Season and reproductive status rather than genetic factors influence change in ewe weight and fat over time. 2. Spline analysis of crossbred ewes
S. F. Walkom A B E , F. D. Brien A B C , M. L. Hebart B , N. M. Fogarty A D , S. Hatcher A D and W. S. Pitchford BA 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 South Australian Research and Development Institute, Roseworthy, SA 5371, Australia.
D New South Wales Department of Primary Industries, Orange Agricultural Institute Forest Road, Orange, NSW 2800, Australia.
E Corresponding author. Email: samuel.walkom@adelaide.edu.au
Animal Production Science 54(6) 814-820 https://doi.org/10.1071/AN13248
Submitted: 14 June 2013 Accepted: 2 December 2013 Published: 18 February 2014
Abstract
The success of slaughter lamb enterprises is heavily influenced by the ability of the breeding ewe to produce a lamb annually across variable environments. It has been shown that by maintaining heavier weight and condition across the annual production cycle producers can make significant improvements in maternal performance. This paper follows on from a previous analysis of crossbred ewes within the Maternal Central Progeny Test and examines the potential to select for reduced fluctuation in weight and fat across the production cycle. A cubic spline model was fitted to the weight and fat score data from the first three parities of 2688 first-cross ewes. The analysis partitioned the influence of environment, reproduction and genetic effects on the shape of the weight and fat score splines across three parities. Yearly and seasonal variation in feed supply and the demands of raising a lamb are the major influences on fluctuations in the weight and fat score of the breeding ewe. The genetic effects were constant across time with 98 and 92% of the genetic variation for weight and fat, respectively, associated with the spline’s intercept. In agreement with the findings of the first paper of the series it can be concluded that genetic lines do not re-rank for weight or fat score over time. The influence of sire breed on weight and fat score was constant across time with sire breeds fluctuating in parallel across time. As a result it is concluded that to avoid low fat reserves and the subsequent low fertility during the ‘tough’ periods, selection to improve ewe body condition could be made at any time and under any environmental conditions.
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