Genetic correlations between early growth and wool production of crossbred ewes and their subsequent reproduction
R. A. Afolayan A , N. M. Fogarty A E , A. R. Gilmour A , V. M. Ingham B , G. M. Gaunt C and L. J. Cummins DA The Cooperative Research Centre for Sheep Industry Innovation, NSW Department of Primary Industries, Orange Agricultural Institute, Orange, NSW 2800, Australia.
B Agrisearch Services Pty Ltd, Orange, NSW 2800, Australia.
C Department of Primary Industries, Primary Industries Research, Rutherglen, Vic. 3685, Australia.
D Department of Primary Industries, Primary Industries Research, Hamilton, Vic. 3300, Australia.
E Corresponding author. Email: neal.fogarty@dpi.nsw.gov.au
Animal Production Science 49(1) 17-23 https://doi.org/10.1071/EA08088
Submitted: 7 March 2008 Accepted: 28 July 2008 Published: 5 January 2009
Abstract
Genetic correlations between reproductive and productivity traits of ewes and their early growth, wool production and worm resistance traits were estimated among 2460 crossbred ewes. The ewes were progeny of 74 maternal breed sires and mainly Merino dams. The ewes were born over 3 years and had three joinings with a total of 6824 ewe joining records. The reproductive and ewe productivity traits included: (i) fertility (ewes lambing per ewe joined); (ii) litter size (number of lambs born per ewe lambing); (iii) rearing ability or lamb survival (lambs weaned of lambs born for lambing ewes); (iv) number of lambs born (NLBj) per ewe joined; (v) number of lambs weaned (NLWj) per ewe joined; (vi) total litter weight weaned (TWWj) per ewe joined; and (vii) the component trait average lamb weaning weight in the litter (AWW). The growth traits included the weight of the ewe at birth (BWT), weaning (WWT) and postweaning (PWWT), as well as growth rate pre- and postweaning. The wool traits included greasy (GFW) and clean fleece weight (CFW), yield and average fibre diameter (FD) at their first adult shearing. Worm egg count (WEC) during their first year was also recorded. Bivariate mixed models analyses using ASReml procedures were used to estimate the genetic correlations. The genetic correlations between TWWj and growth traits were positive and moderate to high and ranged from 0.34 for BWT to 0.61 for PWWT. Those for the other composite reproductive traits were slightly lower and ranged from 0.27 to 0.54 for NLWj and from 0.07 to 0.46 for NLBj. The genetic correlations between the overall measures of reproduction (NLBj, NLWj and TWWj) and GFW, CFW and FD were negative and generally low to moderate (–0.21 to –0.52). The correlations were generally larger for NLBj than for NLWj and TWWj. The genetic correlations between the reproductive traits and WEC were close to zero, except between AWW and WEC (0.42). The phenotypic correlations between the reproductive traits and the growth, wool and WEC traits were all close to zero. The genetic correlations were generally favourable between ewe reproduction and growth, with early selection for traits such as WWT and PWWT likely to give some improvement in subsequent reproduction and ewe productivity. In contrast, there appears to be a slight antagonism between reproduction and wool production. This study provides estimates of genetic correlations from crossbred ewes that add to the limited knowledge of these parameters that will improve the accuracy of genetic evaluation and prediction of the outcomes from breeding programs for meat and wool objectives that include reproduction.
Additional keyword: heritability.
Acknowledgements
The MCPT was run by the NSW Department of Primary Industries, Department of Primary Industries Victoria and the South Australian Research and Development Institute with the generous financial support of Meat and Livestock Australia. Commonwealth funding through the Cooperative Research Centre for Sheep Industry Innovation and its predecessor is also gratefully acknowledged. We also gratefully acknowledge the many other scientists, technical and other support staff at the various sites who have contributed to and supported the work over several years as well as the ram breeders who entered sires.
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