wheten

Aust. J. Agric. Res., 1975, 26, 1053-62
Whole Wheat Grain Feeding of Lambs. V*
Effects of Roughage and Wheat Grain Mixtures
M. L. ~ i ~ h a and
r n W.
~ ~
R. ~ c M a n u s *
A
School of Wool and Pastoral Sciences, University of
New South Wales, P.O. Box 1, Kensington, N.S.W. 2033.
Present address: Whatawhata Hill Country Research Station,
Private Bag, Hamilton, New Zealand.
Abstract
Two slaughter trials were conducted with lambs to evaluate the effects on production and some
rumen characteristics of the addition of low quality roughage (wheaten straw) and a high quality
roughage (pelletized ground lucerne) to wheat grain diets.
In the first trial one group of lambs was given a 111 mixture of whole wheat grain and chaffed
wheaten straw and another chaffed lucerne hay ad libitum. Lucerne-fed lambs had significantly
(P < 0.001) higher dry and organic matter intakes, grew faster and had higher levels of volatile fatty
acids in their rumens than lambs offered the mixed ration, although there were no differences between
rations in dry and organic matter digestibilities. The apparent nitrogen digcstibility of the mixed
ration was significantly (P < 0.001) lower than that of the lucerne ration. Of lambs offered the
mixed ration, 46% had extensive lesions on the ventral wall of the rumen at slaughter, and these
were associated with marked inappetence and loss in liveweight.
In the second trial comparisons were made of dicts consisting of lucerne (either alone or mixed
with cracked wheat) and whole wheat grain + limestone. The effect of treating the lucerne with
formaldehyde was also studied. There were no significant differcnces in carcass gain with the lucerne
diets; parakeratosis developed in some animals on lucerne-wheat diets but did not affect productive
performance. The animals offered whole wheat lost weight, two died of wheat poisoning, and several
animals developed lesions on the rumen wall.
Introduction
McManus et al. (1972) and Bigham et al. (1973) have shown that young sheep can
be fattened on diets consisting entirely of whole wheat grain if a mineral buffer
supplement is added to the ration. Salivary flow rates were significantly greater for
sheep receiving the mineral buffer supplements than for the control sheep, and this
was associated with an elevated rumen pH, altered proportions of individual VFA in
rumen liquor, and a higher concentration of rumen microorganisms in the rumen
liquor. It is known that when roughages are given with a diet high in readily available
carbohydrates, salivary flow rates are stimulated; roughages are usually included in
such diets to overcome the acidotic problems associated with the feeding of high
carbohydrate diets (Balch and Rowland 1957; Reid et al. 1957; Lawlor et al. 1966).
The two experiments reported here were designed to investigate the effects of the
addition of roughages to wheat grain diets on liveweight gain and on some rumen
parameters.
* Part IV, Aust. J. Agric. Res.,
1975, 26, 729.
M. L. Bigham and W. R. McManus
Material and Methods
Both experiments 1 and 2 were slaughter trials in which animals were slaughtered
at the start, middle and end of the experiment. All sheep in each experiment were
confined to individual pens or metabolism cages. They were fed ad libitum by offering
10% above the previous day's intake, and had free access to drinking water.
Experiment 1
Thirty-six Border Leicester x Merino wether lambs of 28.8 kg mean liveweight
were allocated into two groups of 16 and the remaining four animals slaughtered at
the start of the experiment. Over 9 weeks (period 1) one group was fed on a 111
diet of wheat grainlwheaten straw (W,) and the other a diet of chopped lucerne
hay (LA.
At the end of period 1, five animals in each of the two groups were slaughtered.
Of the remaining 11 animals in the wheat grain-wheaten straw group, six lambs were
maintained on this diet for the next 9 weeks (period 2, group W,W,) and five were
offered the chopped lucerne hay diet (W,L2). These I I animals were then slaughtered.
Of the I I animals remaining in the lucerne group at the end of period 1, six lambs
continued on this diet for the next 9 weeks (period 2, L,L,) and five were offered the
wheat grainlwheaten straw diet (L,W2). These 11 animals were then slaughtered.
Experiment 2
Fifty-nine Border Leicester x (Dorset Horn x Merino) wether lambs of 16.7 kg
mean liveweight were allocated to one of six groups (live groups of 10 and one of
nine animals). One group of 10 were slaughtered at the start of the experiment and
the other five groups were fed on the following rations.
Group I
Group 2
Group 3
Group 4
Group 5
Pelleted ground lucerne.
As for group I but the ration was treated with formaldehyde.
A pelletcd 311 mixture of cracked wheat and ground lucerne.
As for group 3 but treated with formaldehyde.
Whole wheat grain plus 13% ground limestone.
Rations for groups 2 and 4 were treated with fornlaldehyde by the technique of
Ferguson rt al. (1967) and contained respectively 1-96and I .38 % bound formaldehyde.
These levels of bound formaldehyde would normally be considered adequate for
protein protection (Ferguson, personal communication) for material treated and left
to stand for a period before pelleting. Tn the present case it was not practicable to
allow the rations to stand, and they were pelleted immediately after the addition of
formaldehyde.
The experiment was conducted over 20 weeks and consisted of two 10-week periods.
Half the animals in each group were slaughtered after the first 10 weeks (period I) and
the remainder after the second (period 2).
Data Collected
Animals were weighed at the start and finish of each period in both experiments
immediately before feeding. Feed was offered once daily at a level 10% above the
previous day's intake.
Whole Wheat Grain Feeding of Lambs. V
All sheep in both experiments were fitted with faecal bags for total faecal collection
during the last 14 days of each period. During experiment 2, two sheep from each
group in period I and all sheep in period 2 were confined in metabolism cages during
the last 14 days of the respective periods for total faecal and urine collection; 10%
of the daily faecal and urine output for each sheep was retained and bulked for
analysis. Feed and faeces were analysed for ash and nitrogen content and urine for
nitrogen content by standard techniques.
Slaughter
All sheep were slaughtered 4 hr after being offered food. At slaughter the empty
body weight (full body weight minus gut contents) and butcher's carcass weights were
obtained. The rumen was opened, the contents sampled for volatile fatty acid (VFA)
analysis and the pH of the contents determined. The rumen wall was examined for
the presence of lesions. VFA analyses were carried out according to the technique of
Edwards et al. (1971).
A~zaly~es
In both experiments, data obtained from animals at slaughter were used to predict
data for the other animals in that group which were not slaughtered. Such estimations
were made for empty body weight and for carcass weights of all sheep remaining
alive at the end of period 1, by use of a suitable regression technique.
Results
Rations
Little selection among diet components occurred, in that the daily residues reflected
the composition of the grainlstraw ration offered, but the rate at which grain and
straw was consumed within a daily feeding period varied, grain usually being consumed
first. The dry matter composition for all rations is shown in Table 1. Rations for
Table 1. Dry matter composition of rations
Ration
Crude
protein
Crude
fibre
Ash
content
Ether
extract
( %>
( %>
( %>
( %>
17.6
29.6
4.1
8.5
2.2
1.8
Experiment I
Wheatlwheaten straw
Lucerne
8.8
14.0
Experiment 2
Ration
Ration
Ration
Ration
Ration
1
2
3
4
5
groups 1, 2, 3 and 4 were prepared from different batches of lucerne, and the wheat
used for groups 3 and 4 differed from that used for group 5. The lucerne used for
groups 3 and 4 contained 28.1 % crude protein and the wheat 15.0 %.
M. L. Bigham and W. R. McManus
Experiment I
Table 2 summarizes the liveweight and carcass gain, and intake and digestibility
data for all groups in both periods. Sheep offered the lucerne ration consumed
significantly (P < 0.01) more feed and gained more liveweight than sheep given the
wheatlwheaten straw ration. The rations had similar dry and organic matter
digestibilities, but the apparent nitrogen digestibility of the lucerne was significantly
Table 2. Mean gains in empty body weight and carcass weight and intakes of dry matter, organic
matter and nitrogen and organic matter and nitrogen digestibility for all groups in each
period for experiment 1
Standard errors in parenthesis
-
Gam (kg110 weeks)
Empty
Carcass
body wt.
weight
Group
-
-
Intakes @/day)
Dry
Organ~c Nitrogen
matter
matter
Appalent digestibility(%)
Organic Nitrogen
matter
Period 1
Wheatlwheaten
straw (W
Lucerne (L
Period 2
Wheatlwheaten
straw (W,)
Lucerne ( L2)
W1Lz
LiW2
+
(P < 0.001) higher than that of the wheatlwheaten straw mixture (72.0 1.6% for
lucerne and 54.0 2.8 0/, for wheatlwheaten straw). In period 2, the WlL2 group
(wheatlwheaten straw in period 1 and lucerne in period 2) displayed compensatory
growth. The animals in this group gained 13.5 kg + 1.1 kg liveweight, compared with
8.3 +_ 1.0 kg for the group given lucerne in both periods (L1L2). In addition, the
W,L2 group were consuming more feed per unit of liveweight than the group offered
+
Table 3. Mean rumen pH and concentration of VFA and proportions of individual VFA in the rumen
liquor for all groups in experiment 1 at slaughter
-
Group
Rumen
pH
-
Total VFA
(inrnoles/l.)
Proportions (%) of individual acids
C,
C,
iC,
C,
iC5 C,
Period 1
Wheatlwheaten straw
Lucerne
5.5
6.4
95
139
55.4
65.7
30.6
21.8
0.1
0.5
10.9
8.0
0.8
1.2
2.2
2.8
56.2
65.3
66.0
54.5
30.8
23.4
21.5
29.7
0.2
0.3
0.4
0.2
10.2
7.4
8.7
12.3
0.7
1.0
1.0
1.0
1.9
2.6
2.4
2.3
Period 2
Wheatlwheaten straw
Lucerne
WlLz
LIW,
6.2
6.4
6.6
6.3
91
138
169
116
+
lucerne (L,L2). Mean intakes for groups W,L2 and L,L, in period 2 were 38.8 1.7
and 32 3 1 -0 g/kg liveweight respectively, which differed significantly (P < 0.05).
The mean rumen pH, the concentration of VFA and the proportions of individual
fatty acids for all groups at slaughter are shown in Table 3. In period 1 the sheep
+
Whole Wheat Grain Feeding of Lambs. V
given the wheatlwheaten straw ration had a significantly (P < 0.01) lower rumen pH,
less total VFA,and a smaller proportion of C , and a higher proportion of C , and C ,
acids than sheep offered the lucerne ration. The rumen pH differences present in
period 1 were not apparent in period 2, although the rumen pH varied considerably
between sheep in the wheat/wheaten straw groups in period 2. Similar differences to
those present in period 1 in the VFA concentration and proportions of individual
acids were also present in period 2. Significant (P < 0.01 in period 1 and P .= 0.05
in period 2) correlations were found between the concentration of VFA in rumen
liquor and the rumen pH but only for the groups offered the lucerne ration. These
data suggest that factors other than the VFA were contributing towards rumen pH
for sheep given the mixed wheatlwheaten straw ration.
Table 4. Mean dry matter intake (DMI) and liveweight gain during the 10 weeks of each period and
rnmen pH and total volatile fatty acids at slaughter and incidence of rumen lesions for sheep
given the wheatlwheaten straw diet in experiment 1
Incidence
of lesions
DMI
(g/da~)
Liveweight
gain (kg)
Rumen
pH
Total VFA
(mmoles/l.)
5.7
5.4
80
105
Period I
With lesions
Without lesions
371
670
With lesions
Without lesions
388
517
-6.5
-1.8
Period 2
-8.5
-1.9
6.7
5.6
At slaughter, lesions were observed on the floor of the rumen of some sheep given
the wheatlwheaten straw ration, viz. two of the five slaughtered at the end of period 1
and three of the six slaughtered after period 2. These lesions appeared as microvacuoles
in the stratum lucidum and as submucosal oedema. The animals with these lesions,
in general, lost substantially in liveweight and had lower dry matter intakes, and at
slaughter higher rumen pH values (Table 4), compared with sheep without lesions.
Experiment 2
Two sheep in group 5 died, one late in period 1 and the other early in period 2.
The two remaining animals in this group in period 2 were withdrawn from the
experiment. Both animals which died had lost substantial liveweight, and death was
diagnosed as being due to wheat poisoning. One sheep in each of groups 1 and 4
died during period 2. Both sheep had gained substantially in liveweight, and the
cause of death was not diagnosed.
Mean liveweights for all groups in both periods are shown in Fig. 1. No significant
differences were present between groups 1-4 for empty liveweight gain or carcass
gain in period 1 or for carcass gain in period 2. Differences in liveweight shown in
Fig. 1 were associated mainly with differences in the amount of digesta present in the
digestive tract.
The results of the metabolism study for period 2 are shown in Table 5. These
data indicate that formaldehyde treatment may have depressed the digestibility of the
dry and organic matter and nitrogen, particularly for ration 2 in comparison to ration 1,
although intakes for ration 1 were higher than for ration 2. The apparent nitrogen
M. L. Bigham and W. R. McManus
digestibility of ration 4 was significantly lower than that of ration 3. Nitrogen retention
was significantly (P < 0.05) lower for the formaldehyde-treated rations. During both
periods, groups 1 and 2 were consuming significantly (P < 0.05) more digestible dry
matter (DDM) than groups 3 and 4. Group 5 consumed significantly (P < 0.001) less
Fig. 1. Mean liveweight gain of lambs in
experiment 2 given pelleted ground lucerne
(group 1); pelleted ground lucerne plus
formaldehyde (group 2); 311 pelleted
cracked wheat, ground lucerne (group 3);
311 pelleted cracked wheat, ground lucerne
plus formaldehyde (group 4); whole wheat
grain plus 1 . 5 "/, ground limestone (group 5).
S indicates when animals were slaughtered.
10
S
S
S
l
l
i
l
l
l
l
0
2
4
6
8
10
12
l
14
l
16
l
i
18
20
Weeks on treatment
Table 5. Digestibility and intake data for groups 1 , 2 , 3 and 4 for period 2 of experiment 2
Ration
1
2
3
4
1219
58.4
771
1373
50.5
693
786
77.5
609
790
77.5
612
48.1
30.4
56.5
63.7
Dry matter (DM intake &/day)
DM digestibility (%)
Digestible DM intake (g/day)
Organic matter (OM)intake (g/day)
digestibility (%)
Digestible OM intake (g/day)
OM
Nitrogcn intake @/day)
Nitrogen digestibility (%)
Urinary nitrogen (g/day)
Nitrogen retained (g/day)
Urinary nitrogen (% N intake)
than the other four groups in period 1. Relevant mean values for group 5 sheep
in period 1 are : DDM intake, 300 g/day ; digestible organic matter intake, 295 g/day ;
nitrogen intake, 4.5 g/day ; nitrogen retained, 0 . 4 g/day ; dry matter digestibility,
8 1.3 "/,; organic matter digestibility, 83.6 %; nitrogen digestibility, 79.6 %.
DDM
Whole Wheat Grain Fecding of Lambs. V
Table 6 shows the rumen data collected at slaughter. Data for the animals
slaughtered at the end of each period were combined, as differences between periods
were not significantly different. Large differences were found between the three ration
types (lucerne, wheatllucerne, wheat), formaldehyde treatment having no effect.
Lesions of the type described earlier were present on the rumen wall of three of
the five sheep in group 5 slaughtered at the end of period 1. In addition, sheep in
groups 3 and 4 showed parakeratosis of the rumen wall. All sheep slaughtered in
Table 6. Mean rumen pH, concentration o f VFA and molar proportions of individual acids at slaughter
for all groups in experiment 2
Group
no.
Rumen
PH
Total VFA
(mmoles/l)
cz
Proportions of individuaI acids (%)
cS iC4 c4 iC5 c5
c6
group 3 and seven of the nine in group 4 showed parakeratosis. The degree to which
the rumen papillae were clumped together and the area of the ruinen wall covered by
clumped papillae were classified on a 1 to 10 scale. Mean scores for group 3 were
significantly (P < 0.01) higher than those for group 4. Mean scores were 7.0 and
6 . 0 for group 3 in periods 1 and 2 respectively and 3.0 and 3.3 for group 4. No
relationship was present between liveweight gain or dry matter intake and the
parakeratosis score for either group.
Discussion
Grain quality used in the two experiments differed. Lower quality (FAQ)wheat was
used in experiment 1 and group 5 of experiment 2 than in other groups of experiment 2.
The results clearly indicate that rations consisting of FAQ whole wheat grain
and limestone or whole wheat grain and wheaten straw will not allow young sheep
to fatten. The former ration was included to provide a no-roughage control and to
extend data from previous findings especially in regard to diet digestibility and empty
liveweight gain, since there are large gut-fill differences between grain-fed and
roughage-fed sheep. Results for the whole wheat grain and limestone ration agree
with results of McManus et al. (1972), Bigham et al. (1973) and Saville et al. (1973).
Sheep offered both rations had low voluntary intakes of dry matter and nitrogen.
In addition, the apparent digestibility of nitrogen in the mixed whole wheat
grainlchaffed wheaten straw ration was low, which indicated that nitrogen utilization
was low. This may have been due to a high level of microbial activity in the caecum
and lower gut, but the VFA data also indicate a low level of microbial activity in the
rumen. If caecal and lower gut microbial activity were high, owing to the presence
of readily available carbohydrate which escaped fermentation in the rumen, data of
Orskov et al. (1970) would suggest that a loss of nitrogen in the faeces would result.
The major factor responsible for the low apparent nitrogen digestibility is likely to
be the low availability of the nitrogen in the wheaten straw portion of the ration.
M. L. Bigham and W. R. McManus
From data from group 5 of experiment 2, in which 80% of the wheat nitrogen was
digested, it can be calculated that the wheaten straw nitrogen had an availibility of
less than 5 % , whereas the dry matter had an availability of about 20% and the
organic matter about 22%. This assumes that the whole wheat grain in the mixed
ration had a digestibility of 84.0% and an apparent nitrogen digestibility of 80 %.
This may not hold true, owing to interactions between the wheat and wheaten straw.
In vitro determinations of the organic matter digestibility of ground wheaten straw
similar to that used here but supplemented with minerals and urea indicate a value of
40% (Mulholland et al. 1974). Unsupplemented chopped wheaten straw also simllar
to that here used was found to have a dry matter digestibility of 42% (McManus
et al. 1972). These values contrast with the low digestibilities indicated for chaffed
wheaten straw in experiment 1. It is possible that despite the 3 week period allowed
for adaptation to wheat grain, excessive lactic acid production (as indicated by the
ruminal lesions) occurred and acted directly to depress activity and hence reduce the
extent of digestion of the straw.
It is known that levels of lactic acid in the rumen can reach high values, and rumen
pH can decline to a low level when sheep are offered diets high in readily available
carbohydrates (Phillipson 1952; Briggs et a/. 1957; Ryan 1966; Telle and Preston
1971 ; Bigharn et al. 1973). The pH data obtained at slaughter showed that the rumen
pH of sheep given wheat grain and wheat grainlwheaten straw diets was high but
very variable, but at slaughter the intakes had declined to low levels. The rumen
contents of all sheep fed on these rations were also extremely fluid, which indicated
that there was a large inflow of saliva into the rumen. The presence of lesions on the
floor of the rumen of sheep given these diets is typical of the condition termed
ruminitis which results from excessive acidity. It would appear, therefore, that at
some stage in the experiment the rumen pH of these sheep must have been very low.
Gut motility and the extent of mixing of rumen contents could also have been depressed
in these sheep, since Bruce and Huber (1973) have shown secretin-induced inhibition
of the rumen of sheep to be more complete following duodenal administration of
lactic acid. Szegedi and Juhasz (1968) have demonstrated that lactic acid added to the
rumen of sheep to depress the pH to 4.0 is associated with inhibition of rumen
motility after 2 hr.
The pelletized rations of 25 "/, ground lucerne175 % ground wheat grain promoted
generally satisfactory rates of growth (Fig. I), presumably because energy and protein
were less limiting than for diets in experiment 1 and also because excessive lactic
acidosis did not occur. This raises the question as to why a greater intake of ground
wheat grain per unit intake of a higher quality roughage should produce better
animal growth than the whole wheat grainlchaffed wheaten straw diet in experiment 1.
It would appear that the lucerne roughages, despite a greater coincident intake of a
more readily fermentable form of wheat grain, allowed of a more successful microbial
adaptation and stability of the rumen population than did the wheaten straw roughage
given with whole wheat grain. These findings point to the need for a more critical
investigation and resolution of the attributes of a roughage which render it useful in
allowing successful rumen adaptation on diets high in cereal grain.
Data from experiment 2 do not allow too strict a comparison to be made between
rations 1 and 2 and between rations 3 and 4, because of the differences in the sources
of lucerne chaff in the rations. Reasons for the lower growth rates of animals on
Whole Wheat Grain Feeding of Lambs. V
rations 3 and 4 compared with those on rations 1 and 2 are not readily apparent, but
are most probably a function of a lower retention of nitrogen, as energy did not
appear to be limiting (Weston and Hogan 1973). The elevated proportion of dietary
nitrogen appearing in the urine of lambs given rations 3 and 4 is suggestive of a
greater extent of formation of ammonia in the rumen or hindgut and its subsequent
loss via the kidneys. The data suggest that retention of dietary nitrogen is reduced
for lucernelgrain diets as compared with diets of lucerne without grain.
The finding that groups of sheep varying in nitrogen retention from values of 9.5
down to 3 . 4 g/day showed similar rates of growth warrants consideration. While
Martin (1966) has criticized the accuracy of nitrogen balance studies in that animals
waste some feed, this is not thought to operate here. Pfander (1969) suggests that
the short-term nitrogen balance technique overestimates the value of a dietary protein
in that insufficient growth occurs during the trial to allow incorporation in the tissues
or that stress associated with being in a metabolism cage may alter normal protein
deposition patterns in the body.
One could speculate as to whether animals given our diets differed in the water
content of their bodies. If so this could partially explain the seeming lack of a relationship between growth rate and nitrogen retention, presuming nitrogen retention to
reflect deposition of body protein. Osmotic shunts and differences in electrolyte
distribution within the bodies of grain-fed animals may have an effect on nitrogen
recycling processes. We have noted on occasions that grain-fed sheep may show
seemingly aberrant tritiated water space values. Certainly the problem deserves further
attention.
Part of the better response of lambs to lucerne than to the wheat grainlwheaten
straw ration in experiment 1 could arise from the difference in ash content of these
feeds. Lucerne hay had twice the ash content of the grainlstraw ration. There is
firm evidence that lucerne is a better "buffering agent' than oat or wheat hay (Turner
and Hodgetts 1955). The potassium content of wheaten straw on average is less
than half that of lucerne and approximately double that of wheat grain. Unpublished
data (Bigham and McManus; McManus and Choung) clearly demonstrate a substantial decline in the ruminal potassium content of wheat-fed lambs compared with
those on lucerne chaff, and unpublished data (Lee and McManus) show a clear-cut
response of grain-fed lambs to potassium supplementation. Further studies on the
electrolyte composition of the diet and of the rumen content in grain-fed sheep are
being conducted by us and will be reported later.
Data of experiment 2 clearly indicate no advantage of formaldehyde protection
of protein in terms of gain in carcass weight. This may have been due to overprotection of the protein, particularly in the lucerne ration (ration 21, as the nitrogen
digestibility was reduced by c. 20% in ration 2 and by 2 % in ration 4. These data
suggest, therefore, that the amount of formaldehyde used to treat feedstuffs should
be reduced if the material is to be pelleted immediately after application of the
formaldehyde.
Considerable clumping of rumen papillae occurred when the sheep were given
rations 3 and 4, although this did not appear to influence the intake or weight gain
of the animals. Garrett et al. (1961) found that the incidence of parakeratosis is
greatest when finely ground feed is made up into 8-20 mm pellets. Rations 1 , 2, 3
and 4 in the present study were all ground and pelleted, yet parakeratosis was observed
M . L. Bigham and W . R. McManus
in the rumen of sheep fed on rations 3 and 4 only, which suggests that fine grinding
plus the presence of cereal grain contributes towards the condition. In addition, the
greatest incidence of parakeratosis was observed in sheep on ration 3, the ration not
treated with formaldehyde.
These data suggest that the presence of formaldehyde reduced the incidence of
parakeratosis. This indication warrants further investigation, as it may have
significant commercial application if verified.
Acknowledgments
The generous provision of wheat grain by the Australian Wheat Board, of funds to
mpport the analytical programs by the Australian Wool Corporation, and of chemicals
by Silform Chemical Pty Ltd is gratefully acknowledged. One of us (M.L.B.) was in
receipt of a University Postgraduate Scholarship while on Ieave from the New Zealand
Ministry of Agriculture and Fisheries. We are especially grateful to Dr K. A. Ferguson
of the Division of Animal Physiology, CSIRO, Prospect, N.S.W., for preparing and
donating the feeds used in experiment 2. The technical assistance of Mr G. B. Edwards
is acknowledged.
References
Balch, C. C., and Rowland, S . J . (1957). Br. J. Nufr. 11, 288.
Bigham, M . L., McManus, W . R., and Edwards, G . B. (1973). Aust. J. Agric. Res. 24, 425.
Briggs, P. K., Franklin, M . C., and McClymont, G. L. (1957). Aust. J. Agric. Res. 8, 75.
Bruce, L. A., and Hubcr, T . L. (1973). J. Anim. Sci. 37, 164.
Edwards, G. B., McManus, W . R . , and Righam, M . L. (1971). J. Chromatogr. 63, 397.
Ferguson, K. A,, H e m s k y , J . A., and Reis, P. J . (1967). Aust. J. Sci. 30, 215.
Garrctt, W . J., Meyers, J. H., Lofgreen, G. D., and Dobie, J. A. (1961). J. Anim. Sci. 20, 833.
Lawlor, M . J., Giesecke, D., and Walser-Karst, K . (1966). Br. J. Nutr. 20, 373.
McManus, W. R., Bigham, M. L., and Edwards, G . B. (1972). Aust. J. Agric. Rex. 23, 331.
McManus, W. R., Manta, L., McFarlanc, J. D., and Gray, A. C. (1972). J. Agric. Sci. 79, 55.
Martin, A. K. (1966). BY. J. Nutr. 20, 325.
Mulholland, J. G., C o o m b e , J. B., and McManus, W . R. (1974). Aust. J. Exp. Agric. Anim. Husb.
14, 449.
Orskov, E. R., Fraser, C., Mason, V . C., and Mann, S. 0. (1970). Br. J. Nutr. 24, 671.
Pfander, W. H . (1969). Protein Requirements. In 'Animal G r o w t h and Nutrition', ed. E. S. E.
Hafez and I . A. Dyer. (Lea & Febiger: Philadelphia.)
Phillipson, A. J. (1952). Br. J. Nutr. 6, 190.
Reid, R. L., Hogan, J . P., and Briggs, P. K. (1957). Ausf. J. Agric. Res. 8, 691.
Ryan, R . K. (1966). Am. J. Vet. Res. 25, 647.
Saville, D. G., Davis, C . H., Willats, H . G., and McInnes, P. (1973). Aust. J. Exp. Agric. Anim.
Husb. 13, 22.
Szegedi, B., and Juhasz, B. (1968). Acfa Vet. Acad. Sci. Hung. 18, 63.
Telle, P. P., and Preston, R. L . (1971). J. Anim. Sci. 33, 698.
Turner, A. W . , and Hodgetts, V . E. (1955). Aust. J. Agric. Res. 6, 125.
W e s t o n , R . J., and Hogan, J. P. (1973). Nutrition o f herbage-fed ruminants. In ' T h e Pastoral
Industries o f Australia', ed. G . Alexander and 0. B. Williams, Chap. 8. (Sydney U n i v . Press.)
Manuscript received 20 November 1973