ANIMAL BREEDING - VARIOUS METHODS
The following animal breeding methods are followed for improvement of animals in dairy and poultry namely
(1) Inbreeding (2) Outbreeding (3) Mutations.
The crossing of closely related animals is called Inbreeding. If this inbreeding is repeated continuously, it is called Upgrading. Inbreeding is used to retain desirable genetic traits in animals. Inbreeding is required in order to retain as many traits as possible by keeping the combination of genes intact.
However, the inbreeding may result in homozygous recessive genes coming together to express some harmful phenotypic traits. Many breeding scientists have observed that hybrid vigour and fertility were lost due to repeated inbreeding. Such recessive and harmful genes are removed by some special techniques without sacrificing the major quality of the animal. If the race is relatively free of such harmful recessive genes, the process of inbreeding is a safe method for improvement of animals.
The crossing of distantly related animals is called Outbreeding. One of the problems the animal breeder faces in outbreeding is introduction of new genes into population. In this method it is possible to breed a desirable type of animal with a less desirable type and then to increase the degree of desirable traits. New and high yielding genes can be introduced into the population through outbreeding. In many cases these genes may come from a variety of stock.
Out breeding in animals is useful for different purposes viz.,
(i) To produce some valuable traits (ii) To create new breeds (iii) To produce a hybrid of superior vigour and value.
(i) To produce some valuable traits:
Beef cattle may be crossed with dairy cattle to produce calves for superior veal (flesh) production.
(ii) To create new breeds:
A new breed is produced with desired characters from the two original breeds. This process of producing new breeds takes time. The present day breeds of animals have been developed through hybridisation.
(iii) To produce a hybrid of superior vigour and vaIue:
A Mule is produced by crossing Equus equus (mare or female horse) and Equus homonius (jack or male ass). Mules are superior to horses in strength, endurance, resistance to disease and ability to work under unfavorable conditions. When a female mule is crossed with a jack, a colt is produced.
The new traits into populations can also be induced through mutations. Since most of the mutations are harmful and the process of induction of mutations is quite expensive, this method of improvement of animals is impractical. It has been reported that a sheep in New England mutated in the direction of having shorter legs (a desirable quality) and formed the basis for racial improvement of sheep.
Representative examples of improvements in animals by mutations include poultry that is resistant to white diarrhoea, increased egg production in fowls, increased fat content in milk and better meat yielding in Turkeys etc.