I was just wondering when you see certain dog food companies sponsering dog shows and photos of individual winners are the companies saying that those dogs are being fed on that food?

Well they are implying that they are, and as at least oen of the companies gives food vouchers as prizes, unless the owner throws it away theya re not lying as it will be fed to their dogs.

They're saying you use their products - not that you necessarily feed them exclusively. When you win a group say at a champ show the rep will ask you if you use any of their products - your photo can then be included in their ad. It's worth doing as it's usually a full page colour ad in the dog papers - so free publicity for your dog too. As Brainless has said most people do use the freebies you get for BOB etc  :)

Look at the wording on some of the ads ;)

There's <name> would like to congratulate
           fed on <name>
and      exclusivly fed on <name>

If they are exclusivly fed on then it will be the main food.  These will normally be single adds advretisng dog and brand aswell.

Those which include the group winners normally just feed treats :)