Breed Diversity and Results of Inbreeding

Why Is Genetic Variation Important?

Breed Diversity and Results of Inbreeding

Urgent warnings from the United Nations to protect genetic diversity apply to livestock too. The results of inbreeding and a focus on high-yielding, high-maintenance breeds raises sustainability issues in the long term. If farmers are unable to maintain favorable conditions and hardier breeds become extinct, livestock production could collapse. But how can farming be endangered when farm animals are so plentiful?

As livestock spread out from the Middle East and Asia, they adapted to the local environments in which they settled. They became the landraces of the regions, hardy and needing little input from herders, sculpted by natural selection. Their appearance grew to differ between regions. Only within the last 250 years have we focused on selection for traits that characterize breeds. The first herd books were opened in England in the nineteenth century, encouraging breeders to standardize appearance and improve production. Improved technology and industrialization of farming have intensified selection for performance, but to the detriment of the diversity within breeds.

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Genetic Diversity Definition and Importance

Different versions of genes are required for nature and people to select traits to improve performance, survival, or reproduction. If there is wide genetic variety within our animals, there will be a good number that will be able to adapt to change. However, if genetic resources diminish, offspring may not adapt, and the line will go extinct. If our animals are only suited to the current situation, they may not survive future changes.

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American Guinea hogs are landrace pigs adapted to outdoor living.

Changes may occur in the environment, climate, food availability, market preferences, and production systems. Currently, feed and medication are available for high-producing animals in intensive farms. These are high-input systems that are popular in the present economy. However, in future there may be changes in the type of feed we can grow and the availability of medication. We are already seeing resistance to drugs by parasites and disease-causing microorganisms. Local animals that are tolerant of local disease and harsh conditions are better suited to systems that require lower inputs. The variety of such animals is important to long-term food security.

Shifts in consumer demand require flexibility in breeding goals. A wide range of genetic resources is needed if producers are to meet changing requirements. A rise in welfare concerns and preferences for natural products call for animals that are productive at range, forage well, and stay healthy in outdoor conditions.

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Wild ranging black turkey by David Goehring/Flickr CC BY 2.0.

The Importance of Breeds

The difference between breeds is a practical way of recognizing the diversity that exists within farm species. When there are many breeds, we can be sure that there is some genetic diversity among our livestock. The best beef cattle breeds, landrace pig breeds, heritage chicken breeds, and rare sheep breeds for low-input systems in any area are those that have been resident for many hundreds of years. However, when few breeds become dominant in the market, such as Holstein cattle and commercial hybrid chickens and pigs, local breeds become marginalized and their population numbers drop. This threatens their very existence. Once the diversity is lost, those genes are gone forever.

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Florida Cracker and Pineywoods cattle are hardy landraces, having adapted over 500 years to the southeastern American States.

In addition, highly productive, international breeds have become very inbred. The results of inbreeding hugely diminish variation within their gene pool. If they are unable to adapt to a new system or circumstance, their survival and our food supply will be threatened. Marginalized rare breeds will then be needed to revive breeding stock.

The Danger of Narrow Trait Selection

The dairy industry has made extraordinary progress in the amount of milk produced by each animal. This was achieved by selecting for a few, easily measurable and inheritable traits: milk quantity, milk quality, and dairy conformation. However, this narrow focus has led to fertility and health issues in Holstein cattle, including the emergence of genetic disease. Although health issues are partly due to management systems and the heavy load of high-yield lactation on a cow’s metabolism, they are also related to the loss of genes for functional traits that enable an animal to stay healthy. These are much more difficult to measure, but more breeders are now incorporating health, fertility, and adaptive traits into breeding plans.

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America’s oldest landrace chicken breed, the Dominique, is still on the Livestock Conservancy watch list. Photo by Sam Brutcher/Flickr CC BY 2.0

How Results of Inbreeding Cause Diminishing Diversity

As Holstein sires’ offspring produced increased yields, a few select males were used extensively to mate thousands of cows. This initially led to great leaps in production, but also dramatically increased the level of inbreeding. Although the Holstein–Friesian population is huge, the effective population is now very small. This is because the whole population shares very few sires. If the effective population is less than 50, then conservationists consider it critically endangered. American Holsteins numbered hundreds of thousands in 2001 but their effective population size was only 37.

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Rare breed Barbados Blackbelly sheep are a rare hair sheep breed. Photo by Jennifer Kleffner/Flickr CC BY-SA 2.0.

Risks Facing Local Breeds

Local breeds have been largely displaced worldwide by high-yielding breeds. This means that their numbers have dwindled and many have already become extinct. Crossbreeding schemes result in fewer purebred animals remaining to sustain the effective population. Many local breeds are now endangered, not only due to small population sizes, but also because the results of inbreeding reduces their effective population size, with a consequent loss of diversity within the breed.

As fewer owners keep local breeds, it can be harder to source sires, and parentage is often unknown, leading to inadvertent inbreeding. Disasters and disease may further diminish small populations.

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Highland cattle by Mitchell Haindfield/Flickr CC BY 2.0.

Dilution Through Crossbreeding

The temptation to improve local breeds by crossbreeding with high-production international breeds is often driven by economic and market conditions, as well as agricultural policies. This gives a short-term benefit in increased production but has huge long-term costs. The new animals may not adapt well to local environmental, climatic, or production conditions, resulting in production losses, reduced fertility, and shorter productive lives. High-yielding animals also need higher inputs in the form of better quality nutrition and management facilities, requiring greater expenditure by the farmer. The effect on the local breed composition is devastating as local genetic traits are diluted.

There are cases where crossbreeds have saved a production system as well as a local breed. In Wales, Lleyn sheep were built up by repeatedly backcrossing crossbred females with pure sires until the population was restored. Where two breeds are well adapted to a region, their crosses may mix complementary genes and add hybrid vigor.

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Hog Island sheep heritage breed ewe by Sam Brutcher/Flickr CC BY 2.0.

The Dangers of Breed Standardization

Landraces fit their environment and cultural use while retaining the natural variation that allowed them to be improved for production. In recent years, breed societies have set standards assigning a characteristic appearance to each breed. Although landrace animals may vary widely in coat and other superficial traits, many animals are excluded on the basis of being the wrong color, having asymmetrical horns, or because of other benign external variations. The diversity of these animals is removed from the gene pool, even though some of their other traits would have been useful to production or survival. In this way, potentially useful diversity within the breed is lost.

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Smart Breeding to Future-Proof DNA

Modern breeding strategies aim at improving breeds for future needs in a sustainable way. Inbreeding is controlled by using higher numbers of unrelated males, minimizing the number of females they cover, and keeping long genealogy records. Breeding goals give higher weighting to functional traits, namely health, survival, efficiency, robustness, and fertility. The latest technology is being used to study complex characteristics such as adaptation to various environments and disease resistance.

Universities are active in the conservation of local breeds, including breeding, improving, and stocking gene banks. These efforts will not only preserve robust animals, but also optimize improvement for production while maintaining genetic diversity. Improvement of a local breed for production by straight breeding is a slower strategy than restocking with an already improved breed or by crossbreeding with it. However, in the long run, straight breeding is a sounder policy, as local adaptations will be retained.

Organizations involved in breed preservation and promotion are important to the continued survival of local breeds. Equally valuable are the backyard and alternative farmers who commit to keeping heritage breeds. In Europe, government schemes encouraging regional specialties have helped farmers to create niche markets for artisan products derived from traditional animals.

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Red Devon Cattle

The Food and Agriculture Organization of the United Nations (FAO) is concerting a worldwide effort to catalog and preserve livestock genetic resources. We can be a part of this by supporting rare-breed conservation efforts, keeping local breeds, planning functional breeding goals, employing a wide range of selection criteria, minimizing inbreeding, and finding ways to utilize local breeds in small enterprises. Niche products, the organic market, landscape management, and agritourism ideas are growing opportunities for creating income from local breeds. By keeping heritage breeds in production and through careful breeding plans, we can safeguard their genetic resources for the future.

References:

FAO. 2007. The State of the World’s Animal Genetic Resources for Food and Agriculture. Rome: Food and Agriculture Organization of the United Nations.

FAO Domestic Animal Diversity Information System (DAD-IS).

FAO. 2012. Progress made in stopping decline of livestock genetic diversity.

FAO. 2016. Genetic diversity of livestock can help feed a hotter, harsher world.

The Livestock Conservancy.

Taberlet, P., Valentini, A., Rezaei, H. R., Naderi, S., Pompanon, F., Negrini, R., and Ajmone‐Marsan, P. 2008. Are cattle, sheep, and goats endangered species? Molecular Ecology, 17(1), 275-284.

Tisdell, C. 2003. Socioeconomic causes of loss of animal genetic diversity: analysis and assessment. Ecological Economics, 45(3), 365–376.

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