Physiological parameters are important measures in animal welfare assessment. To assess the amount of stress an animal experiences, stress hormones like cortisol are frequently used. However, measuring cortisol has major disadvantages due to its rapid reactivity and decline and many influencing factors. Other potential alternative markers are acute phase proteins, since stress is known to affect the immune system. A pilot study was conducted to investigate the response of the acute phase protein, plasma haptoglobine (HP), in pigs subjected to a stressor (food deprivation) and to examine the correlation between HP levels and average daily growth (ADG). Forty grower pigs (25.1 ± 4.4 kg, mean ± SD) (sex and former pen mates balanced), were allocated to 4 conventional pens, 2 treatment (T) and 2 control (C) groups (10 pigs per pen). After 10 days of adaptation the experiment started and ran for 3 weeks. In the 2nd week, T groups were repeatedly subjected to an 8-hour food deprivation (day 1, 3, 5 and 7 of week 2), C groups had normal, unrestricted, access to food. Pigs were weighed twice a week and blood was collected once a week (every 5th day). Mean levels of plasma HP of C and T groups showed large variation between individuals (C groups, week 2: 1.84 ± 3.11 mg/ml; T groups, week 2: 1.40 ± 1.16 mg/ml). No significant differences (Kruskal-Wallis test) in HP levels or growth were found between the C and T groups or between the different weeks within the T groups. Significant negative weak to moderate correlations were found between ADG and HP levels (HP week 1 and ADG week 1: rs = -0.47, p=0.005; HP week 2 and ADG total; rs= -0.60, p=0.015; HP week 3 and ADG total: rs = -0.43, p=0.025; average HP total and ADG total: rs= -0.41, p=0.017). Large variations in HP levels between individuals were shown and no effect of treatment on HP levels or growth was found. Possibly, food deprivation had no apparent stress eliciting effect. Despite these results, interesting correlations between the level of HP and ADG were found, corroborating the inverse relationship between the acute phase response and growth. To further investigate the relation of the acute phase response and stress a successive experiment will be conducted in which we apply a stronger stressor (mixing pigs) and combine the physiological data with behavior
