Concerns over adverse effects from methane inhibitors

IN recent years, animal nutrition has assumed a central role in promoting safer and more sustainable food production within a One Health framework. Through targeted nutritional strategies, antibiotic use in veterinary medicine can be reduced, limiting antimicrobial resistance through microbiota modulation by functional feeds. At the same time, animal nutrition is no longer aimed solely at meeting the productive and physiological requirements of livestock, but also at mitigating the farming environmental footprint. In particular, efforts have focused on reducing greenhouse gas emissions, especially methane (CH4) from ruminants. In this context, 3-nitrooxypropanol (3-NOP) (Bovaer, DSM-Firmenich), an ‘environmental inhibitor’ has been authorised for use in animal feeding and has been shown to reduce CH4 by approximately 30 per cent through inhibition of ruminal methanogenesis by obligate anaerobic archaea.1 The use of environmental additives is incentivised under the EU Common Agricultural Policy and supports front-of-pack environmental labelling schemes recognisable to consumers. However, postmarketing concerns have recently emerged regarding potential adverse effects of 3-NOP on animal welfare and performance. Despite long-standing authorisation, dairy farmers in several countries have reported reduced intakes and milk yield, and lethargy, prompting precautionary and temporary suspensions of the product in some EU member states. A plausible hypothesis is that inhibition of methanogenesis leads to excess ruminal hydrogen being redirected towards hydrogen sulfide (H2S) production, particularly in the presence of elevated sulfur levels. These may originate from certain circular-feed ingredients (eg, gluten feed, distillers, beet pulp), drinking water and mineral supplements aimed at supporting microbial synthesis of sulfur-containing amino acids such as methionine and cysteine.2 Notably, recent sustainability-oriented recommendations by the European Feed Manufacturers' Federation favouring feed materials with higher sulfur content,3 may have inadvertently increased this risk through interactions between feed substrates, rumen microbiota and environmental inhibitors. The reported clinical signs are consistent with chronic H2S toxicity, with ruminants potentially acting as sensitive ‘sentinel’ species due to both ruminal absorption and inhalation of eructated gas in indoor housing systems. These considerations highlight the need for veterinary postmarketing surveillance of environmental feed additives, especially in light of rapidly evolving feeding strategies. Unlike the USA, where 3-NOP is regulated as a veterinary medicinal product and subject to pharmacovigilance under the Food and Drug Administration, such monitoring does not occur under EU legislation for feed additives.4 Finally, chronic occupational exposure of farm operators and vets to low airborne H2S concentrations in intensive livestock facilities represents an additional One Health concern.5 Addressing these interconnected risks reinforces the pivotal role of the veterinary profession in safeguarding environmental sustainability, animal welfare and human health simultaneously.