My border Collie did the same, you name it if it was an animal he growled or barked at the telly, even a stick insect has set him off before now. Some how he always knows when it is an animal.

I saw The dog Whisper a few months back with a dog with the same problem and the solution he gave worked a treat. every time your dog even shows interest in the animal on TV ie lick his lips, prick his ears, sit up, growl or bark you make a aggressive shhhht noise if this does not work then you move it up a step and touch the dog just under the ear (this is done if you hold your hand like your holding an imaginary ball in your hand with finger spread out/ or claw like and not hard but firmly touch/ gently jab the neck and quickly pull away). This imitates the pack leader going to bite or hold the dog in place (natures way)but only replicates the pack leadership of 'i am the boss and i don't like what your doing'. Repeat without fail every time he does it and 3 days into it my dog learnt that its not acceptable. its not cruel and does not need you to raise your voice smack or hurt your dog just gets you to assert your authority.

Good luck