Farmnote 64/91 [Reviewed June 2006]
By Peter Doyle, Research Officer, Ruth Reuter, Veterinary Pathologist and Ken Greathead, Adviser, Albany
Many farmers like to test new products, such as mineral licks or bullets, on a small scale before adopting them. Usually this test also involves a cost/benefit analysis. However, unless the trials are designed properly and done carefully, the results can be misleading or even useless.
This Farmnote outlines how you can set up a simple 'plus and minus' trial with animals. In this type of trial, you are comparing a new treatment, such as a new supplementary feed, lick or worm treatment (the 'plus' treatment), with your old treatment (the minus' treatment). The 'minus' treatment could be no treatment at all.
Apart from the 'plus' and 'minus' treatments, the two herds or flocks are run under identical conditions - or as close to identical as you can make them.
For more complex trials, such as using different pasture grazing systems, we suggest that you contact your local Agriculture Western Australia adviser. This type of trial is difficult to plan correctly.
For best results
Three points need to be kept in mind to get the most out of your trial.
- Decide which sort of treatment you want to test and its possible effects.
- Choose your test animals and grazing land care fully so that they are as uniform as possible.
- Eliminate any other factors that are not part of your treatments, so that they do not affect the performance of the animals. For example, worms or a nutrient deficiency could mask the effects of the treatments.
If in doubt about setting up your trial, contact someone with experience. Otherwise you could waste much time sorting, weighing and monitoring the animals.
The test site
The grazing land used for the trial must be as uniform as possible.
One paddock can be used if the treatments are administered directly to the animals (for example, bullets or vitamin injections). If you are testing a supplement that the animals have free access to (for example, a mineral lick or block), then two paddocks are needed.
Animals used for the two treatments ('plus' and 'minus') should be in paddocks of the same size. The pasture must be of a similar availability per hectare, botanical composition and quality in each of the two paddocks.
It may be worthwhile fencing a paddock in half to achieve this. If so, divide it at right angles to the contour.
Every fortnight, change the animals (and their treatments) around so that each group of animals spends time in both paddocks. Swapping the animals will help even out differences in the results that were caused by differences in the feed available in the two paddocks.
The test animals
The animals need to be as similar to each other as possible. Use a unique number for each animal and tag each ear in case one tag is lost. If the numbers in each ear are different, record both. It is best to avoid using tags having the same number but a different colour on different animals, since often only the number is recorded.
Here is a suggested checklist to follow.
- Treat the whole herd or flock for worms before you begin the trial.
- Take out any animals that look substantially different - for example, much smaller, leaner, larger or fatter than the rest of the bunch.
- Weigh all the animals you have chosen.
- Make a list of the weights and ear tags, ranking them from the lowest to the highest weights.
- Take the two highest animals and allocate one to each treatment. Take the next lightest pair and repeat the process until all animals have been allocated a treatment. The animals are now 'paired'.
- Make sure you have the same number of animals for the 'plus' as you have for the 'minus' treatment.
How many animals are needed?
The more animals you use, the more chance you have of measuring the real effect of the treatment.
We suggest that at least 30 sheep or goats, or at least 20 cattle are used for each treatment. For a 'plus and minus' trial with sheep, this means that you would need at least 60 animals.
How many more animals you use depends on the standard of your facilities and on how much time you are prepared to spend making measurements.
Good handling facilities are essential for trials. You will need good yards, a restraint crate or crush and a reliable set of scales. For trials with sheep, experienced shearers are important to ensure that the animals are shorn consistently.
What should be measured?
Liveweights
Liveweights need to be taken regularly. Weigh the animals every month or every fortnight, depending on how quickly you expect to get results. Make sure that you record the tag number with each measurement.
Before you start weighing, have the list of animal numbers ready in numerical order within treatment groups. This speeds up finding the animal number when you are recording the weights. It also allows a quick check of missing or wrongly identified animals during and at the end of weighing.
Before you weigh the animals, standardize the scales. This means that when you place a known weight (for example, a tractor tare weight or a counterweight) on the scales, it always gives the same reading. It is best if the standard weight you use is similar to the weight of your animals.
Always weigh the animals at the same time of the day. Try to weigh them roughly the same length of time after yarding. Ruminants can lose 5 to 10 per cent of their body weight if they are kept off food and water overnight.
The fleece or coat must be dry. Avoid weighing animals within three days of a summer thunderstorm, because they will not have eaten for some time after heavy rains.
If you are using goats, do not pen them up for long periods, since they dehydrate easily.
In some trials with sheep, the 'plus' and 'minus' treatments might be continued for several months, then all the flock run together until shearing. In these trials, it is essential to weigh the animals periodically during the trial months and again just before shearing. This will help you to decide if the sheep on the worst treatment (the lightest animals at the end of the trial) were able to catch up with the other animals later in the year.
Other measurements
The slaughter weight and level of fatness are useful for beef herds. These are available from the abattoir. However, it is important to match the animal's identity tag with the kill order at slaughter. You will need to arrange for this to be done, or to do it at the abattoir yourself.
For dairy herds, the milk yield per animal is the most useful measurement.
For sheep, the wool quality is important. This includes:
- the yield wised to calculate clean weight;
- the fibre diameter (microns); and
- the strength.
Remember that consistent shearing and skirting are essential.
For goats, fibre measurements are useful.
What do I do with the results?
The results may be clear cut. For example:
- Eighteen out of 20 of the cattle fed the new supplement ('plus' treatment) were heavier than all 20 of the cattle fed an old supplement ('minus' treatment), with an average increase in liveweight of 20 kg per animal. This 20 kg can be expressed as a percentage of the liveweights of the animals receiving the 'minus' treatment.
- None of the 30 sheep that were given the new worm treatment('plus' 'treatment) had eggs in their faeces, but 10 out of the 30 sheep given the old treatment ('minus' treatment) did.
However, if five of the 30 sheep on the new worm treatment showed eggs in their faeces, the effectiveness of the new treatment would be doubtful. It would pay to repeat the trial. Consult your local adviser or veterinary officer if you are unsure of the results of your trial.
Repeats of the trial
To increase confidence in your trial results - to be sure that the result was not a 'fluke' - you will need to repeat the trial, perhaps in different seasons. Think about arranging a similar trial with neighbours - this will help to get over some of the differences between paddocks and seasons.
Finally, remember that it is always better to do a few simple trials well than to do a complex trial that you cannot interpret.
Acknowledgements
This Farmnote is adapted from Farmnote No. 24/86 'So you want to do a farm trial' (Agdex 100/00), written by John Hamblin. It was edited by Jo McFarlane, with funds provided by the Wheat Industry Research Committee of Western Australia.