Common genes, and therefore genetic linkage, is required to be able to compare the genetic merit of individual animals across environments. Genetic linkage is when two or more flocks/management groups share common genes, often through the use of a common sire.
Linkage allows us to compare the genetic merit of animals across different flocks and environments.
In the figure above, the colour indicates animals with the same sire, where grey = sire 1, green = sire 2, and blue = sire 3. Flocks 1 and 2 can be compared because animals from the same sire are used in both flocks. The common sires act as a genetic benchmark to compare the genetic performance across environment and management. The analysis uses their performance in relation to each other to account for environmental effects on performance. Group 3 has only been used in one environment and cannot be compared to any other animals. Therefore, it is not linked, and its breeding values cannot be compared to other flocks in the analysis.
Genetic linkage is required at a trait level. This means that you must use an external sire in your flock (either a sire from another Sheep Genetics flock, or a home bred sire that has been used in other Sheep Genetics flocks) that has progeny measured for the same traits. This sire is referred to as a ‘link sire’. You must also regularly use link sires to maintain this linkage, as linkage looks at the last five years of data.
Within each year of joining, a link sire is required to be used between each year drop – this may be a home bred ram used across multiple years of joining, or an outside you include in multiple AI programs.
Animals in different management groups within the same joining year should also have a common sire, to provide linkage between the different management environments.
Participating in progeny test programs such as Resource Flocks, sire evaluations and young sire programs help to build and maintain linkage between flocks. Sires from a range of flocks are entered into these programs, where they will go onto have progeny, which are managed alongside each other. This generates linkage across the traits these progeny are measured for. For a program such as the MLA Resource Flock, this includes measurements on hard to measure trats like carcase and eating quality traits, as progeny are measured through an abattoir and meat science lab.
To ensure you have linkage across flocks, the following are recommended:
- Use at least one link sire in every 10 sires joined per drop. A link sire has been used in other Sheep Genetics flocks. Artificial Insemination (AI) is a good way multiple breeders can use the same sire.
- Purchase sires (or semen) from other flocks that have data in Sheep Genetics.
- Sell rams (or semen) to other Sheep Genetics recorded flocks for use as sires.
- Participate in a sire evaluation or Young Sire Program that shares sires across flocks.