It's not playable without patch. When it comes to the technical stability, the Pet is the worst expansion pack ever...

User Rating: 3 | The Sims 3: Pets PC
The Pet expansion pack has enjoyable aspects such as raising pets, horse racing, and training. Everyone who loves the sims3 expected that the pets would give the unprecedented pleasure. Unfortunately not like our expectation, the Pets has many glitches to trouble you.

After 6~7 hours, the game starts to bring hidden glitches. It starts normally the lag or the dragging of the motion and finally becomes freezing. Once freezing appears, no one can stop or change the situation even though you start the game again.
In addition, some users have graphical issues such as invisible fur and distorted shapes of pets.

To my think the pet expansion pack isn't optimized and finalized for the end users. It's like the just beta game product.
Everybody is waiting for the patch. But for two months (since the launch of the Pets) EA did not show any efforts to fix the game.