Here is some info on animals in the game of Harvest Moon 64.

Cow: The cow will give you milk when it is mature, it will give you small milk for about a week at first, then it will start giving medium milk for about another week, large milk will give you 300 harvest dollars, to get special milk your cow will have to win the cow festivle. To win the cow festivle you will have to brush feed and milk your cow everyday, it also has to be giving large milk, you'll have better chances if you let your cow eat the grass you grow once in a while and if you get your cow pregnant. ITEMS NEEDED: Brush, milker. COST:6,000

Sheep: The sheep will give you wool when mature, the wool gives you 900 harvest dollars, if you take care of your sheep very well by talking to it, brushing it, and feeding it everyday it will eventually give you special wool which sells for 1,800 harvest dollars. You can not breed sheep! ITEMS NEEDED: Brush, sheers. COST:4,000

Chickens: Chickens do not have a happy meter so all you have to do is feed them and keep them out of rain, snow, and typhoons. Chickens are the cheapest, and you can get more for free by putting an egg in th incubator, but the catch is if one of the breeded chickens dies, all of the others coming from that family will also die. Baby chicks do not need to be fed. You can only have six chickens at one time. ITEMS NEEDED: NONE. COST: 1,500. You can breed chickens for free

Horse: You get your horse at the Grenn Ranch by talking to Karen early on in the game. The horse only serves the purpose of carrying crops and racing in the horse race. It doesn't eat and it just stays outside even in typhoons, all you have to do is brush it, talk to it when its small, and ride it for at least two hours when its big everyday. ITEMS NEEDED: Brush. COST: Free

Dog: You will start out the game with the dog, just feed it once in a while, keep it in your house in bad weather, pick it up once a day, whistle for it once a day, and I also heard it becomes faster if you whistle for it then get on your horse and ride around with the dog following. You do not have to do anything in the dog race just hope that you have taken care of it and it is fast. COST: Free. ITEMS NEEDED: None

Different Animals: These are diffrent animals you can find in the wild, they don't serve a purpose, but you can bring them to different people for different responses.

I want to thank KrisP1986(look at staff section) for this info he gave me for my site.