Breeding of Animals

Breeding of Animals

By selective breeding variety of breeds have been developed. Only good pedigree bulls are selected for breeding as per their draught ability and milk yield of its mother. The rest are castrated to make bullock.

When breeding is between animals of the same breed it is called inbreeding, while crosses between different breeds are called outbreeding. Out-breeding is the breeding of the unrelated animals, which may be between individuals of the same breed (but having no common ancestors) is called out-crossing. The cross between different breeds is called cross-breeding or different species (inter-specific hybridisation) Inbreeding increases homozygosity. Thus inbreeding is necessary if we want to evolve 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. Therefore, this approach, where there is selection at each step, increases the productivity of inbred population. However, continued inbreeding, especially close inbreeding, usually reduces fertility and even producitivity. This is called inbreeding depression.

Methods of breeding

There are two methods : Natural breeding and artificial insemination.

Natural breeding : It may be random or controlled.

• Random breeding : A few high quality bull are kept along with the grazing cows. This brings about random breeding.
• Controlled breeding : It involves mating of native cows with superior exotic (foreign) bulls. These include Europe an breeds like Holstein, Brown Swiss, Jersy, Red Dane and others. An average cow produces 8-10 calves during its productive life time. The pregnant mare serum gonadotropin to is used to increase fertility and induce lactation in sterile cows.

Heat period : It lasts for 12-24 hours during this period a cow shows restlessness and reduced appetite and milk-yield. The average gestation period for the cow is 280 days.

Parturition : It is the birth of the foetus by the rupturing of the placental membranes. The cause of parturition is that towards the end of pregnancy, the level of oestrogen usually increases and the level of progesterone decreases. The oestrogen sensititises the uterus for the action of oxytocin. At the time of parturition oxytocin is released which directly brings about strong uterine contraction and thus initates parturition.

Artificial Insemination : The process of storing a desired male animal semen and then introducing it into the genital tract of a selected female animal by the use of suitable instruments to produce a better breed of the offspring animals is called artificial insemination. (More than 6000 artificial insemination centres have been established in different parts of our country.

Different steps involved during artificial insemination are : Collection of semen from a healthy male having desired characters; Preservation of semen by freezing or chemical methods; Injection of preserved semen, artificially into the vagina of the chosen female cattle, during its heat period; Normal reproduction process is then allowed to take place and the young animal of hybrid breed is obtained.

Advantages of Artificial Insemination : It is economical (cheaper) because semen from a single bull can  be used to impregnate several thousand cows (about 3000). Semen can easily be transported, even to remote places; High quality semen is available all the time and at all the places. A high quality bull is not always available at all the places; The method is more reliable and hygienic than the natural method of

breeding animals by mating; This method is economical and gives high rate of successful fertilization.

Fertility control

Majority of the Indian cattles are infertile, pregnant mare serum (PMS) gonadotropin is used to enhance the fertility. Stillestrol tablets are used to induce lactation in sterile & immature females. Super Ovulation and Embryo Transplantation A pedigreed bull and a high milk yielding cow are chosen for this purpose.

By hormone injection cow is induced to produce many eggs at a time.

By artificial insemination and test tube technique many embryos are formed and separately transplanted into the uterus of a carrier cow or surrogate mother.

Each blastomere of 16 cell stage if separated forms individual embryo and many embryos are formed from single zygote.

This technique is adopted also for sheep, goat and other livestock.

Cryopreservation

By deep freezing (i.e., at –196°C) in liquid nitrogen a seven days old embryo can be preserved for several years in arrested form to be used when required.