Céline Tallet

Encoding of Situations in the Vocal Repertoire of Piglets (Sus scrofa): A Comparison of Discrete and Graded Classifications

Two important questions in bioacoustics are whether vocal repertoires of animals are graded or discrete and how the vocal expressions are linked to the context of emission. Here we address these questions in an ungulate species. The vocal repertoire of young domestic pigs, Sus scrofa, was quantitatively described based on 1513 calls recorded in 11 situations. We described the acoustic quality of calls with 8 acoustic parameters. Based on these parameters, the k-means clustering method showed a possibility to distinguish either two or five clusters although the call types are rather blurred than strictly discrete. The division of the vocal repertoire of piglets into two call types has previously been used in many experimental studies into pig acoustic communication and the five call types correspond well to previously published partial repertoires in specific situations. Clear links exist between the type of situation, its putative valence, and the vocal expression in that situation. These links can be described adequately both with a set of quantitative acoustic variables and through categorisation into call types. The information about the situation of emission of the calls is encoded through five call types almost as accurately as through the full quantitative description.

Human perception of vocalizations of domestic piglets and modulation by experience with domestic pigs (Sus scrofa).

Interspecific communication between humans and pets is possible through vocal cues. We studied how humans with differing experience with domestic pigs (Sus scrofa) interpret pig vocalizations. Forty-eight ethologists studying pigs, 31 pig-caretakers and 54 naive students evaluated the emotional intensity and valence (negative/positive) of recordings from two negative (castration, isolation) and two positive (reunion with the sow, postsuckling) contexts. They also identified the context in which the recordings were made. Castration vocalizations were evaluated as highly intense and unpleasant. The positive contexts were evaluated as low in intensity and positive in valence, and isolation fell in the middle for both intensity and valence. Compared with the other two groups, pig-caretakers evaluated the intensity of vocalizations as lower, and ethologists evaluated the valence as more negative. The level of successful classification exceeded that expected by chance for all four contexts but was especially accurate for castration. Ethologists achieved better recognition than students. Classifying (right context) and understanding the emotional content (valence, intensity) of pig vocalizations is thus a general ability of humans, although it varies according to an individuals experience with pigs.

Influence of housing and season on pubertal development, boar taint compounds and skin lesions of male pigs.

Rearing entire pigs may lead to meat quality and welfare problems in relation to pubertal development. A better knowledge of the sources of variation of pubertal development, behaviour and boar taint is needed before generalizing entire male pigs. From 84 days of age, entire male pigs were reared in groups of 10 either in a conventional (C, 1 m²/animal, slatted floor) or an enriched (E, 2.5 m²/animal, straw bedding, outdoor run) housing during spring or autumn and fed ad libitum (n=10/housing/season). Mounting behaviour was observed for 3 h during the third (M3), fourth (M4) and fifth (M5) months of age. The total number of skin lesions was counted on both sides of the pigs 1 day before the behavioural recordings. The time spent in the outdoor run was also recorded during 3 days per month. The animals were slaughtered at 161±1 days of age (122±9 kg live weight). Blood samples were collected at 89 (M3), 119 (M4) and 152 (M5) days of age and at slaughter for the testosterone and oestradiol measurements. The testes were collected at slaughter, freed from the surrounding tissues and weighed. The fat samples were collected for the androstenone and skatole concentration measurement. Plasma testosterone and oestradiol-17β (oestradiol), fat androstenone and skatole and weight of the testes did not differ between the housing systems. Plasma testosterone (8.3 v. 3.9 nmol/l, P<0.05) and oestradiol (12.0 v. 9.2 pmol/l, P<0.1) at M3, fat skatole (0.124 v. 0.043, P<0.03) and weight of the testes (587 v. 512 g, P<0.05) were higher in the autumn than in the spring trial, suggesting that the pubertal development was accelerated. The number of received mounting behaviours was slightly higher in the autumn (P=0.08) trial and was markedly higher in the E than in the C environment (P<0.003). Skin lesions were more numerous in the C than in the E housing at M4 and M5 and in the spring than in the autumn trial at M3 and M4 (P<0.05). Fat androstenone and the number of performed mounting behaviours were significantly correlated between each other and with numerous indicators of the pubertal development (P<0.05). The number of skin lesions was correlated with plasma testosterone and live weight (P<0.05). Overall, this study suggests the effect of season on sexual development, the effect of the housing system on behaviour, and demonstrates the links between sexual hormones, behaviour and boar taint.

Calling by Domestic Piglets during Simulated Crushing and Isolation: A Signal of Need?

This study examined whether piglet distress vocalizations vary with age, body weight and health status, according to the predictions of the honest signalling of need evolutionary model. Vocalizations were recorded during manual squeezing (a simulation of being crushed by mother sow) and during isolation on Days 1 and 7 after birth in piglets from 15 litters. We predicted that during squeezing, younger, lighter and sick piglets would call more intensely because they are in higher risk of dying during crushing and therefore they benefit more from the sow’s reaction to intensive vocalization. For isolation, we predicted that lighter and younger piglets would call more because they are more vulnerable to adverse effects of the separation. Calls were analyzed in their time and frequency domain. The rate of calling, call duration, proportion of high-pitched calls and eight acoustic parameters characterizing frequency distribution and tonality were used as indicators of acoustic signalling intensity. Piglets that experienced “squeezing” on Day 1 produced more intense acoustic distress signalling than on Day 7. Lighter piglets called more during squeezing than heavier piglets. Health status did not significantly affect any of the indicators of intensity of vocalization during squeezing. In isolation, none of the parameters of vocalization intensity were affected either by the age or by the weight of the piglets. In summary, the model of honest signalling of need was confirmed in the squeezed situation, but not in the isolation situation.

Pig–human interactions: Creating a positive perception of humans to ensure pig welfare

Domestic pig fear of humans is common, certainly because a lot of the human interactions are aversive and the current intensive pig husbandry systems do not leave much place for positive interactions. However, the situation may change because the quality of human–animal relationship is being included in many welfare evaluation systems. The development of the relationship with humans involves different sensory channels (acoustic, visual, tactile or chemical). Memory is central in the relationship, and it leads pigs to discriminate and even recognise individual humans. The nature of the relationship matters as it will modulate not only pig health and welfare but also productivity and product quality as well as stockpeople work quality and job satisfaction. Future research aiming at improving the human–pig relationship will have to focus on the pigs’ sensorial capacities and social behaviour, as well as stockperson training.

Postnatal auditory preferences in piglets differ according to maternal emotional experience with the same sounds during gestation

Prenatal sensory experience, notably auditory experience, is a source of fetal memories in many species. The contiguity between sensory stimuli and maternal emotional reactions provides opportunity for associative learning in utero but no clear evidence for this associative learning has been presented to date. Understanding this phenomenon would advance our knowledge of fetal sensory learning capacities. In the present study we tested the hypothesis that sounds (human voice) broadcast to pregnant sows while they experienced positive or negative emotional situations influences postnatal reactions of their offspring to these same sounds. The results show that: 1) from the first testing at the age of 2 days, the experimental piglets were less distressed by a social separation than controls if they heard the “familiar” voice, 2) piglets generalized to any human voice although the influence of novel voices was less pronounced, 3) in a challenging situation, piglets were more distressed if they heard the voice that was associated with maternal negative emotional state in utero. These findings open a whole line of new research on the long term effect of in utero associative learning that goes well beyond pigs, providing a framework for reconsidering the importance of sensory and emotional experiences during gestation.

Influence of prenatal experience with human voice on the neonatal behavioural reaction to human voices with different emotion

Chronic stress is a long-lasting negative emotional state which induces negative consequences on animals’ behavior. This study aimed at assessing whether unpredictable and repeated negative stimuli (URNS) influence feeding behavior in quail, and whether this can be modulated by their emotionality. Two lines of quail divergently selected on their inherent emotionality (low emotionality, STI; high emotionality, LTI) were either daily exposed to URNS or undisturbed from 17 to 40 days of age (n=32 for each line, in each group). During this time, quail were submitted twice to a sequential feeding procedure: they were offered a hypocaloric diet (7% less caloric than the normocaloric diet) on odd days and a hypercaloric diet (7% more caloric) on even days, for 8 days; then, they received a normocaloric diet (metabolizable energy=12.56 MJ) for 3 days. This sequential feeding procedure was used to assess anhedonia and diet preferences thanks to choice tests (hypo vs. hypercaloric diets) performed at the end of each period. Short-term (30 min) and daily intake were also measured each day. Behavioral tests were performed to assess quail’s emotional reactivity. Results showed that URNS enhanced quails’ emotional reactivity, e.g. in the reactivity to human test, disturbed quail came later (P=0.011) and spent less time (P 0.1), but URNS reduced their daily intake during the 2nd period (P<0.05). Motivation for each diet (assessed by their short-term intake) was differently affected by URNS during the 2nd period: STI quail decreased their motivation to eat the hypercaloric diet (P<0.01) whereas LTI increased their motivation to eat the hypocaloric diet (P<0.01). In conclusion, both lines of quail experienced a chronic stress as URNS induced an increase of their emotional reactivity. Interestingly, URNS induced opposite changes in quail’s feeding behavior: LTI disturbed quail seemed to express a short-term compensatory behavior because of their high motivation to eat, whereas STI disturbed quail seemed to be in a devaluation process as shown by their anhedonia and their decrease of daily intake.Farm animals have to adapt to human presence from birth and being handled may lead to fear and stress reactions. It is known that the mother can be used as a postnatal model in the development of young-human relationship. Through her, some information like auditory ones may even be learnt prenatally. We tested this idea in pigs because they communicate a lot by acoustic signals. The hypotheses were that prenatal experience with human voice could modify behavioural reactions to the experienced voice and to an unfamiliar voice expressing different emotions. We worked with 30 pregnant sows from the last month of gestation. Ten sows (treatment A) were submitted to recordings of human voices during handling: vA during positive interactions and vB during negative interactions, twice a day, 5 days a week, for 10 minutes. Ten other sows (treatment B) received the contrary, i.e. vB during positive interactions and vA during negative interactions. Ten last sows (treatment C) received no vocal stimulations during handling sessions. Two days old piglets (36 A, 39 B, 35 C) were submitted to a 5 min choice test between voices vA and vB in a testing pen (2×1 m). Each voice was played back through loudspeakers positioned at each end of the pen. At 15-18 days of age, 20 other piglets from each treatment were tested in the same conditions except that we played back the voice of an unknown person, reading the same text with a joyful or angry intention. In both tests we recorded vocalisations and locomotion. Data were analysed using non parametric statistics (Statview). In both tests, A and B piglets started to move sooner (P 0.05) to be and the time spent (178 s (46s)) close to the loudspeakers did not depend on the treatment (P>0.05). We also found no difference between the time spent close to one loudspeaker or the other, neither for vA versus vB, nor for joyful versus angry intention (P>0.05). The results show that the prenatal experience of human voice reduces postnatal behavioural reactions of stress (vocalisations, latency to move) during the playback human voices. However, it does not seem to induce specific attraction toward human voice, or human emotional intention. Therefore prenatal experience with human voice may be a good way of reducing fear reactions to human voice after birth.