A study conducted by researchers in the Animal Breeding and Genetics Department at Wageningen University and Research in the Netherlands in coordination with the KFPS examined the historical inbreeding trends in the Friesian horse population and evaluated via simulation the effectiveness of various potential breeding strategies the KFPS might employ to address inbreeding.
Due to small population sizes and uneven ancestor contributions, the Friesian horse population has historically experienced high levels of inbreeding. Twenty years ago, the studbook introduced a mating quota (180 matings per sire per year for the first three breeding years) and began publishing individual kinship values for adult breeding stock. These actions successfully reduced inbreeding rates to less than 1% per generation. However, the breeding population has since declined, underscoring the need to reassess current breeding strategies to maintain inbreeding rates at the desired levels.
Historical Trends
The studbook was established in 1879, with a low annual foal registration rate that persisted for many years until 1986, when it first reached 1000 foals. Between the 1980s and 2000s, there was a rapid growth in the population size, leading to a peak of 6713 registered foals in 2004. After remaining steady for some time, the number of registered foals started to decline in 2009. Since 2017, approximately 3900 foals have been registered annually.
Studbook data indicates that 47.9% of female foals eventually become mothers, while only 3.5% of male foals father at least one foal in their lifetime. Of the male foals that eventually become sires, only 17% are approved stallions, while the remaining 85% are foalbook stallions. It is essential to highlight that foalbook stallions have made minimal individual contributions. For instance, in 2022, most foalbook sires only fathered a single foal, with the highest number being 12 foals sired by a single foalbook stallion.
In contrast, the contributions of approved stallions can and have been significant. From 1945 to 1974, the top 10 approved stallions produced approximately 80% of the annual foal population. That has decreased over time, and in 2022, the top 10 approved stallions account for 35% of the total foal population. Although this might seem like a favorable reduction of influence at first glance, further analysis indicates that this decline is mainly attributed to the increased number of approved stallions today rather than a more balanced distribution of contributions among approved stallions.
Simulation Results
In this study, researchers determined the two factors that affect inbreeding and kinship rates most negatively are 1) selection choices made by breeders and 2) unequal contribution of breeding sires in relation to the number of offspring. Using a pedigree analysis to review past inbreeding trends and their main causes, researchers then assessed the effectiveness of current breeding strategies and additional approaches through simulations. They determined that the current inbreeding rate is 0.72% per generation. Below are the results of the various breeding strategy simulations.
Selecting Approved Stallions Based on Kinship. This strategy was most effective at decreasing inbreeding rates. It involved only selecting breeding sires with a below-average mean kinship. However, for various reasons, including the relatively small number of low kinship-approved stallions, it could be less desirable than other approaches.
Increasing the Number of Approved Stallions. While breeders frequently suggest simply increasing the number of approved stallions, simulating this approach indicates that it is only effective when combined with mating quotas (breeding limits). However, even then, its effect remained limited.
Increasing the Number of Breeding Mares. In another simulation, the impact of increasing the number of breeding mares was evaluated. Regrettably, the findings suggest that a significant and unrealistic increase in breeding mares would be necessary to achieve a substantial decrease in population inbreeding rates.
Stratified Mating Quotas. Finally, researchers simulated a creative strategy utilizing stratified mating quotas. In this simulation, each approved stallion was allocated a mating quota (ranging from 60 to 120 offspring per year) based on its average kinship with recently born foals. This approach resulted in a lower rate of inbreeding (0.43%) compared to a general mating quota of 90 offspring per sire each year (0.55%).
Key Takeaways
The overall takeaway from this study is that while the current inbreeding rate is below 1%, researchers recommend that the studbook implement additional strategies to further reduce inbreeding rates below 0.5% in the Friesian horse population. To accomplish this goal, researchers recommend that the KFPS adopt a strategy based on mating quotas for approved stallions tied to their individual average kinship compared to the population's average kinship.
This study was exceptional and comprehensive. To delve deeper into the details, we strongly suggest reviewing the manuscript provided below. It will be intriguing to observe the recommendations that the KFPS Breeding Council presents to the board and, ultimately, the strategy proposed to the KFPS Member Council for deliberation.
How Will Stallion Owners React?
There is likely to be some level of pushback from stallion owners if the recommendation is to adopt a stratified mating quota approach to lowering inbreeding. Stallion owners incur significant costs in obtaining approval for their stallions, keeping up with their training, and promoting them to breeders. Over the past few decades, the prices of fresh and frozen semen from approved stallions have remained relatively stagnant despite rising inflation. Stallion owners seem hesitant to increase their breeding fees, possibly concerned that doing so could push customers towards other, more affordable stallions.
Implementing breeding limits for popular high kinship stallions might prompt what some feel is a largely overdue correction in the market for breeding fees. For example, in 2022, Jehannes 484 Sport Elite AAA had a staggering 226 breedings. However, due to the influence of his high kinship father, Tsjalle 454 Preferent (19.5% kinship), Jehannes himself has a kinship of 19.1%. Under a stratified mating quota approach, Jehannes would likely face a reduced mating quota. Jehanne's breeding contract is currently €1,000 plus VAT. This equates to roughly $1,089 plus tax at the time this article was written. With 226 breedings, that's a potential income of € $226,000. Theoretically, if Jehannes received a mating quota of 60, this would reduce his potential annual revenue by as much as 73%.
To offset these losses, some stallion owners would likely increase their breeding fees, and the effect that higher breeding fees would have on the market is unpredictable. It's possible some mare owners might turn to foalbook stallions or reduce their breeding programs. Still, it is also possible that mare owners will gladly absorb increased breeding fees to select the stallion they feel is the best choice for their mare. Stallion owners with popular high kinship stallions that receive reduced mating quotas might also become more discriminating as to which mares they accept breeding contracts for, choosing only the mares likely to produce higher-quality foals.
Irrespective of the approach chosen in the end, this marks a particularly intriguing period in the history of the studbook. Health has never been given such prominence before, and the concerns of members and the studbook appear to be closely aligned on this matter. Nevertheless, the direction we are headed in and the path we will take to get there are still uncertain. Nonetheless, it is evident that the board is focused on gathering the necessary scientific data to chart the studbook's course rather than depending on emotions.
Reference: Steensma, M. J., Doekes, H. P., Pook, T., Derks, M. F. L., Bakker, N., & Ducro, B. J. (2024). Evaluation of breeding strategies to reduce the inbreeding rate in the Friesian horse population: Looking back and moving forward. Journal of Animal Breeding and Genetics, 00, 1–17.
duce ΔF below 0.5% in the Friesian horse popul'ation.
For this breed and similar
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