Understanding the feeding strategies of growing-finishing pigs: Exploring links with pig characteristics and behaviour

A large variation in feeding patterns between pigs and over time hampers the use of data from electronic feeding stations in the continuous monitoring of growing-finishing pig welfare. Individual feeding strategies (i.e. differences between pigs that are consistent within a pig across time) likely explain part of this variation, both at the daily level - based on feeding components intake, frequency and rate - and at the diurnal level - based on feeding components circadian rhythms and night feeding. It is, however, not known exactly which feeding strategies pigs display, nor which types of pigs display which strategies. This study aimed 1) to test which (combinations of) feeding components contribute to independent feeding strategies; and 2) to see whether pigs with different feeding strategies also differ in other physical and behavioural characteristics. To identify feeding strategies, we calculated the intra-class correlation coefficient (ICC) for each day-level feeding component, which reflects the proportion of variation explained by an individual pig effect (n=98 pigs). Subsequently, high ICC day-level components were correlated to diurnal-level components known to contain feeding strategies, to assess possible overlap. Pigs with different strategies were then characterised based on physical (n=52) and behavioural (home pen and play tests, n=22-27) variables at different ages, using (generalised) linear mixed models. Four dimensions of individual feeding strategies emerged: nibbling/meal eating, fast/slow eating, day/day-night eating and consistent/inconsistent eating from day to day, sustaining after correction for pig sex or body weight. All dimensions except day/day-night eating partially overlapped at the beginning of the growing-finishing phase, but became more distinct over time. Pigs with different feeding strategies also differed in their general activity, diurnal activity and possibly dominance rank. Feeding strategies did not relate to behaviours possibly indicative of more positive or negative emotional states of pigs. Our results demonstrate that pigs showed individual differences in their feeding behaviour that are consistent across time, along continua in four distinct dimensions. These differences went beyond differences in body weight and sex, and were related to other behavioural characteristics of pigs. The presence of feeding strategies suggests that the use of pig feeding behaviour data should be corrected for individual differences between pigs.