From which animals phenotypes should be recorded, depends heavily on traits the characteristics of the trait: growth can be measured in males and females from birth to death; milk production can only be measured in females after the first delivery of progeny; eggs can be counted after the start of the laying period. Carcass traits will be known after slaughter. Disease resistance is only expressed in the presence of pathogens. Longevity can be fully established at the end of life of an animal. Therefore for categories of traits different sources of information are used to get an impression of the genotype of the animal to be considered for selection. These sources of information are informative because they are related to the animal under consideration.
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