A breeding system in which unrelated livestock are mated is known as crossbreeding. The offspring (or progenies) of crossbred livestock are heterozygous for those traits that differ in their parents and the greater the degree of heterozygosity on the offspring. A crossbred progeny
inherit the totality of parental characteristics and tend to resemble each other.
First-cross generations are usually superior in productive traits to the mean values of both parents. This phenomenon is known as Hybrid Vigour or Heterosis. The degree of hybrid vigour depends on the extent to which the characteristics of the parental stock are complementary.
In general, the greater the differences in the parental genetic make-up the greater the degree of hybrid vigour which may be expressed in terms of improved fertility, viability and general thriftiness. The degree of heterosis depends also upon the level of the environment (Barlow, 1981), such that the more stressful the environment the greater the heterosis.
Hybrid vigour, however, disappears when hybrids are mated and in the offspring produced. As such new parental stock are continually required if livestock owner wishes to apply or use hybrid vigour optimally.
Read Also: Livestock Breeding in the Tropical Environment
Crossbreeding may be useful in three ways to livestock owner in the tropics. It can be used for breeding replacement stock. The indigenous and low-producing livestock can be upgraded by continually backcrossing them to more highly productive exotic/introduced stock.
New synthetic breeds can be produced by cross breeding indigenous with introduced stock and then selecting the type of animal or trait required. Both advantages: hybrid vigour and being complementary can be achieved by using some form of systematic crossbreeding between 2 or more breeds of indigenous and introduced stock.
Genetic engineering or recombinant DNA technology is a new practice likely to become needful in the near future as it is possible to use it for modification of the function of animals for better adaptation and productivity. New generation of animals may be made through this technology.
Presently, the technique is being exploited in production of vaccines for use against some animal viruses. It is possible to copy genes or manipulate to increase bulk of genetic materials by introducing genes into bacteria and inducing the same to multiply or reproduce very rapidly, attenuated and used for vaccine production. This method is known as gene cloning. Foot and mouth disease vaccine of cattle is being prepared by this technology.
Read Also: Modern Approach to Livestock Breeding
