Kim, pet photography is an interesting niche market. I do both outdoor environmental portaits and studio portraits. I have yet to have a big sale on a dog running outdoors, like the lake shot. Artistically, it is a wonderful photo. Possibly very saleable as a stock photo

I find action photography much easier than portaiture. With action/event photography, you just wait, watch and shoot when the action is going on. Shoot enough, you will come out with some cool stuff

Portraiture and posed photographs add in a much different level of photography. If you have ever had strangers dogs to photograph that were not trained to do what you need them to do(aka sit still at all) Or a terrified animal, or a person who is nervous and doesn't like to be photographed, you see the new challenges

With show dogs, the people want specific things. I don't find this as hard as true pet portraiture. Those clients are usually very good at setting their dog up. Those dogs are usually quite used to standing still. The true skill there comes in knowing WHAT people want.

I do agree with Jim, the most challenging of all is true posed portraiture. There is so much one has to get right