An Example of a Conservation Breeding Program
While there is no single, simple recipe that can be applied to all breeds or circumstances, the ALBC has designed a breeding plan to illustrate key requirements and to allow a breeder to more easily manage a flock within a conservation breeding program. This plan allows a breeder to keep three lines, but to use only one ram per year on his or her flock, by managing the three as one unit and using rams from different lines in different years. Each ram is used for only 1 year in the flock, so that his genetic influence is not excessive, and the genetic diversity within the line can be retained.
First, three groups of sheep must be identified to form the lines. Each group should be of approximately equal size, and consist of a number of ewes and 1 or more rams. Ideally, the sheep within a group should be more related to each other than to the flock as a whole, but the method of grouping is not critical. For instance, groups could be made by pedigree, with all descendents of a particular sire or dam in the same group. Or, if the flock has been built from several other flocks, the groups can be formed according to these foundation flocks. These groups will then be considered lines within the flock, and will be designated in this discussion as lines A, B and C.
In the first cycle, the ram from Line A will be used on the entire flock. Ewe lambs that are sound representatives of the breed are retained in their mother’s lines, but may produce progeny for more than one line. For instance, lambs sired by the A-line ram and out of A-line ewes will be A/A (linebred, more than ½ A), but lambs sired by the A-line ram and out of B-line ewes will be A/B (linecross, with no line more than ½) and can produce lambs for the B line when bred to a future B-line ram, or for the A-line when bred to a future A-line ram. Ram lambs are kept only out of A-line ewes, and when mature, the best A-line ram is used for breeding (see cycle 4).
In the second cycle, the ram from the B-line is mated to all the ewes in the flock. Again, both linebred (B/B) and linecross (B/A, B/C) lambs are produced. Ewe lambs are retained in their mothers lines, but ram lambs are retained only out of B-line ewes.
|Cycle||Ram used||Ewes bred||Offspring Produced|
|Linebred —save males and females||Linecross|
—save only females
|1||A||A, B, C||A||A/B, A/C|
|2||B||A, B, C A/B, A/C||B (includes B/AB)||B/A, B/C, B/AC|
|3||C||A, B, C, A/B, A/C, B/C, B/AB, B/AC||C (includes C/AC, C/BC, C/BAC)||C/A, C/B, C/AB, C/BAB|
|4||A||A, B, C, A/B, A/C B/C, B/AB, B/AC C/A, C/B, C/AB, C/BC, C/AC, C/BAB, C/BAC||A (includes A/AB, A/AC, A/BA, A/CA, A/ABC)||A/B, A/C, A/BC, A/CB, A/CBC|
*Table modified for the short generation time of sheep. From Sonenberg & Christman. 1995. A Conservation Breeding Handbook. Page 81.
The key to this breeding program is that the genetic makeup of each line is alternating between inbred (linebred) and outbred (linecross). The distinct genetic identity of the line is retained, while the linecross individuals provide input of new genes, reducing the amount of inbreeding that the line accumulates. These linecross animals may also show hybrid vigor. Inbreeding is occurring in as many directions are there are bloodlines, so the genetic distance between the lines is maintained through time.
In contrast, most breeding programs attempt to reduce inbreeding across the entire flock at the same time. The consequence is that inbreeding slowly accumulates in the same direction throughout the flock. Thus, there is no outcross available within the flock and the breeder must seek outside the flock to bring in new vigor or to address other inbreeding problems. If other breeders have used similar strategies in managing their flocks, there may not be any flocks with enough genetic distance remaining to provide a true linecross, and the vigor sought may not be obtainable within the breed.
For a conservation breeding program to succeed, there must be enough individuals within each line to produce a good replacement male and several replacement females at every breeding cycle. Additional animals are required if the breeder wishes to select for better conformation, size, or production. The ALBC suggests a minimum of 10 females per line (including both linebred and linecross females). However, if your flock management results in a large percentage of twins and triplets, this number can be reduced somewhat.
Part 1: Conservation Breeding
Part 2: What is Conservation Breeding?
Part 4: Three Disadvantages of Conservation Breeding