Line breeding is a method that sheep breeder use to improve a flock of sheep. Line breeding focus on the genes of one strong animal in the flock. While line breeding uses the genes of an individual animal across multiple generations, it also include some of the blood of unrelated sheep to avoid the issue caused by inbreeding.
Line breeding is used to lock in certain trait from the sheep that are being bred. If true inbreeding is used instead of line breeding, the sheep may have a decrease in fertility or the vigor of there lambs. There is three main methods of line breeding that utilize the traits of a few sheep in the flock and ignore the traits of the remainder of the flocks sheep.
Line Breeding in Sheep
Sire line breeding allows a breeder to quickly produce offspring with desired trait if the breeder owns an exceptional ram whose lambs exhibit the desired traits. Half-sib mating is used to even out the genetic contribution to the flocks lambs and is a more risk free breeding process for those who own sheep who cant afford for their lambs to decrease in number. Dam line breeding allows a breeder to focus on the traits of the female in the flock and breed only those who exhibit the desired traits, such as those with strong milking abilities or even traits in there wool fiber.
A sheep breeder will depend upon the traits of the sheep that are to be improved and which trait will increase the profitability of the flock to determine the specific breeding method that should be utilized. The process of line breeding use the concept of generations to concentrate the genes of the sheep that exhibit the best traits. The first step in line breeding is to select a foundation sheep and to record the traits of that sheep.
The second generation of sheep are the offspring of the foundation sheep, and only the lambs with the best traits are to be kept in the flock. The third generation of sheep are to be bred with the daughter of the foundation sheep or with a brother of the foundation sheep. The fourth generation of sheep will have similar trait, and at this stage in the line breeding process, a breeder may wish to introduce new (and unrelated) sheep into the flock to restore the hybrid vigor of the flock.
Certain trait will manifest in response to line breeding at a different rate than others. Traits like fleece weight and fiber diameter will manifest quick in response to line breeding because these traits is heritable from one ram to its lambs. Growth rate is another trait that will quickly manifest with line breeding for the same reasons as fleece weight and fiber diameter.
The trait of prolificacy will manifest at a slower rate than growth rate, but a breeder can increase the prolificacy of their flock by breeding only the ewe that have twins or more. Sheep breeders often ignore structural soundness, but it is important to ensure that the feet of the lambs are healthy, as poor feet will lead to lameness. Not all breed of sheep respond to line breeding in the same way.
For instance, Merino sheep are bred to produce wool with low micron counts and staple length, so their line breeding focuses on these traits. Suffolk sheep are bred for muscle and clean point in their lambs, and thus, the line breeding for Suffolk sheep focuses on these physical trait of the lambs. Rambouillet sheep are bred for both the quality of their wool clip and their ability to endure the ranges condition, so the line breeding of Rambouillet sheep focuses on these two traits.
The breed that is used will impact which trait quickly manifest in the lambs, but the logic for line breeding is the same for all breed of sheep. Line breeding require that a breeder keep specific record of the traits and offspring of each of their sheep. The breeder must keep four-generation pedigrees and the performance weight of each of the sheep in the flock, as the coefficient of inbreeding cannot be calculated without these record.
Each lamb should be tagged at birth, and that tag should be link to the dams milk score and the weaning weight of the lamb. By keeping these record, a breeder can continue to monitor the effectiveness of the line breeding program and know when to cull certain sheep from the flock. If a breeder chooses to keep the lambs with the worst trait, it will slow the rate at which the good gene spread through the flock.
In order to ensure that the line breeding program is successful, there is three habit that the sheep breeder should of utilized. The breeder should control the mating window for the flock so that all lambs born in the flock are born within a narrow time frame. By doing so, the breeder can compare the growth rate of all lambs of the flock.
The second habit is to use genomic testing to confirm the pedigree of each ram and lamb in the flock. This allow the breeder to ensure that there are no error in the pedigree that may slow the rate at which the flock gain the genetic improvement that are desired.