Are Behavioral Tests Capable of Measuring Positive Affective States in Growing Pigs?

SIMPLE SUMMARY: This study aimed at deriving potential indicators to assess fattening pigs’ positive affective state in order to be able to assess animal welfare more objectively. For this purpose, 297 fattening pigs from two different housing systems (a barren and an enriched environment) were subjected three times to the human approach test and novel object test (at the start, middle and end of fattening). The barren-housed pigs showed quicker approach latencies to come into contact with the unknown human and the novel object compared to the enriched-housed pigs (e.g., latency time in the human approach test at the end of fattening: barren housing system: 7.4 ± 1.1 s vs. enriched housing system: 57.1 ± 1.1 s, respectively 58.3 ± 1.3 s). They also indicated longer durations of contact in the human approach test but not in the novel object test (e.g., duration of contact in the human approach test at the end of fattening: barren housing system: 83.8 ± 1.1 s vs. enriched housing system: 6.3 ± 1.1 s respectively, 7.6 ± 1.3 s). However, taking the literature into account, interpretation of these results is not straightforward as the reasoning for these findings could be boredom, and thus a higher motivation to explore, or less fear. Hence, behavioral tests as solitary indicators are probably less useful in the assessment of an affective state. ABSTRACT: This study examined whether the human approach test (HAT) or novel object test (NOT), which are considered as suitable tests for assessing the level of fear or anxiety in animals, are suitable to detect a positive affective state in 297 fattening pigs from three different farms. The investigated farms consisted of a barren (farm 1, n = 160) and an enriched (farm 2, n = 106; farm 3, n = 31) husbandry. Each pig was subjected three times to the HAT and NOT during fattening (at the start, middle, and end of fattening). The pigs housed in the barren environment showed quicker approach latencies than the enriched-housed pigs (HAT: farm 1: 7.4 ± 1.1 s vs. farm 2: 57.1 ± 1.1 s, respectively, farm 3: 58.3 ± 1.3 s (end of fattening); NOT: farm 1: 4.5 ± 1.1 s vs. farm 2: 23.0 ± 1.1 s, respectively, farm 3: 9.0 ± 1.2 s (end of fattening)). The same pattern of behavior was observed for the duration of contacts in the HAT but not in the NOT (HAT: farm 1: 83.8 ± 1.1 s vs. farm 2: 6.3 ± 1.1 s, respectively, farm 3: 7.6 ± 1.3 s (end of fattening)). However, due to controversially discussed literature, it is difficult to conclude whether the described differences in the pigs’ behavior between the two housing systems might indicate useful indicators to detect their affective state.