How to make an on-farm ram comparison
The procedure for comparison of individual rams is similar to that for teams of rams. The key design features are:
- Identify potential ram sources. Sheep Genetics provides objective information on potential ram sources which may perform better than your current ram source.
- For ram source comparisons, use the same standard you would normally set to purchase rams to use in your flock. The same standard of ram should be selected from each source — don’t compare high performing rams from one source against average rams from another source. A minimum of five rams from each ram source must be used for comparison.
- The rams must be syndicate mated to ewes of equivalent merit — that is, a similar standard and age profile in each mating group. The ewes must be split randomly into the ram source mating groups by drafting the mob through a race and taking one for each group in turn (simply counting the ewes out a gate is not a satisfactory method of random selection). The number of animals from each age group and class must be the same in each mating group. Ewes must be identified with easily read and durable tags or brands.
- A minimum of 20 progeny from each ram, or 100 progeny from each ram source mating group, are preferred for evaluation. As a guide, 130-150 ewes per ram source should be regarded as a minimum for accuracy (the actual minimum number depends on the anticipated weaning rate). If the wether lambs are sold you will need to double the number of ewes mated. Aim to keep the mating groups in the same condition score when not running as one mob. The total number of ewes for all groups must be manageable with the available farm resources (a small paddock for each mating group at joining and lambing time, sufficient larger paddocks to run the combined mob outside mating and lambing periods). There may be other options for running the boxed mob, depending on your situation.
- Draft ewes into the required number of mating groups and run them separately for the duration of mating. After mating, box mating groups and run as one mob through pregnancy until lambing. Before lambing begins draft the ewes into their original mating groups and manage them separately until marking. At marking, tag the lambs according to the mating group.
- Combine the different groups and run them together as one mob from lamb tagging until assessment is completed (usually after hogget shearing if benchmarked for wool production). Ewes and wether progeny can be run in separate groups or together. Do not cull any progeny unless to alleviate suffering due to abnormalities or injuries as culling some progeny before assessment may distort the results. Record any such culling against the sire(s).
- Animals to be assessed must be bred on farm.
- Progeny can be assessed for any desired trait — in general, the more the better. A basic starting point is with the traits in your breeding objective, with other traits added as desired. The basic records to collect would normally include:
- reproduction rate — lambs weaned to ewes joined
- number of progeny culled — record reasons, including pigmentation and conformation
- weaning weight and growth rate from weaning to set turnoff date
- number of progeny at turnoff date and class
- hogget liveweight at shearing
- hogget greasy fleece weight and bin class
- hogget fleece measurements from a fleece sample (yield, fibre diameter, and so on) — keep samples from sexes separate within each progeny group
- as well as the procedures above, additional information can be obtained if wool from the different groups is classed, pressed into separate bales, and each bale tested separately — this can also give an indication of the performance of the different group
- all progeny from evaluation matings must be measured — some measurements may be made on samples of the mating group rather than the whole group, in which case accuracy will be reduced.
How to increase the accuracy of the test
- Avoid using maiden ewes because of poorer fertility and mothering ability.
- Minimise differences in nutrition between ewe groups during joining and lambing — record condition scores of the different groups and adjust nutrition accordingly.
- Manage weaners at an acceptable nutritional level.
- Shear lambs after weaning to standardise the wool growth to hogget shearing.
- Minimise the spread in lambing time by restricting mating time to five weeks.
How confident can I be in the results?
Most comparisons suffer from inaccuracies caused by factors such as:
- range in birth dates
- no allowance for singles and twins
- variations in worm burdens in different lambing paddocks
- accidental deaths due to disease or premature culling
- other chance environmental effects.
Small differences (3-4%) between groups may not be real (significant) as they may be due to one or more of the above factors that you cannot control. The number of progeny per ram, the number of rams per ram source and the level of difference to be detected should all be considered when comparing groups of rams.
Small numbers of progeny per ram can affect accuracy but a reasonable practical minimum is 20 progeny for most wool and body weight production traits. Increasing this minimum has little effect on increasing accuracy.
At least five rams per ram source should be mated to produce at least 100 progeny. This will allow differences between progeny groups of 5% or greater in fibre diameter and 10% or greater for fleece weight to be identified with reasonable confidence that the difference between ram sources is real. When reproduction rate is considered then large numbers of ewe progeny are required to get an accurate indication of genetic differences. However a minimum of 100 ewes (or 50 ewes assessed over two lambing seasons) is considered to be a reasonable and practical number of daughters to test per ram source. When comparing small numbers of rams (as in using a small sample of the ram source, such as less than 10) it is vital to select the rams in a fair and unbiased way.
What is the real genetic difference between the ram sources?
Since you would normally use ewes from your current ram source, the difference between progeny groups will generally be only half the difference between the ram sources run in your environment. For example, if you run sheep based on ram source A and wish to compare this with ram source B, you will mate groups of rams from ram source A and B with ewes from ram source A. Progeny groups will then be AA (purebred A) and AB (half ram source A from the ewes, and half ram source B).