Vocalisations of the adult female domestic pig during a standard human approach test and their relationships with behavioural and heart rate measures

Vocal communication in the domestic pig is generally not well documented. T he aim of this experiment was to categorise and ascribe the function of the vocalisations of 67 Large White x Landrace gilts during a standard human a pproach test. At testing, each group of 3-5 gilts was moved to a handling a rea where each individual in turn was fitted with a heart rate monitor and introduced individually to a 2.4 m x 2.4 m test arena. After 2 min familiar isation, an unfamiliar human entered the pen and stood for 3 min against on e wall. Behaviour and sound were recorded continuously with sound recording s transferred onto computer for analysis. Three categories of calls were in itially identified: single grunts, single squeals and rapidly repeated grun ts. Sixty-six gilts performed single grunts, whereas only 28 and 16 gilts p erformed the other two categories, respectively. Single grunts could be sub -divided into two types based on sound amplitude profile. These types diffe red significantly in duration. Gilts performed more short and long grunts p er minute during the 3 min test period than during the familiarisation peri od. Most short grunts observed in a subset of 15 gilts were performed with the snout close to a pen surface or the human. The rate of short grunts dur ing the test period was negatively correlated with the time taken to make c ontact with the human and positively correlated with the amount of locomoto r behaviour carried out, the total number of interactions with the human an d the total time spent within 0.5 m of the human. Most long grunts observed in a subset of 15 gifts were performed with the snout away from any surfac e. The rate of long grunts during the test period positively correlated wit h amount of locomotor behaviour and heart rate, after the effect of activit y had been removed. Squeals could similarly be sub-divided into long and sh ort types on the basis of amplitude profile. Gilts that squealed carried ou t more locomotor behaviour, interacted with the human more, had higher mean heart rates and lower heart rate rise when touched by the human, suggestin g a higher degree of arousal. Rapidly-repeated grunts were associated with close human interaction. The results indicate that the domestic pig perform s a number of distinct vocalisations during isolation. Short single grunts appear to be associated with investigatory behaviour. Long single grunts ma y be a form of contact call, the rate of which is related to physiological and behavioural activity. Squeals may have similar function but result from a higher level of arousal. Short, rapidly-repeated grunts appear to have e ither a greeting or threat function. With further research, certain pig voc alisations may be identified as providing useful additional information abo ut an individual's welfare. (C) 2001 Elsevier Science B.V. All rights reser ved.