Q: When dog training with a whistle do different gundog breeds need different whistles? Why are 210.5 whistles recommended for spaniels, but 211.5 for Labradors and retrievers?

The number refers to the pitch of the whistle, and for some reason a 210.5 is always referred 
to as a two-ten-and-a-half, and a 211.5 
as two-eleven-and-a-half.

As far as I am aware, there is no difference in the hearing of a Labrador 
or a spaniel, or for that matter a poodle or a pointer. All dogs, regardless of breed, hear a frequency range of 40Hz to 60,000Hz, while the human range is between 20Hz and 20,000Hz. This explains why a dog can register a so-called silent whistle, which is sufficiently high-pitched to be inaudible to the human ear. Choice of whistle comes down to the handler’s individual preference and it really doesn’t make any difference to the dog. I’ve always used 210.5 whistles because I’ve always had spaniels and this is the whistle I was recommended.

Similarly, most of my Labrador-owning friends use 211.5 whistles for exactly the same reason — it was what they were advised. And once you have bought your first whistle you are likely 
to remain faithful to the same one for the rest of your life.