A study of the incisor teeth of beef cattle

Abstract

The width of the dental bridge across the four pairs of incisors was measured in Hereford, Angus, and Shorthorn cattle. Width across the incisors increased rapidly from birth until the age of 7 months. It then remained practically unchanged until the age of 20 months after which width increased rapidly during the eruption of the first pair of permanent incisors. Further rapid increases occurred during the eruption of other permanent incisors. At the age of 13 months when all animals in one group of cattle had reached mature width across their deciduous incisors, this measurement was significantly greater in steers than in heifers. At this same age width across the incisors was significantly greater in Hereford and Angus cattle than in Shorthorns, and significantly greater in Hereford than in Angus cattle. No significant relation was found between width across the incisors and body weight or body weight gain in cattle with normal deciduous incisors. Similarly, the reduction in width following the extraction of the outside lateral deciduous incisors had no significant effect on body weight gain. The heritability of width across the incisors was calculated as twice the standard correlation coefficient between measurements of cows and their qffspring, and was found to be high (2r = 0.656). It is concluded that width across the incisors is a character which was of no economic importance under the grazing conditions used. The mean age (days) at which one or both of the first pair of permanent incisors were fist observed in steers was significantly less in Shorthorns (681.2 ± S.E. 11.5) than in Hereford (724.9 ± S.E. 14.9), with Angus cattle (708.3 ± S.E. 10.7) not significantly different from either of the other breeds. The eruption process for the first permanent incisors has been described in six stages, and the periods to pass through three of these stages have been estimated. The medial time for the whole process was 99 days. No check in body weight gain was associated with the eruptioa process.