The age at which the four pairs of permanent incisors emerged, and the interval between first emergence and the attainment of full size, was recorded from observations taken every 2 weeks on 332 female cattle of a herd comprising the Ayrshire, Friesian and Jersey breeds, and the reciprocal crosses among them.

The 1st pair of incisors emerged at a mean age of 101 weeks of age and later pairs at approximately 30-week intervals, with the s.d. increasing proportionately from 7 to 14 weeks. Full size of the incisors was attained, on average, 4·0, 2·4, 3·0 and 5·6 weeks after the initial observations on incisor pairs 1 to 4 respectively.

Breed (or cross) and season of birth significantly affected the age at emergence of the 1st and 2nd pairs of teeth, and breed also affected the age for the 4th pair. Relative to the Friesian breed, an Ayrshire parent delayed emergence of both 1st and 2nd incisor pairs by approximately 4 weeks, and a Jersey parent delayed emergence of all four pairs. The maternal effect was opposite in sign to the effect of breed substitution; in particular, a Jersey dam caused a reduction in the age at emergence. There was no evidence of heterosis in the crosses. On average, each pair of incisors erupted approximately 4 weeks earlier for cows born between October and December than for those born in the period April to June.

Age at calving, lactation length, milk yield, body weights and the ratio of 18-month body weight to that at 42 months (as an estimate of proportion of maturity) were not significantly correlated with the dental traits. Correlations between age at emergence of adjacent incisor pairs were approximately 0·7, a value higher than that between pairs separated by longer time intervals.