Proc. Assoc. Advmt. Anim. Breed. Genet. 16: 223-226 THE ROLE OF SELECTED WETHER FLOCKS IN MERINO WOOL ENTERPRISES
J.S. Richards and K.D. Atkins
Australian Sheep Industry Co-operative Research Centre and
NSW Department of Primary Industries, Orange Agricultural Institute, Forest Rd. Orange 2800 SUMMARY
Adult wethers as wool growers are one source of income within a Merino flock. Wether numbers can be quickly and easily modified without losing any genetic progress that has been made from the selection program within the breeding flock. The economic value of different proportions of wethers within flocks of varying fibre diameter was considered at different meat values of surplus sheep.
Without effective selection among wethers, there is little economic incentive to keep an adult wether flock. But selection of wethers on fibre diameter in fine and medium wool flocks can lead to substantial economic benefits. The optimal number of adult wethers reduces as the meat value of surplus animals increases.
Keywords: Merino, wether, selection INTRODUCTION
Many Merino producers keep some proportion of their flock as wethers for wool production as a means of managing risk. Wethers allow short-term decision-making without risking the genetic improvement made by the breeding program of the whole flock. The number of wethers can be adjusted according to current conditions, with no genetic loss occurring when destocking or increasing their number in seasons of excess feed. This paper describes a study to determine whether wethers are a beneficial addition and to identify the optimal proportion of wethers in a Merino flock.
The study also outlines the effect selection of the wethers has on the productivity of the flock.
The first concept is what proportion of wethers is optimal when no wether selection is used? Even if the wether itself is producing a profit, does it outweigh the benefit that could be achieved by running the equivalent number of breeding ewes? It is this level of balance that needs to be determined and will be affected by the potential meat value of surplus wethers. At what price does the immediate meat value of a wether outweigh the benefits of keeping adult wethers for their wool value?
The other concept is that of the impact of current generation selection. What difference is there between having an unselected wether flock compared to a selected wether flock? By using individual animal measurement we have the ability to exploit within-flock phenotypic variance and therefore have the ability to identify the top performers for selection and eliminate the poor performers in the flock. The economic benefit of doing this is examined in this study. Just by taking a single measurement of fibre diameter (FD) at first shearing, animals can be ranked and selected according to the number of animals to be retained and the rest can be culled. The selection process can involve a number of options, but for simplicity only FD selection was used for this study. By using selection for lower FD we can increase the quality of the product using the same inputs (finer micron Merino wethers from the same drop of animals).
223
Young Scientist Papers 3
MATERIALS AND METHODS
This study was based on a deterministic model developed by the authors that traces the flow of genes in a commercial Merino flock for fleece weight (FW), FD and body weight (BW) arising from various selection scenarios. The model uses base flock information and makes predictions using this information and phenotypic (and genetic) parameters about future levels of FW, FD and BW. These were then used to determine the dollar value of the wool and meat production from these animals.
Flock structures were set on the assumptions of 2000 breeding ewes in 5 age groups, reproduction rate of 80% and an annual mortality rate of 5%. The number of wethers included in the flock was varied from 0 up to 50% of breeding ewes, that is up to a 1000 adult wether flock. All ewe and wether progeny were retained until hogget age and then selections were made. Once the selection has been made that is the group the animal remains in for its life. Selection intensities were calculated for wethers from the animals available and the number required for replacement. Three of an infinite set of production scenarios were investigated, representing flocks with an adult FD of 18, 20 and 22µm.
The starting FW and FD of age/sex groups within these flocks were set according to generalised relationships developed by Coelli and Atkins (2000) (Table 1).
Table 1: Initial production values (FW=greasy fleece weight, FD= fibre diameter)
18µm flock 20µm flock 22µm flock
Hogget FW 3.9 5.0 5.9
Adult ewe FW 4.3 5.6 6.6
Adult wether FW 4.8 6.2 7.2
Hogget FD 16.7 18.6 20.5
Adult ewe FD 18.0 20.0 22.0
Adult wether FD 18.0 20.0 22.0
Genetic and phenotypic matrices were used in the calculation of the impact of selection. For simplicity, no ewe or sire selection was assumed so that there was zero genetic change in any trait over time. The only selection was that amongst wethers through FD only. The parameters assumed were phenotypic correlations between hogget and adult FW (0.6), hogget and adult FD (0.75) and between FW and FD (0.2). Coefficients of variation of 15% and 7% for FW and FD respectively were assumed.
The prices used to value wool production came from the last five selling seasons (1999-2004, Source:
AWEX Weekly Wool Market Report). Meat prices were set in $20 increments for a 45kg animal to determine the sensitivity of the results to meat value. These values are converted back to a dollar per kg basis and the actual meat value is determined by the body weight of the animal. The value of a breeding ewe contained the fleece value of the ewe and her hoggets at first shearing, the meat value of sale hogget ewes and wethers, the salvage value of cull ewes less the costs involved for management and selling (Coelli and Atkins 2000). Similarly, the value of an adult wether contained its fleece value, salvage value of cull wethers less costs. All results were expressed as enterprise gross margins (GM) per DSE using the expressions for DSE equivalent for ewes and wethers derived by Coelli and Atkins (2000).
224
Proc. Assoc. Advmt. Anim. Breed. Genet. 16: 223-226
RESULTS
Table 2 shows that with no selection there is no financial benefit of retaining any wethers in comparison to just running a breeding ewe flock. The GM per DSE decreases as the proportion of wethers increases. This is the case for all scenarios. This suggests that with no selection, the cost of running more wethers and fewer breeding ewes is not as beneficial as running more breeding ewes.
Table 2. Gross margins per DSE with no selection GM/DSE $/45kg
animal No
wethers 10%
wethers 20%
wethers 30%
wethers 40%
wethers 50%
wethers
20 31.27 31.03 30.81 30.61 30.43 30.26
40 36.80 36.19 35.63 35.13 34.67 34.25
60 42.32 41.34 40.45 39.64 38.91 28.24
18µm flock
80 47.85 46.50 45.26 44.16 43.16 42.22
20 20.12 19.97 19.82 19.70 19.58 19.47
40 25.70 25.17 24.69 24.26 23.87 23.50
60 31.27 30.37 29.55 28.82 28.15 27.53
20µm flock
80 36.84 35.57 34.42 33.38 32.43 31.56
20 16.29 16.26 16.24 16.22 16.20 16.18
40 21.91 21.51 21.14 20.82 20.52 20.24
60 27.52 26.76 26.05 25.42 24.85 24.31
22µm flock
80 33.14 32.00 30.96 30.02 29.17 28.38
Table 3 shows that there are benefits in using a selection process to allocate the wethers to be retained. The addition of selected wethers in place of the equivalent breeding ewes is more beneficial than a straight ewe flock in many scenarios. The micron ranges as well as the meat value determines the optimal wether proportion.
In a fine wool flock (18µm), there is benefit from having a high proportion of wethers (up to 50% of the size of the breeding ewe flock) when the meat value of hoggets is low. As the meat value increases, the proportion of wethers at the optimum decreases, although with all scenarios at 18µm there is benefit in retaining some wethers. In a broader micron flock (22µm) there is only some benefit of retaining wethers when meat value is low ($20/45kg animal). In a medium micron flock (20µm) the optimal proportion of wethers is heavily dependent on meat value, varying from 40% at
$20 meat value to close to zero at $80 meat value.
The benefits in wether fleece value of selecting on FD are clearly shown when comparing the value of unselected and selected animals (Table 4). The high fleece value per DSE of wethers at low proportions is due to the higher selection intensity; the fewer animals to be selected the finer the animals to be retained. But even at 50% wethers, the selected wethers make more money per DSE from their fleece than breeding ewes. However, the large difference in fleece value between ewes and wethers is reduced in total income because the income from a ewe includes progeny income, whereas for wethers, the fleece value is the main income source.
225
Young Scientist Papers 3
Table 3. Gross margins per DSE with FD selection in wethers GM/DSE $/45kg
animal No
wethers 10%
wethers 20%
wethers 30%
wethers 40%
wethers 50%
wethers
18µm 20 31.27 32.90 33.55 33.83 33.96 34.00
flock 40 36.80 38.06 38.39 38.37 38.23 38.01
60 42.32 43.23 43.23 42.91 42.49 42.02
80 47.85 48.39 48.06 47.44 46.76 46.03
20 20.12 21.06 21.35 21.44 21.45 21.41
40 25.70 26.27 26.24 26.02 25.76 25.47
60 31.27 31.48 31.12 30.60 30.06 29.52
20µm flock
80 36.84 36.70 36.00 35.18 34.37 33.57
22µm 20 16.29 16.62 16.68 16.67 16.65 16.62
flock 40 21.91 21.88 21.60 21.29 20.99 20.71
60 27.52 27.13 26.52 25.91 25.34 24.80
80 33.14 32.39 31.45 30.54 29.69 28.89
Table 4. Fleece values ($/DSE) of breeding ewes and selected wethers
18µm flock 20µm flock 22µm flock
Ewes 40.06 28.32 23.96
Unselected wethers 39.83 29.85 28.10
10% FD-selected wethers 77.05 51.86 35.51
20% FD-selected wethers 68.54 46.03 32.92
30% FD-selected wethers 63.33 42.70 31.57
40% FD-selected wethers 60.02 40.65 30.82
50% FD-selected wethers 57.66 39.22 30.33
DISCUSSION
From a purely economic perspective, there is no value in keeping unselected wethers as adult wool growers. The higher the proportion of wethers in the flock, the more money is foregone. But wethers can make a positive economic benefit to the flock simply by using FD to select the more valuable animals to be retained. In fine wool flocks, when meat value is low the higher the proportion of wethers the better. As the meat value increases, the value of having more wethers is reduced, but it is still beneficial to have at least 10% of the flock as wethers. The largest economic benefits from selection were achieved in fine- and medium-wool flocks. In broader wool flocks the benefit of retaining wethers on FD alone was of little value, although the possible use of FW and/or BW in addition to FD has yet to be examined. There may be other factors such as feed availability or the increased risks with breeding ewes in some situations throughout the year that may influence the size of the wether flock, but selected wethers will always be a better proposition than unselected.
REFERENCES
Coelli, K.A. and Atkins, K.D. (2000) Wool Technol. Sheep Breed. 48:277 226
