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RESEARCH ARTICLE

Season and reproductive status rather than genetic factors influence change in ewe weight and fat over time. 4. Genetic relationships of ewe weight and fat score with fleece, reproduction and milk traits

S. F. Walkom A B D , F. D. Brien A B , M. L. Hebart B , N. M. Fogarty A C , S. Hatcher A C and W. S. Pitchford B
+ Author Affiliations
- Author Affiliations

A Cooperative Research Centre for Sheep Industry Innovation, Armidale, NSW 2351, Australia.

B School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy Campus, SA 5371, Australia.

C New South Wales Department of Primary Industries, Orange Agricultural Institute Forest Road, NSW 2800, Australia.

D Corresponding author. Email: samuel.walkom@gmail.com

Animal Production Science 56(4) 708-715 https://doi.org/10.1071/AN15090
Submitted: 17 February 2015  Accepted: 15 July 2015   Published: 9 October 2015

Abstract

The profitability of a sheep enterprise is greatly influenced by the ability of the ewe to produce a lamb annually. This paper examines the between- and within-breed association between the liveweight and fat score of the adult ewe and key fleece, reproduction and milk production traits. The study analysed the performance of 2846 first-cross Merino and Corriedale ewes from the maternal central progeny test (MCPT) over their first three production cycles. Breed (9 sire breeds) and within-breed (91 sires) correlations were calculated from bivariate correlations of adult liveweight and fat score with fleece, reproduction and milk production traits. The mean liveweight and fatness of the breeds were low to moderately negatively correlated with greasy fleece weight (–0.55 and –0.25, respectively) and moderate to strongly positively correlated with fibre diameter (0.88 and 0.41, respectively). However, the within-breed correlations were generally low to negligible. The genetic relationships between ewe fat score and reproductive traits at the breed and within-breed level was generally low to negligible and, in some cases, negative under production conditions where the ewes were well managed and averaged a fat score of 3.5 pre-joining and became too fat across the production cycle. Strong breed correlations between ewe fat score and milk fat concentration (0.88) suggest that selection of fatter sire breeds will lead to increased fat in their progenies’ milk, which was associated with larger lambs. The potential advantages of selecting for more fat to improve the maternal performance of the ewe seem to be limited in enterprises where the production system can easily be adjusted to restrict the influence of temporary and long-term feed deficiencies, as was achieved within the MCPT research flocks.

Additional keywords: first-cross Merino, maternal efficiency, maternal productivity.


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