Photo of a man in a checked shirt (Tomas Bergström, SLU) standing next to a brown horse in a stable.
Tomas Bergström leads the newly launched research project involving horses, dogs, cows, and sheep. Photo: Lisa Chröisty, SLU

The price of perfection: Opting out of variety - a danger to animal immunity and survival

News published:  02/09/2025

For thousands of years, humans have been controlling the breeding of dogs, horses and farm animals. Despite the benefits, this has led to unexpectedly high risks for the animals. With knowledge from research, now might be the time to re-evaluate breeding decisions.

 

Breeding today can be compared to a quest to fint the “perfect” - healthy, high-performing, or high-producing - individual. But the idea that this is beneficial is an illusion.

This is how researcher Tomas Bergström begins the conversation about the newly launched research project on sustainable genetics in animal species such as dogs, horses, sheep, and cows. He then continues:

But what we need to understand is that a “perfectly” healthy animal is only optimal for a certain period of time and under certain conditions. In our changing and vulnerable world, what is really needed within species is not uniformity, but variety. 

So how can breeding strategies that actively avoid diseases and work to produce the healthiest and best performing animals possible actually be harmful? Doesn't that sound like a paradox?

It does: Let's go through it from the beginning.

How breeding for health can actually increase the risk of disease

For many thousands of years, humans have controlled the breeding of domestic animals and thus the evolution of dogs, horses and farm animals. This means that natural evolution (through natural selection), where the animals best suited for survival are those that pass on their genes, is partially disrupted. In many cases, we instead breed for attributes like appearance, performance and production but have too little focus on health and the preservation of genetic variation for long-term resistance to new forms of infectious diseases.

Something that is perhaps more important than ever today: global warming and international travel are increasing the number of infectious diseases in circulation, and our animals, just like us, are becoming increasingly vulnerable. This makes a highly functional immune system more important than ever for the health of our animals and the long-term survival of species.

"So todays idea of 'breeding for health' is not really valid: we have become too good at selecting out animals with a predisposition to certain diseases, that we risk weakening the immune system of entire species," says Tomas Bergström.

Why? Because it has been shown that genetic variation is one of the most important characteristics of resilient species with strong immune systems.

Thinking about the stock market and spreading the risks

Many people are aware that it is considered wise to spread your risks when investing in the stock market. The same seems to apply in genetics:

The body's immune system, which protects our animals as well as ourselves against intruders in the form of viruses, bacteria, fungi, and parasites, is designed differently in different individuals. This makes us as individuals more or less susceptible to different types of infections and diseases.

But what many people overlook, says researcher Tomas Bergström, is that the same animals that are susceptible to certain diseases may be the most resistant to other infections. The same individual can therefore be both “vulnerable” and “resistant.”

In humans, this became clear not least when the COVID-19 pandemic struck. Some people were affected severely, some got a normal flu, and some hardly got ill at all. This is partly because our immune systems are... different.

And therein lies the major risk associated with both matador breeding (see fact box below) and the extreme selection of breeding animals that is currently taking place in an attempt to “weed out” disease carriers: we are losing variation and creating animal species where all individuals are far too similar to each other. This poses a huge risk for the future, when pandemics can arise also among our production and domestic animals.

About: Matador breeding

Refers to the overuse of a single breeding animal, often a male dog, stallion, or bull, which produces an unreasonable number of offspring because the animal is very popular. This leads to reduced genetic variation and thus increased risks for the species.

A new approach to “healthy” breeding – well thought-out and inclusive

Of course, the research does not advocate breeding freely from animals that carry or risk passing on serious diseases. Instead, it is about examining each individual and matching them correctly. For example, many diseases require both the female and male animal to carry the predisposition for the specific disease in order for it to develop in their offspring. 

Therefore, it is more about making the right match than ruling out breeding animals, something this project can help with, says project manager Tomas Bergström, researcher at SLU.

How can research contribute?

This research project focuses on mapping an important part of the immune system called MHC. One of the aims is to make it easier for breeders of animals such as horses, dogs, cows, and sheep to make breeding matches that promote health in a long-term and resilient way. An opportunity to once again improve the species' chances of a strong, varied, and resilient immune system.

In very simple terms, MHC functions as a “grabber tool” that locates, captures, and alerts the rest of the immune system when a harmful substance in the form of a virus, bacterium, parasite, or fungus enters the body. And here's the important part: different variants of MHC detect different types of infectious agents.

An important aspect of future breeding may therefore be to match individuals with different MHC variants, in order to contribute to breeds and species where the immune system is capable of handling as many different types of harmful attacks as possible, says Tomas Bergström, research leader.

In order to make the right matches, a test is needed to see which variant of MHC each breeding animal has in its immune system. And before that can be developed, it is necessary to map which variants of MHC exist in these different species of animals: horses, dogs, sheep, and cows.

That is what the research group will now do. Map variants, develop an MHC typing system, and finally enable application linked to various diseases.

The goal is that in four years' time, we will have gained knowledge about how breeders can test which type of immune system each breeding animal has and breed smart combinations of animals based on this. 

The research project is expected to run until at least fall 2029, and you can follow it on the project page through this link.

Facts about this project:

Definition of terms:

MHC = Major histocompatibility complex

About this project:

  • The research project is funded by FORMAS, the Birgitta Carlsson Fund (SBCF), the Ögren Fund (IÖF), the Swedish Kennel Club, and the Thure F and Karin Forsberg Foundation, and will run from 2025 to 2029. 

  • This project is led by Tomas Bergström, associate professor in molecular genetics at the Swedish University of Agricultural Sciences (SLU), together with a research group consisting of:  
    • Suvi Mäkeläinen, researcher in comparative disease genomics at SLU. 
    • Eva Tydén, Associate Professor of Parasitology at SLU.  
    • Magnus Åbrink, Associate Professor of Biochemistry, specializing in immunology, at SLU.
    • Göran Andersson, professor of molecular genetics at SLU.
    • Björn Ekesten, licensed veterinarian and professor of clinical neurophysiology at SLU.
    • Thomas Simon, doctoral student at SLU.
    • Daniel Goncalves, doctoral student at SLU.
  • Official name: “The Major Histocompability Complex (MHC) - Genetic variation and its impact on endoparsite susceptibility in cattle, sheep, horses and dogs.”

The project components can be broadly described as:

  1. Characterize MHC in dogs, horses, sheep, and cows.
  2. Design a MHC typing system to enable sequencing of a large number of individuals within each group, race, and species.
  3. Apply the new knowledge to some diseases that may be linked to MHC.

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