Lecture 10: Breeding and Genetics

Part 1 (20 minutes) – Explain the topic in an understandable way

Breeding means that humans select and mate animals so that certain traits become more common in the next generation. These traits can concern appearance, behavior, or performance. Breeding is a targeted process of selection and reproduction: people set intentions (breeding goals) and promote animals with desired traits as parents of the next generation. This is how many dog breeds, different livestock breeds and forms of domestic cats have arisen.

An easy picture is sorting building blocks: if you only want to keep red blocks, you remove all other colors and build only with red ones. After many rounds you will have almost only red blocks. In breeding it works similarly: whoever repeatedly selects for certain traits increases the associated genes in the population. This is not a miracle, but biology.

With companion animals such targeted selection can become problematic. Harmful breeding (German: Qualzucht) means that animals are bred in ways that frequently cause health problems or suffering because the desired appearance or behavior is extreme. A typical example are short-faced (brachycephalic) dog breeds like the pug. In these breeds the skull is so shortened that the airways are constricted. This can lead to breathing difficulties, sensitivity to heat and, in some animals, also eye or skin problems. German animal-welfare organizations and veterinary institutions describe these connections clearly and see considerable animal welfare problems in some bred traits (see Deutscher Tierschutzbund; RSPCA).

In livestock the counterpart is high-performance breeding: breeders select animals for maximal performance, for example very high milk yield in cows, rapid growth in broiler chickens or many eggs in laying hens. This selection has greatly increased productivity, but it also brings side effects. Consequences can include metabolic strain, fertility problems, increased susceptibility to disease or locomotion issues. Institutions dealing with animal health and agriculture document these relationships and recommend designing breeding goals so that animal welfare is not systematically worsened (see FAO; EFSA).

Important: breeding works across generations. Positive changes for health take time; negative effects can also become entrenched in a population over long periods. Therefore breeding decisions are always decisions about the future of animals and about the responsibility of the people who keep, breed or manage them.

Part 2 (20 minutes) – Technical terms and in-depth explanation

Some basic terms of genetics and breeding are useful to conduct the discussion factually. A gene is a segment of hereditary information (DNA) that carries a specific unit of inheritance. Different variants of a gene are called alleles. The visible expression of a trait (for example "short face" or "high milk yield") is called the phenotype; the underlying genetic information is the genotype.

Heritability is a term that indicates how much of the observed variation of a trait in a population can be explained genetically. A trait with high heritability can be changed well by breeding; traits with low heritability will respond less to selection because environmental factors have a large influence. For many performance traits in livestock heritability is moderate to high, which is why breeding programs are very effective.

Inbreeding means mating closely related animals. Inbreeding increases the probability that offspring inherit two identical alleles of a gene (homozygosity). This can cause harmful recessive alleles to become more likely to be expressed, i.e. hereditary diseases become more visible. At the same time inbreeding can temporarily stabilize desired traits. The loss of genetic diversity is, however, a long-term risk because fewer different genes are available to respond to new challenges (e.g., diseases, environmental changes).

Another important term is breeding goal: the desired bundle of traits toward which breeding is directed. Breeding goals can be purely cosmetic (e.g., a specific head shape), performance-related (e.g., milk yield) or also include health and behavioral traits. Modern, responsible breeding programs recommend formulating breeding goals that include animal health and welfare and do not promote only external traits or pure performance figures (see FAO).

Genetic correlations describe that two traits can be genetically linked. If, for example, high milk yield is genetically correlated with lower fertility, then selection solely for milk quantity will unintentionally lead to poorer fertility. Such correlations explain many observed side effects of high-performance breeding. Therefore multidimensional breeding goals and index selection, which weight multiple traits simultaneously, are important to manage trade-offs.

Methodologically there is traditional breeding (selection based on visible traits and studbook data) and modern methods such as genomic selection. In genomic selection many DNA markers are used to estimate an animal's genetic predisposition early and more accurately. These methods can help spread positive traits faster and reduce unwanted health traits, provided the right targets are measured and prioritized.

In companion animals — especially in cases of harmful breeding — selection for extreme optical traits often plays a larger role than in livestock. Examples: extremely shortened muzzles (brachycephaly), very flat noses, excessive skin folds, very short legs or extreme eye shapes. Animal-welfare authorities state that there is a scientific consensus that these traits are associated with increased health risks; therefore they advise breeding changes or restrictions (see Deutscher Tierschutzbund; RSPCA).

In livestock, international organizations have pointed out that selection for maximal performance without consideration of animal health can systematically exacerbate animal welfare problems. In response, recommendations and programs exist to expand breeding goals to include health and robustness traits. Nevertheless, practical limits remain: economic incentives, long generation intervals and the lack of standardized data collection for health traits often impede rapid changes (see FAO; EFSA).

In conclusion on the terminology: breeding is a powerful tool. Whether it serves or harms animal welfare is decided by the breeding goals, the type of selection, the maintenance of genetic diversity and the willingness to systematically measure and reward health traits.

Part 3 (10 minutes) – Applications, limits and thought exercises

Applications: Responsible breeding programs can improve animal welfare. Examples of sensible measures are introducing health checks as mandatory selection criteria, promoting outcrossing when it introduces health-promoting genes, and collecting health data (e.g., breathing problems, joint status, fertility) that feed into breeding decisions. In livestock operations breeding indexes can be designed so that not only performance but also robustness, longevity and fertility are weighted positively. International bodies also recommend conservation programs for genetic diversity to secure long-term adaptability (see FAO).

Limits and transparency: There are scientific uncertainties for many complex traits. Not all diseases or poorer welfare states are easy or early to measure; some genetic relationships are complex and environmental factors play a large role. Economic pressures can lead to short-term profitable but long-term problematic breeding practices persisting. Moreover, ethical decisions — for example whether a certain form of outcrossing or limitation of breeding animals is acceptable — are not purely scientific but require societal discussion.

Short class thought exercises (brief discussions, each 3–5 minutes):

1) Imagine you are breeders of a dog breed in which many animals show breathing problems. Which three criteria would you propose for a new breeding goal that consider both animal welfare and breed-specific traits? Briefly justify your choices.

2) You operate a dairy farm: the current herd gives very high milk yields, but many cows have fertility problems. What speaks in favor of weighting fertility higher in future breeding, and what disadvantages could this have (e.g., accepting lower milk yield)?

3) Briefly consider: What role do legislation, breeding associations and buyers (e.g., dog buyers, farmers) play in changing breeding practices? Who can influence most — and why?

For each of these points: there is no simple, universal solution. Progress requires transparent data collection, clear breeding goals, involvement of practitioners and scientists, and societal debates about which compromises we are willing to accept. There is scientific consensus that excessive selection for extremes often endangers animal health; corresponding recommendations from animal-welfare and specialist organizations are based on this (see Deutscher Tierschutzbund; RSPCA; FAO; EFSA).

Note on uncertainties and data gaps: For many specific breed problems and for different types of operations there is often a lack of standardized, comparable health data. This makes it difficult to precisely estimate the extent of some problems and to evaluate countermeasures. Likewise, genetic relationships for complex traits are partly still the subject of current research. These uncertainties should be openly acknowledged in political and professional decisions.