, as long as he drinks, but it's horrible seeing them so unhappy isn't it
Does he like a filled Kong or a treat ball? They might tempt him to eat and also distract him from his discomfort and he could spend some time without the cone if he was focussed on that.
I have a comfy cone for William and would loan you that to see if it was easier than the plastic cone, but a neighbour's Labrador is currently borrowing it after getting an ear ripped in a fight.
Hopefully this will be the worst day and by tomorrow he will be more comfortable and have his appetite back
