My 3 year old lab seems to be sick some mornings ( early hours ) and there seems to be a pattern, I give him a big walk every other day through a field that has just been harvest for hey/straw and its on these days that he seems to be sick the following morning. Yesterday we did the walk, this morning he was sick but his stomach was empty. He seems fine in himself and he had scrambled egg for breakfast and has kept it down. Could there be a link to where we walk ( though my other dog came with us yesterday and she is fine ), he is due to be wormed so I'm going to do that today though I haven't seen any evidence of worms. Any ideas what it could be?