This manual goes into some detail the various characteristics of the horses, cats, dogs, unicorns and small animals that are included in the Sims 3 Pets game.
There is this a small amount of duplication, as it discusses cats separately from dogs, and there is a lot of common ground between the two.
You should buy this book if you want to know how playing horses especially, with its career structure, more obvious, and how to attract a unicorn. However, I do not think that it is essential to buy this manual compared to the purchase of the "World Vacations" manual was to get the best out of the game. Nevertheless, it is a good read.