Methane Emissions from Grazing Holstein-Friesian Heifers at Different Ages Estimated Using the Sulfur Hexafluoride Tracer Technique
Date
2017-05-17
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Although the effect of animal and diet factors on enteric methane (CH4) emissions from confined cattle has
been extensively examined, less data is available regarding CH4 emissions from grazing young cattle. A study
was undertaken to evaluate the effect of the physiological state of Holstein-Friesian heifers on their enteric
CH4 emissions while grazing a perennial ryegrass sward. Two experiments were conducted: Experiment 1
ran from May 2011 for 11 weeks and Experiment 2 ran from August 2011 for 10 weeks. In each experiment,
Holstein-Friesian heifers were divided into three treatment groups (12 animals/group) consisting of calves,
yearling heifers, and in-calf heifers (average ages: 8.5, 14.5, and 20.5 months, respectively). Methane emissions were estimated for each animal in the final week of each experiment using the sulfur hexafluoride
tracer technique. Dry matter (DM) intake was estimated using the calculated metabolizable energy (ME)
requirement divided by the ME concentration in the grazed grass. As expected, live weight increased with
increasing animal age (P < 0.001); however, there was no difference in live weight gain among the three
groups in Experiment 1, although in Experiment 2, this variable decreased with increasing animal age
(P < 0.001). In Experiment 1, yearling heifers had the highest CH4 emissions (g·d–1) and in-calf heifers produced more than calves (P < 0.001). When expressed as CH4 emissions per unit of live weight, DM intake,
and gross energy (GE) intake, yearling heifers had higher emission rates than calves and in-calf heifers
(P < 0.001). However, the effects on CH4 emissions were different in Experiment 2, in which CH4 emissions
(g·d–1) increased linearly with increasing animal age (P < 0.001), although the difference between yearling
and in-calf heifers was not significant. The CH4/live weight ratio was lower in in-calf heifers than in the other two groups (P < 0.001), while CH4 energy output as a proportion of GE intake was lower in calves than in
yearling and in-calf heifers (P < 0.05). All data were then pooled and used to develop prediction equations for
CH4 emissions. All relationships are significant (P < 0.001), with R2
values ranging from 0.630 to 0.682. These
models indicate that CH4 emissions could be increased by 0.252 g·d–1 with an increase of 1 kg live weight
or by 14.9 g·d–1 with an increase of 1 kg·d–1 of DM intake; or, the CH4 energy output could be increased by
0.046 MJ·d–1 with an increase of 1 MJ·d–1 of GE intake. These results provide an alternative approach for estimating CH4 emissions from grazing dairy heifers when actual CH4 emission data are not available
Description
Publication history: Accepted - 9 May 2017; Published online - 17 May 2017
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Article
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Keywords
Methane emission, Grazing dairy heifer, Prediction, Sulfur hexafluoride tracer technique
Citation
Morrison, S. J., McBride, J., Gordon, A. W., Wylie, A. R. G. and Yan, T. (2017) ‘Methane Emissions from Grazing Holstein-Friesian Heifers at Different Ages Estimated Using the Sulfur Hexafluoride Tracer Technique’, Engineering, 3(5), pp. 753–759. doi: 10.1016/j.eng.2017.03.018.