Information of ancestors
When an animal is born, or even when an embryo is available, a breeder likes to know the value of this individual for breeding. Is this young animal only capable to perform the intended job, production, leisure activities or company or can I use this animal also as parent for the next generation? Can I use it to improve future generations? The first opportunity is to study the pedigree and to collect all the information of the ancestors in the pedigree. The information of the parents is very valuable as the additive genetic relationship between parents and its progeny is 0.5. Information of grandparents and ancestors in later generations is only valuable when the information of parents is absent or limited. For, alleles that are not passed from a grandparent to a parent cannot be present in the animal at stake. Pedigree information is very useful at the time that the traits or performance of an animal itself cannot be established (yet). You may think of males you want to select for traits only expressed in females and of traits only expressed after puberty (milk and egg production, fertility), after slaughter (carcass traits) or late in life (age related defects, longevity).
Information of the animal itself
As soon as a trait can be measured on the animals itself, the value of the information of its ancestors becomes less. Then, the genetic value of the animals is expressed and it becomes clear which 50 % of the genetic value of the sire and of the dam went to this particular animal. Own information is very valuable when a trait has a high heritability. Hence, the measurement errors or environmental effects for that trait are very limited.
Information of sibs
In some species, poultry and pigs, full sib families exists. In poultry, hens and cocks can be mated and subsequently they may produce hundreds of full sibs. In pigs an average litter comprises 14 piglets being full sibs. The additive genetic relationship among full sibs is 0.5 and this means that full sib data give indeed information on the breeding value of an individual full sib. In case were full sibs are born spread over time, older full sibs might be informative for the breeding value of a younger one. An application of sib selection is seen in pigs were carcass data of a slaughtered full sib is used as information for the carcass traits of a full sib to be selected for breeding. In dogs a full sib trained as seeing-eye dog can give information for a full sib to be selected for a seeing-eye dog breeding program. In most species sires are mated to several dams and in this way half sib groups are created. The additive genetic relationship among half sibs is not that high (0.25). Information of a single half sib has a rather low value for an individual half sib to be selected. Only when a high number of half sibs is available, this information is valuable.
Information of half or full sib groups
In most species sires get relatively large half sib groups. The most pronounced example are dairy bulls used in artificial insemination programs. In the traditional dairy cattle breeding programs young sires produce a first group of daughters. With the first crop of daughters often consisting of more than 50 daughters each with an additive genetic relationship with the sire of 0.5, it is a very informative half sib group. In some species, pigs, poultry, dogs or fish full sibs are born. The individuals within a litter all have an additive genetic relationship of 0.5 with their dam and with their sire. Full sib groups can be a very valuable source of information.
Combination of information sources
In breeding programs data of animals are sampled and stored continuously in databases. These databases contain traits from ancestors, living breeding animals to be selected, their sibs and their progeny. For living animals, to be selected for breeding, all these data can be combined in statistical methods to estimate their breeding value. The number of generations between the animal to be selected and the animal from which interesting data are stored in the database determines the additive relationship and the usefulness in estimating the breeding value of the animal to be selected. In addition the value of the information depends on the nature of the character (sex limited, when can it be measured in life etc.). And numbers of relatives with data are important: one granddaughter with carcass data is hardly informative for the genetic value of a grandsire, but when there are thousands of granddaughters, as is the case in pork production, these data are very valuable.