I'm after some advice. My 14 month old Lab (Radley) has been trained to the whistle and is pretty good. Over the past week or so he is completely ignoring it. Even out on open fields with no distractions and the promise of a treat on return he is not coming back. I'm at a loss to understand why this has happened or indeed how I can correct it.
He comes from excellent working stock, is intelligent and was castrated about 6 months ago.
Any suggestions ?