We get it every year there does not seem to be any definitive percentage in any given year of birds effected,some severe and some not so severe some seem not to have any symptoms at all. In recent years we have had it during racing with no sign what so ever ie sickness or visually,but birds failing to return raises alarm.we usually get it 4 to 6 weeks before racing begins and we let it run its course with out treatment the strong survive and the weak don't quite happy with that out come and our views with regards to that will never change.we don't treat YBS and we don't treat OBS for nothing and quite happy with that,the birds get one spot on the neck once a year and thats it no canker no coci nothing,always hoping for that good win but for us treating will not enhance our chances.