Management of a sheep flock is best learned by actual practice. Because dozens of years are required to evaluate selection and management strategies, an excellent alternative is to simulate the experience on a computer.
Simulation of selection
The simulated animals show many of the important characteristics of sheep. A 10-year simulation can be done in a few hours. Every animal has a genetic value for each trait, such as weight and reproductive ability. This value is determined by the contributions of genes from the individual's sire and dam, plus a random genetic component due to Mendelian segregation and recombination. Crossbred animals also exhibit heterosis. In addition, a random environmental component is added to the genotype to obtain the phenotype.
Economics of selection
Selection is only beneficial if improvement can be observed in biological and economic efficiency of the sheep flock. SimSheep allows the user to describe the major economic components of the farm including such things as types and sizes of pastures, investment in equipment, and cost of labor. Yearly income statements can be compared to determine the effect of selection on profitability.
Procedures for running SheepSim
1. Assume that you have inherited a former dairy farm that includes 50 to 200 acres of hay and pasture land. You decide to set up a sheep farm on this land:
a. Choose View -> Farm options and set up the number of acres on the farm to total 50 to 200 acres by choosing acres for each type of forage species on the farm. Fewer acres will mean your flock will be smaller and make it easier to find and keep track of "superior" animals.
b. Be sure to include enough equipment and labor to make hay from most of the farm the first few years, because SheepSim will sell any forage as hay that is not used by the sheep.
c. Set up other economic factors, such as labor, to match the size and activity of the farm.
d. As the numbers of sheep grow, the economic inputs to the farm, such as labor or equipment, may need to be changed.
2. Start with 25 Dorset ewes, 25 Finnsheep ewes, and 2 rams of each of those breeds (4 rams).
3. The first step will be to create as many Finn ´ Dorset ewes as the farm can support:
a. Do this by breeding most of your Dorset ewes to Finn rams and vice versa.
b. Breed some purebred Dorsets to create replacements for the Dorset flock and some purebred Finnsheep to create replacements for the Finnsheep flock.
c. As the flock expands, sell most of the crossbred rams as lambs but keep all the white-faced (Dorset, Finnsheep, F1, F2, F3) ewes.
d. Keep some F1 rams to breed to the crossbred ewes.
e. When your farm is fully populated with sheep (you don’t have much hay to sell based on the Report), start using Suffolk sires on most of the crossbred ewes to increase production. Continue to breed about 10% of the Finn ´ Dorset ewes to Finn ´ Dorset rams to create replacements.
f. Continue the project over the semester until you have run the sheep farm for 10 years.
4. After the Reports menu becomes available at the end of the first year, choose one of the five periods of the year to print the Report and also save the report to a text file each simulated year.
SimSheep Report
This report contributes 15% to your grade. It is to be turned in at class time as indicated on the course calendar. Do not delay doing the simulation and writing the report as time will go by at a record pace this semester. Below is a suggested outline for the report. Feel free to alter the outline as long as the main points are covered.
Remember what you learned in your introductory courses about writing. If you don’t have a copy, purchase (Strunk and White, 1979) and pay attention to rule 17.
I. Introduction.
A. Description of farm.
1. Include the report for year 10, only, of the simulation.
2. Place the farm in a geographic location, describing the pastures, equipment, buildings and marketing strategies for your lambs.
3. Selection objectives. Describe which traits you used as the basis for selection and explain why you decided to base selection on those traits.
4. Economic objectives. Explain whether you need this farm to make a profit and, if so, what the most important measure of profitability is for you. If it is not important to you that the farm makes a profit, please indicate why. (Note: Your grade will be completely independent of how well your farm does, economically.)
B. Selection.
1. Criteria used for selection. How and when did you measure traits that you used for selection?
2. Average culling rate. You might have been able to cull some of the poorer producing ewes. For example, you could have checked for ewes that didn’t lamb in the last year and culled them. About what percentage of ewes did you cull and why?
3. Outstanding good or poor individuals. Report a few outstanding ewes, or rams that sired ewes that were outstanding or lambs that grew fast; describe them by number and indicate what made them outstanding
4. Losses. Indicate the percentage of lambs that died prior to weaning each year. Lamb losses can be calculated from the yearly economic report as follows: (lambs born – lambs weaned)*100/lambs born.
II. Biological progress.
A. Prepare the following figures (see note on preparation of figures in Appendix 1 of this document):
1. Lambs weaned per ewe lambing on the Y-axis against year on the X-axis.
2. Total weight of lambs sold per year on the Y-axis against year on the X-axis. Total weight of lambs sold per year must be calculated adding the weight for each category of ram lambs and ewe lambs sold. The weight for each category of lambs sold must be calculated by multiplying the number of lambs in each category by the average weight of lambs in each category.
B. Discuss the trends in each figure.
III. Economic progress.
A. Prepare the following figure:
1. Net cash income or net farm income (y-axis) against year (x-axis) or ROLCM or ROLM (y-axis) against year (x-axis).
B. Briefly, describe the trend in the figure.
C. Describe what factors most affected profitability of your farm.
Grading of report
Please submit your report stapled in the upper left-hand corner. Do not submit your report in any kind of binder. Each section of the report (I to III) will be graded separately for 1) clarity of presentation of data and 2) logic, clearness and conciseness of discussion.
Approximate percentage distribution of points will be:
Section |
Points |
I |
20 |
II |
40 |
III |
40 |
Reference List
Strunk, W. and E. B. White. 1979. The Elements of Style. 3rd ed. Allyn and Bacon, Boston.
Appendix 1. Construction of figures.
Figures may be constructed using pencil and paper or any computer program. They should be simple scatter plots with no background and as uncluttered as possible. An example using an Excel spreadsheet is given below. Note that the figure legend appears below the figure. The legend briefly describes what is in the figure. For an income figure, which can contain negative values, be sure that the X-axis crosses the Y-axis at the bottom of the Y-axis and not in the middle of the Y-axis.
Download Excel file used to create this figure.
Figure 1. Relationship between lambs weaned per ewe lambing and year.
