Originally Posted by Grouchy.Otaku

If your Tribbles have snacked on 54% food or drink items, that would 'poison' their ability to breed more advanced tribbles... You might need to start over creating a 'virgin' breeding pool to get proper results...

I've been breeding Tribble (val) all this month in quantity, (last batch was this morning) and posting them for a very reasonable price on the Exchange, so I know this still works...