Sponenberg, DP

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Sponenberg DP

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Genetics Selection Evolution

Dominant curly coat in horses

DP Sponenberg

Springer

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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
produced 17 curly and 20 normal coated foals. These data are more consistent with
a dominant mode of inheritance (x2 = 0.277, 1 df, P > 0.05 for curly x curly
matings, x2 = 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 X2 = 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 x2 = 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
parent of either sex.

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 x2 = 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
Shchekin VA, Kalaev VV (1941) Inheritance of curliness in the horse. CR (Dokl)
Acad Sci URSS, NS, Animal Breeding Abstracts (1940) 26, 262-263, 9: 7


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Dominant curly coat in horses

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