Links between ruminants' food preference and their welfare.

Nutrition is an important aspect of welfare, and in most recommendations for the welfare of animals adequate nutrition is a primary requirement. However, in intensive livestock production systems the decision for adequate nutrition is made based on traditional paradigms of feeding monotonous rations or plant monocultures, frequently with excesses or imbalances of nutrients relative to the individuals' physiology, which can compromise welfare. Individual ruminants can better meet their needs for nutrients and regulate their intake of secondary compounds when offered a variety of foods than when constrained to a single food, even if the food is nutritionally balanced. The concept of food variety is central because monotonous flavors and feeds and excess nutrients all cause animals to satiate, which in turn causes animals to eat a variety of foods. When offered a variety of foods, satiety for single foods stimulates the selection of a diverse diet and thus food intake, but when restricted to a monotonous diet satiety is aversive and limits food intake. Moreover, if a monotonous diet is aversive to animals then this could be stressful, even if monotony implies consuming a balanced diet. A diverse diet may also increase resistance to disease in ruminants, by allowing consumption of small amounts of compounds with antimicrobial/antiparasitic effects and immunity-enhancing properties. Herbivores also experience the benefits of ingesting compounds with medicinal (i.e. antiparasitic) benefits and they learn to prefer foods containing such compounds as their preferences are associatively conditioned by the food's homeostatic utility to the body. Such learned patterns of behavior begin in utero and feeding experiences early in life cause changes - neurological, morphological and physiological - in animals, which influence on their subsequent behavior and welfare. Such experiences with the environment enable animals to adapt to local diets and stressors and reduce the levels of fear. Finally, feeding behavior in farm animals could be an aid in the early detection and mitigation of pain or sickness, and as such become an important tool in the identification of welfare and health of animals before the appearance of clinical signs. Management strategies in ruminant production systems could benefit by allowing animals to manifest their feeding preferences, thereby acknowledging the animals' role as active players in feeding systems, instead of regarding them as passive entities that just respond to prescriptions and formulations.