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579. A study of variation in twin cattle: IV. Emergence of permanent incisor teeth

Published online by Cambridge University Press:  01 June 2009

G. Wiener  and
H. P. Donald
G. Wiener
Affiliation:
Agricultural Research Council Animal Breeding Research Organization, Edinburgh
H. P. Donald
Affiliation:
Agricultural Research Council Animal Breeding Research Organization, Edinburgh
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Extract

1. Data are presented on variation in age at eruption of permanent incisor teeth in one-egg (MZ) and two-egg (DZ) twins and in pairs of half sisters (HZ). The 1st pair of incisors erupted when animals were on average 100 weeks old and the other three pairs came at roughly 26-week intervals thereafter. Variation in age at eruption increased from 1st to 4th incisors, but the coefficient of variation remained constant at about 8%. The mean interval between eruption and complete emergence was about 5 weeks for the first three pairs of teeth and nearly 10 weeks for the 4th pair.

2. Variation in age at eruption within MZ pairs was no greater than that between left and right sides of the same animal. DZ displayed greater within-pair variances than MZ twins, and HZ pairs greater than DZ.

3. Correlations of age at eruption of teeth with body weight and with gain in weight were negative but non-significant. Age at eruption of 1st and of 3rd teeth was positively correlated with age at 1st and 2nd calving, but eruption of 2nd and of 4th teeth was not.

4. For 2nd, 3rd and 4th incisors, the intra-pair variance of the HZ group was in excess of that expected. This can be interpreted to mean that the estimates of environmental and genetic variation derivable from MZ and DZ pairs are not adequate to account for all the variation within HZ pairs.

Type
Original Articles
Information
Journal of Dairy Research , Volume 22 , Issue 2 , June 1955 , pp. 127 - 137
Copyright
Copyright © Proprietors of Journal of Dairy Research 1955

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