Insect bite hypersensitivity in horses: genetic and epidemiological analysis
Schurink, A. - \ 2012
University. Promotor(en): Johan van Arendonk, co-promotor(en): Bart Ducro; Klaas Frankena. - S.l. : s.n. - ISBN 9789461733566 - 168
dierveredeling - overgevoeligheid - paarden - genetische analyse - epidemiologie - insectenbeten - nederland - fries (paardenras) - shetland pony - animal breeding - hypersensitivity - horses - genetic analysis - epidemiology - insect bites - netherlands - frisian (horse breed)
Insect bite hypersensitivity (IBH) is the most common allergic skin disease in horses and is caused by bites of Culicoides spp. IBH reduces welfare of affected horses and at present no effective preventive measure or cure exists. Aim of our research was to increase knowledge of the genetic background of IBH in horse populations and to explore opportunities to reduce IBH prevalence through selection and breeding.
Data on Shetland pony and Friesian horse mares were gathered at obligatory inspections. IBH prevalence was 7.5% in Shetland pony mares and 18.2% in Friesian horse mares. Data were analyzed to identify risk factors. Combined effect of month and year of IBH scoring, region within the Netherlands and inspector were associated with IBH in both breeds. IBH prevalence significantly differed with coat colour and withers height category in Shetland pony mares. Moreover, prevalence was higher in Shetland pony mares with high body condition score (9.4%).
Quantitative genetic analyses revealed substantial genetic variation for IBH in both breeds. Heritability on the observed scale and on the underlying scale was 0.08 and 0.24 respectively in Shetland pony mares, 0.07 and 0.16 respectively in Friesian horse mares. Therefore, IBH is a heritable phenotype in both breeds. Repeatability was 0.30 in Shetland pony mares and 0.89 in Friesian horse mares. Maternal effect (0.17) was estimated in Friesian horse mares only.
To identify genomic regions contributing to the genetic variance, Shetland pony mares and Icelandic horses were selected according to a matched case-control design. Odds ratios of allele substitution effects of the unfavourable allele were between 1.94 and 5.95. Also, 13 and 28% of genetic variance was explained by all SNPs in respectively Shetland pony mares and Icelandic horses. Significant associated genomic regions across breeds suggest interesting candidate regions on ECA3, 7, 11, 20 and 23 contributing to genetic variance. Results support that ELA class II region on ECA20 is involved in IBH etiology, although follow-up studies are needed to confirm this and to identify genes in the other regions.
The general discussion explored possibilities to reduce IBH prevalence through breeding and discussed implications of using clinical symptoms or diagnostic test results. Simulated selection was based on EBV, which included own performance, progeny performance or genomic data. Selection on IBH clinical symptoms should be based on testing at least 10 but preferably more progeny, accompanying strict selection in sires to achieve reasonable genetic gain. Expected genetic gain per year in genomic selection outperformed other strategies, although implementation of genomic selection requires a considerable investment in a reference population. A diagnostic test for IBH (yet unfeasible to perform on a large sample) has the potential to increase genetic gain
Relevance of test information in horse breeding
Ducro, B.J. - \ 2011
University. Promotor(en): Johan van Arendonk, co-promotor(en): Henk Bovenhuis. - [S.l.] : S.n. - ISBN 9789085858553 - 170
paarden - paardenfokkerij - paardrijden - jachtspringen - sportprestatie - heritability - genetische diversiteit - fries (paardenras) - paardenrassen - sporten met dieren - horses - horse breeding - horse riding - show jumping - sport performance - genetic diversity - frisian (horse breed) - horse breeds - animal sports
The aims of this study were 1) to determine the role of test results of young
horses in selection for sport performance, 2) to assess the genetic diversity
of a closed horse breed and 3) the consequences of inbreeding for male
reproduction. The study was performed using existing databases containing
records collected on young horses during inspections, which were linked to
databases containing records on sport performance. Multivariate animal
models were applied in estimation of genetic parameters. Heritability
estimates of movement and free-jumping traits collected at Studbook Entry
and at First Stallion Inspection were moderate to high. Free-jumping traits
collected at both inspections showed high to very high positive genetic
correlations to show-jumping in competition. Movement traits collected at
both inspections showed favourably genetic correlations to dressage in
Subsequently, the effect of limb and foot conformation, in particular the
trait uneven feet, as assessed at Studbook Entry Inspection on performance
and length of sport career have been analysed. Limb and foot conformation
had only weak to moderate genetic correlation to sport performance. Some
foot conformation traits could be identified as risk factors for early
retirement from sports; e.g. occurrence of uneven feet shortened the
competitive life at elite level of jumping.
The development of genetic diversity in a closed breed have been studied
using the pedigree structure of the Friesian horse breed. Considerable loss
of genetic diversity have taken place during the history of the studbook,
corresponding to an average inbreeding rate of 1.3% per generation. Loss of
genetic diversity was mainly due to drift from small effective population size
during several generations. In a subsequent analysis the relation of
inbreeding with semen quality of young Friesian stallions was investigated. It
was concluded that low semen quality in Friesian stallions could not be
attributed to inbreeding. Heritability estimates for semen quality traits were
moderate to high and had substantial variation. Selection can be used to
improve semen quality.
Finally, opportunities for improvement of the breeding program have been
discussed. Selection potentials are calculated to gain insight in the relative
importance of each of the young horse tests to the breeding program.
Additional opportunities to increase selection response have been
Het paard in Nederland
Weerdt, M. de; Oldenbroek, J.K. - \ 2010
Wageningen : Centrum voor Genetische Bronnen Nederland (CGN) (CGN rapport 17) - 44
paarden - paardenrassen - gelderlander (paardenras) - paardenfokkerij - domesticatie - zeldzame rassen - fries (paardenras) - groninger paard - nederlands trekpaard - horses - horse breeds - gelderland (horse breed) - horse breeding - domestication - rare breeds - frisian (horse breed) - groningen horse - dutch draught horse
Paardenrassen, die hun oorsprong hebben in Nederland, zijn het Friese paard, het Gelderse paard, de Groninger en het Nederlands trekpaard. Dit verslag over de rol en de toekomst van de Nederlandse paardenrassen beschrijft de domesticatie van het paard en het ontstaan en de ontwikkeling van deze rassen. Daarna komt de huidige paardenfokkerij aan bod. Het verslag wordt afgerond met een hoofdstuk over het belang van het behoud van deze rassen.
Genetic diversity in the dutch friesian horse
Ducro, B.J. ; Bovenhuis, H. ; Neuteboom, J.H. ; Hellinga, I. - \ 2006
dierveredeling - paarden - paardenrassen - paardenfokkerij - stamboom - voorouders - inteelt - populatiegenetica - genetische diversiteit - fries (paardenras) - animal breeding - horses - horse breeds - horse breeding - pedigree - ancestors - inbreeding - population genetics - genetic diversity - frisian (horse breed)
The pedigree structure of the Dutch Friesian horse breed (n=79,962) was analysed to asses the genetic diversity still present in the population. The effective number of founders explaining the genetic diversity in the reference population (i.e female horses born between 1995 and 2005) was 26, whereas the effective number of ancestors was 16. The rate of inbreeding was 1.5% per equivalent generation which is beyond the critical level of 1%. The analysis indicated that the population has suffered from a bottle-neck shortly after the establishment of the population, and that a substantial loss of allelic diversity has occurred due to drift because of small population size. The increase of average kinship during recent generations has declined and this coincided with a substantial growth of the population. A decline of the rate of inbreeding might be expected, but a proper conservation programme is still needed to further reduce allelic loss from the population