Use of second molar eruption in age estimation of cattle.

The intra-oral development of the second molar in cattle was examined using a system of molar codes based on degree of eruption. Observations on eight Friesian heifers seen more than once were compared with those from 320 cattle studied by the cross-sectional method. The average ages of the Friesians for a given degree of eruption tended to be higher than those in the larger survey. There were too few data to provide a statistical comparison but, by using the age range for each stage of second upper molar development, it was found that in absolute terms an animal showing no emergence of the tooth was younger than one exhibiting complete eruption of the rostral and caudal units. In addition, in most cases an animal at molar code 1 (rostral unit emerging, caudal unit not visible) was younger than one at molar code 8 (rostral and caudal units both fully up). Although the method of second molar development had limitations in age estimation it did provide an indication at a time before eruption of the first permanent incisor tooth pair and the age range at each stage of molar development tended to be lower than for the permanent rostral teeth.