Piglet vocalization rates are used as welfare indicators. The emission rates of the two gross categories of piglet calls, namely low frequency calls ("grunts") and high frequency calls ("screams"), may contain different information about the piglet's internal state due to differing communicative functions of the two call types. More knowledge is needed about the sources of variation in calling rates within and between piglets. We examined to what extent the emission rates of the two call types are codetermined by individual and litter identity, i.e., whether the rates are repeatable within individuals and similar between littermates. We recorded frequency of grunts and screams in one mildly negative (short-term Isolation) and one moderately negative (manual Restraint) situation during the first week (week 1) and the 4th week (week 4) of life and asked the following questions: 1) Are within-individual vocalization rates stable across the suckling period? 2) Are within-individual vocalization rates stable across the two situations? 3) Is there within-litter similarity in vocalization rates? 4) Does this within-litter similarity increase during the suckling period? Within-individual vocalization rates were stable between week 1 and week 4 (grunts in Restraint P < 0.05; grunts in Isolation P < 0.001; screams in Restraint P < 0.001; screams in Isolation P < 0.001). Across the two situations at the same age, the vocalization rates were not stable for grunts but were stable for screams at week 1 and week 4 (P < 0.05). Vocalization rates were more similar between littermates than between piglets belonging to different litters (grunts in Restraint P < 0.001; grunts in Isolation P < 0.01; screams in Restraint P < 0.001; screams in Isolation P < 0.001). This litter effect did not grow stronger from week 1 to week 4 as the within-litter coefficient of variance did not decrease between the two ages. Sex of the piglet had no influence on vocalization rates while greater body weight was associated with lower screaming rates in the Restraint situation (P < 0.05). In conclusion, our study demonstrates that both individuality of the piglet and litter identity affect the vocalization rates of piglets in negatively valenced situations. For screams, the repeatability of individual vocalization rates holds even across situations, while for grunts, the rates are repeatable during ontogeny within the situations, but not across situations.

Department of Ethology Institute of Animal Science Uhríneves Czech Republic

Department of Ethology Institute of Animal Science Uhříněves Czech Republic

Department of Zoology Faculty of Science University of South Bohemia in České Budějovice Branišovská České Budějovice Czech Republic

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Bates D., Mächler M., Bolker B., and Walker S.. 2015. Fitting linear mixed-effects models using lme4. J. Stat. Softw. 67:1–48. doi:10.18637/jss.v067.i01

Friel M., Kunc H. P., Griffin K., Asher L., and Collins L. M.. 2016. Acoustic signaling reflects personality in a social mammal. R. Soc. Open. Sci. 3:160178. doi:10.1098/rsos.160178 PubMed PMC

Garcia M., Gingras B., Bowling D. L., Herbst C. T., Boeckle M., Locatelli Y., and Fitch W. T.. 2016. Structural classification of wild boar (Sus scrofa) vocalizations. Ethol. 122:329–342. doi:10.1111/eth.12472 PubMed PMC

Illmann G., Hammerschmidt H., Špinka M., and Tallet C.. 2013. Calling by domestic piglets during simulated crushing and isolation: signal of need?PLoS One 8:e83529. doi:10.1371/journal.pone.0083529 PubMed PMC

Kiley M. 1972. The vocalizations of ungulates, their causation and function. Z. Tierpsychol. 31:171–222. doi:10.1111/j.1439-0310.1972.tb01764.x PubMed

Linhart P., Ratcliffe V. F., Reby D., and Špinka M.. 2015. Expression of emotional arousal in two different piglet call types. PLoS One. 10:e0135414. doi:10.1371/journal.pone.0135414 PubMed PMC

Marchant-Forde J. N., Lay D. C. Jr., McMunn K. A., Cheng H. W., Pajor E. A., and Marchant-Forde R. M.. 2009. Postnatal piglet husbandry practices and well-being: the effects of alternative techniques delivered separately. J. Anim. Sci. 87:1479–1492. doi:10.2527/jas.2008-1080 PubMed

Marchant-Forde J. N., Lay D. C., McMunn K. A., Cheng H. W., Pajor E. A., and Marchant-Forde R. M.. 2014. Postnatal piglet husbandry practices and well-being: the effects of alternative techniques delivered in combination. J. Anim. Sci. 92:1150–1160. doi:10.2527/jas.2013–6929 PubMed

Marx G., Horn T., Thielebein J., Knubel B., and von Borell E.. 2003. Analysis of pain-related vocalization in young pigs. J. Sound Vibration. 266:687–698. doi:10.1016/S0022-460X(03)00594-7

Puppe B., Schon P. C., Tuchscherer A., and Manteuffel G.. 2005. Castration-induced vocalisation in domestic piglets, Sus scrofa: complex and specific alterations of the vocal quality. Appl. Anim. Behav. Sci. 95:67–78. doi:10.1016/j.applanim.2005.05.001

R Core Team 2016. A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing.

Syrová M., Policht R., Linhart P., and Špinka M.. 2017. Ontogeny of individual and litter identity signaling in grunts of piglets. J. Acoust. Soc. Am. 142:3116–3121. doi:10.1121/1.5010330 PubMed

Tallet C., Linhart P., Policht R., Hammerschmidt K., Šimeček P., Kratinová P., and Špinka M.. 2013. Encoding of situations in the vocal repertoire of piglets (Sus scrofa): a comparison of discrete and graded classifications. PLoS One 8:e71841. doi:10.1371/journal.pone.0071841 PubMed PMC

Taylor A. A., and Weary D. M.. 2000. Vocal responses of piglets to castration: identifying procedural sources of pain. Appl. Anim. Behav. Sci. 70:17–26. doi:10.1016/S0168-1591(00)00143-X PubMed

Weary D. M., and Fraser D.. 1997. Vocal response of piglets to weaning: effect of piglet age. Appl. Anim. Behav. Sci. 54:153–160. doi:10.1016/S0168-1591(97)00066-X PubMed