How to determine the age of a cow

The age of a cow is determined by examination of the teeth and less perfectly by the horns. The temporary teeth are in part erupted at birth and all the incisors are erupted within twenty days.
The first, second and third pairs of temporary molars are erupted in thirty days. The teeth have grown large enough to touch each other by the sixth month. They gradually wear and fall in eighteen months. The fourth permanent molars are through at around the fourth month. The fifth at the fifteenth month and the sixth at two years. The temporary teeth begin to fall at twenty-one months and are entirely replaced by the thirty-ninth to the forty-fifth month.