- International genetic evaluation is an important development in modern animal breeding that allows animals from different countries to be compared according to their genetic merit. Livestock breeding has become increasingly international because genetic material, including semen, embryos, and breeding animals, is exchanged across national borders. However, animals are raised under different climates, feeding systems, management practices, disease conditions, and production environments. These differences make it difficult to compare their performance directly. International genetic evaluation addresses this challenge by combining genetic and performance information from multiple countries and using statistical methods to produce comparable estimates of breeding merit. This approach helps breeders identify superior animals internationally and supports the long-term genetic improvement of dairy cattle, beef cattle, sheep, pigs, and other livestock species.
- The main purpose of international genetic evaluation is to provide a reliable basis for comparing animals that have been evaluated in different national breeding systems. Each country may use its own recording procedures, genetic evaluation models, trait definitions, and reference populations. For example, dairy cattle breeding programs may measure milk yield, fat percentage, protein percentage, fertility, udder health, longevity, and other functional traits. Although these traits may have similar names across countries, their definitions, measurement periods, and economic importance may differ. Directly comparing national breeding values without accounting for these differences can lead to misleading conclusions. International evaluation systems attempt to overcome these limitations by developing methods that allow genetic merit to be compared more meaningfully across populations.
- One of the main challenges in international genetic evaluation is the influence of environmental conditions on animal performance. An animal’s observed performance reflects both genetic potential and environmental effects, including nutrition, housing, climate, disease exposure, and management. A genetically superior animal in one country may not perform in exactly the same way under the production conditions of another country. In addition, some genetic differences may be expressed differently across environments. For example, a dairy cow selected for high milk production under intensive feeding conditions may not have the same relative advantage in a low-input production system. International genetic evaluation must therefore account for environmental variation and, where relevant, differences in the expression of genetic merit across production environments.
- The concept of genotype-by-environment interaction is particularly important in international evaluation. This interaction occurs when genetic differences among animals depend on the environment in which they are raised. In some cases, environmental conditions change the magnitude of genetic differences without substantially changing the ranking of animals. In other cases, the ranking itself may change, meaning that an animal considered genetically superior in one environment may be less favorable in another. When these interactions are important, a single international ranking may not fully represent the genetic suitability of animals for every production system. Statistical models can account for these differences by treating the same trait measured in different environments as related but distinct traits, allowing breeders to evaluate genetic merit for specific production conditions.
- International genetic evaluation is strongly associated with the exchange of breeding information between countries. National breeding organizations collect performance records, pedigree information, genomic data, and other relevant measurements. These data are analyzed within national genetic evaluation systems to estimate breeding values. International evaluation organizations then use information from participating countries to establish comparable international evaluations. In dairy cattle, for example, the International Committee for Animal Recording (ICAR) supports international cooperation on animal identification and performance recording standards, while Interbull coordinates international genetic and genomic evaluations for dairy cattle. These organizations help improve the consistency and comparability of genetic information used by breeders around the world.
- Interbull has played a major role in international dairy cattle genetic evaluation. Its international systems allow participating countries to compare dairy bulls and other evaluated animals using information from multiple national breeding programs. A widely recognized approach is the multiple-trait across-country evaluation method, commonly referred to as MACE. Under this approach, the same biological trait measured in different countries can be treated as a separate but genetically correlated trait. This allows the evaluation to account for differences in trait definitions, national evaluation procedures, and genotype-by-environment interactions. International evaluations can then provide breeding values that help breeders assess the suitability of animals for different national production systems.
- The multiple-trait across-country evaluation approach is important because national breeding values are not always directly comparable. Different countries may use different genetic bases, measurement units, statistical models, and trait definitions. MACE uses genetic relationships between national expressions of a trait to estimate international genetic merit. The method also uses information from connected populations, including bulls with progeny records in more than one country, to improve the comparison of animals across national systems. This makes it possible to use information from a wider international population rather than relying only on the records available within a single country.
- International genetic evaluation may also involve conversion equations that translate breeding values from one country’s scale to another. Conversion equations are generally developed using animals evaluated in both countries or other suitable genetic links between populations. These equations account for differences in the scale and genetic base of national evaluations. However, conversions are not perfect substitutes for comprehensive international evaluation because they may not account fully for all differences in genetic relationships, trait definitions, and environmental conditions. The reliability of converted values depends on the quality and number of reference animals, the genetic relationship between populations, and the suitability of the conversion method.
- Genomic selection has introduced additional opportunities for international genetic evaluation. Genomic estimated breeding values are predicted using DNA marker information, often combined with phenotypic and pedigree data. International cooperation can increase the size and diversity of genomic reference populations, providing more information for predicting the genetic merit of young animals. A larger reference population may improve prediction accuracy, especially for traits that are expensive or difficult to measure. However, genomic predictions do not always transfer equally well between countries or breeds. Differences in allele frequencies, genetic relationships, linkage disequilibrium, trait recording, and production environments can affect genomic prediction accuracy. International genomic evaluation therefore requires careful validation and appropriate methods for combining data from different populations.
- The accuracy of international genetic evaluation depends on the quality of the information supplied by participating countries. Reliable animal identification, accurate pedigrees, standardized performance records, and consistent trait definitions are essential. Errors in identification or data recording can affect the estimated genetic merit of individual animals and their relatives. Differences in national data collection procedures may also introduce inconsistencies that need to be addressed before international comparisons can be made. International organizations and national breeding programs must therefore cooperate to maintain high standards of data quality, documentation, and statistical analysis.
- International evaluation also depends on genetic connectedness among countries. Connectedness refers to the extent to which populations are genetically linked through shared animals, ancestors, or breeding material. For example, when bulls or their close relatives have offspring recorded in several countries, their genetic information can help establish relationships between national populations. Greater connectedness generally improves the ability to compare animals across countries and distinguish genetic differences from differences in environmental conditions. When populations have limited genetic links, international comparisons may be less precise. The expansion of international artificial insemination, genomic testing, and the exchange of genetic material has increased connectedness in many livestock breeding populations.
- One of the major benefits of international genetic evaluation is the wider range of breeding candidates available to farmers and breeding organizations. Instead of selecting animals only from a national population, breeders can identify superior animals evaluated in other countries. This can accelerate genetic progress by increasing access to favorable genetic characteristics for production, fertility, health, longevity, and other important traits. International evaluations also allow countries to use information from animals that may not be directly available for testing in their own herds. This is particularly valuable for traits that require large populations or extensive progeny testing to evaluate accurately.
- International genetic evaluation can also improve the efficiency of breeding programs. The development of reliable genetic evaluations requires considerable investment in performance recording, pedigree management, genomic testing, and statistical infrastructure. By participating in international evaluation systems, countries can benefit from a broader pool of information and established evaluation methods. International collaboration can reduce duplication of effort, improve the quality of genetic comparisons, and provide access to breeding values supported by more extensive data. Smaller breeding populations may benefit particularly from international cooperation because they can use information from larger connected populations to improve the evaluation of their own animals.
- Although dairy cattle have been at the forefront of international genetic evaluation, similar principles can be applied to other livestock species. Beef cattle breeding can benefit from international comparisons for growth rate, carcass quality, fertility, calving ease, feed efficiency, and maternal traits. Sheep and goat breeding programs may exchange information about wool production, meat quality, milk yield, parasite resistance, and adaptation to challenging environments. Pig breeding programs can use international data to evaluate growth, feed conversion, reproductive performance, and carcass traits. Poultry breeding programs may also benefit from international data sharing for egg production, growth, feed efficiency, fertility, and disease resistance. The specific methods used depend on the species, the trait, the structure of the population, and the availability of comparable data.
- International genetic evaluation must also consider differences in breeding objectives among countries. The economic value of a trait can vary depending on feed costs, product prices, climate, production systems, animal welfare standards, and market requirements. For example, high milk yield may be especially important in one production system, while fertility, heat tolerance, or disease resistance may receive greater emphasis in another. International breeding values provide information about genetic merit, but the most suitable animal for a particular farm depends on the breeder’s objectives and local conditions. Selection indexes should therefore be developed or interpreted according to the needs of the target production system rather than assuming that the highest-ranked animal internationally is automatically the best choice for every farm.
- The genetic base used in international evaluation is another important consideration. National and international breeding values may be expressed relative to different reference populations, average values, or base years. As a result, numerical breeding values from different systems may not be directly comparable without appropriate adjustment. International evaluation organizations provide defined scales and reporting systems to support interpretation, but users must understand the meaning of the published values. Rankings should be interpreted alongside information about trait direction, units, reliability, and the population for which the evaluation is intended.
- Reliability and uncertainty are also important in international genetic evaluation. An animal’s international breeding value is an estimate based on the information available from participating countries and the statistical relationships among their populations. Reliability depends on the number and quality of records, the genetic connectedness of the populations, the accuracy of national evaluations, and the suitability of the international model. Animals with extensive progeny information across several countries may have highly reliable evaluations, while young animals with limited records may have greater uncertainty. Genomic information can improve evaluations for young candidates, but its reliability depends on the quality and relevance of the reference data. Breeders should consider these factors when using international rankings to make selection decisions.
- International genetic evaluation also presents practical and organizational challenges. Countries may use different recording technologies, data formats, trait definitions, privacy arrangements, and policies governing the exchange of genetic information. The cost of data collection and genomic testing may differ considerably between breeding systems. Some countries may have limited access to advanced recording infrastructure or large reference populations. These differences can reduce the completeness and comparability of international datasets. Continued collaboration, standardized procedures, transparent reporting, and investment in data infrastructure are essential for addressing these challenges and expanding the benefits of international evaluation.
- The future of international genetic evaluation will likely involve closer integration of genomic information, advanced statistical models, automated recording technologies, and larger international databases. Improvements in DNA sequencing and genotyping may provide more detailed information about genetic variation, while machine-learning approaches may help researchers analyze complex datasets. However, advanced technology must be supported by accurate phenotypic records, sound quantitative genetics, and independent validation. International breeding systems will also need to consider animal welfare, climate resilience, environmental sustainability, and the conservation of genetic diversity. These objectives are increasingly important as livestock production faces changing climates, evolving disease risks, and growing demands for efficient and sustainable food production.
- In conclusion, international genetic evaluation is a valuable tool for comparing the genetic merit of animals across countries and improving the efficiency of global breeding programs. By combining information from national evaluations, pedigree records, performance data, and genomic technologies, international systems provide breeders with a broader and more informative basis for selection. Methods such as MACE help account for differences among national evaluation systems and the possibility that animals perform differently across environments. Although challenges remain in data quality, genetic connectedness, trait comparability, and prediction accuracy, international cooperation continues to strengthen genetic evaluation. When international breeding values are interpreted in relation to local breeding objectives and production conditions, they can support faster genetic progress, better animal selection, and more sustainable livestock production worldwide.
