The potential of feeding patterns to assess generic welfare in growing-finishing pigs

Abstract

The welfare of growing-finishing pigs is important inherently to the pigs, but also for the societal acceptance and environmental impact of the husbandry system. Nevertheless, methods to monitor pig welfare throughout the whole growing-finishing phase have not yet been successfully developed. One possibility is to use electronic feeding stations to identify the feeding pattern of individual pigs, which consists of feed intake and the behaviours underlying intake (i.e. feeding frequency, duration and rate), and to process this data using an algorithm that links feeding patterns to pig welfare. Before such a monitoring system can be developed, a thorough understanding of both pig feeding patterns and their relationships with pig welfare is required. The aim of this review was to assess the current state of this understanding. We begin with a narrative review that describes the feeding patterns of growing-finishing pigs, and subsequently provide a systematic review of the relationships between pig feeding patterns and welfare. We focused on animal-based parameters of pig welfare, but also included resource-based parameters known to influence welfare (e.g. space allowance, environmental enrichment). We found that so far, studies have focused on physiological and behavioural welfare problems, while the affective part of welfare, both positive and negative, has been largely overlooked. Deviations from basal feeding patterns may occur during reduced welfare states, sometimes even preceding other clinical or behavioural manifestations of the problem. Particularly clear are the links between feed intake and physiological causes of reduced welfare, such as clinical health, thermal stress and tail biting wounds. The behaviours underlying intake provide further information, as they show distinct deviations in response to different physiological welfare problems and as their rapid responses may enable detection of disease at a subclinical stage. However, a wider range of clinical diseases should be studied before this knowledge can be applied. Behavioural welfare problems, such as abnormal behaviours and feed competition, mostly induce deviations in the feeding behaviours underlying intake but not intake itself, though more knowledge is required to confirm this finding. We conclude that feeding patterns are a promising tool to monitor generic pig welfare. Feed intake and the behaviours that underlie it should be used simultaneously, on a short time scale (i.e. within the day). It should be considered that the variation in feeding patterns between and potentially within pigs is large, and that this variation should be well-understood before welfare-relevant variation can be interpreted.