Reduced enteric methane emissions alters carbon isotope ratio of animal-derived products

Numerous strategies to reduce methane emission from ruminant livestock are being developed, but evaluating their effectiveness is limited by the lack of widely available methods to quantify emissions. Here, we explore stable carbon isotope ratios of animal-derived products as a potential biomarker for inferring changes in enteric methane emission. Methanogenesis in the rumen preferentially uses the light isotope of carbon, ¹² C, concentrating the heavy isotope, ¹³ C, in the animal. It is hypothesised that reducing methane production changes the carbon isotope ratios (d ¹³ C) of the animal-derived products relative to diet. To test this hypothesis, a randomised controlled feeding trial was conducted on sheep with variable levels of methane suppression. The trial involved a baseline period (no suppression) and an experimental period with four treatment groups with different levels of supplementation with the methane inhibitor 3-NOP (Bovaer®). Methane yields measured in respiration chambers decreased by 22.2%, 33.5% and 52.9% for low, mid and high doses, respectively. Biomatter (i.e. wool, blood plasma, and rumen fluid) d ¹³ C values were compared to diet to establish the biomatter-diet d ¹³ C offset (D _biomatter ). The D _biomatter values differed significantly for the 3-NOP treatment groups versus control groups for wool and plasma, providing support for this novel biomarker approach.