Breeding of animals is an important aspect of animal husbandry. Animal breeding aims at increasing the yield of animals and improving the desirable qualities of the produce.
For what kind of characters would we breed animals? Would the selection of characters differ with the choice of animals? What do we understand by the term ‘breed’?
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. Find out the names of some common breeds of cattle and poultry in the farms of your area.
When breeding is between animals of the same breed it is called inbreeding, while crosses between different breeds are called outbreeding.
Inbreeding : Inbreeding refers to the mating of more closely related individuals within the same breed for 4- 6 generations. The breeding strategy is as follows – superior males and superior females of the same breed are identified and mated in pairs.
The progeny obtained from such matings are evaluated and superior males and females among them are identified for further mating. A superior female, in the case of cattle, is the cow or buffalo that produces more milk per lactation. On the other hand, a superior male is the bull, which gives rise to superior progeny as compared to those of other males.
Try to recollect the homozygous purelines developed by Mendel as discussed in Chapter 5. A similar strategy is used for developing purelines in cattle as was used in case of peas. Inbreeding increases homozygosity. Thus inbreeding is necessary if we want to evolve a pureline 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 productivity. This is called inbreeding depression. Whenever this becomes a problem, selected animals of the breeding population should be mated with unrelated superior animals of the same breed.
This usually helps restore fertility and yield.
Out-breeding : Out-breeding is the breeding of 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 (inter-specific hybridisation).
Out-crossing: This is the practice of 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 mating is known as an out-cross.
It is the best breeding method for animals that are below average in productivity in milk production, growth rate in beef cattle, etc. A single outcross often helps to overcome inbreeding depression.
Cross-breeding: In this method, superior males of one breed are mated with superior females of another breed. Cross-breeding allows the desirable qualities of two different breeds to be combined.
The progeny hybrid animals may themselves be used for commercial production. Alternatively, they may be subjected to some form of inbreeding and selection to develop new stable breeds that may be superior to the existing breeds.
Many new animal breeds have been developed by this approach. Hisardale is a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.
Interspecific hybridisation: In this method, male and female animals of two different species are mated. In some cases, the progeny may combine desirable features of both the parents, and may be of considerable economic value, e.g., the mule (Figure 9.2).
Do you know what cross leads to the production of the mule?
Controlled breeding experiments are carried out using artificial insemination. The semen is collected from the male that is chosen as a parent and injected into the reproductive tract of the selected female by the breeder.
The semen may be used immediately or can be frozen and used at a later date. It can also be transported in a frozen form to where the female is housed. In this way desirable matings are carried.
Artificial insemination helps us overcome several problems of normal matings. Can you discuss and list some of them? Often, the success rate of crossing mature male and female animals is fairly low even though artificial insemination is carried out.
To improve chances of successful production of hybrids, other means are also used. Multiple Ovulation Embryo Transfer Technology (MOET) is one such programme for herd improvement.
In this method, a cow is administered hormones, with FSH-like activity, to induce follicular maturation and super ovulation – instead of one egg, which they normally yield per cycle, they produce 6-8 eggs. The animal is either mated with an elite bull or artificially inseminated. The fertilised eggs at 8–32 cells stages, are recovered nonsurgically and transferred to surrogate mothers.
The genetic mother is available for another round of super ovulation. This technology has been demonstrated for cattle, sheep, rabbits, buffaloes, mares, etc. High milkyielding breeds of females and high quality (lean meat with less lipid) meat-yielding bulls have been bred successfully to increase herd size in a short time.