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Beyond the Bale : September 2012
seLLing more wooL September 2012 Beyond the Bale 38 on-farm fertile ewes so the poor performers can be culled earlier, regardless of age, and high- performing sheep retained longer. This lifts the reproductive rate across the whole flock, by proportionately reducing the number of maiden ewes and retaining the high reproductive performance of the older ewes. This practice would also address the relatively poor reproductive rate of Australia’s national flock. The average marking percentage of the Australian flock is just 77 per cent. Keeping productive older ewes in the flock for an additional one or two years is a vital strategy to increase reproductive efficiency. Improving the reproductive efficiency of Merino ewes in particular is crucial to the future of the Australian sheep industry, as Merinos now make up 85 per cent of all ewes. on-farm researCh To try and identify the effect of ewe age on fertility and some of the management issues which may arise if ewes are retained to an older age, a two-year study has been conducted on two commercial sheep new research has shown, among other findings, some older ewes can outperform their younger rivals well beyond the age at which they are traditionally culled. The work is out of the NSW Department of Primary Industries (NSW DPI), supported by AWI and the Cooperative Research Centre for Sheep Industry Innovation (Sheep CRC). The key is identifying these highly properties in the Central West Plains and South West Slopes regions of NSW. On each property three Merino ewe age groups (3–5 years) were monitored over the annual reproductive cycle, with measurements continued into the second year when six-year-old ewes were retained in the breeding flock. Liveweights and condition scores were regularly measured, pregnancy rates determined using commercial scanners and lamb survival and dam/offspring pairings recorded using Pedigree Matchmaker. The research took into account environmental effects on reproduction, and the influence of fat scores. Although fat scores tended to be lower in older ewes, the number of lambs conceived by each ewe increased with age, as shown in Table 1 opposite. While the oldest ewes in this study to date are six years old, other research on the reproductive performance, mortality rates and the productivity of Merino ewes studied sheep to eight years and found age had little influence on reproductive performance. In general, the overall ewe reproduction rate is better than for maidens until at least seven years of age. Environmental factors have a greater influence on net flock reproduction than age, and nutrition is especially influential in young ewes in determining their future reproductive performance. performanCe inDiCaTors While reproductive performance is a key component of flock productivity, it is important to look at other traits such as fleece weight and quality when considering whether to retain older ewes in a breeding flock. Most research, including the recent NSW DPI study, indicates again environmental factors have a significantly greater influence on fleece weight and wool quality than ewe age. For clean fleece weight, most of the research indicates a decline of up to 20 per cent at eight years of age compared to a peak at three or four years of age, although this was variable between flocks. In contrast, fibre diameter tends to increase with age to about six years and then declines, but again is variable between flocks. Both clean fleece weight and fibre diameter are more influenced by pregnancy status and stocking rate than ewe age. Ewe age also appears to have less impact on the performance of her lamb compared to factors such as whether it was a single or multiple birth and the sex of the lamb. fasT faCTs l research funded by AWI indicates that sheep producers could dramatically improve the fertility of their flock by identifying and retaining their most reproductive ewes for one or two extra joinings. l Older ewe reproduction rate is better than the reproduction rate for maiden ewes until the older ewe is at least seven years of age. l Environmental factors, such as nutrition, influence reproduction rates more than ewe age. Keeping productive older ewes in the flock for an additional one or two years is a vital strategy to increase reproductive efficiency. Keeping productive older ewes