The highest percentage fat in the milk of

Jersey cows are renowned for producing milk with the highest percentage of fat among the given options.

Their milk is rich and creamy, making it ideal for dairy products like butter and cheese.

Haryana: Produces good milk yield but has lower fat content compared to Jersey.

Gir: Known for high milk yield and good quality milk, but their fat content is also lower than Jersey.

Holstein: Primarily known for high milk yield, but their milk has the lowest fat content among these breeds.

Thus, the correct choice is Option A: Jersey, as their milk has the highest fat content.