Analysing the effective population size in the partially closed and fragmented breeding population of the Trakehner Horse breed

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Ferdinand Hicks
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Faculty of Agriculture and Nutritional Science

Breeding and Husbandry Analysing the effective population

population of the Trakehner Horse breed Rike Teegen C. Edel G.

1 Faculty of Agriculture and Nutritional Science Christian-Albrechts-University of Kiel Institute of Animal Breeding and Husbandry Analysing the effective population size in the partially closed and fragmented breeding population of the Trakehner Horse breed Rike Teegen C. Edel G. Thaller Institute of Animal Breeding and Husbandry Christian-Albrechts-University of Kiel

2 Introduction Aim of the study - to examine the population structure of the Trakehner breed in terms of: 1. generation interval 2. effective population size 3. gene contributions of thoroughbreds General aspects of Trakehner breeding: - one of the oldest horse breeds in the world - partially closed population (closed studbook) - 10 (14) local breeding societies, centrally managed

3 Material and methods Central pedigree (n = 36,620) - birth register of all animals in the Trakehner Association to the years Actual breeding population (n = 6,746) - records of mare conformation tests (n = 6,505) - records of sires presented to the commission for breeding approval at the central stallion certification (n = 241) - only mares and sires with the identification label 09 Pedigree of actual breeding population (n = 13,793) - birth years before 1950 and/or ancestors with unknown pedigree information were treated as founder animals (non ibd, n = 198)

4 Generation interval Ø L = 10.2 years male-male male-female number of animals x = s.e.= 0.66 number of animals x = s.e.= age in year age in year female-male female-female number of animals x = 9.55 s.e.= 0.19 number of animals x = s.e.= age in year age in year

5 Effective population size Effective population size (N e ) estimated by the increase in average inbreeding coefficient ( F x ) and average coancestry ( f xy ) (year-wise and generation-wise) : 1 2 x Numerator-Relationship- Matrix (NRM) all missing sires and x dams treated as unrelated to the actual breeding population Uncertain-Parentage- Matrix (UPM) all potential sires or dams within 3-7 years before the birth of the animal were accounted with the same probability as sires and dams

6 Results: coancestry, inbreeding and N e average coancestry average inbreeding coefficient Ne(year) = Ne(generation) = birth years Ne(year) = Ne(generation) = average coancestry (NRM-method): average inbreeding coefficient (NRM-method):

7 Results: coancestry, inbreeding and N e hockey stick regression (NRM-method): average coancestry N e (generation) = birth years N e (generation) = 72.58

8 Results: coancestry, inbreeding and N e average coancestry Ne(year) = Ne(generation) = average coancestry (UPM-method): average inbreeding coefficient birth years Ne(year) = Ne(generation) = average inbreeding coefficient (UPMmethod):

9 Coancestry in and between breeding societies BR (11) MV (344) Sa (246) TH (11) former GDR SaA (108) SH (864) BY (515) BW (339) HE (467) RLP/S (376) former FRG RL (693) WF (467) NS/H (826) NS/NW (204) BR MV Sa TH SaA SH BY BW HE RLP/S RL WF NS/H NS/NW former GDR former FRG

10 Variance of family size of sires percentage rel. numbers of born animals per year rel. family size rel. family variance birth year n = 13,973

11 Contribution of genes thoroughbreds number of animals with contribution min x max English (xx) % 22.3% 87.5 % Arabian (ox) % 11.7% 75.0%

12 Summary Decreasing number of breeding animals Long generation interval in each selection path Estimates of N e analysed with NRM- and UPMmethod differ from calculations with census data (BMVEL, 2004) Estimates of N e on a low level

13 Summary cont. Upper limit of N e analysed with NRM- and lower limit of N e analysed with UPM-method Average inbreeding coefficient is lower than average coancestry one generation before Genetically fragmented population Increasing variance of family size of sires since 1989

14 Conclusion There is a need to manage the breeding population more carefully in order to minimise inbreeding where possible.

15 Christian-Albrechts-University of Kiel Institute of Animal Breeding and Husbandry Thank you for your attention! This project is supported by the H. Wilhelm Schaumann Foundation and the Foundation Trakehner Horse. Photo: Beate Langels

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