whys my pitbul so agressive with other dogs?

Question
hey! i have a pitbul, hes about 2 years old! every time i take him for a walk hes always alert! and if he sees a cat/sheep/bird/fox/horse/cow/ anything!  he starts starts pulling the lead towards them and starts yelping really loud! like a screech! its like he wants to kill them! its getting to the point i don't really want to take him out for walks anymore! please help!

Answer
Your dog may not be demonstrating aggression, he may be simply extremely over excited.  Aggression is not normally accompanied with loud yelps!  This is more a sign of over the top excitement and, possibly, even fear.  He heads TOWARD them because this breed is very determined.  You need to learn how to read your dog's body language so you can be certain that what you see is aggression and not simply excitement.  Read Turid Rugaas' book on calming signals, or try her web site:  http://www.canis.no/rugaas/index.php

First: you need to use positive reinforcement training to give this dog the confidence that YOU are in charge (you clearly aren't right now.)  Visit clickertraining.com for this information.  Proceed slowly, one behavior at a time, for short training intervals each day.  Teach him to 'sit' first (but use a different word).  Once he can offer you this behavior 100% reliably (about two weeks), begin teaching him outdoors (go back to square one, teach it as if he doesn't know it for a day or two until his excitement at being outdoors is overriden by his desire to perform the behavior).  If you are able, find a head collar to fit your Pit Bull (this will give you complete control and lessen your own anxiety, which is going right down the leash right now.)  Use TWO LEADS, one for the collar (martingale only, NO CHOKERS: see this site:
http://www.things4yourdog.com/product/407064

and one lead for the head collar.  DO NOT LEAD THE DOG BY THE HEAD COLLAR, merely use the leash to change direction carefully, using the neck collar for basic control.  When another dog/cat/horse/goat, etc., approaches and YOU SEE THE DOG beginning to react, change direction quickly with a "come along" signal (using the head collar, he cannot maintain control) and, after he has visibly calmed (use your skill at reading body language for this), ask him to 'sit', reward it, and go back toward the animal (cat,dog,horse,etc.) and try again.  Interrupting his over excitement by changing direction and then, when he's no longer in the grip of excitement, asking him for a trained behavior, will engage his cognition and problem solving skill and MAY help him to learn to manage his excitement.  This dog is obviously not at all socialized to other animals; this behavior modification may take a while (months) and you may need the help of a certified applied animal behaviorist in person.