Basil Tsiokos at What (Not) to Doc on the dangers of assuming that your pet cause merits a feature-length documentary:
If you are a filmmaker, and you enjoy making films about things happening in your life, you may feel that your pet cause is as worthy of being filmed as any other issue out there. More power to you. Make your film about why you think male dogs should be forced to wear pants, and enjoy watching the final product with your friends, family, and pets. However, if you think your two-hour long pantalooned dog advocacy project is likely to resonate with the masses, I’d wager you are probably wrong.
I would add to Tsiokos' sentiments that even if your cause does merit a feature-length doc, be careful not to conflate the film and the cause.
Chances are your film will be rejected from more than a few film festivals. That doesn't mean that the festival and its staffers don't believe in the cause – it just means they don't want to play your film.
In the months and years immediately following Hurricane Katrina, I saw this a lot at various festivals. A fest would reject a film about pets who were orphaned after the storm or the plight of displaced kids and the filmmakers would start hurling accusations.
"You don't care about starving animals!" they'd say, usually in an hastily (and angrily) composed email. (This charge leveled at one fest was particularly silly, as the head programmer was married to the director of an animal shelter.) The filmmakers just couldn't wrap their heads around the idea that rejecting a film isn't the same thing as rejecting the ideas behind it.
If you find yourself in this situation, consider the fact that a documentary doesn't have to play festivals to benefit the cause. If raising awareness is the goal, getting the film out there online (and perhaps creating a few versions of different lengths) will probably get more eyes on the issue and effect more change.