Animal Breeding: Objective and Methods of Animal Breeding!
A group of animals related by descent and similar in most characters like general appearance, features, size, configuration, etc. are said to belong to a ‘breed’.
Animal breeding is producing improved breeds of domesticated animals by improving their genotypes through selective mating.
Objectives of Animal Breeding:
The main objectives of animal breeding are :
(i) improved growth rate,
(ii) increased production of milk, meat, egg, wool, etc.,
(iii) superior quality of milk, meat, eggs, wool, etc.,
(iv) improved resistance to various diseases,
(v) increased productive life, and
(vi) increased or, at least, acceptable reproduction rate.
Methods of Animal Breeding:
Two methods of animals breeding are: inbreeding and out breeding, based mainly on breeding work with cattle.
When breeding is between animals of the same breed for 4-6 generations, it is called inbreeding. Inbreeding may be explained by taking an example of cows and bulls. Superior cows and superior bulls of the same breed are identified and mated. The progeny obtained from such mating are evaluated and superior males and females are identified for further mating. A superior female, in the case of cattle, is the cow that produces more milk per lactation.
On the other hand, a superior male is that bull, which gives rise to superior progeny as compared to those of other males. As the homozygous pure lines developed by Mendel as described in Chapter 5, a similar strategy is used for developing pure lines in cattle as was used in case of peas. Inbreeding, as a rule, increases homozygosis.
Thus inbreeding is necessary if we want to develop a pure line in any animal. Inbreeding exposes harmful recessive genes that are eliminated by selection. It also helps in accumulation of superior genes and elimination of less desirable genes. But continued inbreeding reduces fertility and even productivity.
This is called inbreeding depression. In this condition, the selected animals of the breeding population should be mated with superior animals of the same breed but unrelated to the breeding population. This often helps in restoring fertility and yield.
2. Out breeding:
Out breeding is the breeding between the unrelated animals which may be between individuals of the same breed (but having no common ancestors) or between different breeds (cross breeding) or different species (interspecific hybridization).
(i) Out crossing:
It is the mating of animals within the same breed but having no common ancestors on either side of their pedigree up to 4-6 generations. The offspring of such a cross is called as an outcross. Outcrossing is the best breeding method for animals that are below average in productivity in milk production, growth rate in beef cattle, etc. Sometimes only one outcross helps to overcome inbreeding depression.
In cross-breeding superior males of one breed are mated with superior females of another breed. Many new animal breeds have been developed by this strategy. It gives better breeds. Cows of an inferior breed may be mated to bulls of a superior breed to get better progeny. Hisardale is a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.
(iii) Interspecific Hybridisation:
In this approach, male and female animals of two different species are mated. The progeny obtained from such a mating are usually different from both the parental species.
But in some cases, the progeny may combine desirable characters of both the parents. Mule is produced from a cross between female horse (mare) and male donkey. Mules are harder than their parents and are well suited for hard work in mountainous regions.
Controlled Breeding Experiments:
These are carried out using artificial insemination and Multiple Ovulation Embryo Transfer Technology (МОЕТ).
(i) Artificial Insemination (AI):
The semen of superior male is collected and injected into the reproductive tract of the selected female by the breeder. The semen can be used immediately or can be frozen for later use. When a bull inseminates a cow naturally approximately 5 to 10 billion sperms are deposited in the vagina. However, when semen is deposited artificially, considerably fewer sperms are required to achieve conception. Therefore, artificial insemination is very economical. The spread of certain diseases can be controlled by this method.
(ii) Multiple Ovulation Embryo Transfer Technology (МОЕТ):
In this method, hormones (with FSH-like activity) is given to the cow for inducing follicular maturation and super ovulation instead of one egg, which they usually give per cycle, they produce 6-8 eggs. The cow is either mated with a best bull or artificially inseminated.
The embryos at 8-32 cell stage are recovered and transferred to surrogate mothers. The genetic mother is available for another super ovulation. МОЕТ has been done in cattle, sheep, rabbits, buffaloes, mares, etc. High milk giving breeds of females and high quality (lean meat with less lipid) meat- giving bulls have been bred successfully to obtain better breed in a short time.