COAT COLOUR VERSUS PERFORMANCE.pdf

POLISH JOURNAL OF NATURAL SCIENCES

Abbrev.: Pol. J. Natur. Sc., Vol. 22(1): 43-49, Y. 2007

DOI 10.2478/v10020-007-0005-8

COAT COLOUR VERSUS PERFORMANCE

IN THE HORSE ( EQUUS CABALLUS )

Anna Stachurska 1 , Anne P. Ussing 2

1 Chair of Horse Breeding and Use

Agricultural University, Lublin, Poland

The Royal Library, Copenhagen University Library North Copenhagen N., Denmark

K e y w o r d s: horse, coat colour, performance, genes.

Abstract

The coat colour in the horse being mainly a protective trait is also a factor which contributes to

the maintenance of the thermal equilibrium in the body. A relationship between the colour and

performance in the horse is possible since the genes producing the colour may be linked with genes

which affect the horse’s performance or can be pleiotropic simultaneously influencing both kinds of

traits. Current studies performed on racehorses have not shown a considerable relationship between

the loci controlling the grey colour as well as eumelanogenesis in bay and black horses and the racing

records. Instead, a few loci are known which control certain colours and involve pathologic signs in

the organism or are lethal in homozygotes.

MAŚĆ A DZIELNOŚĆ KONI ( EQUUS CABALLUS )

Anna Stachurska, Anne P. Ussing

The Royal Library, Copenhagen University Library North Copenhagen N., Dania

S ł o w a k l u c z o w e: koń, maść, dzielność, geny.

Abstrakt

Barwa włosów u koni odgrywająca głównie rolę ochronną jest też czynnikiem wspomagającym

utrzymanie równowagi cieplnej organizmu. Związek rodzaju maści z dzielnością konia jest możliwy,

gdyż geny powodujące powstanie maści mogą być sprzężone z genami wpływającymi na dzielność

Address: Anna Stachurska, Agricultural University, Akademicka 13, 20-950 Lublin, Poland,

anna.stachurska@ar.lublin.pl

Katedra Hodowli i Użytkowania Koni

Akademia Rolnicza w Lublinie

Anna Stachurska, Anne P. Ussing

konia, a także oddziaływać równocześnie na oba rodzaje cech. Najnowsze badania przeprowadzone na

koniach wyścigowych nie wykazały istotnego związku genów maści siwej oraz wytwarzania eu-

melaniny u koni gniadych i karych z wynikami wyścigów. Znanych jest natomiast kilka loci

kontrolujących pojawienie się określonych maści, które równocześnie powodują patologiczne zmiany

ustrojowe, a u homozygot są letalne.

As far as it is known, different wild horses were of different colours, e.g. the

Tarpan ( Equus caballus gmelini ) according to old chronicles was blue dun

(P RUSKI 1959). Paleolithic cave paintings in Middle Asia and Europe (Altamira,

Spain and Lascaux, France; 15.000-10.000 BC) show, among horses of basic

(bay, chestnut and black) and dun (wild type pattern) colours also leopard

pattern (white areas with spots, most pronounced on the hips). The Przewalski

Horse (Equus caballus przewalskii) , the last living wild representative of the

species, is of a yellow dun colour with wild type pattern. White markings on the

head and legs probably appeared in the domestic horse. Domestication in

horses and later breeding caused a great coat colour diversity among breeds.

Some of them are of a particular coat colour, whereas others show a wide

variety of colour phenotypes (K LUNGLAND ,V ´ G E 2000).

The coat colour is a protective trait which helps the wild horses hide and

escape predators (S TACHURSKA et al. 2004). Currently, in California-Nevada

a significant difference is observed in the proportion of variously coloured foals

killed by pumas (Felis concolor) relative to the distribution of colours born into

the feral horse population. The pumas select for sorrel (light chestnut) foals,

probably because this colour more closely approaches the colour of the mule

deer (Odocoileus hemionus) of this region than any other foal colour does

(T URNER ,M ORRISON 2001). The coat colour also plays a role in maintaining the

body temperature: dark colours quickly absorb sunrays and easily eliminate

the heat, while light colours retain the heat longer and are advantageous when

it is cold (C ENA et al. 1957).

Horse breeders and users have been always interested in knowing whether

the performance of variously coloured horses differ. Usually, the preferences

for certain coat colours are the consequence of a belief that they can be

associated with better or worse performances. Such relationship is possible,

since the genes producing the colour may be linked with genes affecting the

horse’s systemic traits. Certain genes can also be pleiotropic, i.e. they can

influence both the colour and the systemic features (F ALCONER 1981). The

colour is a quality trait which is controlled by several loci (S PONENBERG 2003,

S TACHURSKA 2002, U SSING 2000). Most of the loci have already been assigned

to particular chromosomes (Table 1). They are closely linked to some genes

producing e.g. various blood protein variants, which may be important for the

systemic functions (A NDERSSON ,S ANDBERG 1982). The performance traits

Coat Colour Versus Performance...

depend on the activity of additive polygenes and possible Quantity Trait Loci

(QTLs) of a great phenotypic effect (E DWARDS et al. 1987). Up to date, no QTLs

affecting the horse’s performance have been found. The characters which

make it up are complex and difficult to measure. Moreover, they are consider-

ably influenced by the rider, exercise, feeding and many other factors (S AAS-

TAMOINEN ,B ARREY 2000). The polygenetic nature of the horse’s performance

hinders the search for its relationship with the coat colour.

Table 1

Loci controlling the horse coat colours assigned to chromosomes

Locus

Chromosome

Colour/Colours

Locus bibliography

ECA1

leopard

T ERRY et al. 2004

MC1R (E) ECA3

chestnut, bay, black

A NDERSSON ,S ANDBERG 1982, M ARKLUND et al.

1996, R IEDER et al. 2001

ECA3

tobiano

A NDERSSON ,S ANDBERG 1982, B ROOKS et al. 2002

ECA3

roan

A NDERSSON ,S ANDBERG 1982, M ARKLUND et al.

1999

ECA3

sabino

B ROOKS ,B AILEY 2005, M AU et al. 2004

EDNRB

ECA17

associated with overo

and other white

patterns

S ANTSCHI et al. 1998, 2001

MATP (C) ECA21

palomino, buckskin,

cremello

L OCKE et al. 2001, M ARIAT et al. 2003

ASIP (A) ECA22

bay, black

R IEDER et al. 2001

ECA25

grey

H ENNER et al. 2002, L OCKE et al. 2002,

S WINBURNE et al. 2002

ECA3

dominant white

M AU et al. 2004

Opinions on such connections are reported to be common worldwide

(K EELER 1947, S PONENBERG 2003, S TACHURSKA et al. 2001). The issue has been

investigated since a long time. Many studies have been performed on

racehorses since the racing records are more numerous and scored under more

similar circumstances than show jumping, three day eventing or other eques-

trian sports (R ICARD et al. 2000). However, the racehorses are not much

differentiated with regard to the colour (usually bay, black, chestnut and grey)

and thus only few loci controlling the colour could have been investigated. The

results are mostly negative, and solely S KORKOWSKI (1976) found a consider-

able difference in the endurance and speed between bay and chestnut Thor-

oughbreds. The bay mares were more enduring and won more at the age of

three years, particularly over distances above 2000 m, compared to the

chestnut mares, which were faster at the age of two years, over shorter

Anna Stachurska, Anne P. Ussing

distances. These findings do not agree with results of other studies. An

investigation performed on winners of five English classical races in 1777-1938

showed no difference associated with the colour (G ALIZZI V ECCHIOTTI 1986).

According to D U ˇ EK (1980), the performance in chestnuts, bays, blacks and

greys, as well as in chestnuts with different amounts of white markings, is

similar. Recently, S TACHURSKA et al. (2006) and S TACHURSKA ,P IĘTA (2006)

examined nearly 15 thousand starts of a great number of Thoroughbreds and

Purebred Arabians, with regard to current knowledge on the loci controlling

the colour. The results indicate that G locus assigned to ECA25 is not

associated with the performance, i.e. grey and non-grey horses gain similar

scores. Regarding locus MC1R located on ECA3, eumelanic (bay and black)

horses show an insignificant tendency towards better results than

phaeomelanic (chestnut) horses. However, it cannot be excluded that the effect

might be expressed in homozygous grey (GG genotype) and eumelanic (EE

genotype) horses since dominance of G and E genes may be not complete. Most

of Thoroughbreds are heterozygous (Gg and Ee genotypes, respectively).

Physiological actions ruled by the combined action of dominant and recessive

genes can lead to phenotypic traits a little bit similar to those found in

recessive genotypes (gg and ee). Horses of overall darker colours had inconsid-

erably better scores than lighter ones. Such tendencies may be due to the

physiological properties related to the brightness of the hair. The ASIP locus

on ECA22 was not studied since black horses were few. The relationship

between the coat colour and racing performance in horses at particular age,

suggested by S KORKOWSKI (1976) has not been found.

The difference in the temperament in horses of various colours was not

proved (E STES W ORTH 1948). J AKUBEC at al. (1997) found the conformation of

grey and black Old Kladrub horses varied. Nevertheless, this could result from

the isolated selection of those subpopulations and not from the relations

among the traits in question and the colour. B LESA et al. (1999) and D RING et

al. (1981) did not find any correlation between the mare’s colours and gestation

length in Thoroughbreds.

Although an important relationship of the coat colour with the perform-

ance and physiological traits in the horse was not found, the fact that certain

loci controlling the coat color involve pathological signs in the organism was

documented. For instance, 67%-80% of grey horses older than 15 years develop

melanomas (neoplasms) which turn malignant in 66% of the cases (S ¨ LKNER et

al. 2004). Probably that is the reason the life span of the grey horses is on

average by two years shorter than usual (G ALIZZI V ECCHIOTTI 1986). Some

observations have not been scientifically investigated, yet, e.g. homozygous

leopard horses are reported by Danish Knabstrub breeders to have impaired

night vision (U SSING 2000) and some splashed white horses in Australia seem

Coat Colour Versus Performance...

to be deaf (G OWER 1999). In horses, like in many other mammalian species,

certain colours are produced by lethal or semi lethal alleles. It was proved that

among dominant white horses, homozygotes WW are lethal at early stages of

embryo development (P ULOS ,H UTT 1969). Similarly, dominant homozygotes

in Roan (Rn) locus may be lethal in intrauterine life (H INTZ ,V LECK V AN 1979).

Overo lethal white syndrome (OLWS) is an inherited fatal disease of foals born

to overo parents. Affected foals are white and die within a few days from

intestinal aganglionosis (V ONDERFECHT et al. 1983). The syndrome is caused by

a mutation in the endothelin receptor B (EDNRB) gene in homozygotes

(S ANTSCHI et al. 1998, 2001). Considering the ratio of foals different than

expected from matings of variously coloured parents, K NYAZEV et al. (1999)

suggest that embryos of grey heterozygotes may be less vital than others.

To conclude: currently, only relationships between the horse coat colour

and some physiological functions of the organism are known. No important

relationship between the coat colour and the horse’s performance has been

found. The research to date on the racing performance of horses of different

colours has considered solely two loci controlling the colour. In future,

provided the genetic basis of the performance is known better, a molecular

approach may give an unequivocal answer whether such relationship exists

and if so, which particular traits are associated with which colours.

Translated by A NNA S TACHURSKA

Accepted for print 21.12.2006

References

A NDERSSON L., S ANDBERG K. 1982. A linkage group composed of three colour genes and three serum

protein loci in horses. J. Hered., 73(2): 91-94.

B LESA F., V ALERA M., V INUESA M., M OLINA A. 1999. The gestation length of the Andalusian and Arabian

Horse . Book of Abstracts 5, 50 th An. Meeting of Europ. Ass. for Animal Prod., Zurich (Switzer-

land). Copyright Wageningen Pers, Wageningen, pp. 348.

B ROOKS S.A., B AILEY E. 2005. Exon skipping in the KIT gene causes a Sabino spotting pattern in horses .

Mamm. Gen., 16(11): 893-902.

B ROOKS S.A., T ERRY R.B ., B AILEY E. 2002. Association of PCR-RFLP for KIT with Tobiano coat color in

horses . Anim. Genet . , 33: 301-303.

C ENA M., C ZYSZEK W., S ŁOMKA J. 1957. Badania nad wpływem umaszczenia koni na pochłanianie

promieniowania słonecznego . Med. Wet., 6: 261-264.

D RING L.A., H INTZ H.F., V AN V LECK L.D. 1981. Coat color and gestation length in Thoroughbred mares.

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D U ˇ EK J. 1980. P ˇ isp ˇ vek k ˇ e ˇ eni vztahu v´konnosti a barev u anglick´ch plnokrevniku. V´zkumn´

Stanice pro Chov Kon´, Slati ˇ any: Bull., 34: 77-87.

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E STES W ORTH B. 1948. Lack of correlation between coat colour and temperament. J. Hered., 39: 84.

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