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Journal of animal breeding and genetics = Zeitschrift fur Tierzuchtung und Zuchtungsbiologie2024; 141(6); 668-684; doi: 10.1111/jbg.12872

Evaluation of breeding strategies to reduce the inbreeding rate in the Friesian horse population: Looking back and moving forward.

Abstract: In the past, small population sizes and unequal ancestor contributions have resulted in high inbreeding rates (ΔF) in the Friesian horse. Two decades ago, the studbook implemented a mating quota and started publishing individual kinships and reduced ΔF below 1% per generation. However, since then, the breeding population size has decreased and this raises the question whether current breeding strategies are sufficient to keep ΔF below desired rates. The aim of this study was to (1) reflect on past inbreeding trends and their main determinants, using pedigree analysis and (2) evaluate the effectiveness of the current and additional breeding strategies using stochastic simulations. We estimated the current ΔF (2013-2022) at 0.72% per generation. While the total contribution of the top 10 sires to the number of offspring per year has decreased from 75% in 1980 to 35% in 2022, this was mainly due to an increased number of approved studbook sires, and not due to more equalized contributions among sires. Of the simulated breeding strategies, selecting only breeding stallions with a below average mean kinship (i.e., "mean kinship selection") was most effective to decrease ΔF (from 0.66% to 0.33%). Increasing the number of breeding sires only had an effect when also a mating quota was applied. However, its effect remained limited. For example, a ~1.5 fold increase, combined with a mating quota of 80 offspring per sire per year, reduced ΔF from 0.55% to 0.51%. When increasing the number of breeding mares, a practically unfeasible large increase was needed for a meaningful reduction in ΔF (e.g. twice as many mares were needed to reduce ΔF from 0.66% to 0.56%). Stratified mating quotas, a novel approach in which we assigned each sire a mating quota (of 60, 80, 100 or 120 offspring per year) based on its mean kinship to recently born foals, resulted in a lower ΔF (0.43%) than a general mating quota of 90 offspring per sire per year (0.55%). Overall, while the current ΔF is below 1%, we recommend to implement additional strategies to further reduce ΔF below 0.5% in the Friesian horse population. For this breed and similar populations, we recommend to focus on breeding strategies based on kinship levels to effectively reduce ΔF.
© 2024 The Authors. Journal of Animal Breeding and Genetics published by John Wiley & Sons Ltd.
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Publication Date: 2024-05-15 PubMed ID: 38745529DOI: 10.1111/jbg.12872Google Scholar: Lookup
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Summary

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This research evaluates breeding strategies in the Friesian horse population with the aim of reducing the inbreeding rate. Despite implementing a mating quota and publishing individual kinship data, there are concerns that the reduction in population size may pose challenges in maintaining the desired inbreeding rates. The study uses pedrigree analysis and stochastic simulations to reflect on past inbreeding trends, identify key determinants, and assess the efficacy of current and additional potential breeding strategies.

Past Inbreeding Trends and Their determinants

  • The inbreeding rate in the Friesian horse population has previously been high due to small population sizes and unequal ancestor contributions.
  • About two decades back, a mating quota was implemented, and individual kinships were published, resulting in the inbreeding rate reducing to below 1% per generation.
  • Despite these measures, the breeding population size has since decreased, raising concerns over the ability of existing strategies to maintain the desired inbreeding rates.

Evaluation of Current and Alternative Breeding Strategies

  • The researchers estimated the current inbreeding rate (2013-2022) to be 0.72% per generation.
  • There has been a decrease in the total contribution of the top 10 sires to the number of offspring per year from 75% in 1980 to 35% in 2022. However, this drop is attributed to an increase in approved studbook sires, rather than more balanced contributions among sires.
  • From the simulated breeding strategies, it was observed that selecting breeding stallions with a below-average mean kinship – a strategy referred to as “mean kinship selection” – was the most effective in reducing the inbreeding rate.
  • Merely increasing the number of breeding sires did not significantly affect the inbreeding rate, unless it was accompanied by the application of a mating quota. Even so, this effect remained rather limited.
  • Trying to reduce inbreeding by increasing the number of breeding mares proved to be practically infeasible, requiring a much larger increase to have any significant impact on the inbreeding rate.
  • The introduction of a novel approach of assigning mating quotas to each sire based on its mean kinship to recently born foals (stratified mating quota) reduced the inbreeding rate more than a general mating quota.

Recommendations

  • Although the current inbreeding rate is below 1%, additional strategies are recommended to further reduce the inbreeding rate to below 0.5% in the Friesian horse population.
  • For the Friesian breed and similar populations, breeding strategies should be based on kinship levels to effectively reduce the inbreeding rate.

Cite This Article

APA
Steensma MJ, Doekes HP, Pook T, Derks MFL, Bakker N, Ducro BJ. (2024). Evaluation of breeding strategies to reduce the inbreeding rate in the Friesian horse population: Looking back and moving forward. J Anim Breed Genet, 141(6), 668-684. https://doi.org/10.1111/jbg.12872

Publication

Journal of animal breeding and genetics = Zeitschrift fur Tierzuchtung und Zuchtungsbiologie
ISSN: 1439-0388
NlmUniqueID: 100955807
Country: Germany
Language: English
Volume: 141
Issue: 6
Pages: 668-684

Researcher Affiliations

Steensma, Marije J
  • Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.
  • Koninklijke Vereniging het Friesch Paarden-Stamboek, Drachten, The Netherlands.
Doekes, Harmen P
  • Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.
Pook, Torsten
  • Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.
Derks, Martijn F L
  • Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.
Bakker, Nynke
  • Koninklijke Vereniging het Friesch Paarden-Stamboek, Drachten, The Netherlands.
Ducro, Bart J
  • Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.

MeSH Terms

  • Animals
  • Horses / genetics
  • Horses / physiology
  • Inbreeding
  • Male
  • Female
  • Breeding / methods
  • Pedigree
  • Population Density

Grant Funding

  • 4164023400 / TKI PPS Het Behouden Paard

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Citations

This article has been cited 1 times.
  1. Steensma MJ, Doekes HP, Derks MFL, Ducro BJ. Genome-wide association study reveals candidate loci on ECA1 and ECA9 for withers height in Friesian horses. Anim Genet 2025 Oct;56(5):e70049.
    doi: 10.1111/age.70049pubmed: 41090464google scholar: lookup
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