It depends on multiple factors such as purchase price of the animal, milk yield, milk sales price, feeding costs, worker charges, medicines, etc. The calculation can be for a lactation and cannot be directly derived for a single day or a month because a Murrah Buffalo is a living being and not a milk yielding machine!. So let’s calculate for a lactation and then derive your profit or loss for a month.
Say if you purchased a second lactation Murrah Buffalo which yields 12 liters per day for Rs 80,000 with an expected yield of 2400 liters per lactation . Assume the lactation period (the period when the buffalo gives milk) as 270 days and a dry period (the period when the buffalo is not giving milk) of 120 days. Lets say your selling price of milk is Rs 45 liter so total selling price per lactation is 2400 x 45 = Rs 108,000.
Now lets calculate the expenses for 390 days ( 270 lactation days + 120 dry days)
Green fodder = 25 kgs x .5 paise x 390 = Rs 4,625
Dry Fodder = 10 kgs x 1 Rs x 390 = Rs 3,900
Feed concentrate/dhana (avg) = 4 kgs x Rs 15 x 390= Rs 23,400
Labour charges (1 worker for 10 buffaloes @Rs 9,000/month) = Rs 30 x 390 = Rs 11,700
Interest for Rs 80,000 investment (18% rate) = Rs 40 x 390 = Rs 15,600
Medicines, mineral mixture, etc = Rs 10 x 390 = Rs 3,900
Miscellaneous = Rs 5,875
So total expenses is Rs 69,000
So Profit is Rs 108,000 – Rs 69 ,000 = Rs 39,000 per cycle (13 months).
So for profit for 1 month is Rs 3,000.
The value of calves and sale of dung is not included in this calculation. If you take good care of the calves, it will cover for the replacement cost of the buffalo at the end of it’s productive phase.
You can frankly optimize many variables and increase your profit. For instance, if you directly sell the milk you can get a better price for milk. If you don’t borrow money to buy buffalo that also will increase your cash flow. If you do all the work then you can eliminate worker salary.
On the other side you can also make losses, for instance the buffalo can have a shorter lactation, buffalo could die, the calf could die or the buffalo might take longer to conceive for next cycle or the buffalo might have reproductive issues and not conceive at all. So all these factors can lead to losses. In some places, you milk sale price might not even be Rs 45 but there are lot of places where the demand for buffalo milk is so good that the price is as high Rs 70.
Conclusion is that Murrah buffalo is not a machine and so your profit or loss depends on how well you take care of the buffalo, keep the input costs low and sell milk for a higher price. And also few factors such as disease attacks are beyond your control.