Litter size at lambing influences genetic evaluation of maternal rearing ability
Kim L. Bunter A D , Andrew A. Swan A , Daniel J. Brown A , Forbes D. Brien B and Jennifer Smith C
+ Author Affiliations
- Author Affiliations
A Animal Genetics and Breeding Unit (AGBU)*, University of New England, Armidale, NSW 2351, Australia.
B School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, SA 5371, Australia.
C CSIRO Agriculture and Food, Armidale, NSW 2350, Australia.
D Corresponding author. Email: kbunter2@une.edu.au
Animal Production Science 58(5) 791-800 https://doi.org/10.1071/AN16422
Submitted: 1 July 2016 Accepted: 7 November 2016 Published: 27 April 2017
Abstract
The genetic parameters for maternal rearing-ability of ewes were investigated by ignoring or defining the rearing ability trait separately by litter-size class (singles versus multiples) using multi-generational data from three, fully pedigreed Merino flocks differing in prolificacy, production level and environment. Genetic correlations (ra) between litter size (LSIZE) and the percentage of lambs surviving (PLSURV) were more negative with an increasing mean flock litter size (ra: –0.21 ± 0.17 to –0.73 ± 0.08), while the corresponding range in phenotypic correlations (rp) was substantially lower (rp: –0.15 ± 0.01 to –0.33 ± 0.01). Rearing-ability traits defined separately by litter-size class were highly correlated (ra: 0.49 ± 0.19 to 0.64 ± 0.38), but not genetically identical traits in the most prolific flock. Defining rearing-ability traits separately by litter-size class reduced the antagonistic genetic correlations between LSIZE and PLSURV to between –0.39 ± 0.14 and 0.14 ± 0.28, through accommodating the change in mean and variance of PLSURV with LSIZE. Similarly, linear transformation (TSURV) of PLSURV within each litter size to a common mean and variance reduced the antagonistic trend in genetic correlations between LSIZE and TSURV to range between –0.05 ± 0.17 and –0.43 ± 0.13. Since genetic correlations are low to moderate between TSURV and LSIZE, it is possible to select for improvements in both the number of lambs born and lamb survival simultaneously. Defining rearing-ability traits separately by litter-size class and the role of transformation will be investigated further for improving the accuracy of genetic evaluation for rearing ability across a range of flocks, breeds and environmental conditions using more extensive industry data.
Additional keywords: correlation, heritability, lamb mortality, lamb survival, reproduction.
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