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Biometrical exercise 1
This material addresses aspects of the following syllabus outcome:
H4.1 applies appropriate experimental techniques, technologies, research by methods and data presentation and analysis in relation to agricultural problems and situations.
The work presented in the following section contributes towards achieving the following syllabus content areas:
- experimental analysis and research in plant/animal systems
- the role of a control, randomisation, replication and standardisation of conditions
- the collection and analysis of data
Source: NSW Board of Studies Agriculture Syllabus
In this biometrical exercise you will examine the results of a growth trial, measuring the liveweight gains of two groups of lambs up to 24 weeks. This trial was part of a series of trials examining the differences in carcases of lambs sired by different rams. These results are from one of the trials.
After you have read the aim, method and results of the growth trial, you should answer the questions.
Aim: To determine the difference in liveweight gain between two groups of lambs sired by different rams.
Method:
- All lambs were approximately the same age (within one week of each other).
- All lambs were from ewes with similar history, i.e. Border Leicester x Merino crosses of similar age with similar nutritional history.
- The ewes were randomly allocated into two groups which determined which ram they were mated to.
- The ewes were all provided with similar nutrition throughout their pregnancies.
- Prior to lambing all the ewes were put into one paddock (both groups) and all ewes and lambs were kept together until weaning. Once weaned, all weaners were kept together for the duration of the trial.
- The weaners were weighed and fat scored at 24 weeks old.
- Both groups of weaners were of mixed sexes, all ram lambs were castrated at marking time.
Results: The table below shows the liveweights of the lambs at 24 weeks old (kg).
| Lamb number | Sire breed one (kg) | Sire breed two (kg) |
|---|---|---|
| 1 | 54 | 60 |
| 2 | 41 | 53 |
| 3 | 42 | 49 |
| 4 | 51 | 62 |
| 5 | 50 | 60 |
| 6 | 43 | 52 |
| 7 | 54 | 46 |
| 8 | 36 | 57 |
| 9 | 58 | 53 |
| 10 | 46 | 51 |
| 11 | 43 | 57 |
| 12 | 44 | 66 |
| 13 | 48 | 68 |
| 14 | 50 | 38 |
| 15 | 47 | 37 |
| 16 | 41 | 63 |
| 17 | 58 | 59 |
| 18 | 58 | 43 |
| 19 | 63 | 51 |
| 20 | 44 | 42 |
| 21 | 54 | 40 |
| 22 | 56 | 51 |
| 23 | 52 | 65 |
| 24 | 46 | 36 |
| 25 | 46 | 53 |
| 26 | 52 | 59 |
| 27 | 48 | 35 |
| 28 | 41 | 49 |
| 29 | 41 | 62 |
| 30 | 39 | 61 |
| Mean | ||
| Standard deviation | 6.7 | 9.5 |
Conclusion:
Questions
Answer the following questions using the information in the aim, method and results along with your knowledge of data collection and experimental analysis.
- Suggest a method of randomly allocating ewes to each group.
- Calculate the mean for each group.
- Compare the means for the two groups.
- Which group has the better mean for liveweight at 24 weeks?
- Compare the standard deviations for the two groups.
- In what way is the standard deviation a useful statistic to know, (what does it tell you about the results)?
- List three features of the experimental design that contribute to standardisation of conditions in this trial.
- What is the variable that is being examined in this trial?
- What other information would be useful for drawing some conclusions about any differences in carcases from lambs sired by the different rams?
- What recommendations for other and further trials would you consider useful in examining the effects of different sires on lamb carcases produced?
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