Is early life programming a promising strategy for methane mitigation and sustainable intensification in ruminants?

Sustainable animal production requires lowering emissions and adapting to climate change. Numerous nutritional and management interventions that enhance adult ruminants' efficiency and resilience produce only temporary results, reducing the sustainability of the programs. This is because only short-lived changes in the host and rumen microbiome occur, which revert to the original levels when the intervention ceases. Early life programming (ELP) is a promising approach to increase sustainable livestock production, enhance efficiency and reduce greenhouse gas emissions. Early influences using ELP have profound and enduring effects on molecular pathways, physiological adaptations, and long-term phenotypic consequences later in life. These effects occur from the embryonic stage to birth (foetal programming, FP), birth to weaning, and beyond. The underlying mechanisms of ELP include the sequential development of the rumen and microbial colonisation in the rumen, orchestrated through molecular changes, including transcriptomic and epigenetic modifications. This review highlights the key mechanisms behind ELP and explores strategies across different production systems that can improve livestock performance while helping to achieve net-zero emissions. Management strategies like step-down weaning, dietary modifications including increasing solid feed and high-fibre diets and adding anti-methanogenic agents and other feed additives to target the desired rumen microbial community, such as propionate-producing Prevotella, Sharpea, Coprococcus and Megasphaera, are promising strategies for implementing ELP. Creating alternate hydrogen sinks through ELP by favouring metabolic pathways that enhance propionate production can also be targeted. Furthermore, recent innovative strategies, such as using methanotroph-methylotroph consortium as probiotics and oxidising feed additives, are worth researching for ELP.