Research Partner: Aberystwyth University
Project Duration: October 2010 – September 2013
PhD Student: Sophie Doran
Methane production by ruminants is a significant contributor to agricultural greenhouse gas emissions (Webb et al., 2013). However, current values used to estimate methane output by sheep are default values and do not take into account animal and dietary factors that may affect methane output (Bernstein et al., 2007). Strategies to reduce ruminant methane output are the focus of a large body of research (Iqbal et al., 2008) and, in order to implement these strategies fully, a greater understanding of factors that influence ruminant methane emissions is necessary.
The “gold standard” method for measuring methane output by sheep is the use of respiratory chambers (Blaxter and Clapperton, 1965). However, this method is expensive, time-consuming and labour intensive, making it unsuitable for use in an on-farm situation. The work presented in this thesis explores the potential of three proxies to estimate methane output by sheep, which could be used or adapted to be used as a practical means of estimating methane emissions from sheep on a large scale.
The proxies investigated here are a Laser Methane Detector (LMD), used to take measurements of methane concentration from air expired by sheep, in vitro gas production analysis of feeds offered to sheep, and Fourier-transform infrared spectroscopy (FTIR) analysis of feeds offered to sheep. Predictions of methane output obtained from each of the proxies are validated using respiratory chamber measurements taken from sheep offered a variety of feeds during different experiments.
With further development and validation, all three proxies presented in this thesis demonstrate potential to be used to successfully estimate or predict methane output by sheep as measured in respiratory chambers. A novel and very successful approach to the method for use of the LMD and calculation of daily methane emissions from LMD data is presented in this thesis. However, the methods used were relatively labour intensive and time-consuming. Further work should, therefore, focus on simplifying these methods as much as possible. To my knowledge, the results presented for in vitro gas production and FTIR spectroscopy are also novel, although these are established methods. Both of these methods are rapid-throughput techniques and, therefore, have real potential to be used on a large scale. Further work using larger data sets may provide a more comprehensive idea of the aspects of feeds that affect their methane potentials.