Written by Mirjam Hommes. (translated to English)
The Friesian horse has been on the verge of extinction a number of times in the course of history. The breed survived only thanks to a number of persistent breeders and studbook administrators. At the bottom, there were about 300 broodmares and only three studbook stallions. These animals form the basis of the current Frisian population, which is estimated at about 75,000 horses, 50,000 of which are in the Netherlands. Because all these horses descend from a narrow base and because the population has not received any blood from outside for 44 years, the mutual kinship is high. This poses a risk of hereditary disorders and of a so-called ‘inbreeding depression’, in which the horses are less healthy, fertile and sustainable.
DWARFISM AND HYDROCEPHALUS
There have long been concerns about the genetic health of the Friesian horse. At the end of the twentieth century, those concerns became increasingly acute. Two highly visible hereditary conditions plagued breeding: dwarfism and hydrocephalus. Dwarf foals are born with too short limbs. Often these animals survive, but their lives are usually not long and healthy. A foal with hydrocephalus is not viable and also poses a serious threat to the mare.
TESTING FOR DWARFISM AND HYDROCEPHALUS
When the science was ready, genetic testing of the DNA of dwarf and hydrocephalus foals pinpointed the genetic markers for these conditions within a few years. In both cases it turned out to be simple recessive abnormalities. That is to say: only if a foal receives the defective gene from both parents will it be sick.
Tests have been available since 2014 to check hydrocephalus and dwarfism carriers so that breeders can avoid mating two carriers. This way the risk of a hydrocephalus or dwarf foal can be excluded. All young star mares and studbook stallions are now tested and for other breeding animals the owner can easily arrange this through the studbook. The studbook explicitly chooses not to exclude carriers from breeding, because you also lose other favorable characteristics. The fewer breeding stock you use, the smaller the genetic diversity becomes. You don’t want to make that genetic diversity narrower than necessary. All breeders are asked to test their mares and to avoid so-called ‘risk matings’. The responsibility is thus placed with the mare owner. Several breeders suspect that the genetic information for hydrocephalus lies in a gene that also brings a number of positive properties for the sport. Animals that carry the hydrocephalus gene remarkably often have favorable characteristics that are rewarded in sports and inspections. For that reason they are often used as breeding animals. Some breeders even feel that for this reason there are more and more carriers of the hydrocephalus gene in the population. However, figures on the numbers of carriers are not public.
ARE THERE ANY DWARFS AND HYDROCEPHALUS FOALS?
Several foal buyers I spoke to over the past few months said they still occasionally encounter dwarf foals. The vets who contributed to this article say they see little or no abnormal foals. Marco de Bruijn, internist at the Wolvega veterinary clinic: “I have practically not seen dwarfs and hydrocephalus foals for a long time, since the genetic tests came into being, but actually before that.” Former veterinarian Siebren Boerma was very concerned in the past about the genetic abnormalities in Frisians: “For the first time, I collected material from foals that were born with hydrocephalus or dwarfism, together with Professor Bak from Utrecht. That was in the late 90s. The aim was to develop a reliable gene test so that these two disorders could be selected out. The studbook and many keepers of Friesian horses wanted absolutely nothing to know about the large amount of likely hereditary defects within the Friesian breed. The problem did not exist, they thought. Or at least I exaggerated. But it was now abundantly clear that hydrocephalus and dwarfism were much more common than in other breeds and that this indicated a hereditary problem. The observant vet also knew that there was much more at play. In 2007 a bill was passed to ban breeding with animals that have a genetic defect. After a lecture by me about the various genetic problems in the Friesian horse, the press translated this with the words that I would have said that you were no longer allowed to breed with Friesian horses. That has caused a lot of fuss and negativity.” Boerma stopped his veterinary practice in April 2021. Lately he has seen a turnaround: “I think the number of deviations has fallen sharply in the last five or six years. The number of foals born with dwarfism and hydrocephalus has become very low since the tests started. If I may be optimistic, I think things are going in the right direction. But to be sure you would like to have numbers about how often something occurs. Dwarfs and hydrocephalus were covered up in the past, so we didn’t have good numbers on that.” Stories from the Frisian community on the internet seem to indicate that sufferers from one of these conditions still occasionally occur, but that this is in fact always the result of not testing the mare or of a ‘calculated risk’. The latter sometimes occurs when a mare does not become pregnant with the chosen stallion and then just before the end of the breeding season another stallion from the same stallion owner is put on it. This under the motto ‘it will not go so fast’ and with all the consequences that entails.
THE RISKS OF INBREEDING
The two best-known hereditary disorders in the Friesian horse, dwarfism and hydrocephalus, now appear to be reasonably under control. Unfortunately, that does not mean that all problems for the breed are over. The narrow genetic basis of the Friesian breed continues to have an impact. There is therefore a lot of scientific research into genetic disorders, with the complex of connective tissue disorders currently appearing to be the most urgent. Before we talk further about the risk of inbreeding in a breed, let’s talk a little more about the basic principles and how this is made transparent in the Frisian studbook.
MAKING INBREEDING AND KINSHIP VISIBLE
Inbreeding is the result of mating between animals that are related to each other. Animals share genetic information when they have a common ancestor. How strong the inbreeding is depends on the degree of kinship between the parents. This relationship is relatively high in the Friesian horse, because the breed has been on the verge of extinction a few times. Inbreeding and kinship are confusing terms that are not always used in the same way. This creates uncertainty, even among breeders. When KFPS members log in to the studbook website, they can see for their own horses what the inbreeding percentage of the animal itself is over five generations, the relatedness percentage compared to the entire population and they can calculate what those numbers will look like for their foals, when they cover their mares with specific studbook stallions.
STATE OF AFFAIRS: INCREASE IN INBREEDING
A commonly used number to see whether the inbreeding of a population is getting worse is the increase in inbreeding per generation. The United Nations Food & Agriculture Organization (FAO) uses this number to determine whether a variety is in danger of extinction. The FAO urges studbooks to keep the inbreeding rate well below 1% per generation and asks to aim for a growth rate of less than 0.25%. The organization finds a temporary increase to 0.5% acceptable. The textbooks state that an increase in inbreeding of more than 0.5% per generation poses a lot of risk: hereditary disorders manifest themselves and an accumulation of adverse effects on fertility, health and longevity can be expected. An inbreeding increase above 1% increases the chance that the population will not survive in the long term. Around the year 2000, the increase in inbreeding among Friesian horses was around 2% per generation, in 2012 that number fell below the critical 1% increase. At the moment, the increase in inbreeding within the Frisian studbook has been around 0.5% for several years and therefore within the FAO standards.
WHAT THE NUMBERS SAY
Figures on inbreeding and kinship are one thing, but even if they were completely undisputed and crystal clear to everyone, the question remains: what do those numbers mean? The kinship percentage will probably soon rise above 20% among the Frisians, but is that really bad? Hydrocephalus and dwarfism appear to have become a fringe problem within the breed thanks to the testing. But what are the other risks of a related, closed population where only a limited part of the animals are used for breeding? Genetic diversity allows for flexibility in a population. If a bottleneck occurs, it results in a drastic decrease in population size, followed by a recovery. A bottleneck often has an enormous negative influence on genetic diversity and that effect is irreversible. Such bottlenecks have been discussed several times with the Frisians. Steven Janssens, geneticist at KU Leuven: “At one point there were very few approved stallions. Then you have a greater chance of certain health effects and hereditary diseases.” However, genes are not static, although change is slow. Bart Ducro: “Because the Frisians form a closed population, there will always be an increase in inbreeding. That’s not a problem, as long as it doesn’t go too fast. If the increase in inbreeding is not too great, the loss of genetic diversity through inbreeding is compensated by all kinds of other genetic processes, of which mutations are the most important. Those mutations bring new information to the population and therefore more diversity.”
INBREEDING DEPRESSION OR NOT?
In genetics, one speaks of the risk of an ‘inbreeding depression’ if animals are too closely related. With inbreeding depression, genetic abnormalities have arisen and the animals have become less durable and less fertile. A decreasing height can also be a signal. The problem with this is that you only really see this when it’s actually too late. Inbreeding depression is also described by geneticists as a kind of snowball effect, you do not know at the beginning that you are already in it. It is therefore very difficult to know whether there is currently an inbreeding depression in the Friesian horse. It is even very difficult to research that. Because the Frisian population has been very small on a number of occasions, the kinship among all Frisians is quite high. This limits the research possibilities, because truly unrelated animals simply do not exist. You cannot therefore make a scientific comparison between animals with very little and a lot of inbreeding. That makes it difficult to draw conclusions. The answer to the question of how the Friesian breed really stands can therefore only come from practice. Are the horses healthy, fertile and fit for the purpose people keep them for? However, there is no central registry of conditions and opinions about the general health of the breed are varied. This makes the evidence anecdotal and the impression you get about the status of the Frisian breed varies enormously per person you ask. Known current problems in Friesian horses are: connective tissue disorders such as aortic rupture, dilatation of the esophagus and esophagus blockage (food plugs get stuck), gastric impaction (the stomach is not emptied into the intestines), fertility problems and sticking to the afterbirth (the placenta does not detach on its own after birth ).
CONNECTIVE TISSUE AND COLLAGEN: HOLDS EVERYTHING TOGETHER
Connective tissue (fascia) has a supporting and caring function. It protects the organs and determines their shape and mobility. Connective tissue also leads the blood vessels and nerves to the organs. Connective tissue disorders are still under investigation, both in humans and in animals such as horses and dogs. Aortic rupture, esophageal dilatation and gastric impaction are examples of connective tissue problems in Friesian horses. Hypermobility is also related to connective tissue. At the moment it seems that the connective tissue problems in Frisians are related to the wrong production and breakdown of collagen. Collagen is a glue-forming protein and is a very important part of connective tissue. It seems that collagen formation in Friesian horses is often chaotic, so that the connective tissue does not get the right structure. The Fenway Foundation reported in early February that there may be a common collagen problem in many of the genetic disorders that affect Friesian horses. These include aortic rupture, esophageal dilatation or paralysis, and gastric impaction and gastric rupture. Also with hydrocephalus and dwarfism there seems to be an error in the production of the collagen fibers. In addition, (often at a later age) the ‘bear-footedness’ of Friesian horses has a link with weak collagen production in both the superficial and the deep flexor tendon. The structure of the tendon tissue is different in these horses. A previous scientific study found that Frisians in general have more elastic tendons than English Thoroughbreds and ponies. Friezes with dwarfism were found to have extremely elastic tendons.
‘CONNECTIVE TISSUE PROBLEM IS UNDERESTIMATED’
Marco de Bruijn sees about 30% Friesian horses in his clinic. He is most concerned with the connective tissue problem in the Friesian horse. De Bruijn: “I have been collecting the cases of aortic rupture that I come across for years. I send blood samples from these horses to Ghent. Initially, the horses also went there for section. Cases of aortic rupture are also sent in from Utrecht. The same goes for esophageal dilatation. We work together with Ghent University, Utrecht University, WUR and the University of Kentucky on genetic research into Friesian horses. Since a few years I regularly see gastric emptying problems. The stomach then stretches to the point where it can no longer empty itself. This leads to a blockage or blockage of the stomach, and sometimes even to a stomach rupture.” Breeder and former stallion selection jury member Bauke de Boer is also concerned about the disorders related to connective tissue and collagen. “The health problems are underestimated. I regularly meet people who have had to say goodbye to several young horses in quick succession. All with underlying conditions, which are mainly collagen-related. People are very sad about that, but there is also a lot of money involved. People often don’t choose a Frisian again.”
MEGAESOPHAGUS STICKS OUT
Research into the connective tissue problem is currently taking place under the umbrella of the American Fenway Foundation. Former KFPS studbook director and geneticist Ids Hellinga is now scientific advisor there. Hellinga: “We are currently fully focusing on research into dilatation of the esophagus (mega-oesophagus). We see that this is an increasing problem. It seems that aortic ruptures are somewhat less common. It is unclear why this is, but it could be because individual stallions have a lot of influence. The faculty in Utrecht has tried to find out the incidence, but in the Netherlands it has not been officially registered how many horses suffer from this. The Fenway Foundation has kept a reasonable record of that in the US. There you see that the esophagus problem is a lot higher than that.”
FENWAY STUDY ON MEGAESOPHAGUS
Ids Hellinga explains what the American research on esophageal dilatation entails: “In the US, they are very good at DNA technology and detecting the genetic mutations that cause conditions such as esophageal dilatation. We have already conducted research into this in the Netherlands and Belgium in the past, but it came to nothing. The phenotyping for this disease is more difficult, by which I mean that esophageal dilatation is much less recognizable than, for example, dwarfism or hydrocephalus. You do not always see that a horse suffers from this condition. Sometimes it only shows up at a later age, for example we recently had an 18-year-old mare and she had already had twelve foals. That is also the dangerous thing about this condition: sufferers of megaesophagus could be breeding stallions in an extreme case. Therefore, this problem may be even greater than previous genetic disorders in the Friesian horse.” This fearful suspicion of Hellinga seems to be confirmed by the many stories about esophageal dilation and paralysis that have appeared in recent years in, for example, Facebook groups of Frisian lovers. Many horses don’t show the first symptoms until later in life, although the problem certainly also affects foals and younger horses. Hellinga: “We now only have foals in the study and use the newer and more accurate technique of whole genome sequencing. The starting point is that it concerns one gene, but we are also expressly looking more broadly for more complex forms of inheritance. Fortunately, there is a good chance that it is a single recessive gene, which would make research easier. Thanks to the new techniques, we can limit the research to a smaller number of families. In America in particular, we have collected quite a few families, although we could add a few more. The research does not focus on individual horses, but on father, mother and some brothers and sisters, preferably young horses and foals.” Hellinga calls on owners of horses who have esophageal dilatation to participate: “If owners can provide us with data and hair samples from multiple family members, they are cordially invited to come forward.” Hellinga continues: “I used to have the feeling that this was an unsolvable sudoku, but every time we add a family to the study, we see that we are getting closer to a solution. When that will be, I can’t say. We will also have to validate the results and that takes time. But we’re doing everything we can, and the investigation is going well. I think we can develop a gene test for esophageal dilatation.”
TAIL AND MANE ECZEMA
Bart Ducro: “Both aortic rupture and esophagus blockage are not pleasant at all for a horse owner, but we don’t really have an idea of what the biggest problems are with the breed. For example, tail and mane eczema will also not make you happy as an owner, but that is not life-threatening. This concerns an allergy and it is already clear that not one single gene plays a role, but several. This means that a gene test such as for dwarfism or hydrocephalus is simply not possible for tail and mane eczema. Research has contributed somewhat to the extent to which genetic predisposition plays a role, but without knowledge of the DNA behind it, breeding eczema-free is still very difficult.”
FERTILITY PROBLEMS AND SPERM QUALITY
Fertility is an important characteristic by which you can tell if inbreeding is causing problems in a population. Steven Janssens of KU Leuven: “One way to investigate inbreeding depression is to plot a hereditary characteristic, such as height or fertility, against the degree to which the animals are inbred. The more inbred an animal is, the lower the height at the withers or fertility could be. It is difficult to find out for fertility.” Bart Ducro of WUR: “Currently, about 75% of the matings with Friesian mares actually lead to a registered foal. That may not seem like much, but compared to other pedigree breeding farms it is not very bad. I don’t see a very big problem with mare fertility yet, the concerns are greater on the stallion side. A relatively large number of young Friesian stallions are removed from the stallion selection process, because their semen quality is insufficient in the tests. That percentage is much higher than in other breeds. That is a real shame and it will be at the expense of your selection space. Years ago I myself investigated whether there is a relationship between sperm quality and inbreeding, but I could not prove that. Such research fails because all Friesian horses are inbred to some extent. For such a study you compare stallions with a higher and lower inbreeding, but that is not possible if there is not a big difference between much lower and much higher inbreeding percentages. You can’t see the difference then. What struck me ten years ago in that study is that the parameters of sperm quality, such as the number of cells and motility, were much worse in Frisians than in warmbloods and even Shetlanders. In my opinion, the fertility problem of the Frisians is more on the male side.”
RESISTANCE AND DURABILITY
In 2021, the breeding goal of the Friesian horse breed has been adjusted at the request of the KFPS Members’ Council. From now on, health comes first, before breed type and sports aptitude. Health and sustainability go hand in hand. Obviously, many breeders and owners are concerned about durability. Horses are sometimes unusable at a young age or have to be put to sleep early. There is also no good overview of this, because the registration of mortality is not (yet) in order. Many people do not hand in their horse passport after their horse has died and do not report the cause of death to the studbook. Other horses disappear abroad. There is therefore a lack of really reliable figures about the average life expectancy of the Friesian horse. This means that we continue to rely on anecdotal ‘evidence’. Veterinarian Marco de Bruijn: “In our clinic I see that the Friesian horse is less able to solve things itself these days, whether that is a respiratory infection, roundworm or a recovery after colic surgery; it is very difficult. To be honest, I am increasingly dreading operating on a Frisian with colic. Another breed often returns home within a week, but with Friesians you often first see diarrhea or an infection, if things start at all. The horse is just not that strong. I understand that people want a beautiful Friesian horse, but in my experience that comes at the expense of resistance. You can also see problems that may have to do with resistance, such as poor uterine emptying and fluid. I think it all comes down to immunity and little genetic diversity.” The afterbirth can also be related to inbreeding, explains De Bruijn. “A placenta is basically foreign tissue and is therefore rejected by the mare. But with a high relatedness, the mare’s immune system may no longer recognize the placenta as foreign.” In 2004, M. Sevinga and colleagues from Utrecht University already investigated the influence of inbreeding on the mare’s retention on the afterbirth, after the number of cases increased spectacularly between 1980 and 2000. The researchers found a connection with the relatedness percentage of the foal. “A high incidence of afterbirth is at least partly due to inbreeding,” they concluded. Veterinarian Siebren Boerma says that the number of problems seems to be decreasing in recent years. “But that doesn’t have to be because the hereditary factor has decreased,” says Boerma. “Today hygiene is better and people are also more alert to the afterbirth than before, which means that interventions are taken faster and fewer problems arise.”
FULL OF PAPER AS HOLY GRAIL
When you read the advertisements for Friesian horses on Marktplaats or the KFPS website these days, you immediately notice that people often talk about ‘full paper’. This is an important recommendation for a Friesian horse. ‘Full paper’ means that the horse comes from a maternal line of at least three generations of mares with a star predicate or higher (crown or model). Mares receive a star predicate when they receive a minimum average of 7 for conformation, walk and trot from the jury on a studbook inspection or breeding day. Horses born from a studbook mare (less than a 7 on average at the inspection) or a foalbook mare (never attended the inspection as an adult or underperformed there) do not have a ‘full paper’. These are still full Friesians, who are in the closed studbook or in the foal book, but they are often worth a lot less than the ‘full paper’ animals. Even for horses that are only used for sport and not for breeding, such as geldings, it has become a distinguishing feature that often makes thousands of euros difference in the resale value. As a result of this common obsession with a full paper, breeding is mainly done with star mares. That limits the breeding population. In recent years, only about 3,200 foals were registered per year. The studbook aims for 4,500. It is expected that several hundred more foals will be born this year.
REGISTRATION AND OPENNESS REQUIRED
Vets, owners and geneticists see that there are several problems with the Friesian horse breed, but how often they occur and where they come from remains unclear. Bauke de Boer is a big proponent of registration and openness: “You have to map out which lines are sustainable and which ones fall over. Of course you also have to be lucky in breeding, but I hear too much doom and gloom. There are breeders and stallion owners who want to keep everything under wraps, but I think that’s stupid. It has to be open and exposed, only then will you get out of misery. Breeding is foresight. We must all work together to ensure that you breed a healthy horse, which does retain the breed characteristics, but which you can do something with. It is a duty to breed a healthy horse.”
Until now, there has been no systematic registration of genetic problems, disorders and longevity of the Friesian horse. This despite previous recommendations from scientists. For example, in 2011, Siem Korver argued for a completely closed (and mandatory) registration of matings, pregnancy and birth defects. Bart Ducro: “At the moment we lack a good overview of what exactly is going on and what the priorities are. If it had been properly registered, I could now have said: ‘These are the big problems’. You would prefer to have some sort of database of the identified problems, with some DNA added in the form of blood or hair. Then you can make meters, because the techniques are getting better, cheaper and more reliable. You could even make such a hotline anonymous. Once you have the DNA profile, it doesn’t matter which horse it is. As long as you know what condition was seen in that horse. The DNA pattern is a kind of barcode, which we can then use to investigate which gene is behind which condition. But now we have little material or only material that has been selected very strongly.”
HIDING AND CONSPIRACY THEORIES
The old culture in the Frisian studbook, which veterinarian Boerma also encountered in the 1990s, meant that there was no registration and that data on the occurrence of genetic abnormalities was not shared. It remains unclear how often deviant foals are born. Some breeders and stallion owners still choose to keep problems under wraps as much as possible, because openness would be bad for reputation and trade. A hotline on the internet that claims to register defects in the Friesian horse, despite repeated attempts, remains completely unreachable for comment and does not even want to anonymously indicate how many deviations they have registered in recent years. Over the years, the supposed ‘shaming’ of hydrocephalus or dwarfism foals has led to suspicion among members of the association and sometimes even the spread of conspiracy theories among some of the breeders. For example, the theory regularly crops up that there are several types of dwarfism and that the existing test only detects one of those types of dwarfism. Geneticist Bart Ducro of Wageningen University said about this earlier in De Paardenkrant: “Disproportionate dwarfism (chondrodysplasia) occurs in Friesian horses, that is the form we have always seen. This shape is specific to the Friesian breed.” This form of dwarfism is therefore tested. However, the lack of transparency and (public) registration of problems gives critics room to argue that the test is unreliable.
COLLECT KNOWLEDGE AND IMPROVE REGISTRATION
Veterinarians such as Marco Bruijn have been keeping their own lists for years and sometimes data has been collected for specific investigations, but the studbook therefore does not have a numerical and structural overview of what is going on in terms of hereditary disorders in the population. Even the death rates are largely incomplete. In 2021, the studbook therefore started an action to encourage people to deregister their horses from the studbook if they die. In such a report, the cause of death can also be entered. Studbook director Marijke Akkerman: “The deregistration of deceased horses is still not done enough by our members. We hope to gain more insight thanks to the Identification and Registration of Horses that was started in 2021 via RVO. The studbook can link that data and thus gain a better insight into the mortality rates.” The studbook also wants to link the data on the causes of death to other data registered about the horses. Akkerman: “A working group from the Breeding Council is working on this. The idea is to compare certain linear scores for, for example, leg position and height with lifespan. This research into sustainability is still in its early stages. But of course everyone wants to enjoy their horse for a long time. In addition to sustainability and longevity, there is also a study into fertility, together with Utrecht University. That focuses specifically on sperm quality.” Akkerman indicates that the studbook now also wants to keep better track of which studies are being conducted in different places in the world and how far along these studies are. “We also want to be more on top of this ourselves and in 2022 we will communicate more about this,” the director promises.
“WE KNOW TOO LITTLE”
A growing group of breeders and enthusiasts are now pressing for transparency. The current board and the breeding council now seem to want to move in that direction. Tjitze Bouma, the new chairman of the KFPS breeding council, said in the online lecture tour of March 31, 2022: “You will have to collect more data about health and sustainability in breeding. In fact, we still know far too little about our horses. Few horses are deregistered when they are deceased. And if they have died, you would also like to know the reason. Not to publish misery about that, but because you want to be able to see from the data which line is aging on average, for example.” Bouma also said that they are considering putting the dipstick in older horses as well. Now almost only the young horses are assessed, but that does not provide any information about durability. “One possibility is to ride and test the horses again sometime between the ages of 12 and 15, to see how they are doing.”
‘RESOLVE AT THE FRONT’
Systematic registration of deviations would also be an important step. Marco de Bruijn: “I don’t think we have made any progress with the Frisians in the past 20 years. In the context of preventive medicine, you have to see if you can do something up front, because management alone will not save you. So you have to find the solution in breeding. The question then is whether there is still enough genetic diversity in the breed to solve the problems. In my opinion, to be able to answer that question, you must first map out the connective tissue problem, after which you can examine whether the current diversity is still sufficient to put this in order. And if the answer is no, then you have to think outside the box. That’s swearing in church, I know. And will hurt some people. But the problem is: Now that pain is also there, but it is distributed among the individuals, among my customers. I fight for that.”
FORMULATE HEALTH CHARACTERISTICS AND SELECT THEM
Stallion owner Erwin Spliethof would also like to see more attention for health in the existing population: “I think it would be good to formulate more health characteristics, in addition to X-rays, cornage examination and the tests for dwarfism and hydrocephalus. Just as we once came up with the characteristics for the linear score, you can now start with a list of health characteristics. That has two major advantages. In the first place, health is universal and equally important to every owner or user of the horse. Whether you want to go for a ride in the forest, harness a class of honor or ride a Grand Prix, everyone benefits from a vital horse that can age healthily with little veterinary costs. A second important point of health is that it is hard to measure. Unlike jury judgments, which always carry a certain amount of subjectivity. I would therefore argue in favor of placing much more emphasis on health, especially in the stallion selection, and less on sports aptitude and exercise. Because however capable the jury corps may be, no one, absolutely no one, can tell from a three- or four-year-old horse what he has to offer by the time his talents reach their full maturity. Let alone that you can estimate at such an early stage what his qualities could be as a breeding stallion. So it is also quite pointless to judge and test until you weigh an ounce and prematurely knock a large number of stallions overboard. You miss good breeders if possible. My advice: raise the lower limit for health traits considerably, leave the rest of the selection largely to the market and rely on the knowledge and skills of your breeders. Over the years, they have shown that they are capable of building successful mare lines, each according to their own insight.”
WAYS TO CURB INBREEDING
In addition to collecting more information about the current population of Frisians, there is a lot of thought and discussion inside and outside the studbook about possible solutions to limit inbreeding in the next generations of horses. Some breeders have dropped out of the KFPS and will now cover their mares with stallions from other studbooks, but many involved think it is still too early for that, or warn of unwanted side effects. Over the years, scientists have provided several reports about inbreeding in the Friesian breed and how to control it. Although a number of recommendations from this have since been adopted by the studbook, such as publishing the kinship figures and assigning a breeding value to kinship, there is still a lot to be done.
HOW DOES THE STALLION SELECTION COME ABOUT?
Breeding decisions revolve around a mother’s or father’s genetic predisposition, which is what is passed on to the offspring. Breeding values and total indexes are frequently used in Frisian breeding when making the choice of stallion. A breeding value is a substantiated estimate of the genetic predisposition. The number indicates to what extent a parent animal will pass on a particular trait. Breeding values are always calculated relative to the population average and are reassessed every year. The average breeding value is always 100, in practice this is a variation between 96 and 104. The more offspring an animal has, the more reliable the breeding value. For the Friesian breed, breeding values are calculated for breed appearance, build, legs, walk, trot and canter. In addition, a breeding value is calculated for each characteristic in the horse’s linear score. The information that is used to calculate breeding values comes from studbook inspections and talent tests, of the animal itself and of the offspring. Unique to the Frisians is that since 2020 breeding values for character have also been published for the studbook stallions. This arose from the desire to maintain the fun-loving nature of the breed. In addition, a breeding value for relatedness is included in the rankings of active studbook stallions and of the 1,500 best mares. The more closely related the horse is, the higher the breeding value for that trait. In the so-called ‘total index’, all breeding values are taken together in order to make a ranking of the most interesting broodmares. Unfortunately, the mare list also includes several animals that are no longer alive or have disappeared abroad. A problem with these rankings is that you are comparing very reliable breeding values of older animals with the much less reliable breeding values of young horses. As a result, breeders may place too much value on this index.
USE OF EXPECTED BREEDING VALUES
In a special module on the studbook website, mare owners can see which stallions are expected to improve their mares in certain areas. For example, a better step or a lighter head and neck connection. Breeders can also calculate the expected value of any foals in a web module for the breeding values of breed, build, legs, walk and trot. The expected inbreeding percentage over five or six generations and the relatedness percentage is stated here. A warning will also appear on the screen if the relevant mating poses a risk to a dwarf or hydrocephalus foal. The expected value of a foal is the average of the two parent animals. This means that the potential offspring of the highest scoring young stallions at inspections and in the performances also show very high expectations. The fact that the young stallions often do not yet have such reliable breeding values is a little out of the picture. Low-related stallions are often at a disadvantage in these calculations because they do not protrude far above the masses in terms of breeding values for, for example, breed and movement. All this influences the choices that breeders make. Sometimes there is even a self-reinforcing effect: when a young stallion has lower expectations, he gets fewer opportunities. Such a stallion is used less on the better mares and as a result the offspring are less good, so that the breeding values do not increase either. In the top 20 of studbook stallions with the highest breeding values there is only one lower related stallion: Omer 493. Only breeding for high expected breeding values, for example because you breed for commerce or sport, therefore easily leads to a lower genetic diversity. Ultimately, the athlete or trader is also the victim of this, because less diversity causes problems in the long term.
LOW RELATED BREEDING
The use of relatively low-related breeding stock is one of the ways to curb the increase in inbreeding. The family of Roelof Tjeerdsma (stable name fan ‘e Boppelannen) bred for years with the (very) low related mares from the Onyx line. From the mare Onyx (born 1988 Naen x Ewoud x Nuttert and 15.5% relatedness), Tjeerdsma’s father-in-law Marten van der Meer bred some even lower related horses between 2007 and 2010 using embryo transfer, using embryo transfer. “We rinsed her seven times, we were a bit ahead of our time. We chose Gjalt 426 and Fabe 348 because of their low relatedness. At the time, we hoped that the colts could mean something in breeding. But these descendants from Onyx were not real eye-catchers, not the most luxurious horses or outstanding in movement. Of course they would have been very suitable within the studbook breeding service, but that insight was not really alive ten years ago. They didn’t become a star in the end. There were also mares from the combinations, but all but one of them were sold abroad or died. At the time, there was no interest from the studbook in using such mares as potential stallion mothers and no advice to keep this type of mares for breeding. Now we might do it differently. But yes, there was not necessarily the ideal horse.”
FEW LOWER RELATED STALLIONS
Of the newest batch of studbook stallions, approved at the end of 2021, only the two older stallions are somewhat below average related. The four other stallions are all relatively closely related. We have to go back to 2019 for approval of two young stallions that are significantly lower related, namely Wibout 511 and Wolter 513. The latter is the least related stallion in the studbook at 15.8, but is used relatively little. Omer 493, who is from the same dam as Wolter, currently has a 16.3% relatedness and is more popular.
MEASURING IS KNOWING
Stallion owner Erwin Spliethof believes that time is of the essence: “The idea behind reducing inbreeding and encouraging lower kinship is ultimately to improve the health and sustainability of the population. You hope that with this the typical Frisian ailments will occur less in the future. That is why it is important to collect good data in the coming years to see whether this policy is having an effect. Will the offspring of low-related stallions have less ossified hoof cartilage, aortic ruptures and esophageal strictures? Are the daughters with a low kinship on average less interested in the afterbirth? Do low-related horses score better on heart rate and lactate measurements during exercise? If this turns out not to be the case, it could mean that we took the wrong turn. And that we should start thinking about other instruments, such as more DNA tests, for example. But it can also mean that we are on the right track, but that a low kinship within our closed population turns out to be a drop in the ocean. If we can no longer make a difference with that, then we may have to go one step further. At a certain point, foreign blood seems inevitable.”
SUFFICIENT BREEDING AND MAINTAINING THE MARE POPULATION
Geneticists recommend keeping genetic diversity as high as possible in a closed population, such as the Frisian studbook. Breeding only low relatives is then not enough. You have to breed a lot and also use as many animals as possible. That’s not happening now. Every year about 1,800 Friesian mares are born and 400 mares are declared ster. The generation interval of horses is 10 years. With the current birth rates, 18,000 mares are added every ten years, of which approximately 4,000 mares receive the star predicate or higher. You don’t take mortality into account. But even with such a simple calculation it can be seen that breeding almost exclusively with the star mares, crown mares and model mares will mean that the population will continue to decline. It is therefore essential for the preservation of the breed and the preservation of diversity that many more mares are bred. The studbook can actively encourage this, for example by placing less emphasis on full paper and inspection results. Or even by actively approaching the owners of mares who can contribute something to the breed. The studbook has already started to do this by publishing a list of low-related mares, which also includes mares without a star predicate.
BETTER USE OF THE STALLION FILE
The Frisian studbook currently has about 80 active studbook stallions worldwide. The influence these animals have on the entire population varies enormously per stallion. About half of the studbook stallions cover more than 50 mares per year, while a quarter only cover less than 10 mares per year. There are families of stallions with great influence and there are bloodlines that are hardly used. In 2007, the KFPS already received a report from the WUR, in which it was recommended, among other things, to designate more sires and fewer sons per sire. Since then, between two and six stallions are approved per year. Every year there are also stallions who ultimately have few offspring or who leave the stallion with a quiet drum. The WUR report: “More important than the number of sires is the extent to which they are used. Approving more sires will not lead to a more balanced use without additional measures such as a breeding restriction per stallion. The increase in inbreeding can be considerably limited by standardizing the number of matings per stallion. Limiting the increase in inbreeding within the Frisian studbook is not possible without some form of breeding regulation.” In addition to the contributions of individual stallions, stallion families are also important. There is no official limit within the Frisian studbook on the number of sons that may be approved, although, according to the inspection, stallions are judged more strictly if their sire already has several approved sons.
BREEDING LIMITS AND LIFE TOTALS
There were always breeding limits in the Frisian studbook. In the initial period, this grew along with the population, from 50 to 75 matings per year, for example. Sometimes that was also a lower limit, based on a comment on the stallion in question. Such a stallion was only allowed to cover more after he had been approved for offspring. At the beginning of this century, the studbook experienced great growth. Since 2003, a young Friesian stallion, who has not yet been approved for descendants, may cover a maximum of 180 mares per year. After the stallion has been definitively approved, the number of coverings is free. There is no mention of a life total in the studbook, which population geneticists often advocate. According to scientists, applying breeding limits can result in a more equal contribution of sires to the next generation. Individual sires cannot then gain too much influence. However, the figure of 180 matings for the young stallions is controversial and was challenged, among other things, in a lawsuit between stallion station De Nieuwe Heuvel and the KFPS, in 2011. An independent report – by Siem Korver – in response to that case states that the current standard is only a very rough approximation. A life total per stallion may be more effective, if this total is based on population size.
COVERING LIMITS IN A DECLINING POPULATION?
The current breeding limit for young stallions was thus established at the time when the breed was booming, at the beginning of this century. For years there has been less breeding than the studbook would like, but it is difficult to stimulate breeders. The total number of Friesian horses is expected to decrease in the coming years. In the online autumn meeting of 2020, a KFPS member therefore asked whether it would not be desirable for blood distribution to reduce the breeding limit for young stallions from 180 matings per year to 120. Ids Hellinga, studbook director at the time, replied: “The rule of thumb is that the contribution of an individual stallion should not exceed 5%. Even at the current level of numbers of coverings, we comply with this rule with the breeding limit of 180 coverings per year.” That was almost true, but not quite. At that time there was one stallion – Alwin 469 – who had surpassed that 5% in each of the three previous years. But more important than the influence of one stallion is that of stallion families.
THE INFLUENCE OF STALLION FAMILIES
If you don’t look at the studbook stallions individually, but look at the stallion families, the proportions turn out to be quite skewed. For example, Tsjalle 454 and his sons Jehannes 484, Yme 507 and Tymen 503 and grandson Auwert 514 were jointly responsible for 15.9% of all coverings within the studbook in 2020. In 2021, Jehannes son Foeke 520 was added, but the breeding numbers for that year are not yet public. Norbert 444 now has six approved sons and five approved grandsons, including multi-deckers Hessel 480, Menne 496 and Matthys 504. In the 2020 breeding season there were only two active grandsons and the Norbert stallion family was already responsible for 13.8% of all matings . That year, the stallion Pier 448 and his sons accounted for 7.6% of the matings, Alwin 469 and his son for 6.5%. A grandson has also been added to the latter. A rough estimate shows that about 23 studbook stallions, from these four ‘stallion families’, currently produce half of all Friesian foals. An estimated 23 studbook stallions from four ‘stallion families’ currently produce half of all Friesian foals.
COVERING LIMITS IN PERCENTAGES?
Bart Ducro: “The existing breeding limits are set at a population of 8,000 foals per year. Currently, only about 3,000 foals are born per year. It would therefore perhaps be better not to express the breeding limits in absolute numbers, but in percentages. Then they can move more along with the number of foals per year. It is of course difficult to say exactly how this will work out in practice. But with the current 3,000 foals, a breeding limit of 180 is probably too loose. Although at the same time you see that the kinship level has not risen too much in recent years, so maybe it’s not that bad. There may also be an aftereffect, whereby the effect on the kinship percentage is still to come. It is therefore wiser to switch to percentage coverage limits for the long term.”
WIDER BREEDING WITH YOUNG STALLIONS
The 80 studbook stallions are the only sires in the population in the Netherlands. Abroad, foal book stallions with a breeding license are used, but their descendants end up in the so-called ‘supplementary book’. Many foreign horses even completely disappear from the radar of the KFPS: foreign owners find registration too complex or too expensive, or they start crossing with their Frisians. Bauke de Boer: “It is a shame that the route of the help book is closed. Additions I and II, that’s not getting along. The young stallions already covered for the Central Examination in the 1980s and 1985. They were then provisionally approved in February, after the third viewing and then they were allowed to serve a maximum of 50 mares. Only then did they enter the CO, where stallions also dropped out. When certain stallions are low related, but not good enough in the CO, it can still help a little if they have a few offspring. This can help genetic diversity through the maternal lines.”
COMPLICATION: FERTILITY OF THE STALLIONS
If you study the birth rates closely, you will see that the fertility of the stallions varies enormously. For the 2018 breeding season (foals born in 2019), there were stallions where only about 30% of the matings led to a birth and stallions where that percentage was above 80%. In the Frisian studbook a lot is covered with young stallions. The newly appointed class therefore has a full ball book almost every year: most new stallions cover about 180 mares in their first season. But mare owners who don’t necessarily want to use the youngest generation and keep an eye on the birth numbers, will lean towards the fertile stallions so as not to lose a season. In recent years, the stallions have been given longer in the inspection process to send in an acceptable sample. But a stallion that is at the lower end of sperm quality is not profitable at all for a stallion owner. Many of these animals will not enter the expensive stallion selection process at all, or will be withdrawn prematurely. And if they are nevertheless designated, the less fertile stallions quickly disappear from the picture. Fertility problems in this way limit the choice of stallion.
OUTCROSS AS AN OPTION?
The Frisian studbook has been closed for 44 years now. To keep such a population healthy, it is important to breed enough and use as much of the available genetic diversity as possible. New mutations will always add some diversity to the breed, but that is a slow process. The kinship rate will continue to increase in a closed population. It was around 13% in the early 1980s and was still below 16% in the year 2000. In 2021 it was 17.8% on average. As Rita Hoving, geneticist at WUR puts it: “Inbreeding always continues to grow in a closed studbook. That is why the growth rate is important and not the absolute rate. With very long family trees you always have a base number that you cannot change.” It is important to bear in mind that relatively low-related stallions also have ancestors. You never start from scratch. Hoving: “You have to ensure that the increase in inbreeding remains manageable. At some point, when you have too few animals or when fertility becomes problematic or you develop abnormalities, you should choose whether to bring in animals from outside.” The question that a number of breeders and experts are asking themselves is whether that point has now been reached for the Frisians. Some think it is already time for outcross, others reserve their judgment until more information is available about the current status of the hereditary disorders in the breed. ‘Outcross’ was a taboo in the studbook for a long time, but the discussion about the use of foreign blood is now being conducted here and there.
NO WHITE SPOTS
The Frisian studbook is closed, but that does not apply to all breed studbooks in the Netherlands. The choice for ‘foreign blood’ depends, among other things, on the breeding goal. Among the Frisians, white hair or kolletjes are a real no-go. That limits the possibilities. This works differently with the Groningen horses, they are allowed to have markings and have a slightly less narrow breed description than the Frisians. Lotte Merks, board member of Vereniging het Groninger Paard: “We have an open studbook, whereby the foals of stallions from recognized studbooks from a Groningen mother, or vice versa, can be fully included in the Groninger studbook. In addition, several stallions and mares have been brought in from abroad in the past for blood distribution. A few German stallions from a recognized studbook are also currently being used, and the Association is investigating the possibilities of bringing a stallion from abroad once every year or two years and having it approved according to the standards of the Groningen horse.” Vet Sybren Boerma: “I used to say that you might not be able to get around fresh blood in the population, but at the moment I no longer think it is absolutely necessary. You have to be careful: if you select one of the hereditary abnormalities, you run the risk that others may increase. Especially if you can’t test for that yet. If I’m optimistic, I still think things are going in the right direction. But I would really like to see numbers on how often certain abnormalities occur.” Harness horseman Andries Zandee doesn’t like breeding with stallions from other studbooks: “Then you would have to turn up a good black Andalusian somewhere who also breeds black, that is unthinkable. The Friesian horse is a cultural asset that we have to handle very carefully.”
Bart Ducro of WUR thinks outcross – using stallions from outside – is premature for the Friesian horse: “As far as I’m concerned, that’s a very last resort. It’s so easy to say, but you don’t know what you’re getting. The first generation often looks fantastic, because of the heterosis effect. You then have a 100% crossing advantage. If you start crossing again after that, you will never get all those benefits and diversity again.” The fact that the first generation of offspring of a Friesian and a black dressage bred KWPN look fantastic is confirmed in conversations with three breeders who have experimented with this in recent years. But, says Ducro: “It is not obvious how to successfully introduce foreign blood into the population. All kinds of methods and crossing schemes are possible. You can only do it systematically, when you have control over all steps in the process. It must then be supervised over several generations. That is not the case with a studbook of individual private breeders such as the KFPS. And even if the studbook could guide this, I still have my doubts. You don’t know what you get from pollution and other ailments, which you don’t have any insight into now. The vast majority of the Frisians are very healthy in my opinion, so I don’t see a reason for outcross yet. It is important to breed well balanced. And taking all aspects into account and not just looking at the beautiful moons.” Ducro says emphatically that stallions that are carriers of a recessive hereditary condition, such as dwarfism, should not be excluded. “You can still use the carriers in your breeding, as long as you make sure that you don’t mate with other carriers. And if you test the offspring. You should not discard a stallion with very good qualities, which contribute to the survival of the breed, for one minus. That’s a shame. Fortunately, I have the feeling that the Frisians have a more down-to-earth approach to carrier status than some other breeds.”
“USE ALL INSTRUMENTS”
Former studbook director and geneticist Ids Hellinga does not want to make any firm statements about the use of foreign blood. Hellinga: “That is no longer my role. It will be quite a challenge to solve the problems within the current population. Getting unwanted traits out, while on the other hand you want to keep the population wide enough for sufficient blood distribution, that is really a diabolical dilemma. You certainly don’t solve all problems with blood from outside. You still have to keep developing DNA tests and you also bring in other problems. In any case, it remains important to keep inbreeding low. Introducing other blood could be part of the solution, but it will never be the whole solution. You will still have to track down the genetic defects and have a sound inbreeding policy. Different blood has entered the harness horses and the baroque pintos, but there the inbreeding took place on those stallions from outside. You will therefore have to keep the other instruments against inbreeding sharp when using a different variety.”
‘KEEPING AN EYE ON INFLUX’
Erwin Spliethof likes to leave decisions about outcross to the geneticists, but believes that good policy should be the basis if it happens. “In any case, you first have to know what such a crossing does, what the risks are. It is probably difficult to maintain the black color, for example, but nobody wants a Frisian with three white socks and a blaze. Or on a Frisian with a bad character. If you want to do outcross, you have to regulate it very well and only use very good horses that you know the background of so that you know what you are bringing in. You also want to have a view of the intersections afterwards. It is therefore important to inspect these horses, to have aptitude tests done and to compete in sports, for example. For that you will have to register them in some kind of help book or a separate register. If you keep them with you and let them participate, you also know what kind of horses they are and what they can add to your population. If you then cross back the best horses with, for example, two or three generations of Thoroughbred Friesians, that can add something, without losing the typical Friesian. So embrace the influx, but keep an eye on it and make policy for it.”
“NOT JUST FOR YOURSELF”
Breeder Bauke de Boer fears that it will not work without blood from outside: “In the end, I think you cannot avoid outcrossing with the Frisians. But, that has to be done very carefully, not everyone can do that and it should be coordinated with policy from the studbook. You then have to select the best mares for that, which are free of genetic disorders. And not just randomly use other stallions, but select wisely. That could give a considerable boost to quality, but only if it is done in the right way. Descendants must then be able to be included in the A-register. I do think that you can use warmbloods that inherit a good character and possibly PRE horses that can move well. I myself have a foal by the KWPN dressage stallion Total Design out of a Fabe mare. You cannot distinguish them from a Frisian.” De Boer is cautiously optimistic: “I have the idea that Fokkerijraad is now getting to work with inbreeding and kinship. And involve people who want to do it in a good way, for the breed and not just for themselves.”
CHANGE AND COMMUNICATION
The conclusion may be that a lot of information is still missing, but also that there are more possibilities to limit inbreeding problems than have been used by the KFPS so far. Some options have been suggested by scientists to the studbook for 20 years now, but have so far encountered vested interests, bureaucracy or political entanglements within the association. However, the wind is slowly turning. Although not everyone interviewed for this story wanted to be mentioned by name, many people were willing to do so. Messages about hereditary problems are now widely shared via social media, often including the associated confusion. Breeders’ premiums, designating stallion dams and lowering breeding limits are likely to become part of renewed discussion. It is crucial that there is transparent and clear communication by both the studbook and the scientists involved.
PARTICIPATE IN REGIONAL MEETINGS
That something is tilting in the communication and openness at the studbook became apparent during the online breeders cafe at the end of March. In it, the new chairman of the breeding council, Tjitse Bouma, said, among other things: “We really need to do something with inbreeding and kinship. We can use all kinds of instruments for this, but we do have to make choices. That is why we, as a breeding council, also attend regional meetings. Not to present a bite-sized chunk of ‘this is the advice’, but we want to get into a discussion. Perhaps there should be a ceiling on the number of matings of stallions that cover a lot or are closely related or maybe we should approve more stallions. We all have to make choices about that.” The Breeding Council will present several options in the regional meetings, but also says it would like to hear the ideas of members. Bouma: “I am not in favor of the Breeding Council only giving advice to the board and that the Members’ Council then slaps it. We should all talk about it together.” Bouma stated that the studbook has “a real challenge” with regard to health, durability and fertility of the horses. “On the other hand, it’s not hopeless either, we have to stay a bit positive.” It is important for breeders, members and enthusiasts that they understand basic concepts such as inbreeding, kinship, genetic disorders and carrier status in order to be able to fully participate in the discussions to come. Hopefully this long read will contribute to that.