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RESEARCH ARTICLE
Contents Vol 44(8)

Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability

S. W. P. Cloete A B E , A. R. Gilmour C , J. J. Olivier D and J. B. van Wyk A
+ Author Affiliations
- Author Affiliations

A University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.

B Elsenburg Agricultural Centre, Private Bag X1, Elsenburg 7607, South Africa.

C NSW Agriculture, Orange Agricultural Institute, Forest Road, Orange, NSW 2800, Australia.

D ARC Animal Improvement Institute, Private Bag X5013, Stellenbosch 7599, South Africa.

E Author for correspondence; e-mail: schalkc@elsenburg.com

Australian Journal of Experimental Agriculture 44(8) 745-754 https://doi.org/10.1071/EA02225
Submitted: 29 November 2002  Accepted: 17 October 2003   Published: 17 September 2004

Abstract

Genetic and phenotypic trends and parameters were estimated for reproduction, fleece weight and liveweight in a South African Merino population, divergently selected from 1986, either for (H line) or against (L line) maternal multiple rearing ability. Annual reproduction, ewe greasy fleece weight and pre-joining liveweight data were recorded on 809 Merino ewes, from 1986 to 2002. Phenotypic trends indicated divergence in reproduction traits between the H and L lines. The direct additive variance ratio (h2 ± s.e.) for day of lambing was 0.08 ± 0.02. Estimates of h2 for reproduction traits were: 0.10 ± 0.02 for number of lambs born per ewe; 0.04 ± 0.02 for number of lambs weaned per ewe; and 0.04 ± 0.02 for weight of lamb weaned per ewe, corrected for the gender of the lamb. Corresponding h2 estimates for annual production were 0.57 ± 0.06 for greasy fleece weight and 0.48 ± 0.06 for ewe liveweight at joining. Service sire only exerted a significant (P<0.05) effect on day of lambing, but it accounted for merely 2% of the overall phenotypic variation. Ewe permanent environment variance ratios (c2ewe) for the reproduction traits were: 0.07 ± 0.03 for number of lambs born per ewe; 0.11 ± 0.03 for number of lambs weaned per ewe; and 0.11 ± 0.03 for total weight of lamb weaned per ewe. Corresponding c2ewe estimates for annual production traits were 0.14 ± 0.05 for greasy fleece weight and 0.27 ± 0.06 for ewe joining weight. Genetic and ewe permanent environmental correlations between measures of reproduction exceeded 0.7. Genetic correlations of reproduction traits with greasy fleece weight were low and variable in sign. Genetic correlations of reproduction traits with ewe joining weight were positive and particularly high for weight of lamb weaned. Permanent environmental correlations of reproduction traits with greasy fleece weight and joining weight were generally low to moderate. Genetic trends for the H and L lines (derived from averaged direct breeding values within birth years) were divergent (P<0.01) for all reproduction traits. Expressed as percentage of the overall least squares means of the respective traits, breeding values in the H line increased annually, with 1.3% for lambs born per ewe, 1.5% for lambs weaned per ewe and by 1.8% for weight of lamb weaned per ewe. Corresponding trends in the L line were, respectively, –0.6%, –1.0% and –1.2% per year. Substantial genetic progress in annual lamb output was attainable, despite relatively small h2 estimates. This response was achieved without unfavourable genetic changes in wool and liveweight.

Additional keywords: ewe productivity, repeated records.


Acknowledgments

We thank all those responsible for the maintenance and recording of the experimental animals (Miss E. du Toit at Tygerhoek, as well as Mr J. E. Fourie and Miss A. J. Scholtz at Elsenburg). The maintenance of the animals was partially enabled by a grant from the South African Wool Industry.


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