C-band polymorphism in relation to fertility in boars

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C-band polymorphism in relation to fertility in boars

K Christensen, Jo Pedersen

To cite this version:

C-band

_polymorphism

in relation

to

_fertility

in boars

K

Christensen

JO Pedersen

2

1

The

_{Royal Veterinary}

and

_{Agricultural University,}

Division

_{of Animal Genetics, Department of Animal}

Science and Animal

_Health,

and

2

The Federation

_of

Danish

Pig

Producers and Danish

_{Slaughterhouses, Copenhagen,}

Denmark

(Proceedings

of the 9th

_{European Colloquium}

on

_Cytogenetics

of Domestic

Animals;

Toulouse-Auzeville,

10-13

_July

₁₉₉₀₎

polymorphism

/

fertility

/

C-banding

INTRODUCTION

Nielsen

₍₁₉₆₉₎

has shown that there is a standard deviation of 0.5

piglets

_per litter between boars with ’normal’ semen

_{quality. Investigations}

by

Gustavsson

(1988)

and many others have shown that litter size in swine is reduced when the

animals are carriers of chromosome abnormalities.

Therefore,

it was decided to

include chromosome

investigations

on some of the

low-fertility

boars in the

_study

on boar

fertility

_{among boars with normal} semen

quality.

No gross aberrations were

_found,

but the first

_sample

of

_{low-fertility}

boars had a

_{high frequency}

of C-band

_polymorphism

of the acrocentric chromosomes

_compared

to earlier

_findings

(cf Christensen

and

_Smedeghrd,

_1978,

_1979).

The

_findings

rendered it _necessary to

include a control group, which was

_designated

as the boars with the

_{highest fertility.}

MATERIALS AND METHODS

The

_fertility

_{investigation}

included 98 boars of the Danish Duroc breed stationed at

3 AI centers. All boars had been

approved

for AI use and their semen was

_routinely

collected. When the semen was

_distributed,

a

_registration

card followed

and, just

prior

to the

expected

farrowing,

a new card was sent to record the results. The

registered

data were: herd no, boar no, sow _no,

_parity,

date of

_{mating, farrowing}

date,

number of

_pigs

born

alive,

number of

_stillborns,

eventual

_culling

or

_returning

to heat.

Only

boars with more than 12 litters were included in the

_{investigation.}

The litter size was measured as the total number born. The boars were listed

_according

respectively,

were selected for the chromosome studies. The total number born

is considered to be the best parameter for

_expressing

boar

_fertility,

whereas the number born alive is a better reflection of female

_fertility.

The chromosome

_{study comprised}

22 boars divided into 4

_{samples. Sample}

1

consisted of 6

_{low-fertility}

_{boars, sample}

2 had 5

_{high-fertility}

boars and the last

samples

3 and 4 were added to

_expand

the material of low- and

_{high-fertility}

_boars;

see table I.

Number of

₍₊₎

indicates the size of the

C-band,

(-)

means normal-sized band.

_Samples

1

and 3 had known low

_fertility

_status, whereas

_samples

2 and 4 had

_{high fertility}

status. The

relationship

between average litter size and chromosome

polymorphism

status is indicated.

The chromosome studies were made

_according

to a routine

procedure

(Chris-tensen and

_SmedegArd,

_1978).

The acrocentric chromosomes 16 and 17 were clas-sified for

_polymorphism

at the centromere bands as follows: the size of a band was evaluated and scored as _very

_large

(++),

_large

(+)

or normal

(—).

The

_genotype

used was

_++/—

for

_large

differences between the C-bands of a

_pair

of

_chromosomes;

+/-

was

_{correspondingly}

used for small

_differences,

and

_{++/++, +/+}

or

_-/-

was used when both chromosomes had C-bands of the same size. The first

analysis

of

RESULTS

The average number of

ejaculates

used per boar was 3.2 and

91%

of the semen doses were used within 24 h after

_collection,

6%

on the second

_day,

and

3%

on the third

_day.

239 different herds were

_included,

and 1760

_farrowings

were recorded. All sows were crossbred Landrace x Yorkshire.

Due to the

_management

practice

at the AI

stations,

the chromosome

investiga-tions had to be carried out on boars

_having

litter sizes closer to the _average than wanted.

The individual results are shown in table I. In

_sample

1

_{(low-fertility}

_boars),

there

were

_great

differences in the sizes of the centromere bands

_(C-band

_{polymorphism)}

on either chromosome 16 or 17 in 5 out of the 6 boars. In the second

_sample

(high-fertility boars),

only

one boar exhibited chromosome C-band

_{polymorphism.}

Samples

3 and 4 did not reveal such

_strong

differences between the

_high-

and the

low-fertility

groups as those found in the first two

_{samples: only}

two boars in

_sample

3 had the

_genotype

_++/-.

This

_might

be due to the fact that these animals deviated much less from the mean

_fertility

than the first two

_samples,

as

they

were collected

at a later time from the same

_population

of boars.

The boars

presented

in table I are sorted

according

to _{average litter} size. There was

_clearly

more

_polymorphism

in the boars with the lower litter size.

A

X

2

test

for effect of the

_polymorphism

on either chromosome 16 or 17 was made after

_dividing

the material into two _groups below or above the mean litter size of 11.61. The effect of the chromosome

_polymorphism

was

_{statistically}

_significant

(

X

z

=

7.79,

df =

1;

P < 0.01).

DISCUSSION

The

_frequency

of C-band

polymorphism

should be evaluated

_keeping

in mind that the first 6 boars

_(sample

₁₎

were

investigated

due to low litter sizes. As there were no severe chromosome

anomalies,

other minor

_conditions,

that

might

explain

the lower litter

_size,

were

investigated

at the chromosome level. The

_frequency

of chromosome C-band

polymorphism

in the

_{high-fertility}

_{group is in} accordance with earlier studies

_(Christensen

and

_SmedegArd,

_1978,

₁₉₇₉₎

but the

low-fertility

group

had a much

_higher

_frequency.

This could indicate that there _may be some causal

relationship.

The differences in the sizes of the C-bands in the material studied are very

big,

so it

_might

cause

_{non-disjunction}

of the chromosomes at meiosis and then cause

_higher

_{embryonic mortality}

in litters sired

_{by polymorphic}

boars. In _man,

many of the chromosomes have

polymorphic

C-bands. An

investigation

by

Wevrick

and

_Huntington

₍₁₉₈₉₎

showed that the human C-bands are stable units with a low

_frequency

of recombination.

_They

concluded that

_unequal

crossover within the

repetitive

C-band DNA is a rare event. The C-band

_polymorphism

in man is not

known to cause lowered

fertility.

More studies are

_required

to confirm our

_findings

before

_practical

use in swine

breeding

can be considered. The

possibility

of

_{using genetic}

marker selection for

More details on this

_{investigation}

will be

_given

in a future

_publication

(Chris-tensen and

_Petersen,

_submitted).

ACKNOWLEDGMENTS

Inger

Hvidfeldt Christensen _very

_{skillfully prepared}

the chromosome

samples

and the

photos.

The work has been

_{supported by}

the Danish

_Agricultural

and

_Veterinary

Research Council _grant no 17.4.3.06 and

_by

the Animal

_{Biotechnology Center,}

The

_{Royal Veterinary}

and

_{Agricultural University,}

_Copenhagen.

REFERENCES

Christensen

_K,

_Smedegird

K

₍₁₉₇₈₎

Chromosome markers in domestic

_pigs.

C-band

polymorphism.

llereditas _88, 269-272

Christensen

_{K, Smedegard}

K

₍₁₉₇₉₎

Chromosome markers in domestic

pigs.

A new C-band

polymorphism.

Hereditas _90, 303-304

Gustavsson I

₍₁₉₈₈₎

_Reciprocal

translocation in four boars

_producing

decreased litter size. Hereditas

_{109, 159-168}

Haley CS,

Avalos

E,

Smith C

_{(1988) Selecting}

for litter size in

_pigs.

Ani7a Breed Abstr 56,

317-332

Nielsen HE

₍₁₉₆₉₎

Growth rate,

fertility

and

_longevity

of boars on different diets

_during

rearing,

and some results

_{concerning fertility}

in sows. Beret

Forsoegslab

Statens

Husdyr-brugsudvalg,

375

Wevrick

R, Huntington

F’W

_(1989).

_{Long-range organization}

of tandem arrays of