My guess is look for lameness in the front OR in the back end. At a guess try BOTH front, or back feet.
I have seen this in sheep rather than cattle. If sheep then it has been due to lameness.
Sheep that we have had the vet autopsy had erysipelas (sp?) a bacterial infection in the joints in my sheep mostly affecting the hip joints plus other joints. If it is even both sides you wont necessarily pick the limp.
Next is sheep whose hooves were burnt off and were lame, again if it is both feet, either front or back, equally, then there might not be a very obvious limp. Any chance of foot abscess in both feet?
The suggestion it could be a sore neck also sounds good to me.
If it was a calf of mine, so long as you didnt want to sell it Russian/Saudi eligible, I would give it Tetracycline at the dose you would give a foot abscess. If not then Penicillins. If it stops doing it, then it was an infection.