In addition to just your Cattle Yield you need to look at HOW you will run your Dairy Farm.
Things to consider.
1.) Cattle Disease - Access to a good Veterinary Doctor. - If none is available, do you have access or are you willing to educate yourself about bovine diseases?
2.) Farm Labor - Access to cheap as well as efficient laborers to take care and milk your cattle. If your labor quits work for even a SINGLE day, are you willing to feed as well as milk your cows? Are you willing to clean the cow dung?
3.) Price - Access to buyers and good price for your milk. Is the buyer of your milk trustworthy. Will he pay you at the end of the month? How far do you need to travel to deliver your milk?
4.) Size - You will need to look at the size of your herd. You will not always have cows which will be yielding milk. You will need to feed the cows and take care of cows which are not giving milk currently. How do plan to increase the size of your herd.
5.) Feed and Water - You will need to decide HOW you are going to feed your animals - stall fed or open grazing. Access to plenty of water.
6.) Ability to take Losses - Ultimately, this is a business. Do you have what it takes to be an entreprenuer? Can you withstand losses if the milk is not sold for a few days (for whatever reasons) or you lose your labor (say they are sick or just quit)?
Dairy Farming is not EASY. It will require your total dedication 24/7. It is a 24 hour operation. If you are willing to commit yourself to such an endeavor and put in what is required, the returns are good! Depending on your input costs you can make a profit anywhere between 25-35%.
Just be careful of what you are getting into!
Readers and successful dairy farmers - can you also provide your input as to what makes your farm a success and if the profit projections are as I detailed. Other suggestions are welcome.