Dissertation (PhD(Agric))--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This study was carried out to investigate whether environmental and/or genetic factors
had an effect on the incidence of epistaxis related to exercise-induced pulmonary
haemorrhage among racehorses in Southern Africa. A further aim was to estimate the
heritability of liability to epistaxis in the Southern African Thoroughbred population.
For the purpose of the environmental study, the data covering the period 1986-2001
and involving a total of778 532-race runs, were analysed. This included the following
race start information: date of race (day/month/year), age, sex, breeder, trainer,
distance, jockey, state of going, weight carried, centre of racing and altitude. The
genetic part of the data was two-fold in nature and included firstly the analysis of all
horses that suffered epistaxis whilst racing in Southern Africa from 1986 to 2001 and
involving 1118 individual bleeders. The second genetic analysis included the same
Southern African population plus those Southern African horses exported to Mauritius
and then being recorded as bleeders in that country (1252 bleeders in total). Pedigree
data covering the period 1960-1986 was used as required to calculate the incidence of
bleeding amongst ancestors of the post 1986 era. Only pedigrees of horses that raced were included in this study as it was not possible to predict whether non-runners
would have bled had they raced. Consequently all non-runners and also those that
raced overseas in countries where bleeding occurrence was not recorded were
excluded.
Veterinarians employed by the Jockey Club suspended officially recorded horses that
showed epistaxis as demonstrated by frank bleeding from the nostrils after racing. Oncourse
endoscopy is not employed as a routine on any of the Southern African
racetracks.
In the environmental study epistaxis was identified in 1 287 race starts (0.165%).
Epistaxis related to exercise-induced pulmonary haemorrhage was significantly
(p<0.001) associated with altitude, age, race year, month and the day of racing. More
horses demonstrated epistaxis at sea level than at altitude, between the months of May
- October than the rest of the year, in older horses than in horses less than three-years
old, after 1995 than between the years 1986 and 1995, and on Fridays and Sundays
than on any other week day. No association could be established between epistaxis
and breeder, trainer, distance, jockey, state of going, sex and weight carried.
The heritability of liability method as described by Falconer (1989) was used to
estimate the relative importance of heredity and environment. For the period
investigated, the population incidence for epistaxis in Southern African horses was
2.1%. The estimation of heritability ofliability showed that first-degree relatives had
a figure of 55.4%. The heritability of second- and third degree relatives were 41.3%
and 30.4% respectively. The data investigated depicts horses that bled almost
exclusively on race days as only a small percentage (- 5%) was reported as having
bled during exercise. Accordingly, the full extent of epistaxis amongst racing
Thoroughbreds in Southern Africa is difficult to gauge.
Pedigree and race run data from Thoroughbreds racing in Southern Africa, covering
the period 1986-2002 (63 146) horses in pedigree data-set and 778 532 race runs,
were further analysed in order to study genetic and environmental factors affecting the
incidence of epistaxis as associated with EIPH (exercise-induced pulmonary
haemorrhage). As fixed effects for the model, variables that were tested significantly
in a preliminary data analyses, were included. Various combinations of such variables namely age, weight, altitude, sex, month and going were tested. Fixed
effects that were included in the fmal model were gender, going and altitude. The
heritability estimates from a logit transformed analysis for epistaxis fitting both the
animal and sire generalized mixed models were 0.23 and 0.40 respectively, which
indicated that epistaxis as associated with EIPH in the Southern African
Thoroughbred sires has a strong genetic basis. Genetic trends indicating an increase
in epistaxis were also found.
It is concluded that the frequency of epistaxis related to pulmonary haemorrhage is
associated with altitude, winter and spring months and the horse's age. It is suggested
that racing at a lower altitude may increase the probability of exercise-induced
pulmonary haemorrhage.
It is clear that epistaxis in the racing Thoroughbred has a strong genetic basis. It is
further suggested that horses showing frank bleeding from the nostrils after racing or
exercise, be suspended and not used for breeding purposes. This would result in
relatively fast progress being made towards eradicating this costly scourge of the
modem Thoroughbred racehorse. Affected stallions and those racing whilst being
treated with furosemide, should be barred from breeding and not be considered as
future sires. Estimated breeding values for epistaxis should be used as a tool for
selecting against it and be considered in breeding programmes to decrease the
incidence thereof. / AFRIKAANSE OPSOMMING: 'n GENETIESE ANALISE VAN DIE VOORKOMS VAN
LONGBLOEDING IN DIE SUID-AFRIKAANSE RENPERD: Die doel met hierdie studie was om vas te stelof omgewings- of genetiese faktore
enige invloed op die voorkoms van longbloeding in die Suid-Afrikaanse renperd het.
'n Verdere doelstelling was om die oorerflikheid op die onderliggende verspreiding
van longbloeding in die Suid-Afrikaanse Volbloedpopulasie te bepaal. Vir die
omgewingstudie is data wat oor die periode 1986-2001 strek en wat 'n totaal van 778
532 wedren-deelnames ingesluit het, statisties ondersoek. Die data het die volgende
inligting ingesluit: datum van deelname, ouderdom, geslag, teler, afrigter, afstand van
wedren, jokkie, toestand van baanoppervlakte, gewig gedra, sentrum waar deelname
plaasgevind het en die hoogte bo seespieël van die sentrum. Die studie van die
genetiese aspekte het eerstens 'n analise van al die perde wat longbloeding tydens 'n
wedren in Suider-Afrika gedurende die jare 1986-2002 ondervind het (I118 perde), en
tweedens dieselfde populasie perde, plus die Suiderlike-Afrikaanse perde wat
uitgevoer is na Mauritius en bloeding daar ondervind het, (1252 perde), ingesluit. Ter
aanvulling is uitgebreide stamboomdata van voorouers gedurende 1960-1986 gebruik
om die voorkoms van longbloeding tydens die post 1986 tydvak te bepaal. Slegs
stambome van renperde wat aktief aan renne deelgeneem het, is in die data ingesluit
aangesien dit nie moontlik was om te voorspel of 'n perd wat nooit aan wedrenne
deelgeneem het nie, longbloeding sou ondervind indien dit wel deelgeneem het. Dus
is alle renperde wat nooit aan wedrenne deelgeneem het, asook daardie perde wat in
die buiteland deelgeneem en waar longbloeding nie aangeteken word nie, uitgesluit. Alle perde wat bloeding van die neus na wedrenne getoon het, is deur veeartse in
diens van die Jokkie Klub van Suid-Afrika ondersoek, as 'n bloeier aangeteken en van
verdere deelname aan wedrenne geskors. Endoskopie word op geen van die Suid-
Afrikaanse renbane as 'n standaard praktyk na wedrenne uitgevoer nie.
Longbloeding het in 1 287 perde of gedurende 0.165% van alle wedrenne
plaasgevind. Longbloeding soos geassossieer met EIPH, (exercise-induced
pulmonary haemorrhage), is betekenisvol (p<0.001) met hoogte bo seespieël,
ouderdom, dag van deelname, maand, en jaar verbind. Meer perde het longbloeding
by seevlak in vergelyking met hoër vlakke bo seespieël ondervind, tussen die maande
Mei-Oktober as die res van die jaar, in perde ouer as drie-jaar, na 1995 as tussen die
jare 1986-1995, op Vrydae en Sondae as enige ander dag van die week. en meer by
reuns as by merries of hingste. Geen verwantskap kon tussen bloeding en teler,
afrigter, afstand, jokkie, toestand van baan, geslag en gewig gedra, gevind word nie.
Die oorerflikheid op die onderliggende verspreiding vir longbloeding soos omskryf
deur Falconer (1989), is gebruik om die relatiewe belangrikheid van oorerflikheid en
omgewing te bepaal. Vir die periode bestudeer, was die voorkoms van longbloeding
in die Suid-Afrikaanse renperd 2.1%. Die oorerflikheid van longbloeding was 55.4%
vir eerste-graadse verwantes. By tweede-graadse verwantes was die ooretlikheid
41.3% en by derde-graadse verwantes 30.4%. Die data wat ondersoek is, was bykans
uitsluitlik die van perde wat tydens wedrenne gebloei het en slegs 'n baie klein
persentasie (~ 5%) was aangeteken as perde wat tydens oefening gebloei het. Dus is
die volle omvang van longbloeding in Suider-Afrikaanse Volbloedperde moeilik om
akkuraat te bepaal.
Die stamboom- en wedrendata van Suid-Afrikaanse Volbloedperde is verder ontleed
in 'n poging om die genetiese en omgewingsfaktore se invloed op die voorkoms van
longbloeding, soos geassosieer met EIPH te bepaal. As vaste effekte vir die model is
veranderlikes wat betekenisvol gevind was, ingesluit. Verskeie kombinasies van
hierdie veranderlikes soos ouderdom, gewig, hoogte bo seespieël, geslag, maand en
toestand van die baan is ingesluit. Die vaste effekte wat in die finale model ingesluit
is, was geslag, toestand van die baan en hoogte bo seespieël. Die beraamde
oorerflikheid verkry vanaf 'n "logit" getransformeerde analise vir longbloeding wat beide die diere- en vader- gemengde model gepas het, was onderskeidelik 0.23 en
0.40, wat 'n aanduidending is dat longbloeding, soos geassosieer met ElPH, 'n sterk
genetiese grondslag het. Genetiese tendense het ook gedui op 'n toename in die
voorkoms van longbloeding, veraloor die laaste vyf jaar van die studie.
Samevattend is die bevinding dat die frekwensie van longbloeding 'n betekenisvolle
verwantskap toon met hoogte bo seespieël, winter en lente maande en die perd se
ouderdom. Dit word voorgestel dat renperde wat deelneem aan wedrenne by laer
vlakke van hoogte bo seespieël, meer onderhewig aan longbloeding sal wees.
Uit die resultate verkry is dit duidelik dat longbloeding 'n genetiese grondslag het.
Dit word voorgestel dat perde wat fisiese simptome van neusbloeding na of gedurende
wedrenne toon, geskors word van verdere deelname en ook nie toegelaat word om
mee te teel nie. Hierdie maatreëls behoort aanleiding te gee dat relatief vinnige
vordering gemaak sal word in die strewe om hierdie ongewenste sindroom in die
moderne Volbloed te verminder. Aangetaste hingste, asook die wat aan wedrenne
deelgeneem het terwyl hul behandeling ontvang met furosemide, moet nie toegelaat
word om te teel en nie as toekomstige teelhingste oorweeg word nie. Die waarde van
voorspelde teelwaardes vir longbloeding moet nie onderskat word in seleksie daarteen
nie en moet in teelprogamme om die voorkoms daarvan te verminder, oorweeg word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49819 |
| Date | 12 1900 |
| Creators | Weideman, Heinrich |
| Contributors | Schoeman, S. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 72 p. : ill. |
| Rights | Stellenbosch University |
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