Here another article about Pets. There’s no new info but it’s a good read.
In The Sims 3: Pets you will be able to create a huge variety of dogs, cats, and for the first time ever; horses, with over one hundred different breeds. Once you’ve created your pet you can horse around with the customization tool and produce truly unique pets for your sims. Not only can you determine how your pet will look, but you can also pick the traits of your animal from intelligent and brave to skittish and clueless. The traits you pick will determine the personality of your pet, whether you have a fierce guard dog a destructive cat or a trusty steed.