After any antibiotic Andy the levels of yeast rise, as a precaution you should always put nystatin on the grain for at least the next 3 feeds to eliminate any problems with candida(yeast). The reason why many people will use lemon juice on the grains or cider vinegar in the drinker is to acidity the crop and to brake down the sugar levels which candida feeds on, simple carbs like maize In my opinion Brewers yeast would not cause a candida problem as it is inactive yeast, however if you have a candida or yeast problem brewers yeast will feed the candida, hence many people with Thrush are advised not to take Brewers yeast as a supplement until the patient is completely clear. But you must remember you need an equilibrium as an amount of yeast is need to create good intestinal gut flora Geordie I think your mistaking what I am asking you mate, did you medicate any of your flock before you took the samples for analysis, as I am trying to hit the nail on the head on why your candida levels were high?