Bull update

"No. 28" grazing with the rest of the herd after recovering from his recent illness. 
A few days after the bison bulls were introduced into our ranch I noticed that one of the bull calves wasn't with the group.  After an hour or two searching I found him asleep in one of the forests.  He seemed very out of it and didn't even notice me approaching until I was about thirty feet away.  Once he noticed me he stood up and trotted away.  I followed him at a distance and he continued moving away from me at a good pace and periodically stopping to look back at me.  While I followed, I studied him carefully as he moved.  There were no signs of physical trauma, pain, or neurological issues.  No physical symptoms of any problems.     This continued until he met up with the herd at which point he joined them as if nothing had ever happened.  

The following day I noticed that the young bull was again missing from the herd.  I walked to the forest I had searched before and found him asleep in exactly the same location.  Just as the day before I was able to walk within about 30 feet of him before he noticed me and ran away.  As before I followed him, but this time, rather than rejoin the herd, he looped back and returned to the woods.  

I am in no way a bison health expert, but I'm pretty sure this wasn't normal or a good sign.  At that point it began to rain very hard, the temperature became quite cold, and I had to leave to get more supplies from home.  I didn't know if the calve was going to make it or not, but figured I'd know by the time I returned.  

A day and a half later I returned to a sunny ranch with new supplies and was relieved to see both bison calves grazing normally with the herd.  A few more days later there been no relapse and it appears that our mystery illness has vanished. 
Our new older bull pauses his grazing to examine me with my camera.  I'm using a zoom lens for this photo and standing behind an electric fence.  Note the young bull calf peering at me from the other side of the older bull.