Stardew Valley: Cows
Milking, Caring, and Large Milk
Properly caring for your Cows in Stardew Valley will result in them producing better income for your farm. They can reproduce so long as you have a big barn, and you can sell cattle if you're no longer interested in caring for them. This guide will teach you all you need to know to care for cows and get more large milk.
How to Get Cows
It's generally wise to have a silo and stores of hay built up before investing in animals, as if you run out of food you will have to buy hay. In order to buy Cows, you must first have at least a regular-sized barn on your farm (built by Robin and requiring 6,000G, 350 Wood and 150 Stone). Once the barn is built, you can buy cows from Marnie's Ranch, south of the farm for 1,500G each. You can house up to 4 animals in a small barn, which can be upgraded to 8 capacity (big barn) and 12 (deluxe barn) with further investment of wood, stone and gold. When you first buy cattle, they will be babies and cannot yet produce milk. Care for them a few days, and they'll grow into adults.
Buying a Milk Pail from Marnie, you can milk your cows every day so long as they're properly cared for. The happier a cow (the more hearts it has), the more likely it is to produce a large milk, which sells for significantly more money. You can make even more by turning your normal milk into cheese with multiple presses, and may also use the milk in cooking or providing it as gifts to villagers who like it. Large milk is worth more by itself, turning it into cheese is more profitable. Regular milk is 100G and goes for 160G when turned into cheese. Large milk is worth 150G and becomes 240G as gold-quality cheese. This can be even higher with the artisan profession choice that raises the value of crafted goods.
Caring for Cows and Raising Heart Rating
Every single day, interact with all of your cows at least once to get some heart points and make them happy. When they're old enough, you'll use the milk pail as well and get even more heart points from the two actions. Know that milking them can sometimes fail if they walk outside range, so try to line it up well and pay attention to whether you got milk or not.
On rainy days or during winter, use the hopper inside the barn to get 4 hay each click. Lay it on the platform by the hopper so the animals have access to it. It will stay until it's eaten. This hay comes from your silo reserves, which are filled by chopping grass with the scythe tool. Don't bother opening the barn door on those days, and get your animals one heater per building from Marnie. Just place it anywhere inside the barn.
Cows prefer to eat outside, but will not get upset if it's a rainy day - leave them locked in the barn. If it's a nice day and after you've cared for them and milked them, they can be let out by clicking the barn door from the outside of the barn. It's much easier to milk/give them affection when they aren't wandering. The purpose of letting them out is to give them some sunshine and avoid a heart penalty, while also giving them free food (which doesn't deplete your hay reserves).
Given this knowledge, ensure there is some grass grown outside and, if necessary, spread around a few grass starter kits (bought from Pierre's for 100G) to get it spreading. They'll eat one tile each per day. If the grass is far from the barn, the cow may go hungry. Fencing your animals in an area with grass ensures they can find it, just make sure there's enough to go around and it's not shrinking each day. A larger field will let the grass spread more, and you can take it out with the scythe just before winter (along with all other grass on the lot). Every evening the cows will return to the barn by themselves. Close the barn door before you go to bed at night or you will get another penalty. Doing all these things every day will result in the heart level gradually rising. Failing to do so results in a minor penalty.
Checking their current heart level is doable after you've given them affection. It'll show you the age of the animal as well as give you the chance to turn off reproduction for that particular cow. If you don't have room, nor a big or deluxe barn, they won't reproduce. There isn't any reason to turn this off unless you plan to buy another barn animal, like goats. Reproduction seems to be random, but it is indeed a way to get free cattle. Cows can be sold for nearly 2,000G if they're up to 5 hearts. They're worth a little more for each heart you've gained.
Your cows will live on whether you feed them or starve them, but will be happier and more productive cows with just a little attention. When you get a deluxe barn, it will auto-feed the animals. You should still let them outside, the auto-feed will just ensure you don't forget to give them some food on a rainy day.