T . Yan et al. Livestock Production Science 64 2000 253 –263
259
0.75
weight basis kg . All the above mentioned
also been some studies which showed no reduction methods, where appropriate, were examined. There
in methane production with increment of dietary were no improvements in the levels of significance
forage levels, e.g. Beever et al. 1988 in beef cattle
2
or the R values of the equations. Therefore the
offered grass silage diets. effects of live weight of the cattle were not presented
In the present study, CH -E GEI and CH -E DEI
4 4
in the current paper. Holter and Young 1992 also were both related to S
T , T
T or
DMI DMI
ADFI DMI
reported no significant effect of live weight of S
T . These relationships were all highly
ADFI ADFI
2
lactating or dry dairy cows on CH -E in any of their significant with the R values ranging from 0.402 to
4
six experiments. 0.463. This analysis indicated that an increase of
0.10 in S T
, T T
or S T
DMI DMI
ADFI DMI
ADFI ADFI
would increase
CH -E GEI by
proportionately
4
0.0025, 0.0069 or 0.0048; or CH -E DEI by 0.0035,
4
4. Discussion
0.0107 or 0.0067. A similar technique was also applied to a data set of 89 treatment means obtained
The existing equations for predicting methane in 27 dairy cow experiments published since 1969
production in cattle were developed from data in excluding those carried out at this Institute. In these
animals offered diets containing mainly dried for- studies a range of forages was used and the data on
ages. The present data set with grass silage-based feed composition, live weights of cows and milk
diets is therefore relatively unique, and important to production were also available. The relationships
the industry where accurate prediction of CH -E and
4
obtained with this set of data produced similar results hence ME intake are required.
to those derived from the present study. CH -E DEI
4
was, respectively
increased by
proportionately 4.1. Effect of forage proportion in the diet
0.0049, 0.0150 or 0.0086 with an increase of 0.10 of S
T , T
T or S
T . These rela-
DMI DMI
ADFI DMI
ADFI ADFI
Methane output in the rumen of animals is associ- tionships were all significant P ,0.001, although
2
ated with production of acetic acid, and in general the R values were not high 0.209, 0.217 or 0.164.
fermentation of high forage diets can result in a There are some review papers in the literature
higher molar proportion of acetic acid than those which also indicate the positive relationship between
obtained with high concentrate diets Ørskov and CH -E and forage proportion in diet. For example,
4
Ryle, 1990. There are many studies in the literature Johnson et al. 1991 reported that CH -E in beef
4
showing a positive relationship between CH -E and cattle offered high concentrate diets always ac-
4
dietary forage proportion. For example, Kirkpatrick counted for a low proportion of GEI 0.044. They
et al. 1997 reported a significantly higher CH -E even noted a very low rate of CH -E GEI 0.02 in
4 4
GEI with beef cattle offered diets with a high rather several cases when diets contained 0.90 of concen-
than a low proportion of grass silages at both low trates. Moe and Tyrrell 1979 related CH -E to total
4
0.080 vs. 0.053 and high 0.078 vs. 0.053 feeding intakes of digestible nutrients of soluble residue,
levels. Ferris et al. 1999 noted a linear reduction in hemicellulose and cellulose. The coefficients for the
CH -E GEI from 0.071 to 0.062 when the concen- last two variables were found to be, respectively,
4
trate proportion was increased from 0.37 to 0.70 in 1.875 and 5.103 times of the former variable,
lactating dairy cows offered grass silage-based diets. indicating a higher rate of CH -E produced from
4
A similar linear decrease in CH -E GEI 0.054, fibre than starch. Holter and Young 1992 also
4
0.044 and 0.038 was also reported by Flatt et al. found that CH -E was positively related to forage
4
1969 in lactating dairy cows when dietary forage proportion in diet, hence in their prediction equation
alfalfa concentrations were reduced from 0.60, 0.40 dietary ADF concentration was used as a predictor.
to 0.20. Also when maize silage was used, Tyrrell However, there are other prediction equations in
and Moe 1972 observed a reduction of propor- which the effect of forage proportion in diet was not
tionately 0.25 in CH -E GEI with dietary concen- included. These include equations by Kriss 1930,
4
trate of 0.59 rather than 0.31. However, there have Bratzler and Forbes 1940, Axelsson 1949 and
260 T
. Yan et al. Livestock Production Science 64 2000 253 –263
2
Blaxter and Clapperton 1965. It is thus expected 0.0021 in CH -E GEI or CH -E DEI R 50.336
4 4
that the use of the earlier group of equations in or 0.373; P ,0.001 as feed intake increased one
general would under-predict CH -E for diets with level above maintenance, when using ME
calcu-
4 m
high proportions of forage, but over-predict for diets lated from Agricultural and Food Research Council
with high proportions of concentrates. 1990.
However, the prediction equations mentioned pre- 4.2. Effect of feeding level
viously, except the one of Blaxter and Clapperton 1965, did not consider the effect of feeding level
An increase in feeding level can increase the on CH -E. Therefore, use of those equations which
4
outflow rate of digesta in the rumen and leave less did not take account of the effect of feeding level in
time available for microbial fermentation of the diet. general would under-predict CH -E for cattle at low
4
The consequence is a reduction of nutrient de- planes of nutrition, while over-predict at high levels
gradability in the rumen as well as methane pro- of feeding.
duction. Moe and Tyrrell 1979 reported that in- creasing feeding level changed production rates of
4.3. Validation of the present Eqs. 11 and 12 CH -E from digestible soluble residues and digest-
4
ible cellulose in diets of dairy cows. In a review of Eqs. 11 and 12 as recommended in the present
studies in the literature with beef cattle, Johnson et study have been validated using published studies for
al. 1991 reported that under most circumstances cattle offered grass silage-based diets excluding
increasing intake by one multiple of maintenance studies carried out at this Institute. These studies
would reduce CH -E by proportionately 0.018 of included
five lactating
dairy cow
experiments
4
GEI. Blaxter and Clapperton 1965 reported a Beever et al., 1989, 1991; Sutton et al., 1991, 1998;
reduction in CH -E GEI by b where b 50.050 DE Unsworth et al., 1994 and one beef trial Beever et
4
GE20.0237 with increment of one feeding level al., 1988. A total of 36 treatments were presented in
obtained in the combined data of sheep and beef these studies and the treatment mean data have been
cattle given mostly non-grass silage diets, where used for the present validation. In these studies the
DE GE was measured at maintenance. This equation animals had a mean live weight of 526 kg, DE intake
indicated that the effect of feeding level on CH -E of 202.7 MJ day, CH -E of 19.5 MJ day and FL of
4 4
decreased as dietary energy digestibility at mainte- 3.25 estimated from the Agricultural and Food
nance reduced. Research Council, 1990. S
T , T
T
DMI DMI
ADFI DMI
In the present study the effect feeding level on and S
T were averaged to be 0.541, 0.212
ADFI ADFI
CH -E was obtained by, respectively relating CH - and 0.846, respectively. The validation indicated a
4 4
E GEI and CH -E DEI to feeding level. These two significant relationship P ,0.001 between the actu-
4
relationships were highly significant with CH -E al x and predicted y CH -E for both Eqs. 11 and
4 4
GEI or CH -E DEI equations nos. 3 or 7 in 12 y 50.915 S.E. 0.0093x for Eq. 11 Fig. 1;
4 2
Table 3 being reduced by proportionately 0.0078 or y 50.914 S.E. 0.0113x for Eq. 12. The R value
0.0123 as feed intake was increased by one level of for these two linear relationships were, respectively
feeding above maintenance. The S.E. values for the 0.925 and 0.882 when the constant was omitted. The
coefficient of feeding level were all relatively small mean predicted CH -E for Eqs. 11 or 12 did not
4
in equations nos. 3 and 7 in Table 3 and Eqs. significantly differ from the actual data 18.1 or 17.9
11 and 12 of the present study and the effect of vs. 19.5, S.E. 0.81 when using the paired t-test,
feeding level on CH -E was thus highly significant although the difference was 1.4 or 1.6 MJ day. The
4
P ,0.001 in each of these four equations. A similar marginally lower prediction obtained using the pres-
technique was also applied to the data set of 89 ent Eq. 11 was mainly derived from the study of
treatment means obtained in 27 dairy cow studies as Unsworth et al. 1994 seven treatments. This study
outlined earlier. The regression equation indicated a had a high CH -E, for example CH -E GEI was
4 4
reduction of 0.0062 S.E. 0.0016 or 0.0119 S.E. 0.080, which was proportionately 0.127 higher than
T . Yan et al. Livestock Production Science 64 2000 253 –263
261
Fig. 1. Actual methane energy output against predicted methane energy output using present Eq. 11 on the published data of lactating cows and beef steers offered grass silage-based diets.
the mean value of remaining 27 treatments. Since Acknowledgements
Eq. 11 gave a more accurate prediction than Eq. 12, the former equation should be used if ADF
The authors wish to thank their colleagues at the concentrations in both silage and concentrate are
Agricultural Research Institute of Northern Ireland measured.
for access to the calorimetric data used in the present study.
5. Conclusion References
