The cytogenetic screening of South African artificial insemination bulls

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The cytogenetic screening of South African artificial

insemination bulls

Nd Nel, Ej Harris, Je Weiermans, Ehh Meyer

To cite this version:

Original

article

The

_{cytogenetic screening}

of South

African

artificial insemination bulls

ND Nel*

EJ

_Harris,

JE

Weiermans,

EHH

_Meyer

Animal and

_Dairy

Science Research

Institute,

Private

Bag X2, Irene,

1 675,

Republic of

South

_Africa

(Received

20 March

_{1990; accepted}

14 December

₁₉₉₁₎

Summary -

Following

the

_discovery

of the

_1/29

chromosome translocation in Swedish artificial insemination

_(AI)

_{bulls, cytogenetic}

evaluation of South African AI bulls was

initiated. The _{present paper reports} on the 269 bulls screened over the _{past 11 yr.} The

_1/29

chromosome translocation was found in Brahman and Brown Swiss bulls while chimerism was present in the Friesian bulls. The overall incidence of chromosome abnormalities in these bulls is 1.49%.

_Although

the incidence is

_{low, discovery}

of the abnormalities serves to illustrate the

_importance

of

_{cytogenetic screening}

in the AI

_industry.

cattle

_/

chromosome _abnormality

_/

translocation

_/

chimerism

Résumé - Le contrôle _{cytogénétique} des taureaux sud-africains d’insémination arti-ficielle. A la suite de la découverte de la translocation

_{chromosomique}

_1/,!9

chez des tau-reaux d’insémination

_artificielle

_(IA)

_suédois,

l’examen

_{cytogénétique}

des taureaux d’IA

sud-africains

a été

_entrepris.

Cet article concerne les 269 taureaux examinés au cours des

11 dernières années. La translocation

_{chromosomique}

_1/29

a été trouvée dans les races Brahman et Brune des

_Alpes,

et par ailleurs le chimérisme existe chez les taureaux de

race F’risonne. L’incidence

_globale

des anomalies

_{chromosomiques}

chez ces taureaux est de

1,49%.

Bien que ce taux soit

_faible,

la découverte de ces anomalies illustre

_{l’importance}

d’un contrôle

_{cytogénétique}

_pour les centres d’IA.

bovin

_/

anomalie _{chromosomique}

_/

translocation

_/

chimérisme

INTRODUCTION

Artificial insemination

has,

since its

_inception,

revolutionised the cattle

_breeding

industry.

There

_is,

_however,

an

_ever-present

_danger

in its

_{widespread application;}

undiagnosed

genetic

defects

and less severe chromosome abnormalities _may be

spread rapidly through

the use of a carrier bull’s semen.

_Examples

can be found in

the

_amputated

calf

_syndrome

_present

in Friesian cattle

_(Wriedt

and

_{Mohr, 1928;}

Meyer

et

_al,

_1980),

the

_high

incidence of the

_1/29

chromosome

_abnormality

in

Swedish Red and White cattle

_{(Gustavsson, 1969)}

and inherited

_{immunodeficiency}

diseases such as

_{agammaglobulinaemia}

_{(Perryman, 1979).}

*

These

_examples

illustrate the

importance

of effective

_{screening procedures}

for all bulls used in the artificial insemination

_industry.

Present

_screening

_techniques

are based on

_pedigree

_history,

_progeny

_testing,

semen

_{quality testing, libido,}

linear

trait selection and chromosome

_analysis.

With the advent of recombinant

_technology,

it will be

_possible

in future to screen

for a host

_{of important genetic}

defects

_using

a

_{battery of defect-specific}

DNA

_probes.

Since the

_discovery

of the

_1/29

chromosome

_abnormality

in various cattle breeds

and its effect on

_fertility

_(Refsdal,

_1976;

Blazak and

_Eldridge,

_1977;

_Gustavsson,

1979;

Kovacs and

_Csukly,

1980; Popescu, 1977, 1982;

Swartz and

_Vogt,

_1983;

_Foulley

and

_Frebling,

_1985),

chromosome

_screening

has become an

_important

_component

of bull evaluation.

Following

the

_discovery

of the

_1/29

translocation in Swedish AI bulls

(Gustavs-son,

1969),

cytogenetic

evaluation of South African AI bulls was initiated in 1977 to

ensure that chromosome abnormalities were not

_{spread by}

the use of carrier bulls.

This _paper

_reports

on the

_{cytogenetic study}

of bulls used in the South African AI

_industry

over the

_past

13 yr.

MATERIALS AND METHODS

Peripheral

blood

_samples

taken from 269 bulls

_comprising

20 cattle breeds

(table I)

were submitted for

_{cytogenetic analysis.}

These

samples

were taken from

bulls stationed at AI centres

_belonging

to the Artificial Insemination

_{Co-operative.}

Routine

_screening

was

_performed

on Giemsa-stained

_{metaphase spreads}

obtained

from whole blood cultures. The culture method was

_adapted

from that of Moorhead

et al

_(1960).

In this

_method,

concanavalin A

_{(0.01 mg/ml)}

was used instead

of

_{phytohaemagglutinin.}

The chromosome

_spreads

were

_routinely

stained in

5%

Giemsa and 10 well

_{dispersed metaphase spreads}

were screened for structural or

numerical aberrations.

The chromosomes of animals found to deviate from the standard

_karyotype

were identified

_by

means of an

_{R-banding technique adapted}

from

_Popescu

(1975),

Popescu

et al

₍₁₉₈₂₎

and Di Berardino and Ianuzzi

_(1982).

The

_lymphocyte

cultures were

_exposed

to

5’Brdu

_{(50 pg/ml)}

for 5 h

_prior

to

harvesting.

The

air-dried,

rinsed slides were

passed

through

a series of alcohol

grades

to

_water,

rinsed in

phosphate

buffer and stained in _{acridine orange for 15} min. After

rinsing

for 30

_min,

the cells were mounted in a

drop

of buffer and sealed with nail

varnish. Banded

_{metaphase spreads}

were

_photographed

with Zeiss

_{Epifluorescence}

equipment

on

_Agfaortho

25 film.

In instances where a chromosome

_abnormality

was

found,

follow-up

studies

ascertained the

_origin

and extent of the

_abnormality

in the

_population.

RESULTS

A

_study

of the

_{metaphase spreads}

confirmed the presence of 29 acrocentric

autoso-mal

_pairs

and one

_pair

of sex

chromosomes,

a

_large

submetacentric X chromosome

and a small metacentric Y chromosome in the Bos taurus and Bos indicus

_(Sanga)

bulls. In the B indicus

_(Zebu)

_bulls,

the Y chromosome is

_represented

_by

a small

Screening

of the Giemsa stained and

_subsequent

R-banded

_{metaphase spreads}

revealed the presence of abnormalities in the

_Friesian,

Brahman and Brown

Swiss

cattle

_{(table II).}

Giemsa stained and R-banded

_karyotypes

are shown in

_figures

_1,

2 and 3.

Following

the

_discovery

of the chromosome

_{abnormalities, subsequent}

studies revealed that the Friesian bulls were both co-twins to heifers and that the Brahman bull was descended from carrier cattle

_imported

from the United States of America.

yet

not been ascertained but the normal familial

_pattern

of inheritance has been

established

_(results

not

_shown).

DISCUSSION

The results in table II show that structural chromosome abnormalities _{appear in}

one beef and one dual _purpose

_breed,

while there is a total absence in the 4

_dairy

breeds screened. The chimerism that _{does appear in the Friesian} breed cannot be

considered a

_primary

chromosome defect. The lack of chromosomal aberrations in the pure

dairy

breeds is in accordance with the

findings

of teams across the world

(see

reviews

_{by Popescu,}

1977 and

1982; Gustavsson, 1979;

Foulley

and

_Frebling,

1985).

Possible reasons for this absence are the _pure

_breeding

_practices

and the

constant selection for

_fertility

in these breeds.

_Any

animal which does not meet

the

_{required standard, irrespective}

of the reason, is

automatically

culled from the

As the

_sample

sizes are very

small,

these results do not

_give

_{any indication} of

the incidence of the

_{particular abnormality}

in the national herd. Each case should

be

_{investigated individually}

before such

_predictions

are

_possible.

The chimerism found in the 2 Friesian bulls was traced to the _presence of female

co-twins

_during

_pregnancy. The observed incidence of

1.85%

₍₂

of the 108

_bulls)

is

slightly higher

than the

_{expected figure}

of

1%

for twins of

_opposite

sex. The _average

twinning

rate in South African Friesian cattle is

2%

_(Friesian

Cattle Breeder’s

Society,

1989,

unpublished

results).

This

_discrepancy

is

_possibly

due to the small

sample

size.

The

_condition,

known as freemartinism in the heifer

_co-twin,

is caused

_by

an allantochorionic anastomosis

_during

_{embryo development.}

This condition was

described as far back as 1911

_(Tandler

and

Keller,

1911)

and has since been studied

extensively by

Short et al

_(1969).

In South

_Africa,

the condition was first described

by

Gerneke in 1969. The condition affects the

_fertility

of the heifers

_{and, although}

some of the bulls may not be

_{affected, infertility}

has been

reported.

It

is,

therefore,

advisable to remove such bulls from the selection _programme

_(Dunn

et

_al,

_1968;

The occurrence of

_twinning

in cattle should be

_carefully

monitored

_during

any

long-term

programme aimed at

_increasing

the

_fertility

of a

_particular

breed. An

increase in the

_{twinning frequencies}

would

_immediately

_{oppose any}

_gains

in

_fertility

and this would necessitate a re-evaluation of the selection programme in use. The

_1/29

chromosome translocation found in the Brahman bull was introduced

into the Southern African herd

_by

Brahman cattle

imported

from the United States of America

_during

the 1960’s. The

_{subsequent investigation}

showed that the

_anomaly

was confined to a

_particular

_family

and was not

_present

in a random

The most recent

_abnormality

found was that in a Brown Swiss bull. The

preliminary study

shows a familial

_pattern

of inheritance with the translocation

present

in the dam and maternal half-sister.

During

the

_{period 1974-1986,}

Brown Swiss semen was

_imported

from the United States of

_America,

Austria,

West

_Germany

and Switzerland. It is

_possible

that some

of this semen _may have

_originated

from a carrier bull. Translocation

_carrying

Brown

Swiss cattle have been

_reported

in Switzerland and the United States of America.

The incidence in these 2 herds is

0.4%

and

2.4%

_respectively

_(Blazak

and

_Eldridge,

1977; Tschudi,

1984).

The

_{investigation}

will continue and the detailed results will

be

_published

at a later

_stage.

It is

_interesting

to note that the

_1/29

Robertsonian translocation was not found

in the 12 AI Simmentaler bulls

_tested,

_despite

the fact that the

_anomaly

is

_present

in the South African herd.

_Tests

carried out on 3 stud farms revealed an incidence

of

20%

(25

of the 125 cattle

_{investigated)}

in the herds screened

_(unpublished

observations).

As most of the sires used on these farms

_originated

from a

_single

stud

_herd,

it

cannot be construed as a national herd average but

_merely

serves as an indication

of a

_higher

_{than average}

_proportion

of translocation

_carrying

cattle. Based on the

results of Gustavsson

₍₁₉₇₉₎

a

_figure

of !

2.7%

would appear to be a reasonable

world average. This

study

has been

_suspended

because of the reluctance of the

Simmentaler Breed

_Society

to allow the

_screening

of their cattle.

A similar situation is

present

in the

_{indigenous Nguni}

cattle where an incidence

of

10.2%

was established in the 305 cattle studied

_(Nel

et

_al,

_1985).

After

_facing

near-extinction,

attempts

are

underway

to increase the number of

_Nguni

cattle: a

culling

programme was therefore initiated to ensure that stud animals are free of

the

_1/29

translocation. No abnormalities were found in the 2 AI bulls screened.

The overall incidence of chromosome abnormalities in South African AI bulls is

_low,

1.49%

of which

_only

0.74%

are heritable abnormalities.

_{Nevertheless,}

the

abnormalities found in the bulls screened illustrate the

_importance

of these tests

in situations where a

_specific

animal is

_{extensively used,}

_in,

for

_example,

artificial

insemination

and,

to a lesser

extent,

embryo

transfer from an elite corps of females.

Cytogenetic

laboratories worldwide

_perform

an

_extremely

valuable function and

it is

_imperative

that the tests be continued and

expanded

to include the

_testing

and certification of bulls selected for

_import

and

_export

purposes. The introduction of

the

_1/29

chromosome translocation into the South African Brahman herd as well as

the

_suspected

introduction into the Brown Swiss herd

_through

the use of

_imported

material is indicative of the

_important

role of

_{cytogenetic screening.}

ACKNOWLEDGMENTS

We thank the Taurus

_Co-operative

for their assistance and contribution to this

_study.

We

also thank those farmers who

_permitted

the collection of blood

_samples.

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