Theory:

A breed is a group of animals of common origin within a species with certain distinguishing characters not found in other members of the same species, like general appearance and other striking features.
Breeding entails mating parents of different varieties, each possessing a desirable trait passed onto the offspring.
Animal breeding involves producing improved breeds of domesticated animals by improving their genotypes through selective mating.
  
Objectives of animal breeding:
 
Animal breeding improves the genotypes of domesticated animals. The main objectives of animals breeding are:
 
a. Improved growth rate
 
b. Increased production or increased yield of milk, eggmeat, wool etc. To improve the desirable traits that enhance the yield.
 
c. Superior quality of milk, eggmeat, wool etc.
 
d. Improved resistance to the different types of diseases.
 
e. Increased productive life and reproduction rate.
 
Methods of Animal Breeding:
 
There are two methods of animal breeding. These include:
 
i. Inbreeding - When breeding takes place between animals of the same breed, it is called inbreeding.
  
ii. Outbreeding - The cross between different breeds is called outbreeding
1. Inbreeding:
Inbreeding is mating closely related animals within the same breed for roughly \(4 - 6\) generations.
The superior males and females of the same breed are identified and mated in pairs. It aids in the accumulation of superior genes and the elimination of undesirable genes.
 
Inbreeding increases homozygosity and is adopted to develop a pureline.
  
Inbreeding depression:
 
When continued for prolonged periodsinbreeding has a negative impact on fertility and productivity. It exposes the harmful recessive genes, which are eliminated through selection. When inbreeding depression occurs, the selected animals of the breeding population must be mated with superior animals of the same breed but unrelated to the breeding population. This helps in restoring fertility and yield.
 
Shetland_pony_inbred.jpg
Inbreeding depression exposes the harmful recessive genes
Reference:
https://commons.wikimedia.org/wiki/File:Shetland_pony_inbred.jpg