What can animal breeding do, what does it want, what should it do?
What traits does a livestock inherit, how relevant are these traits for economic animal husbandry or the health of the animals, and are there biological or ethical limits for breeding for performance? This year's spring symposium of the Academy for Animal Health (AfT) on March 7th and 8th at Montabaur Castle wanted to answer these and other questions.
Many speakers explained their topics based on dairy cattle breeding. Today, relevant traits can be recorded via inheritance models via the estimation of breeding values. The instrument of breeding value estimation flows into practical breeding work and is used in practice. In addition to pure performance data, such as the amount of milk in dairy cattle, the focus is on fertility characteristics. The importance of the breeding value "health" is also increasing. Within the framework of breeding value estimation, objectively detectable characteristics, such as milk progesterone values or new methods, such as the identification of chromosome segments, are increasingly being used. Genotype data are particularly suitable for identifying characteristics that never or rarely occur in a homozygous form or are only slightly heritable.
Great Opportunity "Precision Breeding"
Animal husbandry and molecular genetics have made tremendous strides in recent decades. In the meantime, the genomes of important agricultural livestock have been sequenced so that informative gene maps are available, starting with cattle and pigs right through to bees. Knowledge of the molecular structures opens up the use of new breeding methods such as gene editing. The so-called molecular scissors work much more accurately than previous methods. Successful areas of application of new technologies are, for example, breeding for disease resistance, breeding polled cattle or sexing. It is also possible to breed animals that can provide specific, nutritionally valuable products. In biomedical animal breeding, animals can already be produced for the production of medicines or transgenic pigs can be bred for organ donation. New breeding methods can thus contribute to more sustainable animal husbandry on the one hand and open up promising perspectives for the treatment of diseases on the other.
opportunities and limits
The symposium was not only about the question "what's up", but also about the physiological limits of the animals that have to be observed. In the past 20 years, for example, the average lactation performance of the breed `Deutsche Holstein Schwarzbunt´ could be increased from 7.000 to almost 9.500 kg milk through selection for milk production. Connections between these high achievements and at the same time lower lifetime achievements due to early departures were discussed. Particular importance must be attached to physiologically appropriate feeding. Studies show that feeding high-yielding dairy cows in the first third of lactation that is not adapted to their needs is closely associated with the occurrence of various diseases. Another point of discussion was the analysis of which animals meet the metabolic requirements and why. An interesting approach to breeding is seen in a flatter rise in the lactation curve immediately after birth. These connections need to be further explored. This includes, among other things, a complete phenotypic characterization of all characteristic areas.
Based on the realization that one-sided breeding for one trait can have negative effects on other traits, so-called functional traits are coming more into focus. Typical examples are the characteristic complexes health, fertility or behavior. Resource efficiency is becoming increasingly important for sustainable agriculture. Functional traits usually have lower heritabilities and are influenced by external factors, which makes it difficult to process them in breeding. With genomic selection, breeding values can still be determined and estimated even without performance information. However, the performance test cannot be replaced with this breeding method. Modern breeding methods and sensor-based precision breeding have meanwhile led to a large flood of data. The big challenge now is to bring this data together and use it for breeding.
breeding per health
Breeding for disease resistance was explained using examples. Efforts are being made to identify the genes involved. Multiple genes are often involved. Due to the complexity, modern methods such as gene editing are increasingly being used. The production of PRRS-resistant pigs was mentioned as a prime example, and similar concepts are being pursued with regard to African swine fever and bovine mastitis and tuberculosis.
Breeding for disease resistance in honey bees represents a special case, the peculiarity of which results from the biology of the bee. The breeding value of a queen is also determined via performance tests. Due to the worldwide trade in "good queens", the question of the transmission of pathogens through breeding material is of particular importance. The ability of bee colonies to ward off diseases depends to a large extent on their hygienic behavior towards damaged brood. One breeding goal is therefore to breed colonies for increased hygienic behavior. In recent years there have also been increased efforts to identify genomic markers for disease resistance or Varroa tolerance. The varroa mite transmits a virus that causes wing deformities.
social discourse
The diagnosis of hereditary diseases and the breeding of special pigs for biomedical research were addressed as special areas in further presentations. For example, genetically modified pigs could be used as donors for cells, tissues or even entire organs. Transplants from a donor pig to a baboon allow for high expectations in terms of reduced rejection behavior. Novel therapies in connection with diabetes seem promising. Socially relevant questions of animal husbandry and the extent to which breeding can contribute to solving conflicts between productivity on the one hand and the human-animal relationship on the other were also discussed. Modern nutritional trends in Western societies are increasingly calling into question the consumption of meat and dairy products. However, experts see the great threat to animal husbandry from the climate protection debate. "Less but better" is a requirement that must also be reflected in animal husbandry. In the future, breeding progress will no longer have to focus on a few high-performance breeds, but on breeding traits such as robustness and health. It is still unclear to what extent consumers will accept methods such as gene editing in animal breeding.
Conclusion
The symposium gave an overview of the wide range of breeding tools available today. It became clear that a lot is feasible, but the benefits have to be weighed up. Social trends and animal-ethical aspects are increasingly influencing science and the goals of animal breeding. However, the potential of breeding methods, including gene editing, also opens up new possibilities for reconciling the different requirements.
