-
A u s t . J . B i o i . S c i . , 1 9 7 6 , 2 9 , 2 0 9 - 1
4
M e t h a n e P r o d u c t i o n a n d D i g e s t i b i l i t
y M e a s u r e m e n t s
i n t h e G r e y K a n g a r o o a n d S h e e p
T . J . K e m p t o n , A R . M . M u r r a y B a n d R . A . L
e n g
A
A D e p a r t m e n t o f B i o c h e m i s t r y a n d N u t r
i t i o n , U n i v e r s i t y o f N e w E n g l a n d ,
A r m i d a l e , N . S . W . 2 3 5 1 .
B D e p a r t m e n t o f T r o p i c a l V e t e r i n a r y S
c i e n c e , J a m e s C o o k U n i v e r s i t y ,
T o w n s v i l l e , Q l d 4 8 1 1 .
A b s t r a c t
T h r e e g r e y k a n g a r o o s a n d t h r e e s h e e p w
e r e g i v e n a d i e t o f l u c e r n e c h a f f a n d m e a s
u r e m e n t s w e r e
m a d e o f f e e d i n t a k e , d i g e s t i b i l i t y c o
e f f i c i e n t s , m e t h a n e p r o d u c t i o n r a t e a n
d v o l a t i l e f a t t y a c i d c o n t e n t
o f t h e ' s t o m a c h ' a n d c a e c u m f o r e a c h a n
i m a l . T h e k a n g a r o o s h a d l o w e r i n t a k e s o f
d i g e s t i b l e d r y
m a t t e r a n d o r g a n i c m a t t e r t h a n t h e s h e
e p ; t h i s w a s r e l a t e d t o l o w e r i n t a k e s o f d
r y m a t t e r a n d l o w e r
a p p a r e n t d i g e s t i b i l i t y c o e f f i c i e n t
s p a r t i c u l a r l y o f t h e c r u d e f i b r e f r a c t i
o n .
M e t h a n e p r o d u c t i o n i n t h e s h e e p ( c o l l
e c t e d i n r e s p i r e d a i r t h r o u g h a m a s k ) w a s
0 8 1 I i t r e / h ;
n o m e t h a n e w a s c o l l e c t e d i n t h e r e s p i r
e d a i r f r o m k a n g a r o o s . A n a l r e l e a s e o f m e
t h a n e i n s h e e p a n d
k a n g a r o o s i n d i c a t e d t h a t s o m e m e t h a n
e w a s p r o d u c e d i n t h e h i n d g u t o f k a n g a r o o
s a n d t h a t a l l o f
t h i s m e t h a n e w a s l o s t v i a t h e a n u s . T h i
s f i n d i n g w a s d i f f e r e n t t o t h e s h e e p w h i c
h a p p a r e n t l y e x c r e t e d
8 0 - 9 0 % o f t h e h i n d g u t m e t h a n e v i a t h e l
u n g s . T h u s i n b o t h s i t e s o f a p p a r e n t h i g h
m i c r o b i a l g r o w t h
i n t h e g u t o f k a n g a r o o s m e t h a n e p r o d u c
t i o n i s n e g l i g i b l e o r l o w e r t h a n i n t h e s a
m e s i t e s i n s h e e p .
P o s s i b l e e x p l a n a t i o n s f o r t h e a b s e n c
e o f m e a s u r a b l e m e t h a n e p r o d u c t i o n i n t h
e k a n g a r o o f o r e -
s t o m a c h s a r e d i s c u s s e d .
I n t r o d u c t i o n
T h e e f f i c i e n c y o f u t i l i z a t i o n o f r o u g
h a g e d i e t s b y k a n g a r o o s h a s r e c e i v e d l i t
t l e
a t t e n t i o n . C a l a b y ( 1 9 5 8 ) s t u d i e d d i g
e s t i o n i n t h e q u o k k a S e t o n i x b r a c h y u r u s
( Q u o y
a n d G a i m a r d ) a n d c o n c l u d e d t h a t i t s d i
g e s t i v e e f f i c i e n c y w a s i n t e r m e d i a t e b e
t w e e n
t h a t o f t h e r u m i n a n t a n d n o n - r u m i n a n t
h e r b i v o r e . F o o t a n d R o m b e r g ( 1 9 6 5 ) ,
M c I n t o s h ( 1 9 6 6 ) a n d F o r b e s a n d T r i b e (
1 9 7 0 ) c o m p a r e d d i g e s t i o n i n t h e r e d k a n g
a r o o
( M a c r o p u s r u f u s , D e s m a r e s t ) w i t h s h e
e p , a n d f o u n d t h e a p p a r e n t d i g e s t i b i l i t
y o f
l u c e r n e i n t h e s e k a n g a r o o s t o b e s i g n i
f i c a n t l y l o w e r . T h e r a t e o f p a s s a g e o f d i
g e s t a
w a s f a s t e r i n t h e k a n g a r o o c o m p a r e d w i
t h s h e e p , w h i c h a p p e a r e d t o r e s u l t i n a l o
w e r
d i g e s t i b i l i t y o f c r u d e f i b r e i n t h e k a
n g a r o o ( M c I n t o s h 1 9 6 6 ) . M o i r ( 1 9 6 5 ) h a
s
e m p h a s i z e d t h e ' r u m i n a n t - l i k e ' d i g e
s t i v e s y s t e m o f t h e k a n g a r o o s , a n d M o i r e
t a l .
( 1 9 5 6 ) m e a s u r e d v o l a t i l e f a t t y a c i d (
V F A ) p r o d u c t i o n i n s t o m a c h c o n t e n t s i n v
i t r o .
H o w e v e r , t h e r e a r e n o r e s u l t s w h i c h i n
d i c a t e t h e e x t e n t o f f e r m e n t a t i o n i n t h e
s t o m a c h
o f t h e i n t a c t a n i m a l .
I n r u m i n a l f e r m e n t a t i o n , h y d r o g e n g a
s i s g e n e r a t e d w h e n a c e t a t e i s p r o d u c e
d
f r o m p y r u v a t e o r w h e n c o - e n z y m e s g e n e
r a t e d i n t h e f e r m e n t a t i o n p a t h w a y s a r
e
r e o x i d i z e d ( s e e B a l d w i n e t a l . 1 9 7 0 ) .
I n r u m i n a n t s t h i s h y d r o g e n i s c o n v e r t e d
t o
m e t h a n e a n d t h e r a t e o f p r o d u c t i o n [ b e
t w e e n 1 0 a n d 5 0 l i t r e s / d a y ( s e e B l a x t e r 1
9 6 2 ) ]
i s s t o i c h i o m e t r i c a l l y r e l a t e d t o t h e
f e r m e n t a t i o n r a t e ( s e e L e n g a n d M u r r a y 1
9 7 2 ) .
A s p a r t o f a c o m p a r a t i v e s t u d y o f d i g e s
t i o n i n h e r b i v o r e s , w e s e t o u t t o u s e m e t h
a n e
p r o d u c t i o n a s a n i n d e x o f f e r m e n t a t i o
n i n t h e s h e e p a n d k a n g a r o o .
-
210
Materials and Methods Animals
T. J. Kempton, R. M. Murray and R. A. Leng
Three mature Merino ewes and three mature female eastern grey
kangaroos (Macropus giganteus Shaw) were housed individually in
metabolism cages. Prior to the experiment all animals were given
lucerne chaff ad libitum and trained to accept the experimental
procedures. All animals were weighed at the beginning of the
experimental period (see Table 2). The lucerne contained 88 % dry
matter comprising 36 % crude fibre, 2 6 % nitrogen and 8 5 % ash on
a dry matter basis.
Experimental Methods To facilitate comparisons of the intake and
digestibility of lucerne by sheep and kangaroos, all
animals were given each day 50 g chopped lucerne hay per unit
metabolic body size, i.e. body weighto,,,. Water was available at
all times.
The experimental period consisted of a 10-day pre-experimental
period and an 8-day digestibility trial. The faeces and feed
refusals were collected daily, a 10% subsample taken, bulked and
stored at -20D C for analysis. Urine excretions were collected
daily in 20 ml of a mercuric chloride-glacial acetic acid mixture
(0'1 % w/v). A subs ample of 10% by volume was stored at -20e.
Chemical Methods
The dry matter content of all samples taken each day was
determined after heating in a forced air oven at 70C for 48 h. The
bulked subsamples were dried and ground through a I-mm screen
before being analysed.
Feed, faeces and feed refusals were analysed for organic matter
and crude fibre (Association of Official Agricultural Chemists
1960). The gross energy content of the dry matter of these
materials was estimated using a Gallenkamp Autobomb Automatic
Adiabatic Bomb Calorimeter (No. DBIIO), and nitrogen content was
determined by the semi-micro Kjeldahl method of Clare and
Stephenson (1964). The concentration and proportions of VFA in the
rumen and caecum of sheep and stomach contents of kangaroos were
estimated (see Leng and Leonard 1965) on materials obtained
following slaughter of two of the kangaroos and two of the
sheep.
Measurement of Methane Production in Vivo All animals were given
t of their daily ration every 3 h for 2 days prior to and during
the
methane production rate measurement. Methane production was
measured by fitting a mask over the mouth of the animal I h after
feeding and collecting respired and eructated gases for 1 h. A
total of three I-h collections with a 2-h interval between
collections was made for each animal.
The gas handling system was essentially the same as that
described by Murray et al. (1976). In this system air was drawn
across the nose and mouth of the animal at a rate of 50 litres/min
and a subsample of 2 litres/min was drawn serially through a
freeze-drying unit and a 'Lira' methane analyser (Mine Safety
Appliances Co., Pittsburgh, U.S.A.). Methane content in the gases
was read directly from a chart recorder attached to the methane
analyser which had been previously calibrated with a standard gas
mixture.
The release of methane from the anus was measured using the same
principle as used for collection of gases from the mouth. A mask
designed to allow the free passage of urine and faeces and yet
retain any gases produced was used in place of the face mask. Air
was drawn across the anus for a single 3-h period per animal and
analysed for methane content as described above.
Measurement of Methane Production in Vitro Mixed digesta from
the rumen of a sheep and the upper stomach of a kangaroo were
obtained
from slaughtered animals. Samples of 100 ml were incubated under
nitrogen gas in conical flasks at 39C and shaken 100 times/min for
I h. Care was taken to keep the samples under anaerobic conditions
at all times. Nitrogen gas was passed through the digesta contents
at about 1 ml/min and passed through a CaCl2 drying train and then
through the methane analyser.
Results
Feed intake and digestibility coefficients for each animal are
given in Table 1. The kangaroo had significantly (P < 001) lower
digestibility coefficients for all feed components than sheep.
Methane production rates for individual animals are given
-
M e t h a n e P r o d u c t i o n i n G r e y K a n g a r o o a
n d S h e e p
2 1 1
T a b l e 1 . M e a n a p p a r e n t d i g e s t i b i l i t y
c o e f f i c i e n t s , n i t r o g e n b a l a n c e a n d i n t
a k e o f l u c e r n e c h a f f b y
k a n g a r o o s a n d s h e e p
V a l u e s s h o w n a r e m e a n s s . e . T h e s i g n i f
i c a n c e o f t h e d i f f e r e n c e b e t w e e n m e a n s i
s a l s o s h o w n
I n t a k e D i g e s t i b i l i t y ( % )
D r y
O r g a n i c
m a t t e r
m a t t e r
D r y
O r g a n i c C r u d e C r u d e
( g / d a y )
( g W - O ' 7 5 d - ' ) A
m a t t e r m a t t e r f i b r e
p r o t e i n
K a n g a r o o
4 7 7 4 6
5 5 1 1 5 6 1 1 3 6 1 8
7 3 0 1
S h e e p
6 4 3
4 7
6 2 0 ' 3 6 3 0 ' 3
4 8 0 7
7 6 0 ' 4
p
* * * * * * * *
N i t r o g e n b a l a n c e ( g n i t r o g e n w e i g h t -
o . ' 5 d a y - ' )
K a n g a r o o
S h e e p
p
F e e d
1 3 6 0 0 0 4
1 ' 3 7 0 ' 0 0 2
n . s .
F a e c e s U r i n e
0 3 7 0 0 0 2
0 3 4 0 O O 8
n . S .
0 9 8 0 0 4 9
0 ' 8 1 0 ' 0 2 1
n . s .
A M e a s u r e d a s g r a m s p e r w e i g h t o '
7 5
p e r d a y .
* * P < 0 0 1 . n . s . , N o t s i g n i f i c a n t .
E n e r g y
5 6 0 5
6 1 0 ' 9
* *
B a l a n c e
0 0 1 0 0 4 8
0 2 2 0 0 1 4
* *
T a b l e 2 . M e t h a n e p r o d u c t i o n m e a s u r e d
o v e r a 3 - h p e r i o d i n k a n g a r o o s a n d s h e e p g
i v e n a l u c e r n e
c h a f f d i e t , a n d i n d i v i d u a l a n i m a l w e i
g h t s
A n i m a l
K a n g a r o o 1
K a n g a r o o 2
K a n g a r o o 3
M e a n
S h e e p 1
S h e e p 2
S h e e p 3
M e a n
S i g n i f i c a n c e o f
m e a n d i f f e r e n c e s
R e s p i r e d
m e t h a n e
( l / h )
0
0
0
0 7 9
0 7 5
0 8 8
0 8 1 0 0 3 6
* *
A n a l
m e t h a n e
( l / h )
0 0 2
0 0 2
0 0 2
0 ' 0 2 0 ' 0 0 0
0 0 1
0 0 2
0 0 1
0 0 1 0 0 1 8
n . s .
T o t a l m e t h a n e
W e i g h t
p r o d u c t i o n
( k g )
( % D E I ) A
0 4 0 1 9 1
0 3 4
2 4 1
0 3 7
2 2 7
0 3 7 0 0 1 7
1 0 ' 6 0
3 0 0
9 ' 9 6
3 2 8
1 1 ' 0 1
3 4 0
1 0 5 2 0 ' 3 0 5
* *
A P e r c e n t a g e o f d i g e s t i b l e e n e r g y i n t
a k e ( D E I ) ; l 1 i t r e m e t h a n e = 3 9 5 4 k J ( B r o u
w e r 1 9 6 5 ) .
* * P < 0 0 1 . n . s . , N o t s i g n i f i c a n t .
T a b l e 3 .
V o l a t i l e f a t t y a c i d c o n c e n t r a t i o n s a
n d p r o p o r t i o n s i n s t o m a c h a n d c a e c a l c o n
t e u t s f r o m
s l a u g h t e r e d s h e e p a n d k a n g a r o o s g i v e
n l u c e r n e c h a f f
E a c h v a l u e i s t h e m e a n o f t w o r e s u l t s
A n i m a l
T o t a l V F A
I n d i v i d u a l V F A p r o p o r t i o n s ( m o l / I O O
m o l )
c o n c n ( m M )
A c e t i c P r o p i o n i c B u t y r i c I s o b u t y r i c
V a l e r i e I s o v a l e r i c
S h e e p
R u m e n f l u i d
6 2
6 8 2 2
7
1 3
0 6
1 9
C a e c u m f l u i d
6 4
7 9
1 4
5
0 4 0 9 0 6
K a n g a r o o
S t o m a c h f l u i d 1 0 0
7 0 1 7 1 2
0 2 0 9
0 2
C a e c u m f l u i d
6 8 8 2 1 3
4
0 5 0 4 0 3
-
212 T. J. Kempton, R. M. Murray and R. A. Leng
in Table 2. No measurable amounts of respired or eructated
methane were detected in kangaroos, whereas sheep released methane
at an average rate of O 81 litre/h. Kangaroos released methane at a
rate of 002 litre/h from the anus which was not significantly
(P>0'05) different in quantity to the O'Ollitre/h released an
ally by sheep. The methane production in kangaroos represented 04 %
of the digestible energy intake (DEI) compared to 10 5 % of DEI in
sheep. No detectable production of methane occurred from 100 g of
stomach contents of kangaroos whereas from the same quantity of
rumen contents of sheep methane was produced at between 20 and 40
ml/h.
The proportions and concentrations of VF A in the rumen and
caecum of sheep and the stomach and caecum of kangaroos are shown
in Table 3.
Discussion
Ruminants can effectively utilize a large proportion of the
cellulose of their diet because of microbial fermentation and a
long retention time of feed particles in the rumen. Moir et al.
(1956) suggested that because of the kangaroo's 'ruminant-like'
digestive tract it could similarly utilize ingested fibre, and
consequently most studies on kangaroo digestion have assumed that
feed is retained in the forestomach where there is substantial
production of VF A and microbial cells.
The intakes and associated digestibility coefficients presented
here for kangaroos and sheep are comparable to those found by
Calaby (1958), Foot and Romberg (1965), McIntosh (1966) and Forbes
and Tribe (1970). Kangaroos had lower digesti-bility coefficients
for all dietary components measured. Even when the effect of the
crude fibre fraction was removed during calculation of the organic
matter digestibility coefficients, there remained an interspecies
difference in 'organic matter' digestibility and therefore the
differences were not entirely due to a difference in fibre
digestion. Thus the kangaroo does not apparently digest the
available dietary components as efficiently as sheep.
In this study it was found that kangaroos produced insignificant
quantities of methane during the period of collection in comparison
with sheep. Of the methane produced by the kangaroos, none was
apparently produced in the forestomach as indicated by mask
collections. The methane analyser used could detect methane at
production rates as low as O' 5 ml/h (Murray 1974). Incubation in
vitro of digesta from the forestomach of both species showed
methane production for the sheep but none from the kangaroo.
Although the mask collections were only for a period of 3 h, Murray
et al. (1976) have shown that methane production in sheep fed
lucerne chaff at hourly intervals is almost constant. The rate of
emission of methane from the anus, however, is quite variable and
so the values reported here must be considered as being only
indicative of relative rates in both species. As sheep excrete a
considerable portion (80-90 %) of the methane produced in the
hindgut via the lungs (Murray et al. 1976) this would indicate that
the overall production of methane in the hindgut of the kangaroo
was less than in the sheep. The absence of methane in respired air
in the kangaroos may indicate that methane is produced in the large
intestine close to the anus and rapidly excreted.
In these kangaroos the concentration of VF A in mixed stomach
contents of slaughtered animals was 85-115 mmol/litre indicating
that some fermentation occurred. The extent of fermentation
relative to the sheep, however, may not be
-
M e t h a n e P r o d u c t i o n i n G r e y K a n g a r o o a
n d S h e e p
2 1 3
i n d i c a t e d b y t h e s e c o n c e n t r a t i o n s s i
n c e t h e s t o m a c h c o n t e n t s f r o m k a n g a r o o s
w e r e
m u c h d r i e r ( 1 5 - 1 7 % d r y m a t t e r ) t h a n t h
o s e i n t h e r u m e n o f s h e e p ( 1 2 - 1 3 % ) o n t h
e
s a m e d i e t .
A p o s s i b l e e x p l a n a t i o n f o r t h e l a c k o f
m e t h a n e p r o d u c t i o n m a y b e t h a t f e r m e n t a
t i o n
o c c u r s i n t h e f u n d u s a r e a o f t h e s t o m a c
h w h e r e o x y g e n , t a k e n i n w i t h t h e f e e d , m i
g h t
a c t a s a n e l e c t r o n a c c e p t o r . S i n c e m e t
h a n o g e n i c b a c t e r i a a r e o b l i g a t o r y a n a e
r o b e s
( H u n g a t e 1 9 6 6 ) t h e p r e s e n c e o f o x y g e n
w o u l d p r e v e n t t h e i r g r o w t h t h e r e b y i n h i
b i t i n g
m e t h a n e p r o d u c t i o n f r o m h y d r o g e n g e n
e r a t e d i n t h e p r o d u c t i o n o f a c e t a t e ( s e
e
L e n g 1 9 7 0 ) . T h e s i m p l e s t r u c t u r e o f t h
e k a n g a r o o f o r e s t o m a c h m a y a l l o w e n t r y o
f
o x y g e n a c r o s s t h e w a l l , a n d t h i s w o u l d
r e s u l t i n a l o w e r r e d u c i n g p o t e n t i a l i n t
h e
w h o l e o r g a n . A l o w r e d o x p o t e n t i a l i n t
h e k a n g a r o o ' s s t o m a c h m a y a l s o e x p l a i n t
h e
l o w d e g r e e o f h y d r o g e n a t i o n o f d i e t a r
y u n s a t u r a t e d f a t t y a c i d s i n k a n g a r o o s (
G r i f f i t h s
e t a l . 1 9 7 2 ) a s i n d i c a t e d b y t h e h i g h c o
n t e n t o f t h e s e i n k a n g a r o o ' s m i l k . S u c h a
h i g h
c o n c e n t r a t i o n o f u n s a t u r a t e d f a t t y a
c i d s i n m i l k f r o m k a n g a r o o s m a y i n d i c a t e
t h a t
h y d r o g e n a t i o n o f d i e t a r y f a t t y a c i d s
i n t h e s t o m a c h i s l o w , w h i c h i n t u r n s u g g e
s t s
l o w h y d r o g e n p r o d u c t i o n a n d a l i m i t e d
r a t e o f f e r m e n t a t i o n i n t h e f o r e s t o m a c h
o f
k a n g a r o o s . C o n v e r s e l y , i f a b s o r p t i o
n o f V F A w a s s l o w t h e h i g h c o n c e n t r a t i o n s
o f
V F A i n t h e d e e p e r f u n d u s a r e a o r t h e a r e
a t e n d i n g t o w a r d s t r u e g a s t r i c f u n c t i o n
m a y ,
t h r o u g h f e e d b a c k m e c h a n i s m s , r e d u c e
f e r m e n t a t i o n . T h u s t h e r e l a t i v e l y h i g h
l e v e l s
o f V F A m a y b e d u e t o a l o w f e r m e n t a t i o n r
a t e c o u p l e d w i t h a l o w a b s o r p t i o n r a t e
.
F u r t h e r r e s e a r c h i s n e c e s s a r y t o e x p l
a i n t h e a b s e n c e o f m e t h a n e i n t h e f o r e s t o
m a c h
o f k a n g a r o o s . S i n c e m e t h a n o g e n i c b a c
t e r i a d e f i n i t e l y o c c u r i n t h e h i n d g u t o f
t h e
k a n g a r o o , a n d u n l e s s o x y g e n i s g a i n i n
g a c c e s s t o t h e s t o m a c h , t h e l a c k o f m e t h a
n e
p r o d u c t i o n a p p e a r s t o b e d u e l a r g e l y t
o a l o w f e r m e n t a t i o n p o t e n t i a l . T h i s i s a
l s o
i n d i c a t e d b y t h e l o w f i b r e d i g e s t i o n i
n t h e s e a n i m a l s . U n t i l m o r e p o s i t i v e m e a
s u r e m e n t s
a r e m a d e i n i n t a c t a n i m a l s t h e r e m u s t b
e c o n s i d e r a b l e d o u b t a s t o w h e t h e r t h e
k a n g a r o o i s ' r u m i n a n t - l i k e ' a n d w h e t
h e r m e t h a n e p r o d u c t i o n c a n b e u s e d a s a b a
s i s
f o r c o m p a r i s o n b e t w e e n t h e r e l a t i v e e
f f i c i e n c i e s o f d i g e s t i o n i n v a r i o u s h e r
b i v o r e s .
A c k n o w l e d g m e n t s
W e w i s h t o e x p r e s s o u r a p p r e c i a t i o n f o
r t h e t e c h n i c a l a s s i s t a n c e o f M i s s e s C y n
t h i a
U n d e r w o o d a n d C l a r e A l l i n g t o n . D r s J .
V . N o l a n , B . W . N o r t o n a n d I . D . H u m e
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c u s s i o n , p a r t i c u l a r l y o f t e c h n i q u e s
.
R e f e r e n c e s
A s s o c i a t i o n o f O f f i c i a l A g r i c u l t u r a
l C h e m i s t s ( 1 9 6 0 ) . ' O f f i c i a l M e t h o d s o f
A n a l y s i s ' . 9 t h E d n .
( E d . W . H o r o w i t z . ) ( A s s o c i a t i o n o f O f
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u t i l i s a t i o n o f f e r m e n t a t i o n e n d p r o d
u c t s . I n ' P h y s i o l o g y o f D i g e s t i o n a n d M e
t a b o l i s m i n t h e
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r g y M e t a b o l i s m ' .
( E d . K . L . B l a x t e r . ) P r o c . 3 r d S y m p . h e
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A s s o c i a t i o n f o r A n i m a l P r o d u c t i o n N o
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Manuscript received 5 November 1975
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