It is probably real.

I have not found anything about this particular one, although there is many hits on Google search for 5 legged cows.

In the Indian culture it is viewed as a big luck. If, for example a pregnant woman touches the 5th leg she "indefinitely" will give birth to a boy.

Here are some news about this:
In 2013 a man had charged 30 woman for this privilege he made $5 on this business:) and every woman give birth to boys. [here]

In February 2017 another man was lucky to receive an offer of around $3100 for his two-day-old 5 legged calf, but he rejected the offer. He later dedicated the cow to his dad. [here]

It's a rare mutation anyway, the chances are about 1:5,000,000.
But in India the cow is a sacred animal and there is somewhere around 190 million cows, 5 legged cows can born fairly easily:)