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Production system

First, the set up starts with a description of the production system (1). In more general terms the analysis of the way we keep the animals and for which purpose. What is relevant in this respect? For a small dog only kept as a companion animal in a comfortable house behaviour and health are important. For heath sheep kept in rough conditions the whole year around fitness traits and grazing behaviour are relevant. For growing broilers in intensive systems with high production costs, daily growth is conclusive.

Breeding goal

Second, the question which traits should be improved in the next generations. What will be the goal(s) for breeding (2)? This question is highly related to the reasons for which we keep the animals. This process deserves a thorough study and a long lasting conclusion as animal breeding is only effective when a breeding goal is consequently maintained for many generations. Examples of breeding goals are defined improvements in traits of production, product quality, health and welfare traits, conformation traits, sport performance, fertility etc.

Collection of information

Third, knowing the breeding goal, relevant information should be collected (3). Relevant in this respect are traits of animals (called phenotypes) that can help to establish the value of an animal with respect to the breeding goal. When jumping performance is a breeding goal trait in horses, data on jumping are collected. When fertility of pigs is in the breeding goal, litter traits are recorded. Other relevant information is the pedigree of the animals. Animal breeding is all about passing genetic abilities from one generation to the next. When you want to trace or influence this process of passing heritable traits, a registration of the parent-offspring relationships, the pedigree of an animal, is crucial. And nowadays, DNA-analysis is possible and practised in animals and can also be used to trace or influence the passing process of genetic abilities for traits.

Breeding value estimation and selection criteria

Fourth, knowing the breeding goal and after recording relevant traits of potential parents, the choice has to be made which animals will indeed be selected as parents (4) and which animals are excluded for reproduction. Based on a genetic model, a statistical model including pedigree information, a breeding value for a trait is estimated. Nowadays, when DNA information of animals is available, it can also be used to estimate breeding values. The estimated breeding value indicates the value of the animal with respect to the breeding goal: the lowest ones will have a negative effect on the breeding goal traits and the highest ones will improve breeding goal traits.

Selection and mating

Fifth, given the estimated breeding values of sires and dams, the actual selection of parents has to take place (5). The parents with a higher than average estimated breeding value will improve the breeding goal traits in the next generation. When for example a group of dairy sires with the highest breeding value for milk yield is selected as sires for the next generations, their daughters will produce more milk than the present generation of dairy cows. Proper selection of parents will give a positive selection response in the next generations. Selection creates progress in breeding goal traits. After the selection of the parents another choice has to be made: which sire should be mated to which dam? The choice can be made e.g. on base of the pedigree information available or on the traits of the sires and the dams.

Dissemination of genetic gain

Sixth, in many breeding schemes the number of animals from which traits are recorded is rather small in relation to the population of animals used for human purposes. The dissemination of the selection response depends of the structure of the breeding programs. In commercial pigs and poultry programs selection takes place in the top of the breeding program and via a few “multiplying generations” the selection response obtained in the top is disseminated to the animals producing meat or eggs are bred. In cattle breeding artificial reproduction techniques, in particular artificial insemination techniques, give the opportunity to produce high numbers of offspring, disseminating the genes of the superior animals widely. Selection of a small number of animals may have a large impact on the traits of a population. Within the commercial breeding schemes e.g. for poultry and pigs specialized lines are crossed. These lines each are selected for specific traits and crossed in the multiplying phases to obtain crossbred progeny with the breeding goal traits by combining the traits of each of the lines.

Evaluation of results

Seventh, the breeding program should be evaluated regularly (7). The first question is: did we reach what we wanted? Is the new generation of animals better with respect to the breeding goal traits? Do we observe unwanted effects of selection? E.g. we realized a better growth of our meat producing animals, but they have more problems with their legs than their parents. The second question is: what has happened with the relatedness among the animals of the new generation. Are they more related to each other than their parents, due to the fact that we have selected only a few heavily related animals as parents for this generation? Did we decrease the genetic diversity of the population?

Then, the breeding circle starts again with a critical review of changes in the production system. Questions to be answered are: do market requirements change, e.g. for pork of a different quality? Do production circumstances change, e.g. are milk production quota for dairy farms expected to be abolished in the next future?As can be seen in the circular figure of the breeding program, 4 steps have to be set to obtain a careful, solid and effective breeding program. These seven steps are: