Back Garden Fancier, be careful with reading to much into your test results!
A friend of mine was using a test facility and his results were coming back showing a high yeast level, he doesn't use brewers yeast or any products containing yeast.
When talking to other fanciers in his area who used the same facility all there results were comeing back with high yeast.
He then sent some droppings of a bird out of interest and the result was again very high yeast, when the lab was asked if he should race the bird, they said no, you will never see it again in that condition!
The owner then told the lab what he thought of there results as the bird topped the fed 2 days before the test and was sent the following week and topped the fed again!
Phil