Ausie chases pets

Question
QUESTION: Hi I have adopted an Ausie from the local pound. I have had a boarder collie in the past so i am use to high energy dogs. The poudn said he is three but his teeth and paws make him apear younger. He is polite, well behaved, and good with my neice and nephew. How ever he likes to chase the cats and today he nipped my horse on the nose! How do I discourage this? is it possible to stop this habbit if he is three years old? When I scold him for it he acts suitably admonished. This is only day two. Am I just worrying too much?

ANSWER: No, you aren't worrying too much - Aussies will make their own jobs up if you don't give them one, and their natural desire is to herd, and if you don't have sheep, cats and horses will do.  You should keep your Aussie away from horses - they don't kick the same way cows do, and a dog can be very severely injured.  Give the cats a place where they can escape and the dog can't follow.
Next, start some classes with a good clicker or positive trainer who can teach you to teach your Aussie to "leave it".  To satisfy the herding instinct, you can let him catch frisbees or tennis balls, or "herd" empty two liter bottles (cheap, but you need to supervise) or herding balls (expensive, but loads of fun for the dog).  Another good tactic is to use puzzle toys, such as Buster Cubes or Nina Ottosan toys to keep him occupied.
If you have no trainer nearby, try www.clickerlessons.com for some free hints on training.  Also, see the videos at www.clickertrainusa.com.

---------- FOLLOW-UP ----------

QUESTION: when the cats are not running he doesn't chase after them. in fact he lets them rub against him and at times he acts afraid of them. (one of the cats slapped him and he barked and chased it but I stopped him.) Should i worry that he will harm them if he catchs a cat?
He chased one again tody but this time did not stop when i called him. This has me worried.

Answer
Yes, you should worry.  But, there is much you can do to prevent him from getting too pushy with the household cats.  Give him an outlet for his predatory drive - chasing a frisbee or nosing the bottles around helps.  The best thing would be to go for herding lessons if there is a trainer in your area.  It's much easier to train an Aussie not to "herd" your horse if he knows that the herd-able animal is the sheep.  In fact, an old time herding trainer once told me that you should not admonish the dog from going after the inappropriate animals (horse, cat) until he has been introduced to the appropriate ones (cows, sheep).  That isn't always practical, but I managed to do it by taking my Aussies to a fun herding day at a training center about 70 miles from my home.  Obedience training is a huge big deal, and I suggest you get in touch with a clicker trainer in your area who has worked with herding breeds.  For now, again, the cat needs an escape place, and the dog needs to be kept away from your horse, until he knows his commands...the most important being "down", "leave it", and "come".