From The Tip Jar:

This month we take a warm, fuzzy, Fox Network-style look at the ethical treatment of fauna throughout Postal history. Pay attention Jeff Corwin , you just might learn something...

Champ:

Appeared in Postal 2 and Apocalypse Weekend. The Dude's (mostly) faithful companion, Champ rolls over and plays dead for no one. Champ is definitely his own dog, though in a pinch he will come through like a vicious and insane cavalry to rescue the Dude from whatever stupidity he's gotten himself into this time. Just make room for him on the heart-shaped bed, 'cause he loves the babes and wants to teach them a new trick...

Bonus Fun Fact: Yes, Champ is real and he will bite your nuts off.

Ostriches:

The only animal to appear in the original Postal. They're pretty dumb and don't really do anything but run around and squawk, though they are great vehicles for fire. Why Ostriches? Someone thought it would be really funny to have Ostriches in the game and the rest of us were too drunk to know any better. Our only excuse was that there were, in fact, Ostrich farms outside Tucson.  I guess someone thought they'd be the "chicken of the future" or something. So I suppose in some drug-addled way, they were "topical". Sorry.

Bonus Fun Tip: Basically combine anything that results in fire with Ostriches for insane fun.

Dogs:

Appeared in Postal 2 and Apocalypse Weekend.  Basically Dogs are man's best friend or sometimes not. Dogs have the most complicated AI of any Postal animal, approaching Tamagotchi levels of crazy. Most Dogs can be trained or bribed into being your friend.  Some are just insane and will kill you no matter what though, so be prepared to either gain a friend or randomly die.  Anyway, there are some things to know about Dogs.  Basically, if you see a yard that has a "beware of aids-infected pitbull" sign, expect to be eaten.  But, even a Dog intent on gnawing your entrails can't resist the distraction of a dog bone, pizza slice or donut.  Cats also work. Just toss something tasty on the ground to buy yourself an extra second or two of life.

If the canine is not hell-bent on your destruction, you can actually befriend them by either feeding them as described, or playing fetch with them.  They'll chase and bring back just about anything you toss or kick their way, (including dismembered human heads) so use something they won't eat, like a "Health Pipe" rather than wasting that jelly donut that might just save your life later in the game.  Toss the item and the Dog will retrieve it and drop it at your feet.  Pick it up and repeat three or four times and you'll find that the Dog will now follow you and will intervene if you are attacked. If you notice your Dog start to limp and whine, feed it some junk food to restore it's health.  If it starts lagging behind, that means it's losing interest in you and you should play fetch with it some more. There is no known limit on the number of Dogs you can befriend, though it does get extremely difficult to maintain a large harem as it's nearly impossible to prevent them from getting into trouble...

Bonus Fun Tip: Give someone a swift kick in order to sic your Dog on them.

Cats:

Appeared in Postal 2. Though cute, Cats basically do nothing but lick themselves and wander around aimlessly.  Sometimes they nap. They are basically the P2 equivalent of an Ostrich. If you are careful not to startle them, you can carefully walk up and catch one.  If you run at them they'll flee.  You can also lure them with catnip (toss the can rather than smoking it, hippie.). If you "use" a Cat in your inventory while carrying a suitable weapon, you'll stuff the feline right on the barrel like a furry corndog.  The Cat-suppressor is handy for making it harder for nosy cops to accidentally overhear your shooting, and also it's pretty funny when the Cat reaches it's ninth life and flies off the gun to explode against whatever it hits. Look, there isn't shit to do in Arizona, okay?

Bonus Fun Tip: Cats make great distractions for Dogs.  Carry lots.

Insane Dervish Attack Cats:

Appeared in Apocalypse Weekend. These are pure feline evil created by moron scientists meddling in things best left unknown. While they retain all the properties of the standard P2 Cat, the Apocalypse Weekend variant has the ability to attack and dismember the unwary.  So don't piss them off.

Bonus Fun Tip: Definitely attempt to collect a few of these, they're very useful!  Just toss one at an enemy and you'll see what I mean.  Plus, if you are killed, they'll often leap out of your corpse and revenge you. Hey, it's better than nothing...

Elephants:

Appeared in Postal 2 and Apocalypse Weekend. The ultimate Postal animal, these massive death machines go completely insane at the drop of a hat. Extremely difficult to kill, and almost impossible to outrun, your best bet is to stay the hell away from them entirely. Their absurdly terrible pathfinding and half-broken collision detection are your only hope for survival.

Bonus Fun Tip: Find some high ground and pop a cap into an Elephant's thick ass.  Sit back and watch the fun as it stomps every bystander it can catch into people-flavored toothpaste. A berserk Elephant will not stop until it can't find any more bystanders to crush. And now that I think about it, it won't even stop then.

Cows:

Appeared in Apocalypse Weekend.  The AW equivalent of Ostriches, Cows mostly just stand around begging you to abuse them. Though, if you piss them off or their brain has been transformed into oatmeal by MadCow disease, they WILL charge and kill the fuck out of you.  So watch out for that. Your best defense is a strong offense. -with a sledgehammer. If you're feeling cocky, try your luck throwing the hammer for an instant-kill headshot at range. C'mon pansy, don't make Ted Nugent cry...

Bonus Fun Tip: While you can't tip the cows in AW, you CAN enjoy a fleeting Beavis and Butthead moment should you throw the hammer towards a cow's ass by accident. And if you're a real man, you'll walk right up to get your goddamn hammer back.  Wuss.

*Special Note to idiots who take this sort of thing way too seriously: I have owned pets all my life and currently have two cranky 13 year old cats that still insist upon sleeping on my damn head every night. I would never hurt an animal for real, and would kick anyone squarely in the nuts who did. It's just a stupid, stupid videogame and it's damn fun, so just work a little harder at differentiating between fantasy and reality, lighten the hell up, and we can all hold hands and sing koombaiya.  -or however the fuck you spell that Kwanzaa shit.