Brief Post on Dairy Cows

Cows are large and can be hard to control, for these reasons most people starting a hobby farm don't have a cow (at least not as the first animal). If you have the space and startup cash, getting a cow can be a great idea that may earn some extra cash.
The ideal amount of space is one acre per cow and calf. However, you can keep a cow in a 10'x10' barn with a 10'x12' run and feed a bale of hay (50lbs) per day. Living on an acre means that the cow doesn't need to be given hay except for the winter months. The calf would also have to live there, so keeping them in an area of 10' x 30' will work until the calf is separated.
Calves take 2 years to grow to full size (butchering weight) but can be sold at 1 year old. The price of a year old calf (around here) is $1,000. A two year old be be around $2,000.
Cows only eat feed when they are being milked, usually 1lb per milking which totals 2lbs per day. They eat sweet feed or a full nutrition feed for lactating cows.
Cows can be milked for a year, but you want the cow pregnant to be milked for the next year. One option is to milk the cow for 10 months and let her rest for the two months before she gives birth.  Another option is a longer rest period, only milk for 8 months instead of 10. A cow will give an average of 5 gallons of milk per day. She also needs to have alfalfa hay to help with milk production.
With 5 gallons of milk a day, you will have to sell the extra or give it away. 

Here are some of the numbers:

• Hay (no/little pasture)- 50lbs/day or 18,000lbs/year
• Feed (10mths of milking)- 2lbs/day or 600lbs/year
• Milk (10mths of milking)- 1000-1500 gal/year , an average family would go through 150-200 gallons/year.

A cow can cost $1,000/year.

To make money back:

• Sell the calf for $1,000, that covers the money you spent.
• Sell the extra milk (for $2-$4/gal) or make and sell cheese (Cheese costs $2/lb for you to make and you can sell it for $4/lb or more). This is extra money that you've made. 

Another option for the calf (male and castrated) is to raise it to slaughter weight and have it butchered. I must warn you that paying a butcher is costly! However, that would be a year's supply of beef.
Most families get a second cow or have goats for when their main cow is out of milking season. This guarantees a steady supply of milk through-out the year. 

Balancing Out Owning Cattle