Animal Breeding

A. Animal breeding : Breeding of animals is a central pillar of animal husbandry, aimed both at increasing the overall yield obtained from an animal and at improving the desirable qualities of whatever product it supplies — for example, increased milk production, better meat or wool quality, or the maximum possible number of eggs laid per year. A breed, in this context, is defined as a group of animals related by descent that closely resemble one another in most characters — general appearance, distinguishing features, body size and configuration.

Inbreeding. Inbreeding is the mating of closely related individuals, carried out for four to six generations. Because related individuals share more of their genes, inbreeding steadily increases homozygosity within the line, and over successive generations it produces pure, true-breeding lines of animals. This is genuinely useful — it helps eliminate harmful recessive genes (since they become homozygous and are then selected against) and helps accumulate superior genes together in one line — but inbreeding also has a real drawback: carried on too long, it tends to reduce fertility and productivity, a phenomenon generally known as inbreeding depression.

Outbreeding. Outbreeding, in contrast, is the mating of unrelated animals — they may even belong to the same breed, provided they share no common ancestor for four to six generations. Outbreeding takes three specific forms in the chapter:

• Outcrossing: mating between unrelated animals of different species, which helps directly remove or reverse inbreeding depression.
• Cross-breeding: mating a superior male of one breed with a superior female of a different breed, in order to combine desirable characters from both breeds into a genuinely new breed. The sheep breed Hisardale is a real Indian example, developed in Punjab by crossing Bikaneri ewes with Marino rams.
• Interspecific hybridization: breeding animals of two different but related species, again to combine desirable characters from both parents — though such crosses are not always successful. The mule, produced by crossing a horse with a donkey, is the classic example. …