Noticed a couple of my hens sneezing. No discharge or whatever, though they do have their mouths open, although I'm not sure whether it's related to the sneezing or the heat (they have a tarp over the top of the run for shade but even so, it's been hot here). They're all still laying regularly, I have five hens and I get 3-5 eggs daily (usually 4) and they have different colors so I know whose eggs are whose. They've all been vaccinated for Mareks which I assume isn't related to this anyways. No other symptoms as far as I can see. Not sure exactly what this is. Should I just try the Tylan first since I have that on hand?