Studies in Ancient Hindu Polity (Based on the Arthashastra of Kautilya), Vol. I c8.s4.2

c8.s4.2

There were also certain rules for the cutting of tusks of elephants. Elephants born in countries irrigated by rivers had speedy growth of tusks, which were cut once in two-and-a-half years; and for mountain elephants, whose tusks grew more slowly, it was done once in five years. The rule was to leave at the root a length equal to twice the circumference of the tusk measured at its base.