Increasing the proportion of female lambs by feeding Merino ewes a diet high in omega-6 fatty acids around mating
E. H. Clayton A C D , M. A. Friend B C and J. F. Wilkins A C
+ Author Affiliations
- Author Affiliations
A NSW Department of Primary Industries, Wagga Wagga Agricultural Institute, Wagga Wagga, NSW 2650, Australia.
B School of Animal and Veterinary Sciences, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
C Graham Centre for Agricultural Innovation (NSW DPI and Charles Sturt University), Locked Bag 588, Wagga Wagga, NSW 2678, Australia.
D Corresponding author. Email: edward.clayton@dpi.nsw.gov.au
Animal Production Science 56(7) 1174-1184 https://doi.org/10.1071/AN14803
Submitted: 9 September 2014 Accepted: 7 January 2015 Published: 22 April 2015
Abstract
In previous experiments, the proportion of female lambs was higher when BL × Merino ewes were offered a diet high in omega-6 (n-6) than when offered one low in n-6 around joining. The aim of the current study was to determine whether the proportion of female lambs increases when Merino ewes are fed a diet high in n-6 and to further test the effect of time of feeding relative to mating. Ewes were fed a low n-6 (ryegrass silage) or high n-6 (oats and cottonseed meal) diet for ~40 days pre-mating or 40 days pre- and 17 days post-mating. Liveweight, fat score, plasma fatty acid status and lamb sex were determined. The concentration of plasma n-6 was higher (P < 0.001) and the time to oestrus shorter (P < 0.001) when ewes received the high n-6 compared with the low n-6 diet. The proportion of female lambs was higher when ewes were fed the high n-6 compared with the low n-6 diet either pre-mating only (71.3% vs 48.7%, P = 0.017) or both pre- and post-mating (69.6% vs 37.3%, P < 0.001). The sex ratio differed from an expected 50 : 50 when ewes were fed the high n-6 diet (P < 0.001), but not the low n-6 diet (P = 0.223). The effect of the high n-6 diet on the sex ratio of lambs in Merino ewes may act pre-conception, as the effect of the diet was not greater when ewes were fed both pre- and post-mating. Altering diet to increase female lamb proportions may be economically viable to producers of first-cross ewes.
Additional keywords: conception, mating, omega-3, plasma fatty acid, sex ratio, time of joining.
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