Sheep are one of the basic livestock animals available in Harvest Moon 64.
They cost 4,000G and are fed fodder (30G per' bag, purchased at the Green Ranch, or through cut grass). Alternatively, they can be left outside and will feed themselves if there is grown grass to eat. They will get sick if they are left outside during the Winter or on a rainy day, if they are beaten, or if they are not fed. Sheep take 1-2 days to recover from being sick and can be made better through the Miracle Potion.
Mature sheep can be sheared once a week, assuming they are not sick. Depending on their affection points they will give you regular wool (900G) or quality wool (1,800G). Wool is generally sold, but can be given as a gift (Ann will enjoy it the most) instead. The quality does not affect how much the person will like it, so give them your normal wool first.
When you buy a lamb it takes 15 days to mature into a sheep. During the time it is a lamb, it does not need to be fed as it cannot be sheared.
Sheep are a good investment if you want to reduce the amount of time you spend on your livestock every morning.
Secrets and Exploits
There are a couple of exploits to get your sheep to high affection, quickly. Attacking a sick sheep will increase its affection rapidly (though it might be sick for a couple of days; at least 12 hits should maximize affection). Alternatively every time a cow or sheep is left outside in good weather they have a chance to gain a large affection boost (represented by the "happy" status). As soon as they get this, leave them inside one day then put them outside again. This boost is meant to be a one-time reward, so over a week you can quickly rack up multiple bonuses.