Comparison of Vocalization Patterns in Piglets Which Were Crushed to Those Which Underwent Human Restraint

SIMPLE SUMMARY: Piglet crushing (the process by which a sow sits or lies on and crushes her piglet) is a welfare issue in pig husbandry. In order to understand why crushing occurs, and avoid hardship to a piglet, recordings of distressed piglets are often used to simulate crushing events to measure sows’ behavior. Unfortunately, it is not known if the call produced by the distressed piglet is similar to a piglet being crushed, making the evaluation of the results difficult. We recorded calls of piglets during crushing and compared the calls to those produced by restrained piglets. When crushed, piglets have a deeper call than piglets which are restrained by a human. Restrained piglets call as loudly as crushed piglets. In conclusion, sufficient differences exist between restrained and crushed piglets that restrained calls alone should not be used to understand the conditions in which a sow will respond to the distress calls of her piglets. Future research should include measuring sow behavior in response to Crushed and Restrained calls. ABSTRACT: Though many studies focused on piglet crushing utilizing piglet vocalizations to test sow response, none have verified the properties of test vocalizations against actual crushing events. Ten sows were observed 48 h after parturition, and crushing events were recorded from all sows. When a crushing event occurred, a second piglet within the same litter was used to solicit a vocalization through manual restraint to compare restrained piglets’ call properties to those of crushed piglets’. A total of 659 Restrained calls and 631 Crushed calls were collected. Variables were gathered at the loudest point in a call, and as an average across the entire call. Crushed piglets had a lower fundamental frequency (p < 0.01; Crushed: 523.57 ± 210.6 Hz; Restrained: 1214.86 ± 203.2 Hz) and narrower bandwidth (p < 0.01; Crushed: 4897.01 ± 587.3 Hz; Restrained: 6674.99 ± 574.0 Hz) when analyzed at the loudest portion of a call. Overall, piglets which were crushed had a lower mean peak frequency than those which were restrained (p = 0.01; 1497.08 ± 239.4 Hz and 2566.12 ± 235.0 Hz, respectively). Future research should focus on measuring sow reactivity to Crushed and Restrained piglets to continue to improve research practices.