Dominant curly coat in horses

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Dominant curly coat in horses

Dp Sponenberg

To cite this version:

Note

Dominant

_curly

coat

in horses

DP

_Sponenberg

Virginia-Maryland Regional

College

of

Veterinary Medicine,

Department

of Pathology,

Virginia Tech, Blacksburg, VA _2.¢061, USA

(Received

18

_January

_{1989; accepted} 20 December

₁₉₈₉₎

Summary - Records from the American Bashkir

_Curly

Horse

_Registry

indicate that of 457

registered

horses, 25 had no

_curly-coated

_parents and this occurred in _purebreds of breeds where curliness is rare, 224 had 1 _curly coated parent, 122 had 2

_curly

coated parents,

and 86 had _parents of unknown status.

_Complete

_production records on some individuals

have revealed that

_matings

between

_curly

coated horses

_produced

47

_curly

coated and 11 normal coated

_{offspring. Matings}

between

_curly

and normal coated horses

_produced

29 _curly and 17 normal coated

_offspring.

The results are consistent with a _{dominant gene}

causing

curly

coat in _horses,

_although

a _separate

_previously

documented _{recessive gene for}

curliness also exists. The _symbol Crd for dominant curliness is

_suggested

for the dominant

gene.

horse _/ curly coat

Résumé - Dominance de la robe à poils bouclés chez le cheval .

_L’analyse

des 457

dossiers de l’American Bashkir

_Curly

Horse _Registry a montré que 25 chevaux provenaient

de _parents sans robe bouclée, 22.j avaient un _parent à robe bouclée, 122 avaient les deux

parents à robe bouclée et 86 provenaient de _parents chez lesquels cette

_information

était inconnue. Les 25 chevaux issus de _parents sans robe bouclée appartenaient à des races où la robe bouclée est rare. Une étude détaillée de certains dossiers a révélé que

l’accouplement

entre chevaux à robe bouclée a

_produit

₄₇ chevaux à robe bouclée et i1 chevaux à robe

normale,

tandis que l’accouplement entre chevaux à robe bouclée et chevaux à robe normale

a

_produit

29 chevaux à robe bouclée et 17 à robe normale. Ces résultats

_indiquent

la présence d’un

_gène

dominant causant la robe bouclée bien _qu’un

_{gène récessif}

ait été décrit

antérieurement. Le _symbol Crd est

_suggéré

pour le gène dominant responsable de la robe

à _poils bouclés.

cheval / robe bouclée

INTRODUCTION

Horses

_having

a

_curly

coat instead of the usual

_straight

hair coat have been documented as

_resulting

from a _{recessive gene in} Percheron horses

(Blakeslee

et

al,

1943).

A further _report

_concerning

curliness of Lokai horses has

_appeared

in

Animal

_Breeding

Abstracts

_(Shchekin

and

_Kalaev,

_1941).

This _report states that such curliness is

_recessive,

but _goes on to indicate that

_curly

x

_{curly matings}

produced

46

_curly

and 13 normal coated

_foals,

and

_curly

x normal coated

_matings

a dominant mode of inheritance

(x2

=

_0.277,

1

_df,

P > 0.05 for

_curly

x

_curly

matings,

x

2

=

0.243,

1

_df,

P > 0.05 for

_curly

x normal

_matings).

In the translated abstract mention is made of the fact that &dquo;about one third of

_{curly offspring}

from

matings

of

_curly

parents show a more marked

degree

of curliness at

_birth,

and it is

_thought

that these may be

homozygotes.&dquo;

It is

_possible

that the abstract was

mistranslated,

and that the

_original

stated that the curliness is dominant.

MATERIALS,

METHODS AND RESULTS

The data

_presented

are those of the records of the American Bashkir

_Curly

Horse

Registry.

These horses are

registered

on the basis of a

curly

coat. Of 457

_registered

horses,

224 had 1

_curly

and 1 normal _parent

_(curly

sires

_produced

74

_curly

colts and 84

_curly

_{fillies, curly}

dams

_produced

36

_curly

colts and 30

_curly

_fillies),

122 had 2

_curly

_parents

₍₆₃

_curly

colts and 59

_{curly fillies),}

25 had 2 normal coated _parents

(12

curly

colts and 13

_curly

_fillies),

and 86 were of unknown

_parentage.

Most of

these 457

_originated

in feral herds in the West of the USA or were the

_products

of

crossing curly

feral horses with established normal haired breeds

_(Quarter

_Horse,

Appaloosa,

Paint).

These

_curly

horses are said to have other

_phenotypic

_{similarities,}

such as

_bulging

_{foreheads, slanting}

_sleepy

_eyes, small nostrils and a

_peculiar

odour. Some normal coated horses of these lines also have some of the same

_phenotypic

characters so these _{may not} be

_pleiotropic

effects of the gene for curliness. One difference between normal coated horses and some of the

_curly

ones is that the mane

and tail hairs of some but not all of the

_curly

horses are shed in

_springtime

_along

with the thick winter

_body

coat. This

_{phenomenon only}

occurs in some individuals.

The 25

_curly

horses

_resulting

from

_matings

of _parents with normal coats occurred

in normal coated breeds

₍₁

Tennessee

_Walking

_Horse,

11 Missouri

_Foxtrotters,

2

_Appaloosas,

4

_{Quarter Horses,}

1

_{Standardbred,}

1 Paso Fino and 12

_others).

These and the other

_curly

_types cannot be

_{reliably distinguished by}

_phenotype.

Complete

results of

_matings

were available for some individual animals

(table

I). Curly

x

_{curly matings}

resulted in 47

_curly

and 11 normal coated animals.

If these are

_heterozygous

for a dominant _{gene then}

X

2

=

_1.126,

1

df,

P _> 0.05.

Curly

x normal coat

_{matings produced}

29

_curly

and 17 normal haired

_offspring.

If these

_curly

horses are

_heterozygous

for a dominant _gene then

_x

₂

=

_3.13,

₁

_df,

P > 0.05. These results are consistent with the action of a dominant _gene

_causing

curly

coat in

_horses,

as are the Russian data. Sex

linkage

is not _present, as indicated

by

the studbook data in which both colts and fillies are

_{produced by}

a

_{single curly}

DISCUSSION

The recessive mode of inheritance for curliness in horses has been

_previously

documented,

and some

_curly

horses are

_{probably homozygous}

for this _gene rather

than attributable to the dominant _gene. This is

_{especially likely}

for the

_curly

horses

resulting

from

_matings

of

_purebred

horses of breeds that are normal coated. In our

data is one such

curly

Missouri Foxtrotter stallion born of normal coated

_parents.

He

_produced

5 normal coated foals after

_being

bred to normal coated horses. If his record is removed from the data of the

_curly

and normal

_matings

then the result is 29

_curly

and 12 normal foals. Under the

_hypothesis

of

_{heterozygosity}

for a dominant

gene

x

2

=

_7.048,

1 df,

P _< 0.01 which is

_{highly significant.}

These

_matings

therefore

produce

an excess of

_{curly foals,}

which would occur if some horses in the

sample

were

_homozygous,

rather than

_{heterozygous,}

for curliness.

The

_breeding

of

_curly

horses is

_{complicated by}

the fact that 2 _separate

_genetic

mechanisms can cause the

_curly

coat. One of these is

_dominant,

the other is recessive. It is

_likely

that the 2 can be

_accurately

differentiated on the basis of

the annual

_shedding

of the mane and tail. This is

expected

of the dominant gene

for

curliness,

but not the recessive. The

_symbol

Crd is

_proposed

for the dominant

gene

causing

curliness

_{(curly dominant).}

ACKNOWLEDGMENTS

The authors thank the American Bashkir

_{Curly Registry}

for

_providing

these data.

REFERENCES

Blakeslee

_LH,

Hudson

_RS,

Hunt HR

₍₁₉₄₃₎

_Curly

coat in horses. J Hered

_34,

115-118