New Zealand Journal of Agricultural Research abstracts
Seasonal variation in methane emission from dairy cows and breeding ewes
grazing ryegrass/white clover pasture 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, New Zealand.
2National Institute of Water and Atmospheric
Research Limited
P.O. Box 14 901
Wellington, New Zealand
Abstract Daily methane emission from 12 Romney-cross-bred
ewes and 10 lactating Friesian dairy cows, rotationally grazed on perennial
ryegrass/white clover dominant pastures, was measured during four seasons
of a year (September, November, March, and June/July). Methane emission was
measured from each animal for 5 consecutive days in each measurement period
using the sulphur hexafluoride tracer gas technique. The pastures varied
significantly in chemical composition between seasons, generally decreasing
in protein, soluble sugars, and digestibility and increasing in acid detergent
fibre (ADF) and neutral detergent fibre (NDF) as the grasses flowered in
November, with an increase in protein and a decrease in soluble sugars in
March, a trend that continued through to June/July. Methane emission (g/day)
from dairy cows was significantly different (P < 0.001) between seasons,
being high at peak lactation in September (430.6) and declining with milk
yield and feed intake in November (247.6) and March (181.5) and maintaining
its level in June (137.4) when the cows were not lactating. Methane emission
expressed per unit of feed intake was significantly higher in September and
June than in November and March, suggesting some inhibition in the latter
2 months. There was less seasonal variation in methane emission (g/day) from
the breeding ewes: March (27.0) and July (27.9) were significantly lower
(P < 0.05) than in November (33.2), but neither differed from September
(30.6). July was significantly lower (P < 0.001) than the other periods
in methane emission per unit of feed intake, presumably because of its higher
feed intake. It is suggested that for inventory purposes a methane emission
factor of 26 g/kg digestible dry matter intake (DDMI) would be suitable for
sheep and dairy cows grazing fresh temperate pasture.
Keywords methane emission; ewes; dairy cows; grazing
pasture; seasonal effects
A02021 Received 28 March 2002; accepted 12 September 2002; published
9 December 2002
New Zealand Journal of Agricultural Research, 2002, Vol. 45: 217-226
0028-8233/02/4504-0217 $7.00/0 © The Royal Society of New Zealand
2002
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