Scientific Farm Animal Production
Quiz 14 :
Three critical decisions have been made by animal breeders; include choosing the individuals that become the parents, determination of rate of reproduction from each individual and decision of choosing a mating system to yield beneficial results. Genetic improvement can be optimized in herds and flocks through the combination of selection and mating systems. Mating systems are chosen depending on genetic relationship of animals selected for breeding.
Mating systems are identified by genetic relationships of animals involved in mating. Two types of mating systems known as inbreeding and out breeding are majorly considered. Inbreeding results in mating of animals in closely related populations than the average of breed or population. Out breeding occurs between different populations that are not closely related as the average of the population. Inbreeding results in increased homozygosity of gene pairs in offspring compared to animal populations that are not undergone inbreeding in the same populations. For example, animal 'A' is produced from mating a sire 'B' to his full sister 'C' therefore B and C are highly related genetically because they are full siblings. But they do not contain identical genetic makeup because each of them have received half of genes from each parent. Inbreeding is of two types called intensive breeding and line breeding. Intensive breeding occurs between closely related animals that have inbreeding ancestors for several generations. Line breeding is a mild form of inbreeding because the inbreeding is kept relatively low to maintain the high genetic relationship to an ancestor or line of ancestor. Out breeding is of four types called species cross, cross breeding, out crossing and grading up. Species cross is crossing of animals involving different species for example, horse to donkey or cattle to bison. Cross breeding is mating of animals that are established as different breeds. Out crossing is the mating of unrelated animals belonging to the same breed. Grading up is the mating of pure bred sires to commercial grade females and their female offspring for several generations. Grading up involves cross breeding to some extent or it may be a type of out crossing system.
Inbreeding results in mating of animals in closely related populations than the average of breed or population. Inbreeding is of two types called intensive breeding and line breeding. Intensive breeding occurs between closely related animals that have inbreeding ancestors for several generations. Line breeding is a mild form of inbreeding because the inbreeding is kept relatively low to maintain the high genetic relationship to an ancestor or line of ancestor. Breeders cannot develop own lines of highly inbred beef cattle. This is because inbreeding depression affects the economics of the operation. Seed stock and commercial producers may have the advantage of highly productive inbred lines by crossing the inbred bulls with unrelated cows. Inbreeding involving sire daughter mating are logical ways to detect the undesirable recessive genes. Seed stock producers use inbreeding in well planned line breeding programs. Inbreeding may have a disadvantage when sires from other herds are introduced that are genetically superior to offspring they produce. Line breeding is the low risk form of inbreeding and maintains high genetic relationships with the ancestor. Sometimes breeder may use sire with superior genetic combination of genes that are inherited to the offspring. But young sires may not out produce some of the sires with superior combination. This can be observed in dairy bulls because they competitively remain superior till they produce the semen.