Technical Note: Effects of age and confinement on pupillary light reflex in sows1

Abstract

Pupillary reflex has been used as a method to examine psychological problems in human clinics and mental disease research. Intensive animal farming has been shown to lead to chronic stress resulting in depression; however, comparing with humans we lack an effective clinical method to clinically inspect these psychological problems in animals. The goal of this study was to investigate the effect of age and housing conditions (confined crates vs. group pens) on pupillary light reflex (PLR) of sows to explore whether PLR can be used as an effective way to measure the psychological state of farm animals. In total, 270 pregnant sows were selected for PLR testing and divided into 6 treatments (45 sows per treatment) of 2 different environments (group-housed pen and confined gestation crates) and 3 parities (first, third, and fifth parities). Six selected pupil parameters: 1) latency of the pupil constriction onset (LAT); 2) the percent of the constriction (CON); 3) average constriction velocity (ACV); 4) maximum constriction velocity (MCV); 5) average dilation velocity (ADV); and 6) time of 75% recovery after constriction (T75) were examined. The results showed that there was no difference found in these PLR parameters between the breeds (P > 0.05) but the significant effects were found on LAT, CON, ACV, and MCV by age (P < 0.01). The group-housed sows had significantly higher CON, ACV, and MCV than those in the confined crates (P < 0.05). In conclusion, the pupillary light reflex of the sows was not affected by breed but by age. The results also indicate that some of PLR parameters were sensitive to housing conditions and suggest that ACV and MCV have potential to be sensitive indicators in relation to the psychological problem of sows.

A 24-h restraint with food and water deprivation: a potential method to establish a model of depression in pigs

“…Some studies have documented that long-term restraint in intensive sow production develops various types of depressive symptoms such as stereotypic behavior, decreased sucrose preference, and pupil rigidity ( 18 , 19 ). However, few have explored the pathogenesis and mechanisms of depression in pigs using animal models of depression induced by acute or chronic stress.…”

Quality of Death in Fighting Bulls during Bullfights: Neurobiology and Physiological Responses

“…When animals are exposed to situations that they cannot control or are unpredictable (such as isolation, acute noise, or confinement) [30], adaptive hypothalamic, sympathetic, immune, and behavioral responses serve to survive [31]. In farm animals, routine situations such as handling, restraining, or transport are events that can induce states of anxiety, distress, depression, or fear [32,33]. Fear is a negative, subjective, and emotional experience derived from the recognition or anticipation of actual danger [34].…”

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

“…Compared with group-housed sows, the PLR latencies and duration of stall-housed sows were longer [14]. Additionally, the PLR of sows is affected by age [18]. Our colleague previously found that there were differences in the psychophysiological states of sows with different PLRs and the differences increased with the increase in parity [19].…”