By Dr Clive Dalton
Good eyesight & clear diction are important for accurate
tag reading to reduce costly errors.
In New Zealand the national performance recording services is now called Sheep Improvement Ltd, (SIL) which is run from within Meat and Wool New Zealand Limited. The main users of SIL are registered stud breeders over the whole range of breeds and their main business is selling rams to commercial farmers. Here are some basic facts about SIL:
- Breeders send their data to any of eight independent bureaus.
- The data are entered on to the SIL database via the Internet for processing in the SIL “genetic engine” to meet the requirements of the particular bureau.
- Results of the evaluation are then emailed back to the bureau for checking before being returned to the breeder.
- All data loaded on the SIL system remains the property of the breeder.
- SIL can only give limited details about breeders to potential ram buyers. However, SIL has a web-based breeder search engine to help farmers find breeders in a particular area with specific breeds of interest.
- SIL cannot recommend individual breeders to commercial ram buyers.
- All enquiries about SIL should be directed to a SIL bureau or adviser in the first instance.
- Contact details for SIL are to phone 0800-745-435, Email
Breeders collect a rang of information and it all starts with identifying each sheep to build the pedigree. Then they record a range of “raw data” on the ewe including birth date, number of lambs born, survival (difference between lambs born and weaned), weaning weight, hogget weight, hogget fleece weight and disease incidence.
Warning! What follows is full of technical jargon and if it’s all too much, then go to the article about buying a ram.
How are the traits classified?
There are two kinds of traits – “Goal” trait and “Predictor” traits.
Goal traits
- Key point: These are a breeder’s goals – or what they want to improve.
- Some can be measured on the animal (e.g. weaning weight, fleece weight), and some can only be measured long after selection has taken place (e.g. carcass weight and adult ewe weight).
- There are some that you just cannot measure (e.g. number of lambs born on a ram).
- Number of lambs born (NLB) can only be estimated from the female relatives of a ram.
- There are 6 important goal traits that SIL can focus on. Breeders may not select for them all.
- These are: growth, meat (carcass quality), wool, reproduction, disease and survival.
- Disease has one or more of three different focuses:
- Internal parasite resistance (faecal egg count or FEC),
- Facial eczema or FE
- Susceptibility to dags (dag score or dagginess).
- These are traits that you can measure on the sheep and which can be used to estimate genetic merit for the goal traits.
- An example is where a breeder would use an ultrasound measurement of fat depth and muscle depth, together with body weight as predictor traits to predict the animal’s carcass weight (the predictor trait).
- Key point: Predictor traits are used to generate BVs for the goal traits.
- After processing the data, Breeding Values (BVs) and Indexes are produced. Breeders use these to compare animals and select the best individuals for flock replacements or for sale.
- An enormous amount of computing is involved to get from raw data to BVs and Indexes, and as computers have progressed these calculations have become much more sophisticated.
- But often with progress comes confusion so it’s important to know what happens.
- First, adjustments are made to the raw data to take account of “non-genetic” or environmental effects that are known to influence performance.
- Examples are the corrections made for date of birth, birth rank (single or multiple), age of dam and grazing mob.
- Then there are the “genetic” effects of the animal’s own performance and that of it’s relatives which have to be taken into account. In past years we didn’t have the computing power to do this.
- So all the data built up over past generations (since 1967) in the database is invaluable.
- We can now make comparisons between sheep in different flocks where there are “genetic links” between these flocks, i.e. the same sheep’s genes in different flocks. Previously this was not possible until statisticians developed a BLUP analysis.
- BLUP stands for Best Linear Unbiased Predictor – if you ever need to know!
Breeding Values (BV)
- A BV is an estimate of the genetic merit of an animal. Note it can only be an “estimate” or “best bet” so the more data that goes into the calculation from as many relatives as possible, then the more accurate the BV is.
- Think of a BV as an estimate of how good the animal will be as a parent – i.e. how good the genes it passes on to future offspring will be.
- One very advanced bit of genetics (and also potentially confusing) is to use traits that are not measured directly on the animal to predict those that are. This regularly used to raise suspicion about “computer-bred” sheep! It’s possible to do this because of genetic correlations described earlier, where selecting the genes for one trait will automatically improve the other.
- Key Point: Just remember the higher the BV- the better the animal. The only exception is for traits like fatness and FEC when the lowest is best.
- Key point: An Index is a single figure expressed in monitory terms, and it simplifies decision making as you only have one value to think about.
- When you are faced with a number of BVs (which may have positive or negative numbers), on a group of individual rams, it’s often very difficult to make a final decision. It also takes far too long.
- The smart thing about an index is that it has a strong smell of money! This is done by weighting (multiplying) the BVs that go into it, by their “relative economic values” (REVs) giving a value in cents per ewe lambing.
- So if one BV brings in more money to the farmer than another, it will get more weight.
- Note that the money values used in the Index for a ram are a “best bet” on what the ram will contribute to your flock, with only half going to his progeny as the other half comes from the ewe.
- It’s not a guarantee in real cents of what the sheep will earn. The cents are the common factor that can be applied to all the BVs to put them together as some are numbers (like numbers of lambs born) and others are weights in kg.
- Key point: Just remember the higher the Index - the better the animal.
Sub Indexes
- This is some extra sophistication where BVs are grouped for “general” goal traits.
- An example is Dual Purpose Growth (with meat) (DPGM) Index. This contains four BVs – two for weaning weight (WWT – lamb growth genes, and WWTM – ewe milking genes), one for carcass weight (CW) and one for ewe adult weight (EWT).
- To end up with one figure for a Sub Index, the BVs are multiplied by relative economic values (REVs), then these are summed to end up with one value for the sub-index.
- Currently the weightings are as follows:
- DPGm = WWTBV x 116 + WWTMBV x 97 + CWBV x 140 - EWTBV x 72
- So in this sub-index, having more weaning weight (either WWT or WWTM) and carcass weight increases value but more adult weight reduces it.
Assembling the overall Index
These are SIL’s real movers and shakers and are called “overall” indexes as they combine the sub-indexes – and really are the only ones you should worry about if you are buying rams (more later). Below is what goes into them:
- Dual purpose overall (DPO) – can include growth, meat, wool, reproduction, survival and disease. Use this index if your main business is both meat and wool.
- Terminal sire overall (TSO) – can include growth, meat, survival and disease. Use this index if your main sale enterprise is prime lamb production.
- Fine wool overall (FWO) – can include growth, wool, reproduction, survival and disease. Use this index if you are a high-quality, low fibre diameter wool producer.
Fear of “computer-bred” sheep!
Over the years, as biometricians and computers got smarter, geneticists got more and more excited about the potential of making genetic progress using BVs and Indexes. But many sheep breeders and stock agents became confused and suspicious and gave up. They resorted to picking rams on their looks in the yards, leaving the records untouched (or at best partially scanned) in the woolshed. Who could blame them?
They talked of “computer-bred sheep” fearing that structural soundness and physical traits (which could not go into an Index) would be ignored by ram breeders unduly influenced by boffins. The argument boiled down to the order in which you did things – and it’s still a relevant question today.
Question: Do you look at the records first to sort out a group of top animals and then go and check the rams for physical faults, or do you work the other way around?
Many stock agents encouraged buyers to look at the rams first and ran out of time (often deliberately) and never got to the records! Technical advisers encouraged buyers to go to the office first and sort out the rams on paper.
Key point: The only sensible thing to do was (and still is) to look at records first and only then look at the rams, because good breeders have already culled any sheep with major defects long before buyers get to the farm, and any concerns will only ever be over a few “minor defects”.
But often these so-called minor defects can be a real can of worms and are massive time wasters, as ram buyers agonised over some minor physical defect like a black spot or teeth that had the remote possibility of sticking slightly over the gum. A boffin would say ignore it but a stock agent would most likely never agree!
Suspicion over an Index
When selection indexes first came in, these were seen as the heart of the black magic mentioned above as after welcoming them as being useful, many breeders and ram buyers suddenly had a fit of panic and wanted to know how they were made up, especially if they were for example very big for a small ram, or small for a massive ram with great eye appeal in the yards.
SIL’s BVs and indexes reward potential genetic performance and not actual performance. A large ram may have a low rating for genetic merit for growth if a lot of information suggests his superior size is not genetic. Conversely, a small ram may be rated highly if his size is attributed to non-genetic factors (e.g. born as a triplet to a hogget mother, late in the season), and there is a lot of good growth genes in other family members.
If panic strikes - go back and see which of the BVs has had most impact on the Overall Index as this will vary between animals. The make-up of indexes (i.e. what BVs are used and the weightings) are described on the front page of all breeders’ SIL Ram Selection lists.
Buying sheep from breeders with performance records
You will mainly be buying rams from stud breeders but the following points apply equally to buying ewes.
- Find out from the SIL website which breeders in your area are breeding sheep of the type that you want. SIL will not recommend individual breeders.
- A stud stock agent who is familiar with SIL will also be able to help, and will have the freedom to recommend breeders.
- At first sight the SIL ram selection list is a visual shock, so you’ll need time to crack its layout and abbreviations!
- Do not go and look at any sheep until you have looked at the records. Otherwise you’ll waste everybody’s time and you wont’ be welcome back next year.
- Explain to the breeder your state of knowledge and take the opportunity to learn about the SIL system from the breeder (and the stock agent) when you visit the farm. Allocate plenty of time for this as you could be in for a fair mind-bending session.
- After you have visited the breeder’s farm, he/she may offer to visit your farm to get a good feel for what your farming system is like, and hence your ram needs. This is an excellent idea so grab the offer, especially if you are sheep farming in a big way.
- You must find out if the breeder is making genetic gains in their flock in the trait areas that you are also trying to improve in. Ask to see genetic trend graphs. There is little point in buying stock from a breeder whose flock is not showing genetic improvement over time.
- You are better to buy average rams from a better performing flock than the best rams from a poorer performing flock.
- A progressive breeder will have culled out all rams with physical defects so this will not be a significant issue. Inspect the rams for structural soundness after you have made an initial selection on paper.
If you just keep a few animals then it may not be worth the costs joining a formal sheep performance recording scheme, but it’s still important to keep records as you’ll forget what happened over time. The simplest system is to have a record card for each animal or an entry in a spreadsheet or database.
Information you could record on each ewe is:
On one side of a card record details of the ewe herself:
- Identification
- Pedigree – sire and dam ID
- Birth weight and date
- Weaning weight and date
- Hogget weight and date
- Hogget fleece weight
- Health records
Lambing 1
- Sire used
- ID of lambs and date born
- Sex of lambs
- Birth weight of lambs
- Fate of lambs
- Fate of ewe
- Health records
Lambing 2
Ditto as above and for subsequent lambings
What does it all hang on?
All the technical information described above hangs on correct identification of the lamb to its dam at birth, and a good tag that's easy to put in and stays there!
Fortunately blood typing can verify the accuracy of parentage but at present it's too expensive for many breeders.
Tagging lambs at docking. After mothering up the ewe they are with is assumed to be their dam. Otherwise blood samples are taken to confirm parentage
Disclaimer This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.
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