AGB 211: Livestock and Poultry Breeding (2+1)

INBREEDING

Inbreeding is the mating between animals, which are more closely, related each other than the average relationship between all individuals in a population or inbreeding is mating between animals related by ancestors. When the animals are considered as closely related when they have one or more common ancestors in common, in the first 4 to 6 generations of their pedigree. Example: Sire-daughter, Son-daughter or Brother-sister. In general, inbreeding refers to close breeding. Inbreeding is classified into two types

• Close Inbreeding: Such as mating between sibs or between parents and progeny in order to achieve inbred lines with relatively high degree of homogenisity. In most of the time we use full sib mating method. The same effect can be achieved by consistently back crossing the progeny to the younger parents. Half sib mating is much slower, rich in homozygosity but it is also less risky.
• Line breeding: It is a system of mating in which the relationships of an individual or individuals are kept as close as possible to some ancestor. In general line breeding is a milder form of inbreeding. As a general rule sire is not mated to its daughters but half sib matings are made among the offspring of the particular sire. Line breeding was used extensively in the past in development of British breeds of cattle such as Angus, Hereford and Shorthorn. The following points should be remembered while practicing line breeding,
  • Line breeding should be practiced in purebred population of high degree of excellence, after identifying outstanding individuals.
  • Line breeding is probably most useful when an out standing sire is dead or not available for breeding purpose.
  • To form new breeds, line breeding can be advocated.

Disadvantage of line breeding

• Line breeding tends to make gene good or bad, homozygous rapidly. Hence choosing of a ancestor (sire) to line breed is very important. Those that are definitely superior should alone be selected. Beside rigid selection, culling of undesirable recessive is highly essential. Line breeding should be practised only in herds distinctly superior to the general average of the breed.