Effect of Nitrate on Variability of Methane Production in Sheep Fed Every 2 Hours

Abstract

Rumen microbes ferment feed organic matter to obtain energy for microbial growth and generate endproducts including volatile fatty acids, H₂ and CO₂. H₂ and electrons from NADH are used by Archaea to reduce CO₂ to CH₄. Therefore, methane represents a loss of digestible energy as well being a potent greenhouse gas and the search for practical methods to reduce CH₄ release is a current priority. Nitrate salts inhibit methanogenesis (Allison et al 1981) and Leng (2008) has concluded that the inclusion of nitrate salts in feed supplements offers a feasible means of reducing CH₄ emissions from ruminant livestock. The study reported here was undertaken to provide a better understanding of the effect of NO₃⁻ on the rate of and variability in CH₄ production in the rumen of sheep. Twelve sheep were slowly acclimated over 2 weeks to a diet of chaffed oaten hay (1 kg/d as fed) containing no KNO₃ (n=4), or 2% (n=4) or 4% KNO₃ (n=4). CH₄ production was then measured over a 22h period while the sheep were in respiration chambers (Bird et al. 2008) and given 1/12th of their daily ration every 2h. Concentrations of CH₄ in each chamber were recorded automatically at regular (c. 14 min) intervals. These concentrations were subjected to serial correlation and spectral analysis to determine if rhythmic variations CH₄ production could be detected. Figure 1 shows the serial correlation coefficients for the mean CH₄ concentrations in the chambers for 4 sheep receiving the control diet or the same diet with 4% added KNO₃⁻. ... There are strong rhythmical cycles of 2h duration in the original signal for both control and nitrate supplemented sheep. Mean CH₄ concentration was 27.5% lower for sheep offered the diet containing 4% KNO₃⁻ (207± 1.6 vs 150 ± 2.4 ppm). This result is similar to that found by Mathers and Walters (1982) in sheep offered feed every 2h. As well as reducing ruminal CH₄ production, the addition of NO₃⁻ to the diet altered the patterns of chamber CH₄ concentrations relative to those for the control diet. Even with addition of NO₃⁻ to the diet to reduce CH₄ production and frequent feeding, there was considerable deviation from steady state in the rate of fermentation in the rumen. Further analysis of this type of data will help improve our understanding of the rumen fermentation mechanisms leading to variations in CH₄ production.