New Zealand Journal of Agricultural Research abstracts
Methane emission from dairy cows and wether sheep fed subtropical grass-dominant
pastures in midsummer in New Zealand
M. J. Ulyatt1*
K. R. Lassey2
I. D. Shelton1
C. F. Walker2
1AgResearch Limited
Private Bag 11 008
Palmerston North, New Zealand
*Present address: 181 Omokoroa Road, RD2, Tauranga.
2National Institute of Water and Atmospheric
Research Limited
P.O. Box 14 901
Wellington, New Zealand
Abstract Methane emission was measured from 10 dairy
cows and 12 wether sheep grazing kikuyu grass- (Pennisetum clandestinum)
dominant pastures at Waimate North, Northland, in February 1997 and March
1999, and from 10 dairy cows grazing summer grass- (Digitaria sanguinalis)
dominant pasture at Edgecumbe, Bay of Plenty, in March 2000. Methane emission
was measured from each animal for 5 consecutive days in each measurement
period using the sulphur hexafluoride (SF6) tracer gas technique.
Analysis of variance of the kikuyu grass chemical composition with sheep
and cow data combined showed that the 1999 pastures were significantly higher
in protein (P < 0.01), soluble sugars (P < 0.001), lipid (P < 0.01),
and dry matter (DM) digestibility (P < 0.001) and lower in ash (P = 0.023),
acid detergent fibre (ADF) (P < 0.001), and neutral detergent fibre (NDF)
(P < 0.001) than the 1997 pastures, presumably as a consequence of urea
topdressing in 1999. The chemical composition of the summer grass-dominant
pasture grazed by cows in 2000 was similar to the kikuyu grass, except that
DM digestibility was higher. Daily methane emissions from kikuyu grass were
363 and 167 g/day for the cows and 15.6 and 4.4 g/day for the sheep in 1997
and 1999, respectively. These corresponded to methane yields (MYs, methane
energy as a percentage of gross energy) of 7.1 and 3.8% for the cows and
6.3 and 1.9% for the sheep in 1997 and 1999, respectively. There was clearly
a significant inhibition (P < 0.001) of methane production in 1999 in
both species fed kikuyu grass. Methane emission was 422 g/day and MY 6.7%
in the cows fed summer grass, values that were similar to the kikuyu-fed
cows in 1997. Methane emitted in g/kg digestible DM intake was 33.8 and 38.2
for the 1997 kikuyu grass-fed cows and sheep and 33.3 for the summer grass-fed
cows. This suggests that methane emitted per unit of digested DM is higher
for ruminants fed subtropical (C4) grasses than those fed temperate (C3)
grasses and we believe it to be related to the higher cell wall content of
C4 grasses.
Keywords methane emission; subtropical pastures; grazing;
dairy cows; sheep
A02022 Received 28 March 2002; accepted 12 September 2002; published
9 December 2002
New Zealand Journal of Agricultural Research, 2002, Vol. 45: 227-234
0028-8233/02/4504-0227 $7.00/0 © The Royal Society of New Zealand
2002
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