I have a rooster that has been sneezing for probably 6 months now, which is how long I have had him. I had gotten him and a hen as adults from not so perfect conditions, which was the main reason why I took them, to get them away from there. No other symptoms, eats well, has lots of energy and he is in with his hen who is not sneezing and they just produced 2 beautiful babies who are just fine too. I have had this little guy to my vet and my vet said it is either damage from unsanitary conditions that he had lived in before, strong ammonia or litter with a lot of dust or chemicals or it simply could be allergies. I have tried different litters with him, but he always sneezes. We do live in one of the top 3 allergen area in the US and I have been dealing with my own allergies all through the winter myself, so it could very well be that. It doesn't seem to bother him in any way, none of my other chickens sneeze and obviously does not affect fertility.