He could have early signs of a respiratory infection. Sometimes the cold weather or other stress can cause a dormant disease to become symptomatic MG or other respiratory diseases can make carriers of those who are exposed, and sometimes those carriers may not show symptoms until they are stressed. I would probably give him some Tylan 50 injectable orally 1 ml twice a day for 5 days. You can find it in the cattle meds at feed stores. It can also be given by injection.