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Informed decisions at ram selection are the key to improving sheep genetics
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Draw on the large pool of genetic differences among rams to improve your flock |
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Key decisions, critical actions and benchmarks
Large genetic differences exist among the rams available for selection each year that can be used to improve your sheep. These differences provide the opportunity to increase productivity. The following examples show what can be achieved in wool and meat production.
You can gain from using genetics to:
Lower fibre diameter and increase fleece weight at the same time
Figure 9.1 illustrates 24 years of hogget fibre diameter and fleece weight records from a commercial flock. Rams were sourced from the same stud during that time. The result has been a reduction in fibre diameter by approximately 4 microns, and a simultaneous increase in fleece weight of 1kg per head. Most of the gains were made after 1992, when the selection emphasis in both the flock and its ram source moved from within-flock performance measurements to across-flock breeding values.
Increase growth rate and reduce sale age
Table 9.2 illustrates the performance of progeny from two sire teams (one selected for high growth and the other for low growth) joined to similar flocks of ewes. At 16 weeks of age, the lambs from the high growth sire team had 46.6% of lambs reaching target sale weight (at least 43 kg). The low growth sire team had only 11.6% of lambs reaching sale weight.
In this example, lambs sired by the high-growth sire team grew at 50g/head/day more than lambs by the low-growth sire team. The higher growth rate allows lambs to be sold earlier, or at higher weights
Using genetics in the breeding program
The opportunity to genetically change characteristics in your flock is determined by a combination of how heritable (genetically controlled) the trait is, how much genetic variation exists and how well you can identify the genetic differences in the sheep you select.
Table 9.3 illustrates the opportunity to make genetic change in several key traits relative to a highly heritable trait such as fleece weight.
Source: R.Gill, Trundle
Table 9.2: The impact of growth rate on age of turn-off
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Sire Group
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Av. post weaning wt. breeding value
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43 kg+ at 16 weeks of age
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High growth
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8.9
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46.6%
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Low growth
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1.6
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11.6%
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Source: Sheep Cooperative Research Centre – commercial flock, 2000 1st cross ewes
While fibre diameter has a higher heritability than clean fleece weight (55% vs 39%) there is more opportunity to make genetic change in clean fleece weight because it has more than double the variation within most flocks. In the same way, the variation in lambs born per ewe joined enables much more progress than the low heritability of 5% would suggest is possible.
The Merino Bloodline Package, funded by AWI in conjunction with the NSW Department of Primary Industries, helps sheep producers to compare Merino sheep bloodlines based on the results from wether trials and on-farm comparisons run across Australia over the past 10 years.
The package highlights relative performance in relation to wool production, wool quality and profitability, and allows sheep producers to easily compare the different bloodlines’ strengths and weaknesses.
You can use this tool to help identify the best ram source for your breeding objective. The analysis takes out all environmental factors between trials and years, leaving only the genetic variation between the bloodlines.
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Trait
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Heritability
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Variation (%)
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Relative response1
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Clean fleece weight
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42%
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16.3
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100
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Fibre diameter
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68%
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7.5
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75
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Hogget weight
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38%
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11.8
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66
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Lambs born per ewe joined
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5%
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63.2
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50
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1 The genetic change achievable compared to change that can be achieved in clean fleece weight.
Source: Fogarty et al, Sheep CRC
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Rams purchased
