Take his temp, seperate and treat. I think his genetics are not the best but he has infection or something too. If he does have swollen joints he is sick and will need long term antibiotics to live. I wonder if this could be a navel infection that has been with him since birth. He has had problems for a while by looking at him and even though his navel is small now it may have gone deeper. Mycoplasma could be the problem too but the way he is humped up in the middle says navel infection that is deep now. I had a calf that had had a navel infection years ago and I treated and got him over it and was about 4 mos. old doing good and I found it dead one day. Opened it up and you could see where the infection discolored some intestine and went on up from the navel. He always had a slight hump in his back too. Just random thoughts. Throwing darts.