Review: An ethological approach for enriching ruminants' feeding environment

In ruminant livestock production systems, feeding strategies primarily aim to maximise animal performance while minimising costs. This often leads to the widespread use of monotonous, nutritionally optimised diets. However, this approach tends to overlook how ruminants perceive and interact with their feed, and how feeding behaviour may contribute to their welfare. This review first proposes an ethological approach to analyse feeding behaviour in ruminants, integrating Tinbergen's four questions (i.e. causation, ontogeny, function and phylogeny). Feeding is a complex behavioural process, and ruminants exhibit decision-making related to whether/when, what, and how much to eat. These decisions are shaped by internal stimuli - such as homeostasis and satiety - and external sensory stimuli from the feeds. Preferences (hedonic values), motivations and learned experiences shape the way animals respond to these stimuli, which are, in return, integrated, associated, and memorised to guide future feeding decisions. Food learning is a dynamic, lifelong process that begins in utero and enables ruminants to adapt to changing feeding environments. From an evolutionary perspective, ruminants have adapted to select diverse diets in complex, variable environments. However, domestic ruminants are often confronted with monotonous feeding environments, limited in diversity and variety, while they exhibit responses that indicate their sensitivity to this. In animal welfare sciences, enrichment is framed as the facilitation of adequate stimulations and motivated behaviours that elicit positive emotions. Therefore, environmental enrichment through diverse and varied feeds is currently emerging in the literature as a promising way to improve ruminant welfare at physical and mental levels. Drawing on Tinbergen's four questions, the review examines dietary diversity, in both space and time, as an environmental enrichment strategy for ruminants, highlighting its potential multifaceted benefits. These include i/ enabling each individual to exert control over its choices that make them to meet its own preferences and needs, ii/ providing stimulation through hedonism and boredom avoidance, and iii/ fostering knowledge acquisition alongside enhanced cognitive and coping abilities. This review invites a shift from viewing feeding solely as a means of nourishment to recognising it as a valuable opportunity to encourage motivated behaviours and positive emotions, and ultimately, improve animal welfare.