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Journal of Animal Science Abstract - Animal Genetics

Merino ewes can be bred for body weight change to be more tolerant to uncertain feed supply1


This article in JAS

  1. Vol. 91 No. 6, p. 2555-2565
    Received: June 08, 2012
    Accepted: Mar 07, 2013
    Published: November 25, 2014

    2 Corresponding author(s):

  1. G. Rose 2,
  2. A. Kause*33,
  3. H. A. Mulder*,
  4. J. H. J. van der Werf†‡,
  5. A. N. Thompson†§#,
  6. M. B. Ferguson†§# and
  7. J. A. M van Arendonk*
  1. Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, 6700 AH, Wageningen, The Netherlands
    CRC for Sheep Industry Innovation, University of New England, Armidale, NSW, 2351, Australia
    School of Environmental and Rural Science, University of New England, Armidale, NSW, 2351, Australia
    Department of Agriculture and Food Western Australia, 3 Baron-Hay Court, South Perth, WA, 6151, Australia
    School of Veterinary and Biomedical Sciences, Murdoch University, 90 South Street, Murdoch, WA, 6150, Australia


Sheep in Australia experience periods with different feed supply causing them to gain and lose BW during the year. It is more efficient if ewes lose less BW during periods of poor nutrition and gain more BW during periods of good nutrition. We investigated whether BW loss during periods of poor nutrition and BW gain during periods of good nutrition are genetically different traits. We used BW measurements from 2,336 adult Merino ewes managed over 5 yr in a Mediterranean climate in Katanning, Australia. Body weight loss is the difference between 2 BW measured 42 d apart during mating, a period of poor nutrition. Body weight gain is the difference between 2 BW measured 131 d apart during a period of good nutrition between prelambing and weaning. We estimated variance compnents of BW change using 3 methods: 1) as a trait calculated by subtracting the first BW from the second, 2) multivariate analysis of BW traits, and 3) random regression analysis of BW. The h2 and genetic correlations (rg) estimated using the multivariate analysis of BW and the BW change trait were very similar whereas the random regression analysis estimated lower heritabilities and more extreme negative genetic correlations between BW loss and gain. The multivariate model fitted the data better than random regression based on Akaike and Bayesian information criterion so we considered the results of the multivariate model to be more reliable. The heritability of BW loss (h2 = 0.05–0.16) was smaller than that of BW gain (h2 = 0.14–0.37). Body weight loss and gain can be bred for independently at 2 and 4 yr of age (rg = 0.03 and –0.04) whereas at 3 yr of age ewes that genetically lost more BW gained more BW (rg = –0.41). Body weight loss is genetically not the same trait at different ages (rg range 0.13–0.39). Body weight gain at age 3 yr is genetically the same trait at age 4 yr (rg = 0.99) but is different between age 2 yr and the older ages (rg = 0.53 and 0.51). These results suggest that as the ewes reach their mature BW, BW gain at different ages becomes the same trait. This does not apply to BW loss. We conclude that BW change could be included in breeding programs to breed adult Merino ewes that are more tolerant to variation in feed supply.

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