I am writing below the main factors.
Availability of fodder at reasonable price. Main factor is availability of green fodder at reasonable price.
Availability of medical aid in time.
You need to learn how to cure an animal for common medical problems.
Particularly Mestities, Simple wounds, Insects , Timely De worming, Pregnancy care , Fever, Milk fever. etc.
- Timely insemination and learn to know " When cow is in heat" .
Do not miss even a single heat otherwise dairy will convert into loss.
- Save calves.
It is a challenging job to keep calves alive in starting.
So you need to take care particularly for initial three months.
De worming is must after one month of birth.
- Mineral Supplements.
Feed any balanced mineral supplement daily to alll the cows.
As far as profitability of dairy is concerned. If you spend time on dairy and take care of few factors it is really a good profitable business.
My sincere advice is to start with just 5 milking cows. and add two to three cows per month. based on the requirement of milk.
One more thing like to share if you purchase a milking cow from market with good yield do not expect that this cow will produce same milk on your farm also.
It is better to purchase pregnant cows/hifers so cow can adjust in your farm before calving and will produce upto max yield.
In nut shell main factors for dairy cows are.
Feed , comfort, wataer , medical aid. and above all your love and care for animal.