Animals have their own personality
If you wish to write about talking animals, keep in mind that the tone of voice, the choice of vocabulary and the spelling should match the size, the looks and the unique personality of the animal. If your character is a horse he should have a deep, meaningful voice. Unless he's in truth a tiny mouse jinxed in a stallion's body, then it makes sense for him to speak in a high pitched, feeble voice. Have you ever heard a thundering scary scream coming from a caterpillar? There's a story there, ready to be told. The cat in my story spoke elegant words in a calm, contained manner, and if there was a tale about a dolphin I would expect him to laugh easily and think positive.
Animals can break the rules
Once your animal character is believable, set free your creativity to find a new, unseen approach for your plot. For example, just think of what Pixar did to bugs. It is quite remarkable how they transformed scary disgusting insects into tiny animated heroes. The cat in my story wants to move in with the next door neighbor, a seducing woman offering him fresh tuna and cuddles. Breaking the rules is fun and readers will go along if you play it smart.
Cute or ugly, animals raise emotions
Most people feel for animals more then they would feel for humans. We laugh at someone getting hit in the sack but we cry in front of an injured animal. As a writer, you can use this enhanced feelings to create a more dramatic or humorous situation. Talking or not, an abandoned dog would cause pity to most people. A lonely cub evokes a sense of protection, and a snake will always be scary, unless of course there's a lion taking care of it.