THE ISSUE OF BLUE DUN SHADE INHERITANCE IN THE HORSE.pdf

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THE ISSUE OF BLUE DUN SHADE INHERITANCE IN THE HORSE
Anna Stachurska, Antoni Brodacki
ABSTRACT
The blue dun colour shade is not a selection criterion in Polish Konik horse breeding, hence it has been possible to undertake the analysis of its inheritance on the example of this population. The
material consisted of Polish Konik horses registered in the Studbook.
Key words: blue dun colour, shade, inheritance, Polish Konik, horse..
INTRODUCTION
The Polish Konik horse derives from Tarpans, which were blue dun. This coat colour was probably the protective colouring helping the horses to survive under harsh
environmental conditions [7]. Since the beginning of breeding, the Polish Konik horse has been to remind the most its wild ancestors. Hence, it has been selected for the
blue dun coat colour without white markings. However, the selection criteria have never concerned the colour shade and light, standard (in Polish literally called blue
dun), dark and yellow shaded blue dun horses have been accepted in the breeding [5]. It should be mentioned that in the world the blue dun shades are also
distinguished otherwise. This may result among others from the activity of additional alleles present in various populations, e.g. the Cremello allele. In the light of
hitherto studies, the blue dun shade in a horse seems to be a constant property, in spite of some fluctuations in the hair colour which occur according to the season of the
y ear [6, 10, 12] and the horses age [7, 9, 10].
The blue dun coat colour appears in the horse of aaE_D_ genotype [1, 2, 3, 4, 13]. Matings of heterozygous blue dun horses may produce aaE_dd black foals, _ _ eeD _
red dun foals and _ eedd chestnut foals [2, 3, 9]. In Polish Konik Studbook, both red dun horses and rare chestnut horses have been recorded as chestnuts and therefore
it is not possible to distinguish the two colours in them. Dominant A allele present in e.g. dun A_E_D_ horses, does not occur in the population any more [11]. The blue
dun shade inheritance has not been still discovered, perhaps because of the lack of sufficiently numerous blue dun horse populations in the world. As it is known, the
blue dun colour occurs in some primitive horse breeds but is a breed property only in the Polish Konik. Former study including 127 Polish Konik matings showed that
the blue dun shades could be determined by two sex-limited genes [9]. However, the suggested inheritance model was not sufficiently documented.
The objective of the study was to try to define the blue dun shade inheritance on the example of the Polish Konik population.
MATERIALS AND METHODS
The study was conducted on Polish Konik horses registered in eight Studbook volumes published up to the present. The shade in 1 107 blue dun horses was considered.
1 066 horses whose parents were of known colours were included in the genetic analysis. These were both blue dun (n=1 016) and non-blue-dun horses (n=7) resulted
from blue dun horses mated inter se , as well as horses of various colours produced in blue dun x non-blue-dun matings (n=43).
The changes of the blue dun shade percentage in the Polish Koniks were analysed between the successive volumes of the Stud Book. The shade segregation ratio was
studied in foals produced in various types of matings. The yellow-shaded-blue-duns which occur very rarely (n=3), were excluded from the analysis. The alleles present
in A locus were not considered, since all individuals were assumed to be of aa genotype [11].
The shade distributions were compared with the use of chi 2 test, provided the horse number was sufficient. The expected phenotype frequency in the population was
estimated on the basis of allele frequency in 514 Polish Konik horses present in the breeding herd in 2002 [11].
RESULTS
Most of the Polish Konik horses were of the standard shade (73.1%), fewer were light blue dun (15.8%) or dark blue dun (10.8%). Solely in the 3 rd volume of the
Studbook almost half of the stallions was light blue dun ( Fig. 1A, B and C ) . The yellow-shaded-blue-duns were rare (0.3%). The percentage of variously shaded blue
dun horses changed significantly in the first three volumes of the Book (p£0.01) and between the 4 th and 5 th volumes (p£0.05). The standard horse percentage lowered
at the beginning, then increased over 80% in the 5 th volume and insensibly decreased again. It can be generally stated that the number of variously shaded blue dun
horses has been remaining at a similar level since quite a long time.
Fig. 1. Percentage of Polish Konik horses registered in the Studbook
341064432.004.png
The distributions of the three blue dun shades in offspring produced by blue dun parents are presented in Table 1 . Foals of all three shades derived from particular kinds
of matings and only few dark horse inter se matings did not result in light shaded foals. The latter is not consistent with the observations by Kownacki [7] who stated
that in Polish Koniks sometimes light foals appeared from both dark shaded parents. They could have been only individuals not registered in the Stud Book or, what is
less possible, recorded with mistakenly described shade. Hence, such cases, if ever happen, are rare.
Table 1 . Blue dun shade dis tribution in Polish Konik horses produced in various kinds of matings
Parents
Progeny
341064432.005.png 341064432.006.png 341064432.007.png
dark
standard
light
total
differenc
e
significa
nce
between
ratios
Kind of mating
n % n % n % n
%
Dark x dark
5
83.3
1
16.7
0
0.0
6
100.0
Dark x standard
26
25.0
71
68.3
7
6.7
104
100.0
AB
Dark x light
1
3.8
21
80.8
4
15.4
26
100.0
Standard x standard
62
10.9
443
78.1
62
10.9
567
100.0
AC
Standard x light
8
3.1
176
69.3
70
27.5
254
100.0
BC
Light x light
2
3.4
36
61.0
21
35.6
59
100.0
Total
104
10.2
748
73.6
164
16.1
1016
100.0
The distributions of variously shaded blue dun horses marked with the same letters significantly differ at p£0.01.
Dark shaded horses mated to standards also produced a low percentage of light shaded foals (6.7%) and mated to light shaded horses produced only one dark foal. In
the offspring derived from inter se standard horse matings, the segregation ratio of dark, standard and light foals was symmetrical: 1:7:1. The lights x standards and
lights x lights matings resulted in a very low percentage of dark offspring (3.1% and 3.4%, respectively). In general, dark horses mated to lighter and lighter horses
were producing fewer and fewer dark foals and more and more standards and lights. Likewise, standards mated to standards and lights, as well as lights mated inter
se were producing fewer and fewer dark and standard foals and more and more light foals. Thus, a distinct tendency appears the darker the parents the darker the
progeny, and vice versa: lighter parents produce lighter progeny. The significant differences (p£0.01) show that the dark, standard and li ght shades genetically differ
which is in agreement with hitherto foundings [9].
Regarding the sex in the parents and foals it should be noted that dark sires did not sire light colts, whereas dark dams gave birth to single light foals of both sexes
( Table 2 ) . Simultaneously, the dark sires produced a little bit more dark daughters (35.7%) than the dark dams (23.3%) did and the light dams foaled more light progeny
of both sexes than light sires did ( Table 3 ) . It could be concluded that the dark sires marked their offspring with the dark shade character more distinctly than dams,
341064432.001.png 341064432.002.png
whereas the dams transferred the light shade more easily, though the differences were not significant (p>0.05). Besides, there is a visible tendency of a greater
percentage of dark daughters than dark sons, produced by dark sires or dark dams. Likewise, light sires and light dams produced relatively a little more light daughters
than light sons. It could be concluded that the daughters easier inherited the parental shade than the sons did. Although the significance of these tendencies could not
have been statistically documented (p>0,05), they do not seem accidental. They are particularly pronounced compared to almost identical shade segregation ratios in
sons and daughters of standard sires, as well as in sons and daughters of standard dams.
Table 2 . Blue dun shade distribution in Polish Konik horses produced in various kinds of matings with regard to the sex
Progeny
Parents
stallions
mares
total
dark
standar
d
light
S
dark
standar
d
light
S
sire
dam
n % n % n % n n % n % n % n n %
Dark
dark
2 10
0.
0
0 0.
0
0 0.
0
2 3 7
5.
0
1 2
5.
0
0 0.
0
4 6 0.
6
standard
2 12
.5
1
4
8
7.
5
0 0.
0
1
6
1
1
3
6.
7
1
5
5
0.
0
4 1
3.
3
3
0
4
6
4.
5
light
0 0.
0
0 0.
0
0 0.
0
0 1 1
2.
5
6 7
5.
0
1 1
2.
5
8 8 0.
8
Standard
dark
3 16
.7
1
3
7
2.
2
2 1
1.
1
1
8
1
0
2
5.
0
2
9
7
2.
5
1 2.
5
4
0
5
8
5.
7
standard
1
9
11
.4
1
2
6
7
5.
4
2
2
1
3.
2
1
6
7
4
3
1
0.
8
3
1
7
7
9.
2
4
0
1
0.
0
4
0
0
5
6
7
5
5.
8
light
1 3.
0
2
1
6
3.
6
1 3
3.
3
3 4 4. 5 5
7.
9
3 3
7.
9
9 1
2
8
1
2.
6
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