Evaluation of Behavior and Affective State of Different-Parity Sows with Strong/Weak Pupil Light Reflex

SIMPLE SUMMARY: Pupil light reflex (PLR) is controlled by the sympathetic and parasympathetic nervous system and is a sensitive indicator of the affective state of animals. Pupil rigidity was observed in sows in long-term confinement, and there were differences in the PLR of sows of the same parity. This study investigated the differences in the behaviors and affective state of sows with different PLR and parity. Compared with sows in the strong PLR group (SR), those in the weak PLR group (WR) performed less standing and lateral lying, and more ventral lying and sitting behaviors. In a novel object test (NOT), the number of novel object contacts and contact duration of WR sows were less than in SR sows, and the response latency time of WR sows was longer than SR sows. High-parity sows showed anhedonia and lack of motivation. The affective state of sows changed significantly with an increase in parity. Sucrose and quinine responses also verified that sows showed more severe affective disorders in higher parity. Thus, PLR may be a potent indicator for evaluating the behaviors and affective state of sows. ABSTRACT: The stall-housing system is commonly used in the modern swine industry in many countries; however, long-term space restrictions can cause affective and physiological abnormalities in sows. The pupil light reflex (PLR) can reflect the psychological and neurological changes in animals, and confined sows show higher pupillary rigidity. However, the PLR differs between same-parity sows, suggesting differences in behaviors and affective states between parity groups. We subjected confined Yorkshire × Landrace sows of parity 0, 2, and 5 to a PLR test and accordingly assigned them to the weak PLR (WR) group (n = 20) or the strong PLR (SR) group (n = 22). We then observed the sows’ behaviors and performed a sucrose/quinine response test and novel object test (NOT) to assess the differences in their affective states. The standing and lateral lying behaviors of the sows were less frequent in WR than in SR (p < 0.05), whereas ventral lying and sitting behaviors was more frequent in WR than in SR (p < 0.05). No changes in chewing behaviors and sucrose/quinine responses were observed (p > 0.05); however, the numbers and duration of novel object contact were lower and the novel object response latency time was longer in WR than in SR (p < 0.05). Regarding parity, standing and lateral lying behaviors were less frequent and ventral lying and sitting behaviors were more frequent at parity 5 than at parity 0 (p < 0.05). Bar-biting, rooting, trough-biting, and sucrose response score were lower at parity 5 than at parity 0 (p < 0.05), and vacuum chewing behavior and quinine response score were higher in sows of parity 5 than in those of parity 0 (p < 0.05). NOT showed that the number of contacts and contact duration in sows decreased with increasing parity (p < 0.05), and the response latency time was longer in sows of parity 5 than in those of lower parity (p < 0.05). In conclusion, the behavioral expression and responses of confined sows to novel objects differed between PLRs. The evaluation of the affective state of sows also revealed marked differences with increasing parity. Thus, confined sows with WR and high parity apparently suffer from more severe psychological problems, and PLR may be a potent indicator for evaluating the affective state of confined sows.