The physiology of skin and wool follicles of finewool and strongwool merinos

(1)

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by

Janelle Elizabeth Hocking Edwards, B. Ag. Sc.

(tlons.)

A

thesis submiaed in fulfillment of the requirements for the degree

of

Doctor of Phílosophy

The University of Adelaide.

Faculty of Agricultural and Natural Resources Departrnent of Animal Sciences,

waite

^":ii.i:':-'- .n

^In^stitute

Ma¡ch, 1993.

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(2)

u Trrr-epncs

TenIe

oF CoNTENTS

Ansrnegr

DsclenauoN

...

PuslrcerroNs

...

ACTNoWI-gDGEMENTS AsnRpvIArroNS ...

Cn¡.pren 1.

INTRoDUcrroN

1.1.

Sheep used

for

the study

of wool growth...

2

1.2.

Physiological

factors affecting wool production per unit

area of

skin

6 1.2.1. Internal and external

environment...

⁶

I.2.2. Nutrition

7 1.2.3.

Metabolism l0 I.2.4.

Endocrine

status ...

13

1.2.5. Blood

flow ...

¹⁵

1.2.6. Summary... ....

¹⁷

1.3,

The

skin, its follicles

and

f¡bre l7

1.3.1.

Follicle development. ...

¹⁹

1.3.2.

Follicle

function and

wool growth... ...

20

1.3.3.

Thefibre... ....21

1.3.4.

Nutrition of

the

follicle ...

23

1.4. Skin characteristics

associated

with

wool

production...

24

1.4.1. Fibre and

follicle number.,... ...

24

1.4.2.

Follicle

distribution and

morpho1ogy... ...

²⁵

1.4.3.

Selection

for

skin

characteristics ...

25

1.5. Influence

of the

follicle

on wool

production

28 1.5.1.

Follicle morphology... ...

29

1.5.2.

Folliclekinetics... ...

³¹

1.5.3.

Distribution of

bulb and

fibre cells... ...

34

1.5.4. Genetic

studies ....

37

1.5.5. Summary... ....

38

1.6. Conclusion...

38

1

ii

vii

ix

x

xi

xii

(3)

CHarrBR 2. For.lrcr-E

AND FIBRE cHARAcrERrsrrcs oF

srRoNc\ryoot,

AND FINEwooL

Menruos

2.1. Introduction....

2.2. Expenmental

Procedure

2.2.I.

Experimental design..

2.2.2.

Sheep, nutrition and

liveweight...

2.2.3. Wool

growth

2.2.4. Histology

2.2.4.

1. Follicle

density...

2.2.4.2.

Volume of germinative tissue

2.2.4.3. Number andvolume of bulb ce\\s...

2.2.4.4.

CelI kinetics...

2.2.5.

Cortical cells ...

2.2.6.

Experimental design..

2.2.7

.

Statistical analysis

2.3.

Results...

2.3.I. Wool growth,liveweight

and feed intake

2.3.2.

Skin and

follicle

characteristics ...

2.3.3.

Cell proliferation

in

the

follicle bulb...

2.3.3.

I.

Colchicine yersus Bromodeoryuridine

2.3.i.2.

CeII kinetics...

2.3.4.

Cortical cell production...

2-3-5. Determinants of fibre production per

follicle

2-3.6.

Determinants of wool production per unit area of skin ...

2.3.7. Wool

growth, liveweight and feed intake

2.3.8.

Skin and

follicle

characteristics ...

2.3.9.

Determinants of wool production

2.4.

Discussion...

2.4.I. Individual

fibre

production... ... 7I 2.4-2.

Determinants of wool production per

unit

area of skin

...

76

4.4.3. Conclusions... ... 7j 4t

43 43 44 44 47 47 47 48 48 50 51 52 53 53 55 58 58 61 62 64 65 66 67 70 70

(4)

tv

CrhptsR 3. Sxnl

BLooD

FLow

oF FINE\üooL aND

srRoNcrvool

MeRrNos

3.1.

3.2.

Introduction

... 79

3.2.2.1. Laser

Doppler technique ...

84

3.2.2.2.

General aseptic surgery

procedure...

85

3.2.2.3. Insertion of

catheters

...85

3.2.2.4. Microspher e administration... 85

3.2.3.

Statistical

analysis ...

86

3.3. Resu1ts...

₈₇

3.3.1. General ...

87

3.3.2.

Blood

flow

variation

within individual

sheep (Experiments 3.1

& 3.2)... ...

88

3.3.3. Validation

of the laser Doppler velocimeter method (Experimenr

3.3)... ...

90

3.3.4.

Blood

flow

in different strains of

Merinos ...

91

3.3.5. Wool

growth,

follicle

density and blood

flow...

^gz

3.4. Discussion...

₉₄

3.4.I. Conclusion ...

98

CHapreR

4.

Cur¿,Neous MIcRovAScULATURE oF FINEwooL aND

srRoNcwoor, Menntos 4.1. Introduction...

99

4.2. Experimental procedure

... 100

4.2.I.Experimentaldesign(Experimenr4)...

...100

4.2.2.

Isolated cutaneous patch

surgery

...101

4.2.3. Microfil@ technique..

...101

4.2.4.

Statistical

analysis

...102

(5)

--

Results.... ...102

4.3.1.

Blood vessel

distribution

...102

4.3.2.

Area of vascular tissue per unit area of skin ...106

4.3.3. Wool

growth

correlates

...109

Discussion

... 111

Cnnpmn 5.

1¡r vITRo uprAKE oF RADToLABELLED NUTRIENTs By rHE sKIN AND FOLLICLFS OF FINEWOOL AND STRONGWOOL MERINOS

5.1. Introduction...

...

ll5 5.2. Materials

and

experimental procedures...

... 117

5.2.I. Materials ...1I7 5.2.2. Design...

...118

5.2.2.1. Trial

5a - Media

tial ...

...119

5.2.2.2. Trial5b

-

Linearity tial...

...119

5.2.2.3. Trial

5c - Site of uptake

...

^...119

5.2-3.

Experiment

5.

Differences in nutrient uptake rates between

finewool

and strongwool

Merinos...

...120

5.2.4.

Statistical

analysis ...I21 5.3. Resu1ts...

... 121

5.3.1. Trial5a

- Media

tria1... ...I22 5.3.2. Trial

5b - Linearity

trial...

...L22

5.3.3. Trial

5c - _Siteof uptake

trial ...

^...123

5.3.4.

The uptake of glucose and cystine by skin and

follicles from finewool

and strongwool Merinos (Experiment 5) ...126

5.4. Discussion...

...128

5.4.L.

Glucose

uptake...

...128

5.4.2.

Cystine

uptake...

...130

5.4.3.

The

in vitro technique...

...131

5.4.4. Conclusions... ...I32

4.3.

4.4.

(6)

VI

CH¡grnn 6.

PnBlnnINARy IN

vrvo sruDy

op 3ss-cysrlNn aND

3H-cLucosn

INCORPORATION BY THE SKIN AND FOLLICLES FROM THE PLASMA OF

FINEwooL AND STRoNGwooL MERn.¡oS

6.1. Introduction...

... 133

6.2. Materials

and Methods. 135

6.2.L. General

...135

6.2.1.1.

Materials.,

...135

6.2.1.2.

9heep...

...136

6.2.1.3.

Skinsamplingandanalysis....

...136

6.2.1.4. Blood sampling and

analysis

...136

6.2.1.5. Isolated cutaneous

patch...

....137

6.2.1.6.

Infusate

...138

6.2.1.7.

Chemical

analyses...

^....138

6.3. Examination

of the isolated cutaneous

patch technique...

140

6.3.1.

Experimental

procedure...

...140

6.3.1.1. Trial 6.1.

....140

6.3.1.2. Trial6.2.

....141

6.3.1.3. Trial6.3.and 6.4...

...141

6.3.1.4. Trial6.5. ....14I 6.3.1.5. Trial6.6.

....142

6.3.1.6. Statistical

analysis.... ...I42 6.3.2.

Results and

Discussion...

...142

6.3.2.1. Infusion of

3H-glucor¿...

_...142

6.3.2.2.

3sS-Cystine

infusion...

...145

6. 3.2.

3.

I solated cutaneous ^patch ^technique ... ¹45

6.3.3. Conclusion

...147

6.4. Radiolabelled nutrient uptake ...149

6.4.1.

Experimental

procedure... ...I49

6.4.

1.6.

Calculations, assumptions and statistical

analysis

...150

6.4.2. Results

...152

6-4.2.1.

Glucose

flow

and 3H retained

in

the

skín...I53 6.4.2.2.

Cystine

flow

^and³⁵⁵retained by the skin...154

6.4.3. Discussion

...159

Gtrt¡nR¡,r, Drs cussrorri

t64

APPENDIcFÆ

BtsLlocRApHv

...194

(7)

AnsrRlcr

Wool

production differences between sheep maint¿ined under similar environmental conditions appear to reside

in

the functioning of

individual follicles.

The investigations presented in this thesis utilise the

differing

wool producing abilities of

two

strains of Merino,

finewool

and strongwool

Merinos.

The relationships between

wool

production (on both a

unit

area and

individual follicle

basis) and skin and

follicle

characteristics, blood

flow

and

microvasculature of the skin and incorporation

of

3H-glucose and 35S-cystine by the skin were examined.

The differences

in

the structure and function of wool

follicles

and their association

with

fibre production were examined

in

6 finewool Merinos (Camden Park) and 6 strongwool Merinos (East Bungaree). The strongwool Merinos produced 2.4 times more

wool

per

unit

area of skin and 3.5 times the volume of fibre per

follicle

than the

finewool

Merinos, when both groups were maintained under similar environmental

conditions.

The

finewool

Merinos had a higher

follicle

density, but a lower average volume

of

germinative tissue in the

follicle

bulb and the skin than the strongwool

Merinos.

The rate of cell production

in

the

follicle

bulb was greater in the strongwool Merinos than the finewool Merinos, but the proportion of bulb cells entering the

fibre

was not significantly different between strains. The number and volume of cells

in

the bulb and the cell length and volume of the cortical cells, and tended to be greater

in

the strongwool Merinos than the

finewool

Merinos, but also were not statistically different between strains due to a

high

'between-sheep,

within-strain' variation. \ilool

production per unit area

of

skin was highly correlated

with

the tot¿l volume of germinative tissue

in

the skin (r = 0.91; P < 0.01). This relationship wíìs true

for

the strongwool and

finewool

Merinos and also

in

two groups of sheep

from

the same genetic base

with

one group selected using ^a

WOOLPLAN

index and the other a randomly-bred

flock. It

was concluded a) that genotype may determine the volume of potential mitotically-active

follicle

tissue

in

the skin, and b) that

wool

production on both a

follicle

and unit area of skin basis is not controlled by a single character, but rather is the result of a cumulative effect of a number

of

characteristics.

(8)

viii

The physiology of the skin associated

with

high levels of wool production was further examined. In particular, blood

flow

through the skin of the strongwool and

finewool

Merinos was investigated using a laser Doppler velocimeter. This method was

highly

correlated

with

estimates obtained using 57Co-microspheres (r =

0.92;P

< 0.01) although the absolute values estimated by the microsphere technique were significantly greater (P <

0.001).

Strongwool Merinos had a

significantly

greater rate of blood

flowing

through the skin than

finewool

Merinos (P < 0.011) and this was associated both

with

wool production per unit area of skin

(r

= 0.58; P < 0.02) and

with follicle

density (r

= -0.M;

^{P <}

0.1). It

was concluded that a) blood

flow

has an important role

in

the level of wool produced both

within

and between strains

of

Merino, and b) the laser Doppler velocimeter is a useful tool

for

the study of blood

flow

in the skin ofsheep.

The microvasculature of the skin was examined using an infusion of silicone rubber into the deep circumflex

iliac

artery

within

the abdominal

flank

region of eight

Merinos.

The area of cascular tissue per unit volume of skin was independent of blood

flow, wool

growth and

follicle

density, both

within

and between strains of

Merinos.

The limitations of the technique used to examine the microvasculature, and its effect on the results are discussed.

The uptake

of

3H-glucose and 35S-cystine by the skin and

follicles

was examined both in

vitro

and in vivo to determine

if

the

follicles

of the strongwool Merinos were capable

of utilising

the large nutrient pool supplied by the high rates of blood

flowing

through the skin.

The skin and

follicles

of strongwool Merinos incorporate similar amounts

of

3H-glucose and 35S-cystine per unit weight of skin than finewool

Merinos. It

was also found that the amount of radioactivity retained by the skin generally was not dependant on the amount

of

radioactivity supplied to the skin and follicles.

In summary, this study determined that strongwool Merinos have higher levels of wool production than

finewool

Merinos due to the presence of a large amount

of

tissue capable

of

producing

fibre.

This characteristic is maintained by a high rate of blood

flowing

through the

skin. Wool

production and blood

flow

through the skin are not influenced by the underlying anatomy of the microvasculature, nor is wool production restricted by the

ability

of the

follicles

to utilise nutrients

from

an extracellular pool

for

fibre

production. Finally,

the implications of this study and the usefulness in, and effect on, programs

for

selection

of

superior wool-producing genotypes are discussed.