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

a r e a l s o t h a n k e d f o r c o n s i d e r a b l e d i s 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 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 : W a s h i n g t o n . )

B a l d w i n , R . L . , L u c a s , H . D . , a n d C a b r e r a , R . ( 1 9 7 0 ) . E n e r g e t i c r e l a t i o n s h i p s i n t h e f o r m a t i o n a n d

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

R u m i n a n t ' . ( E d . A . T . P h i l l i p s o n . ) p p . 3 1 9 - 3 4 . ( O r i e l P r e s s : N e w c a s t l e - u p o n - T y n e . )

B l a x t e r , K . L . ( 1 9 6 2 ) . ' T h e E n e r g y M e t a b o l i s m o f R u m i n a n t s ' . ( H u t c h i n s o n a n d C o . : L o n d o n . )

B r o u w e r , E . ( 1 9 6 5 ) . R e p o r t o f s u b - c o m m i t t e e o n c o n s t a n t s a n d f a c t o r s . I n ' E n e 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 l d a t T r o o n , S c o t l a n d , 1 9 - 2 2 M a y 1 9 6 4 . E u r o p e a n

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 . 1 1 . p p . 4 4 1 . ( A c a d e m i c P r e s s : L o n d o n . )

C a l a b y , J . H . ( 1 9 5 8 ) . S t u d i e s o n m a r s u p i a l n u t r i t i o n . I I . T h e r a t e o f p a s s a g e o f f o o d r e s i d u e s a n d

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 a n d p r o t e i n b y 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 u s t . J . B i o i . S c i . 1 1 , 5 7 1 - 8 0 .

C l a r e , N . T . , a n d S t e p h e n s o n , A . E . ( 1 9 6 4 ) . M e a s u r e m e n t o f f e e d i n t a k e b y g r a z i n g c a t t l e a n d s h e e p .

X . D e t e r m i n a t i o n o f n i t r o g e n i n f a e c e s a n d f e e d s u s i n g a n a u t o a n a l y s e r . N . Z . J . A g r i c . R e s .

7 , 1 9 8 .

214 T. J. Kempton, R. M. Murray and R. A. Leng

Foot, J. Z., and Romberg, B. (1965). The utilization of roughage by sheep and the red kangaroo, Macropus rufus (Desmarest). Aust. J. Agric. Res. 16, 429-35.

Forbes, D. K., and Tribe, D. E. (1970). The utilization of roughages by sheep and kangaroos. Aust. J. Zool. 18, 247-56.

Griffiths, M., McIntosh, D. L., and Leckie, R. M. C. (1972). The mammary glands of the red kangaroo, with observations on the fatty acid components of the milk triglycerides. J. Zool. 166,265-75.

Hungate, R. E. (1966). 'The Rumen and its Microbes'. (Academic Press: New York.) Leng, R. A. (1970). Formation and production of volatile fatty acids in the rumen. In 'Physiology

of Digestion and Metabolism in the Ruminant'. (Ed. A. T. Phillipson.) pp. 406-21. (Oriel Press: Newcastle-upon-Tyne.)

Leng, R. A., and Leonard, G. K. (1965). Measurement of the rates of production of acetic, propionic and butyric acids in the rumen of sheep. Br. J. Nutr. 19, 469-83.

Leng, R. A., and Murray, R. M. (1972). Estimation of the fermentation rate in the rumen of sheep using VFA production, carbon dioxide production and methane production. In 'Tracer Studies on Non-protein Nitrogen for Ruminants II'. pp.21-7. (Int. Atomic Energy Agency, Vienna.)

McIntosh, D. L. (1966). The digestibility of two roughages and the rates of passage of their residues by the red kangaroo, Megaleia rufa (Desmarest), and the Merino sheep. CSIRO Wildt. Res. 11, 125-35.

Moir, R. J. (1965). The comparative physiology of ruminant-like animals. In 'Physiology of Digestion in the Ruminant'. (Ed. R. W. Dougherty.) Ch. 1. (Butterworth: Washington.)

Moir, R. J., Somers. M., and Waring, H. (1956). Studies on marsupial nutrition. I. Ruminant-like digestion in a herbivorous marsupial Setonix brachyurus (Quoy and Gaimard). Aust. J. Bioi. Sci. 9,293-304.

Murray, R. M. (1974). Nutrition and digestive function of the ruminant Ph.D. Thesis, University of New England, Armidale, Australia.

Murray, R. M., Bryant, A. M., and Leng, R. A. (1976). Rates of production of methane in the rumen and large intestine of sheep. Br. J. Nutr. 36, 1-14.

Manuscript received 5 November 1975

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