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Linkage – What does it mean?

What is Flock Linkage?

Flock linkage refers to the genetic connectivity/relatedness between flocks. Providing accurate €uroStars (genetic evaluations) to a performance recording flock is only possible if the flock in question is genetically ‘linked’ to others. Genetic linkage is crucial for accurate genetic evaluation as it allows for fair and accurate comparisons between flocks.

How do I ‘link’ my flock?

Flocks become linked by sharing rams with other LambPlus flocks within the same breeding season (see below different options). The subsequent lambs born must also have weights recorded on them at the recommended times in order to establish the flock linkage. The more lambs produced in your flock by this ‘linkage’ ram the better, but as a minimum we recommend breeders to produce at least 5 live lambs. It is critical that these lambs are subsequently weighed at the prescribed times.

To maximise the period of your linkage status, breeders should where possible retain female lambs produced by the ‘linkage ram’. Typically, once a linkage sire is used by a breeder, the flock will remain linked for a period of three years.

All performance recording flocks should (where possible) use more than one sire each year in order to keep their linkage levels high. If only one ram is used in a particular flock then it is very difficult for the evaluation to determine if the subsequent lamb performance is due to the sire’s genetics or due to the environment the lambs have been raised in.

Unlinked flock €uroStars

Flocks that are unlinked essentially only receive a within flock evaluation. Unlinked flocks are not being compared to any other flocks within their respective breed. In turn, once these flocks/animals become linked they are likely to see fluctuations in their evaluations (as they can now be compared to other flocks) which is not desirable by anyone and the best way to avoid this is to remain linked at all times.

The Sheep Ireland Central Progeny Test (CPT)

The CPT was established in 2009 and its main function was to fast track and maintain genetic linkage among performance recording flocks in Ireland. It carries out this function by bringing together influential bloodlines across the most widely used sheep breeds in Ireland and using them together across commercial ewes contracted by Sheep Ireland to carry out intensive performance recording.

Ewes are impregnated by AI using semen collected from these pedigree rams. A number of carefully selected rams are also purchased by Sheep Ireland annually and used via natural mating within these CPT flocks. This work all contributes to delivering the most accurate €uroStar evaluations as possible to Irish sheep farmers.

In the past semen from these influential CPT rams has been promoted to interested breeders (targeting unlinked flocks) by Sheep Ireland and the relevant sheep breed societies. In the past many sheep breed societies have established sire reference schemes (genetic linkage schemes), whereby semen from promising rams is made available to breeders to establish linkage. These initiatives had hugely positive effects on genetic linkage within the respective sheep breeds.

Categories of linkage status

When it comes to flock linkage, there are three possible categories;

  • Linked – The ideal situation for performance recording flocks. Your flock is being compared to all other performance recording flocks within your respective sheep breed.
  • Weak Linkage – Your flock linkage status is weakening. You may have been linked last year. You should act during the next mating season to prevent your flock from becoming unlinked.
  • Unlinked – Your €uroStar evaluations are within flock evaluations and are not comparable to other breeders within your respective sheep breed, this will be reflected in how your €uroStars will be displayed for the season ahead.

In the example below Link Ram 1 is the most connected ram as it has been used in most flocks including the CPT, this ram is likely to have the highest accuracy, meaning his evaluation will be more dependable.

Home Ram A, B, C & D have all only been used in one flock but are still linked because a second ram has also been used in the flock and that second ram has also been used in another linked flock.

Home Ram F is not linked, therefor the lambs in this flock will not be linked and the data collected in this flock will be of limited use in the evaluation.

How do I become a ‘linked’ flock?

To link with another flock, the same sire (genetics) must be shared by two breeders in the same breeding season. As stated above weights must subsequently be recorded from the shared sire’s progeny in both flocks. Breeders should aim to produce at least 5 live lambs from the ‘linkage’ sire being used.

There are several options available to you to become linked;

  • Use Artificial Insemination (AI) on a number of your ewes, ensure that you are using semen that is also being used by at least one other linked LambPlus breeder. Again, ensure progeny are subsequently weighed in both flocks. From a biosecurity perspective, this is the safest option to become linked. Contact your sheep breed society for advice on carrying out AI.
  • Share a sire with another linked breeder in the same year, and ensure progeny are subsequently weighed in both flocks. Warning – breeders should be fully aware of the biosecurity risks associated with sharing rams with other flocks. It is advised that you carefully consider all risks before making any decision in this regard.
  • Temporarily move a number of ewes to a linked flock at mating time to allow them to be mated by a linked sire. Again, breeders should be fully aware of the biosecurity risks associated with this type of approach.
  • Purchase inlamb females from a linked flock. Ensure the source flock will also have progeny from the sire used across the inlamb ewes. Again ensure progeny are subsequently weighed in both flocks. Warning – breeders should be fully aware of the biosecurity risks associated with purchasing inlamb ewes (or any sheep) from other flocks. It is advised that you carefully consider all risks before making any decision in this regard.

How do I know if I am linked or unlinked currently?

Breeders can go to their €uroStar profile (via their personal online Sheep Ireland account) and view their linkage status at the top of this page.

What will happen if my flock remains unlinked?

Unfortunately, for unlinked flocks, the genetic evaluation information available to ram purchasers is severely compromised. With this in mind, Sheep Ireland has a responsibility to highlight unlinked flocks where genetic evaluations are available to the public – €uroStar sales catalogues, the online ram search etc.

Figure 1. Stars for linked and weak linked flocks will be displayed as normal as seen below.

Figure 2. €uroStars for unlinked flocks are displayed as below (no fill colour) with the message “Within flock evaluation”.

If I am an unlinked flock, will my rams be eligible for the Sheep Improvement Scheme (SIS)?

Yes, if they accomplish the criteria, rams from unlinked flocks will be eligible for the SIS.