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Estimation of heritabilities and correlations between repeated faecal egg count measurements in lambs facing natural nematode parasite challenge, using a random regression model

Published online by Cambridge University Press:  26 April 2007

D. VAGENAS ,
I. M. S. WHITE ,
M. J. STEAR  and
S. C. BISHOP
D. VAGENAS
Affiliation:
Roslin Institute (Edinburgh), Midlothian EH25 9PS, UK
I. M. S. WHITE
Affiliation:
Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, UK
M. J. STEAR
Affiliation:
Department of Veterinary Clinical Studies, Glasgow University Veterinary School, Bearsden Road, Glasgow G61 1QH, Scotland, UK
S. C. BISHOP*
Affiliation:
Roslin Institute (Edinburgh), Midlothian EH25 9PS, UK
*
*To whom all correspondence should be addressed. Email: [email protected]
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Summary

The development of the genetic control of nematode resistance in growing lambs is of biological interest, as well as being important in terms of designing practical strategies to breed for increased nematode resistance. The current paper demonstrates the use of random regression techniques for quantifying the development of the heritability of faecal egg count (Fec), the indicator of nematode resistance, in growing lambs and predicted inter-age genetic and phenotypic correlations for Fec. Fec data from 732 lambs, collected at 4-week intervals from c. 8–24 weeks of age, were analysed using random regression techniques. Random effects fitted in the model included genetic, individual animal environmental, litter and residual random effects. Output (co)variance components were interpolated to weekly time points. Individual variance components showed complex patterns of change over time; however, the estimated heritability increased smoothly with age, from 0·10 to 0·38, and showed more stable time trends than were obtained from univariate analyses of Fec at individual time points. Inter-age correlations decreased as the time interval between measurements increased. Genetic correlations were always positive, with 0·6 of all possible inter-age correlations being greater than 0·80. Phenotypic correlations were lower, and decreased more quickly as the time interval between measurements increased. The results presented confirm biological understanding of the development of immunity to nematode infections in growing lambs. Additionally, they provide a tool to determine optimal sampling ages when assessing lambs' relative resistance to nematode infections.

Type
Animals
Information
The Journal of Agricultural Science , Volume 145 , Issue 5 , October 2007 , pp. 501 - 508
Copyright
Copyright © Cambridge University Press 2007

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