As someone who worked about a year for 911 (I left in August 2011), I'd like to suggest calling 911, but ONLY if you are witnessing animal abuse in progress.
If the abuse is not in progress, don't call. You will be told to call Animal Services at 311. That also goes for stray dogs/cats, raccoons tearing up your roof, etc. (I once got an emergency call from someone who saw a beaver walking down the road and was afraid it would get hurt. Also, another calltaker got a call for a pet parrot that escaped outside and was perched in a tree. Police don't attend for calls like this.)
If the abuse is happening in front of you and there is a very good chance to catch the abuser, call 911 (and concentrate on IDing the suspect if you don't have a camera, get the license plate if you see them get into a car, etc.). Currently, there is no specific protocol for handling an animal abuse in progress call (despite the possibility of pets-locked-in-hot-cars incidents), but many/most of the calltakers are animal lovers and will take sympathy and send the call to dispatch. Please note, though, that HUMAN emergencies take precedence, and if it takes forever for an officer to arrive, it's most likely because 22 Division may have had a lot of other calls pending (it was astonishing how quickly the board filled up with calls for assault, domestic abuse, sexual assault, drunk driving, etc.). If you confront the abuser(s) and they attack you, definitely call 911.
Lastly, a general note for ANY 911 call: stay as calm as possible and answer ALL questions as quickly and clearly as possible, even if you think the question is ridiculous (more about this at the bottom). NEVER tell the calltaker to "stop asking questions and hurry up and get here" - that wastes time. Calltakers are not the ones driving - they're entering the info as you say it, which appears on the dispatcher's screen instantaneously. If there are officers available, and if they are on the way, the dispatcher calls the info out over the radio to those officers, who also see it on their computer screens (if they're in a car that is equipped with them) so that they know what is happening and hopefully what the suspect looks like before they get there. Arguing with the calltakers slows the flow of information. (This also applies when you need an ambulance).
Regarding ridiculous questions, requests for ambulance get transferred to Toronto EMS; they have a system whereby they have a set list of questions they MUST ask so that they can get an answer ON TAPE. Once during a dismembered body call, the EMS calltaker asked if the victim was conscious and breathing, even after being initially told that a headless torso was found in an alley.
