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WilcoxH. Roman-Ponce, W. W. Thatcher, D. Caton, D.H. Barron and C.J.Thermal Stress Effects on Uterine Blood Flow in Dairy Cows

1978, 46:175-180. J ANIM SCI

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T H E R M A L S T R E S S E F F E C T S O N U T E R I N E B L O O D F L O W IN D A I R Y C O W S

H. Roman-Ponce2 , W. W. Tha tch er2 , D. C ato n 3 ,4, D. H. Barron3

and C. J. Wilcox2

U n i v e r s i t y o ] F l o r i d a , G a i n e s v i l l e 3 2 6 1 1

S U M M A R Y

Three ovariectomized dairy cows, fitted with

blood flow transducers around a mid-uterine

artery, were assigned to an experiment of

simple reversal design to determine the effects

of thermal stress (shade or no shade) on the

increased uterine blood flow (UBF) after intra-

venous injection of estradiol-17~ (200 /ag).

Resultant increases in UBF after estradiol were

evaluated both as absolute changes (ml/min)

and percentage change. Tests for heterogeneity

of regression established that treatment re-

sponse curves for both absolu te and percentage

changes in UBF were not parallel. Rate of

increase in UBF was greater and the peaks

higher in cows subjected to shade (n=7) than

those in no shade (n=7; P<.O1). Cows subjected

to shade had an overall 17.4 greater absolu te

change (128 v s 109 ml/min) and a 43.6

greater change (412 v s 287 ) in UBF than cows

in no shade. Uterine blood flow appears to be

significantly affected by thermal stress when

tested under practical farm conditions in which

environm ental modification with shade is

known to improve conception rates.

(Key Words: Cattle, Uterine Blood Flow, Ther-

mal Stress, Estradiol, Shade.)

INTRODUCTION

A decrease in uterine blood flow (ml/min) is

a possible means by which thermal stress may

exert its negative effects on fertility in domesti c

animals. In ovariectomized ewes uterine blood

I Florida Agricultural Experiment Station Journal

Series No. 413.

2Dairy Science Department.

3 Obstetrics and Gynecology DeparUnent.

4 D. Caton is recipient of a Career Development

Award from NIH No. 5K04, HD70552-02. This study

was supported in part by grants from the National

Institutes of Health SR01, HDO 5659-07, The Founda-

tion for Child Development and CSRS Grant No.

616-15-162.

flow (UBF) increased less after estradiol injec-

tion in ewes exposed to 32 C than in ewes

maintain ed at 21 C (Roman-Ponce e t a l . ,

1977b). Oakes e t a l . (1976) detected a 25 to

48 decrease in UBF of ewes in late gestat ion

exposed to irlduced hyperth ermia. During the

warm summer (27 C) in England, Leduc (1972)

observed a 46 reduc tion in placental blood

flow of the rabbit which was associated with an

increase in number of runts and dead fetuses.

Gwazdauskas (1974) suggested that UBF in

dairy cows may be reduced during thermal

stress.

Blood flow to the uterus is a potential

source of nutrients, oxygen and water for the

developing embr yo (Barron, 1970, Senger e t a L ,

1967, Bazer e t a l . , 1969). Furthermore, dissipa-

tion of uterine metabolic heat is dependent

upon rate of blood flow (UBF) in which the

blood temperature is cooler than the uterine

serosa (Abrams e t a l . , 1971, Gwazdauskas e t a l . ,

1974). Estrogens and progesterone appear to be

the principal hormones involved in the regula-

tion of UBF (Markee, 1940, Huckabee e t a l . ,

1970; Greiss and Anderson, 1970; Killam e t a l . ,

1973; eaton e t a l . , 1974). However, the interac-

tion of thermal stress with these regulatory

hormones in modulating UBF has not been

evaluated in cows.

Recently, our laboratory reported that a

shade structure utilized during summer in the

subtropical climate of Gainesville, Florida, re-

duced net solar radiation exposure, and lowered

respiration rates and rectal temperatures of

lactating dairy cattle. Furthermore the shade

management system improved milk yield and

reproductive performance, in comparison to

similarly managed control cattle that had no

artificial or natural shade (Roman-Ponce e t a l . ,

1977a). This management system provides a

practical experimental model with which to

study various physiological and endocrine re-

sponses of cattle to thermal stress.

The present experiment was designed to

175

JOURNAL OF ANIMAL SCIENCE, Vol. 46, No. 1 (1978)



176 R O M A N - P O N CE E T A L .

s t u d y e f f e c t s o f s h ad e a n d n o s h a d e c o n d i t i o n s

d u r i n g t h e s u m m e r o n t h e i n c re a s e i n U B F t h a t

f o l l o w e d a n i n t r a v e n o u s i n j e c t io n o f e s tr a d i o l -

1 7/3 ( E 2 ) i n t o o v a r i e c t o m i z e d d a i r y c o w s .

E X P E R I M E N T L P R O C E D U R E

U t e r i n e b l o o d f l o w w a s m e a s u r e d a n d r e -

c o r d e d c o n t i n u o u s l y a s d e s c r i b e d b y R o m a n -

P o n c e e t a l . ( 1 9 7 7 b ) . T h r e e b l o o d f l o w t ra n s -

d u c e r s ( i n t e r n a l d i a m e t e r s o f 5 . 0, 5 . 5 a n d 6 . 5

m m , ( C a n d C I n s t r u m e n t s , C u l v e r C i t y C a li -

f o r n i a ) w e r e c a l i b r a t e d

i n v i t r o

a s d e s c r i b e d

p r e v i o u s l y ( R o m a n - P o n c e e t a L 1 9 7 7 b ) b e f o r e

b e i n g i m p l a n t e d i n c o w s . T h e o n l y d i f f e r e n c e i n

c a l i b r a ti o n t e c h n i q u e f o r t h e p r e s e n t e x p e ri -

m e n t w a s t h a t b l o o d a n d a r t er i e s w e r e f r o m

c o w s r a t h e r t h a n e w e s . T h e r e l a t i o n s h i p b e -

t w e e n b l o o d f l o w ( m l / m i n a s m e a s u r e d w i t h

s t o p w a t c h a n d g r a d u a t e d c y l i n d e r ; X ) a n d

e l e c t r o m a g n e t i c f l o w m e t e r d i s p l a y ( m l / m i n ; Y )

w a s l i n e a r ( f ig u r e 1 ) . T h e o v e r a l l d i f f e r e n c e

b e t w e e n t h e t w o m e a s u r e m e n t s w a s le ss t h a n

1 % . T h i s r e s p o n s e i s i n a g r e e m e n t w i t h i n v i t r o

c a l i b r a ti o n d a t a o b t a i n e d i n e a r li e r e x p e r i m e n t s

w i t h e w e s ( R o m a n - P o n c e

e t a l .

1 9 7 7 b ) a n d

w i t h o b s e r v a t i o n s o f K i l l a m e t a l . ( 1 9 7 3 ) w h o

u s e d a s i m i l a r s y s t e m o f c a l i b r a t i o n .

T w o h e i fe r s a n d o n e c o w o f t h e B r o w n S w i ss

b r e e d , w i t h a m e a n b o d y w e i g h t o f 3 9 3 -+ 1 4

k g , w e r e u t i l i z e d . A n i m a l s w e r e c o n f i n e d ( 3

w e e k s b e f o r e s u r g e r y ) t o a s m a l l l o t c l o s e to t h e

s h a d e a n d n o s h a d e a r e as , a n d w e r e h a n d l e d

500

3 400

o

~ 3 0 0

.J

~ 2 0 0

Y = .2 f .99x

o

I00

o , d o

are

3 ; 0

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ACTUAL BLOOD FLOW m l/ mi n)

Figure 1 . Ca l ibra t ion of e lec t romagn e t ic b loo d

f low probe .

d a i l y t o a c c u s t o m t h e m t o m a n a g e m e n t c o n d i -

t i o n s r e q u i r e d in t h e e x p e r i m e n t .

P r i o r t o s u r g e r y c o w s w e r e p l a c e d o n a 4 8 h r

f e e d a n d w a t e r fa s t . A n i m a l s w e r e t r a n q u i l i z e d

( A c e p r o m a z i n e M a l e a t e , A y e r s t L a b o r a t o r i e s ,

I n c .; 3 m g / 1 0 0 k g o f b o d y w e i g h t ) 3 0 to 4 5

m i n b e f o r e b e i n g m o v e d i n t o t h e s u r g e ry r o o m .

C o w s w e r e a n e s t h e t i z e d w i t h an i n t ra v e n o u s

i n f u s io n o f s o d i u m t h i o p e n t a l ( 1 g / 1 0 0 k g b o d y

w e i g h t ; A b b o t t L a b o r a t o r i e s ) d i s so l v e d i n st e r-

i l e n o n - p y r o g e n i c w a t e r ( 1 g / 4 m l ) . A n i m a l s

w e r e m o v e d f r o m a r e s t r a i n e d u p r i g h t p o s i t i o n

t o h o r i z o n t a l r e c u m b e n c y u t i li z i n g a p o r t a b l e

m u l t i p l e p o s i t i o n s u r g e r y t a b l e ( D o u g l a s T i l t -

M a s t e r T a b l e ) . A n e n d o t r a c h e a l t u b e w a s p o s i -

t i o n e d w i t h i n t h e t r a c h e a , a n d s u r g i c a l a n e s -

t h e s i a m a i n t a i n e d w i t h h a l o t h a n e ( F l u o t h a n e ,

A y e r s t L a b o r a t o r i e s , I n c .) a n d o x y g e n g i v en b y

a l a r g e a n i m a l a n e s t h e t i c u n i t ( F r a z e r S w e a t m a n

I n c .) . A n i m a l s w e r e p l a c e d o n t h e i r b a c k s , a n d

t h e h i n d q u a r t e rs e l e v a t ed i n o r d e r t o m i n i m i z e

e x p o s u r e o f t h e a b d o m i n a l v i s c er a i n t h e

s u r g i c a l f i e l d .

A f t e r r e m o v a l o f h a i r , t h e r i g h t i n g u i n a l a n d

f l a n k re g i o n s w e r e s c r u b b e d t h o r o u g h l y w i t h

g e r m i c i d a l s o a p ( B e t a d in e ) . A s e p t i c p r e c a u t i o n s

w e r e f o l l o w e d d u r i n g s u r g e r y . A 2 0 c m l o n g i t u -

d i n a l i n ci s io n w a s m a d e l a t e ra l t o t h e m a m m a r y

g l a n d a n d d i s s e c ti o n c o n t i n u e d c r a n i a ll y f r o m

t h e i n g u i n a l c an a l . A n i n c i s i o n w a s m a d e

t h r o u g h t h e a b d o m i n a l w a l l a n d t h e r e p r o d u c -

t i v e t r a c t e x p o s e d . T h e f l o w t r a n s d u c e r a n d i t s

l e a d w i r e w e r e p a s s e d t h r o u g h a 2 . 5 c m i n c i -

s i o n i n t h e a b d o m i n a l w a l l o f t h e f l a n k a r e a .

B o t h o v a r i e s w e r e r e m o v e d . A s m a l l i n c i s i o n

w a s m a d e i n t o t h e a n t e r i o r l e af o f t h e b r o a d

l i g a m e n t p a r a l l e l t o t h e m i d d l e u t e r i n e a r t e r y . A

s e g m e n t o f t h e m a i n u t e r i n e a r t e ry , p r o x i m a l t o

i t s f i r s t b i f u r c a t i o n , w a s e x p o s e d a n d t h e

a d v e n t i t i a re m o v e d f r o m a 1 5 t o 2 0 m m

s e g m e n t . T h e f l o w t ra n s d u c e r h e a d w a s p l a c e d

a r o u n d t h e a r t e r y a n d f i x e d b y s u t u r i n g t h e

l e a d w i r e c l o s e t o t h e t r a n s d u c e r h e a d t o t h e

b r o a d l i g a m e n t w i t h a s e r ie s o f s il k s u t u r e s ( 1 ;

S u t u p a k , E t h i c o n , I n c .) . T h e f r e e e n d - w i r e o f

t h e f l o w t r a n s d u c e r w a s e x t e r i o r i z e d t h r o u g h

t h e f l a n k a n d m a i n t a i n e d i n a c a n v a s p o u c h

a t t a c h e d t o t h e a n i m a l w i t h ad h e s iv e c e m e n t

a n d p o r o u s a d h e si v e t a p e . F o l l o w i n g s u rg e r y

a n i m a l s r e c e i v e d f o u r d a i l y i n t r a m u s c u l a r i n j ec -

t i o n s o f p e n c i l l i n - s t r e p t o m y c i n ( 1 0 c c p e r d a y ,

C o m b i o t i c ; P f iz e r) . T h e e x p e r i m e n t w a s in i t i-

a t e d o n d a y 4 a f t e r s u r g e r y a t w h i c h ti m e

a n i m a l s a p p e a r e d t o h a v e r e c o v e r e d f r o m s u r -

g i c a l s t r e s s s i n c e s t a b l e r e c o r d i n g s o f U B F w e r e



U T E R IN E B L O O D F L O W I N C O W S 177

o b t a i n e d .

A n i m a l s w e r e a s s ig n e d t o s h a d e ( S ) a n d n o

s h a d e ( N S ) e n v i r o n m e n t a l t r e a t m e n t s u t i l i z i n g a

s i m p l e r e v e r s a l d e s i g n . I n S t r e a t m e n t s , a n i m a l s

w e r e e x p o s e d t o t h e e n v i r o n m e n t u n d e r a sh a d e

s t r u c t u r e , w h e r e a s f o r t h e re v e r s al t r e a t m e n t

( N S e n v i r o n m e n t ) a n a re a a d j a c e n t t o t h e s h a d e

s t r u c t u r e w i t h n o a r t i f ic i a l o r n a t u r a l s h a d e w a s

p r o v i d ed ( R o m a n - P o n c e

e t a l .

1 9 7 7 a ) . O n e a c h

e x p e r i m e n t a l d a y , a n i m a l s w e r e m o v e d a n d t i e d

t o a h e a d g a t e e i t h e r i n t h e S o r N S a r e a

b e t w e e n 0 7 0 0 t o 0 7 3 0 h o u r . A t e m p o r a r y r o p e

p e n w a s u s ed t o i s o la t e ea c h e x p e r i m e n t a l

a n i m a l f r o m o t h e r s i n t h e a re a . R u b b e r m a t s

w e r e p l a c e d o v e r t h e c o n c r e t e t o i n s u l a t e t h e

a n i m a l a n d i ts p r o b e f r o m t h e g r o u n d . A

c o n n e c t i n g c a b l e ( 1 6 . 8 m ) p l u g g e d to t h e f l o w

t r a n s d u c e r l e a d w i r e w a s p a s s e d i n t o a n a d -

j a c e n t a i r c o n d i t i o n e d t r a il e r l o c a t e d b e t w e e n

t h e t w o e x p e r i m e n t a l a r e a s . T h e t e r m i n a l e n d

o f t h e c a b l e w a s a t t a c h e d t o a n e l e c t r o m a g n e t i c

f l o w m e t e r ( N a r c o m a t i c M o d e l T r 5 0 0 , N a r co

B i o - s y s t e m s , I n c . ) a n d c o n t i n u o u s r e c o r d i n g s

m o n i t o r e d w i t h a p h y s i o g r a p h ( D e s k M o d e l

D M P - 4 B , N a r c o B i o - s y s t e m s I n c . ).

O n e a c h e x p e r i m e n t a l d a y , 2 0 0 ~ tg o f e s tr a -

d io l -1 7 /3 ( S t e r a l o i d s I n c . ) w e r e i n j e c t e d i n t o t h e

j u g u l a r v e in a t 1 1 3 0 h o u r . T h e e s t r a d i o l so l u -

t i o n w a s p r e p a r e d f r e s h e a c h e x p e r i m e n t a l d a y

f r o m a p a r e n t s o l u t i o n o f E 2 in e t h a n o l ( 1

m g / m l ) i n w h i c h 2 0 0 / ag w e r e d i s s o l v e d i n a 2

m l v o l u m e o f 1 0 e t h a n o l a n d 9 0 i s o t o n i c

s a li n e . U t e r i n e b l o o d f l o w w a s r e c o r d e d c o n t i n -

u o u s l y f r o m 1 0 3 0 t o 1 7 3 0 h r w h e n e n v ir o n -

m e n t a l c o n d i t i o n s w e r e a p p r o p r i a t e ( n o r a in o r

e l e c t r i c a l s t o r m s ) . T h e i n j e c t i o n a n d r e c o r d i n g

p r o t o c o l t h e n w a s r e p e a t e d o n a l t e rn a t e d a y s

w i t h t h e e n v i r o n m e n t a l t r e a t m e n t b e i n g r e-

v e r s e d ( S o r N S ) . A r e c o v e r y d a y w a s a l l o w e d

b e t w e e n e a c h e x p e r i m e n t a l d a y .

W i t h i n e ac h e n v i r o n m e n t a l t r e a t m e n t g r o u p ,

t h e r e w e r e s e v e n i n j e c t i o n r e s p o n s e s w h i c h

r e p r e s e n t e d a m i n i m u m o f t w o i n j e c ti o n s p e r

a n i m a l : h e i f e r A r e c e i v e d f o u r i n j e c t i o n s ( 2 S ; 2

N S ) , h e i f e r B r e c e i v e d fo u r i n j e c t i o n s ( 2 S ; 2

N S ) , c o w C r e c e i v e d s i x i n j e c t i o n s ( 3 S ; 3 N S ) .

D u r i n g e a c h e x p e r i m e n t a l d a y , w a t e r a n d f ee d

w e r e w i t h h e l d .

U t e r i n e b l o o d f l o w r e a d i n g s ( m l / m i n ) w e r e

t a k e n f r o m t h e r e c o r d i n g p a p e r e v e ry 1 to 2

m i n d e p e n d i n g u p o n v a r i a b i l it y o f tr a ci n g s.

A v e r a g e o f 1 5 m i n U B F w a s c o n s i d e r e d a s a

s i n g le o b s e r v a t i o n f o r s t a t i s t i c a l a n a ly s e s t o

c h a r a c t e r i z e t i m e t r e n d s . R e c t a l t e m p e r a t u r e

a n d r e s p i r a t i o n r a t e w e r e m e a s u r e d t w o o r f o u r

t i m e s p e r a n i m a l w i t h i n e ac h e x p e r i m e n t a l d a y .

B l a ck g l o b e t e m p e r a t u r e s , a n e s t i m a t e o f n e t

s o l a r r a d i a t i o n , w e r e m e a s u r e d c o n t i n u o u s l y i n

b o t h e n v i r o n m e n t a l a r ea s f o r 4 e x p e r i m e n t a l

d a y s ( R o m a n - P o n c e e t a l . 1 9 7 7 a ) . E n v i r o n m e n -

t a l c o n d i t i o n s o n t h e o t h e r 6 e x p e r i m e n t a l d a y s

w e r e c o m p a r a b l e t o t h e p r e v i o u s 4 d a y s b u t

w e r e n o t m o n i t o r e d c o n t i n u o u s l y . A l l d a t a

w e r e a n a l y z e d b y m e t h o d o f le a s t s q u a re s

a n a l y s i s o f v a r i a n c e .

R E S U L T S N D D I S C U S S IO N

V e r i f y i n g p r e v i o u s r e s u l t s i n t h e t w o d i f -

f e r e n t e x p e r i m e n t a l a re a s (S an d N S ; R o m a n -

P o n c e

e t a l .

1 9 7 7 a ) , b l a c k g l o b e t e m p e r a t u r e

w a s h i g h e r ( P < . 0 1 ) i n t h e N S a r e a t h r o u g h o u t

t h e e x p e r i m e n t a l h o u r s o f t h e d a y ( f ig u r e 2 ) .

T h i s m e a s u r e m e n t i n t e g r a te s e f fe c t s o f n e t

r a d i a t i o n , d r y b u l b t e m p e r a t u r e a n d w i n d s p e e d

( B o n d a n d K e l l y , 1 9 5 5 ).

E n v i r o n m e n t a l t r e a t m e n t s e x e r t e d d i f f e r e n t

d e g r e e s o f t h e r m a l s t re s s o n t h e c o w s a s

e v i d e n c e d b y d i f f er e n c e s i n r e c t al t e m p e r a t u r e

a n d r e s p i r a t i o n r a t e . A v e r a g e r e c t a l t e m p e r a -

t u r e s ( C ) a n d r e s p i r a t i o n r a t e s p e r m i n u t e w e r e

l o w e r i n S t h a n N S a n i m a l s ( 3 8 . 7 C

v s

39 . 1 C ,

P < . 0 5 ; 6 2 v s 9 3 r e s p i r a t io n s p e r m i n u t e P < . 0 1 ) .

T h e s e p h y s i o l o g i c a l d i f f er e n c e s w e r e c o m p a r a -

b l e t o t h o s e f o u n d i n l a c t a t in g d a i r y c o w s

d u r i n g t h e s u m m e r s e a so n in w h i ch N S c o w s

h a d l o w e r c o n c e p t i o n r a t e s a n d p r o d u c e d l e s s

m i l k ( R o m a n - P o n c e e t a l . 1 9 7 7 a ) . T h u s , t h e

e n v i r o n m e n t a l c o n d i t i o n s a n d p h y s i o l o g i c a l r e-

s p o n s e s o f c a t t l e i n t h e p r e s e n t e x p e r i m e n t

2

7 B 9 I O I I 2 3 4 5 6 7 IS

H O U R S

O F D A Y

Figure 2. L east squares regressions of ho urly blac k

globe tempera tures for shade and no shade exper i -

me ntal areas.



U T E R I N E B I ,O O D F L O W I N C O W S 1 7 9

( 1 7 1 v s 1 3 7 m l / m i n ) . T h e o v e r a ll m e a n s i n U B F

a f t e r e s tr a d i o l i n j e c t i o n w e r e 1 2 8 a n d 1 0 9

m l / m i n f o r c ow s i n t h e S a n d N S t r e a t m e n t s .

A n i m a l s e x p o s e d t o s h a d e h a d a 1 7 . 4 g r e a t e r

r e s p o n s e t h a n N S - t r e a t e d c o w s .

F i g u r e 4 i l l u s t r a t e s t h e t r e a t m e n t r e g r e s si o n

c u r v e s o f U B F r e s p o n s e s e x p r e s s e d a s p e r c e n t -

a g e s o f p r e i n j e c t i o n U B F . R a t e s o f U B F v a r i e d

a m o n g e x p e r i m e n t a l d a y s w h i c h m a y r e fl e c t

c a r r y o v e r e f f e c t s o f p r e v i o u s e s t ra d i o l i n j e c t i o n s

t h a t i n f l u e n c e s e n s i t i v i t y o f t h e u t e r i n e v a s c u l a r

b e d . F o r t h is r e a s o n t h e t r e a t m e n t r e s p o n s e s

w e r e p r e s e n t e d a l so as p e r c e n t a g e s o f p r e t r e a t -

m e n t v a lu e s f o r e ac h e x p e r i m e n t a l d a y ( f i g ur e

4 ) . S h a d e - t r e a t e d c o w s h a d an o v e r al l p e r c e n t -

a g e c h a n g e o f 4 1 2 , w h e r e a s t h e c h a n g e f o r

N S - t r e a t e d c o w s w a s o n l y 2 8 7 . C o n s e q u e n t l y ,

t h e o v e r al l d i f f e r e n c e i n U B F t r e a t m e n t r e-

s p o n s e w a s 4 3 . 6 g r e a t e r f o r s h a d e - t r e a t e d

a n i m a l s .

R e s u l t s f r o m t h is e x p e r i m e n t i n d i c a t e t h a t

t h e r m a l s t r e ss c o n d i t i o n s k n o w n t o r e d u c e

f e r t i li t y a l s o s u p p r e s s U B F r e s p o n s e s a f t e r

i n j e c t i o n o f e s t r a d io l . A p p a r e n t l y t h e a n i m a l ' s

a t t e m p t t o t h e r m o r e g u l a t e u n d e r h e a t s t r e ss

c o n d i t i o n s is a s s o c i a t e d w i t h a d e c r e a s e d r a t e o f

p e r f u s i o n o f t h e n o n p r e g n a n t u t e ru s . T h e s e

e f f e c t s a re i n a g r e e m e n t w i t h o u r e a r l i e r o b s e r -

v a t i o n s o n e w e s i n w h i ch e n v i r o n m e n t a l c o n d i -

t i o n s w e r e m o r e c l o se l y c o n t r o l l e d i n c h a m b e r s ,

6

4 0 0 -

3 0 0 -

2 0 0

1 0 0

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OURS

Figure 4 . L eas t s qua re s reg re s s ions o f u t e r in e b loo d

f l o w r e s p o n s e s ( p e r c e n t a g e c h a n g e ) i n c o w s m a i n -

r a i n e d i n s h a d e o r n o s h a d e t h a t w e r e i n j e c t e d w i t h

e s t r a d i o l ( 2 0 0 p g ) .

a n d t h e r m a l s t r es s d ec r e a s ed U B F ( R o m a n -

P o n c e e t a l . 1 9 7 7 b ) . I t is k n o w n t h a t a c u t e a n d

c h r o n i c t h e r m a l s t re s s es i n c r e a s e d p l a s m a c a te -

c h o l a m i n e s ( A l v a r e z a n d J o h n s o n , 1 9 7 3 ) . C a t e-

c h o l a m i n e s , b y i n c r ea s in g c u t a n e o u s m o i s t u r e

l o ss , m a y p l a y a n i m p o r t a n t r o le in t h e t h e r m o -

r e g u l a t o r y f u n c t i o n o f t h e a n i m a l ( A l v a re z e t

a l .

1 9 7 0 ) . A l t e r n a t i v e l y , e l c v a t e d p l a s m a ca t e -

c h o l a m i n e s a l so m a y r e d u c e U B F d u e to t h e ir

v a s o c o n s t r i c t o r e f f e c t s o n t h e u t e r i n e v a sc u l a r

b e d ( A b r a m s e t a l . 1 9 7 1 ; B a r t o n e t a l . 1 9 7 4 ;

R o m a n - P o n c e

e t a l .

1 9 7 7 b ) . R o m a n - P o n c e

e t

a l .

( 1 9 7 7 b ) o b s e r v e d t h a t t h e r m a l s t re s s a n d

e p i n e p h r i n e r e d u c e d t h e n o r m a l i n c re a s e i n

U B F f o l l o w i n g E 2 i n j e c t i o n a n d t h a t t h e i r

e f f e c t s w e r e a d d i t i v e . U n d e r p r a c t i c a l f a r m

c o n d i t i o n s r e l ie f f r o m s o l al r a d i a t i o n , b y u s e o f

a s h a d e s t r u c t u r e , m o d i f i e d p h y s i o l o g i c a l re -

s p o n s e s o f t h e u t e r u s . O a k e s

e t a l .

( 1 9 7 6 )

d e t e c t c d a d e c r c a s e i n U B F i n r e s p o n s e t o

i n d u c e d h y p e r t h e r m i a o f p r e g n a n t e w e s. L e d u c

( 1 9 7 2 ) a ls o r e p o r t e d a r e d u c t i o n i n p l a c e n t a l

b l o o d f l o w i n r a b b i t s e x p o s e d t o h i g h e n v i r o n -

m e n t a l t e m p e r a t u r e s .

A r e d u c t i o n o f U B F i n r e s p o n s e to t h e r m a l

s t re s s m a y f u r t h e r e l e v at e t e m p e r a t u r e o f th e

r e p r o d u c t i v e t r a c t a n d p r e j u d ic e t h e d e v e lo p i n g

e m b r y o . A d e c r e a s e i n U B F i n r e s p o n s e to

t h e r m a l s t r e s s m a y a l so a f f e c t w a t e r, n u t r i e n t ,

a n d h o r m o n a l a v a i l a b i l i t y t o t h e u t e r u s .

A d d i t i o n a l s t u d i e s ar e n e e d e d u n d e r p r a c t i -

c al f a r m c o n d i t i o n s t o d e t e r m i n e i f t h e r m a l

s t r e ss a l t e rs U B F a n d p r o d u c t i o n r a t e o f h o r -

m o n e s w h i c h r e g u l a te U B F d u r i n g t h e e s t r o u s

c y c l e a n d e a r l y p r e g n a n c y .

L I T E R T U R E C I T E D

Abrams , R . M . , D . C a ton , J . C lapp and D . H . B a r ron .

1 9 7 1 . T e m p e r a t u r e d i f f e r e n c e s i n r e p r o d u c t i v e

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G y n e c o l . 1 1 0 : 3 7 0 .

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3 0 : 9 5 .

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o n e o n t h e r a te o f b l o o d f l o w o f th e u t e ru s o f

o v a r i e c t o m i z e d s h e e p . Q u a r t . J . E x p . P h y s i o l .

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G w a z d a u s k a s F . C . 1 9 7 4 . I n t e r r e l a t i o n s h i p s o f c e r t a i n

t h e r m a l a n d e n d o c r in e p h e n o m e n a a n d r e p r o d u c -

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