Age of eruption of the first permanent incisors varies between Merino genotypes and is related to liveweight

The eruption of the first permanent incisors in sheep determines the classification of lamb and hogget and im-pacts the sale value of animals in Australia. This study tested the hypothesis that the age of incisor eruption would differ between progeny from different Merino sires and would occur earlier for progeny that were heavier at 12 months of age. The study utilised wether progeny at a site in Western Australia from 29 sires born in 2016 (n = 347) or 2017 (n = 553), and ewe and wether (castrated male) progeny at a second site in New South Wales from 29 sires born in 2017 (n = 713 ewes and 343 wethers) or 2018 (n = 638 ewes and 457 wethers). Classing of incisor eruption commenced at 10-11 months of age and was recorded monthly until 19 or 20 months of age at the two sites. The average age of incisor eruption varied by up to 2.5 months between sire groups (P < 0.001) and incisor eruption was completed for all progeny within a sire group over three months for some sires but over 6 months for other sires. Incisor eruption occurred earlier for animals that were heavier at 12 months of age (P < 0.001). The period when animals gained weight up to 12 months also influenced incisor eruption, as differences in liveweight at weaning had twice the effect on age of incisor eruption compared with differences in liveweight gain post-weaning at both sites. Estimated stage of maturity at 12 months of age had minimal effects on sub-sequent age of incisor eruption, and regardless, the large variation in age of incisor eruption between sires were not accounted for by liveweight or stage of maturity at 12 months. In addition to selecting Merino sires that produce progeny that can be sold as lamb at an older age, farmers may also benefit from understanding the pattern of the first permanent incisors eruption specific to their genotype and monitoring liveweights and liveweight change to optimise the time and value of animals at sale.

Automated summary

The eruption of the first permanent incisors in sheep is crucial in determining the classification of lamb and hogget in Australia, impacting the sale value of animals. This study found that the age of incisor eruption varied among progeny from different Merino sires and occurred earlier for progeny with heavier weights at 12 months of age. Furthermore, differences in weight gain up to 12 months also influenced the age of incisor eruption, with variations in liveweight having a significant effect on the timing of eruption. The study also concluded that the large variation in incisor eruption age between sires was not solely explained by liveweight or stage of maturity at 12 months.