Comparison of vocalization patterns in piglets which were crushed to those which underwent human restraint

Authors: CHAPEL, NICHOLE - Purdue University; LUCAS, JEFFREY - Purdue University; RADCLIFFE, SCOTT - Purdue University; STEWART, KARA - Purdue University; Lay Jr, Donald

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2018
Publication Date: 8/8/2018
Citation: Chapel, N.M., Lucas, J.R., Radcliffe, S., Stewart, K.R., Lay Jr, D.C. 2018. Comparison of vocalization patterns in piglets which were crushed to those which underwent human restraint. Animals. 8(8):138. https://doi.org/10.3390/ani8080138.
DOI: https://doi.org/10.3390/ani8080138

Interpretive Summary: Piglet crushing (the process by which a sow sits or lies on and crushes her piglet) is a welfare issue in the pork industry. Many researchers aim to understand why crushing occurs in attempts to minimize the occurrence. As producing a crushing event is undesirable, many researchers seek methods to simulate piglet crushing to measure the sow’s behavior. Often, researchers will record a piglet in distress and play back the recording to the sow for the simulation. Unfortunately, little is 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 calls produced by restrained piglets. When crushed, piglets have a deeper call than piglets restrained by a human. Restrained piglets call as loudly as Crushed piglets. In conclusion, enough 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.

Technical Abstract: Though many studies focused on piglet crushing utilize 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. If a crushing event occurred, a second piglet within the same litter was used to solicit a vocalization through manual restraint to compare call properties of a call to those of a crushed call. Variables were gathered at the loudest point in a call and as an average across the entire call. Vocalizations were assessed for peak amplitude and frequency variations. Crushed piglets had a lower fundamental frequency and narrower bandwidth when analyzed at the loudest portion of a call (p < 0.01). Overall, piglets which were crushed had a lower peak frequency and minimum frequency than those which were Restrained (p = 0.01). No differences were observed for entropy or harmonic to noise ratio between Crushed and Restrained piglets (p > 0.35). In conclusion, differences exist in call structure between piglets which are crushed from those which undergo restraint and therefore restraint vocalizations should not be used as the only stimulus to study a sow’s response to crushing events.