14.7.3 Mating schemes to control and manage relationship

As we have seen in chapter 9.11.1 optimal contributions methods are developed and used in controlled breeding programs for mating sires and dams.

In less controlled breeding programs, e.g. in heath sheep, circular mating is applied among the participating flocks: ram circles. In these flocks of heath sheep a large number of females are kept together with a number of rams. This implies that from individual heath sheep the sire is unknown. Below you find the illustration of the circle:

Open

Example of a ram circle. Each colored spot is a flock. The red flock always (annually) gets young rams from the dark yellow flock and delivers annually young rams to the grey flock, etc. (Source: Wageningen University)

In this example 6 different flocks participate in the circle. That implies that it takes 6 generations before a ram with 1/6 of the genes from the red flock is used again in the Red Flock via rams born in the dark yellow flock and inbreeding will take place for the first time. When more flocks participate it takes more generations before inbreeding starts. It is a very effective scheme to keep inbreeding at a low level and to create a low inbreeding rate. When considering implementing a scheme genetic differences between the flocks and the fixed order of exchanging rams should be thoroughly studied and discussed. A breeder has to accept that he always gets rams from the same flock.