Ž .
Ž .
Bouissou 1993 and Boissy and Bouissou 1995 in studies of the fear responses of Ž
. sheep and cattle. Hemsworth et al. 1993 commonly found that commercial pigs were
highly fearful of humans, based on avoidance of an experimenter in a standard test. The mechanism involved appeared to be a chronic stress response, since in a number of
experiments pigs that were highly fearful of humans had a sustained elevation of free
Ž .
corticosteroid concentrations Hemsworth and Barnett, 1987 . Many other studies,
Ž .
reviewed by Hemsworth and Coleman 1998 , have also demonstrated a strong relation- ship between approachravoidance behaviour and fear.
We have attempted to extend this concept to a broader range of potentially threaten- ing or stressful stimuli and have commenced development of a standard test of
responsiveness, across a number of sensory categories, which may have the potential to discriminate between stressed and unstressed pigs. This work builds on the pioneering
Ž .
study of Broom 1986 , who tipped 200 ml of water onto the backs of lying stall-housed or group-housed sows. Group-housed pigs stood up or sat for longer periods in response
to the tactile stimulus than stalled sows. The method also extends the study by Hutson et Ž
. al. 1993 , which measured responsiveness of stalled sows to 20 different stimuli. One of
the limitations of both these studies was that sows had limited opportunities to express a full range of behavioural responses to the stimuli. In Broom’s, study the sows were lying
down before testing, and in Hutson’s study, the sows were neck-tethered in partial stalls.
We tested the responses of growing pigs to 60 stimuli from five sensory categories. Since approachravoidance is such an important part of an animal’s response to stress,
we tested animals in a test pen where this behaviour could easily be expressed by the animal and easily measured by the experimenter. Our aim was to quantify the magnitude
and variation in responsiveness to the stimuli in normal pigs prior to future selection of fewer stimuli to evaluate differences between stressed and unstressed pigs.
2. Materials and methods
2.1. Animals Ž
. Twenty-four crossbred pigs Large White = Landrace from the Pig Research and
Training Centre herd at Werribee were used in the tests. The study was done in two trials, during spring and summer. For each trial, six males and six females were selected
at random from weaner crates within a weight range of 18–21 kg. Pigs were weaned into the crates at 25 days and ranged from 56 to 63 days old at the time of selection. The
10 experimental pigs for each trial were individually housed in adjacent 1.2 = 1.8 m pens on a concrete floor with individual feeders and drinkers. The two companion pigs
for each trial were housed adjacent to the test pen on concrete in a 1.1 = 3.6 m pen with ad libitum feed and water.
The care and use of the animals in this experiment conformed with the requirements of the Australian Prevention of Cruelty to Animals Act 1986 and the NH and
MRCrCSIROrAAC ‘‘Code of Practice for the Care and Use of Animals for Scientific Purposes’’.
2.2. Test pen The test pen was located in a separate shed from the 10 home pens. It consisted of a
0.5 = 2.4-m steel mesh sided pen erected in the middle of a larger 3 = 5 m concrete- walled pen. Pig entry was via a mesh gate at the rear and exit was via opening of one of
the mesh sides. The pen was parallel to the pen containing the two companion pigs. At the front of the pen, there was a 0.5 = 0.25 = 0.13-m black plastic stand into which a
0.25 = 0.25 = 0.07-m food box containing 200 g pelleted food could be placed. A 2 = 5-m wooden barrier in front of the food box obscured all views forward of the test
pen. A 0.8 = 0.6-m sliding wooden door in the barrier allowed the test pig access to a 0.5 = 0.8 = 0.3-m stimulus box with wooden sides and a black sheet-plastic floor.
A video camera was mounted above the pen and recording commenced before each pig was introduced to the pen. Behaviour was videotaped for 2 min before and after
stimulus presentation, which was cued by the opening of the sliding door. Thirty stimuli, grouped broadly into five sensory categories, were evaluated in each trial. These stimuli
were selected on the basis that they were novel, or had successfully been used by other
Ž researchers Alexander and Stevens, 1982; Broom, 1986; Jones, 1988; Hutson et al.,
. 1993 .
2.3. Stimuli Stimuli 1–30 were evaluated in Trial 1 and Stimuli 31–60 were evaluated in Trial 2.
Ž .
Three stimuli were common to both trials — Control empty 29,59 , Control food Ž
. Ž
. 30,60 and Sitting human 25,56 .
2.3.1. Visual stimuli Ž .
Ž .
1 Funnel. A red plastic funnel 21 = 28 cm was suspended 10 cm above the base of the stimulus box and stayed in this position for the duration of the test.
Ž . 2 Umbrella. The rear panel of the stimulus box was removed and a spring-loaded
umbrella was unfurled when the pig was facing towards the box. The umbrella remained in this position for the duration of the test.
Ž . 3 Torch light. A 10-cm diameter battery powered torch was placed in a circular
opening at the base of the rear panel of the stimulus box. Ž .
4 Mirror. A 50 = 70-cm mirror was attached to the back of the stimulus box. Ž .
Ž .
5 Rod. A novel rod, similar to that used by Jones 1988 in tests of fear in laying hens was used. The 36 = 6 cm steel rod was welded to a 15-cm base and covered with
Ž .
six differently coloured bands of plastic tape green, blue, white, red, yellow and black . The rod was placed upright in the centre of the stimulus box.
Ž .
31 Dropping ball. A 25 = 15-cm red plastic football was released from above and dropped into the stimulus box, if the pig was facing towards the box.
Ž .
32 Standing cross. A 2.5 = 15-cm diameter black paper cross mounted on a
33 = 23-cm yellow card. The card was attached to a spring-loaded base so that on release it rose immediately to a vertical position.
Ž .
33 Flashing light. A flashing orange light, 90 flashes per min, mounted 10 cm above the base of the box.
Ž .
34 Revolving cross. A 2.5 = 15-cm black paper cross mounted on a 28 = 33-cm yellow card. The card was attached to a pulley driven by a small motor so that it
revolved at a speed of 60 rpm. Ž
. 35 Moving tail. A toy ‘‘Funny animal ball’’, which consisted of an 8-cm diameter
orange and pink plastic ball with a 23-cm black and brown striped tail attached to it. The ball was powered by a battery so that it rolled haphazardly about on the floor of the
stimulus box, dragging the tail behind it.
2.3.2. Olfactory stimuli Responses to olfactory stimuli were tested by placing a cotton wool swab impreg-
nated with 10 drops of the chemical on the floor of the stimulus box 10 s prior to opening the sliding door. The following chemicals were obtained from the Sigma, St.
Louis, MO, and presented undiluted, unless otherwise indicated: Ž .
Ž .
6 Eucalyptus oil B.P. Felton, Grimwade and Bickford, Moorabbin, Victoria Ž .
7 Triethylamine Ž .
Ž .
8 Vanillin 4-hydroxy-3-methoxy benzaldehyde Ž .
Ž .
9 Oil of Wintergreen methyl salicylate Ž
. Ž
. 10 Mineral turpentine Mobil Oil Australia
Ž .
Ž .
11 Aniseed oil natural aniseed essence, Queen Fine Foods, Enoggera, Queensland Ž
. 36 Glacial acetic acid
Ž .
Ž .
37 Artificial almond oil benzaldehyde Ž
. Ž
. 38 Ethanedithiol 1,2-ethanedithiol in methanol, 20 ml in 40 ml
Ž .
Ž .
39 Skatole 3-methylindole in methanol, 1 mgrml Ž
. 40 Amyl acetate
Ž .
Ž .
41 Citronella oil Biotech International, Rocklea, Queensland 2.3.3. Auditory stimuli
Ž Recorded auditory stimuli were played back for 60 s using a tape recorder Genexxa,
. Ž
. Ž
. Intertan , amplifier Genexxa, Intertan , and speaker Blaupunkt Hi-Fi mounted to a
25 = 35-cm jute fabric covered opening in the rear panel of the stimulus box. Other auditory stimuli were activated adjacent to the fabric covered opening for 60 s. Sound
levels given below were measured above the centre of the food box, 0.5 m from the
Ž .
sound source, using a Radio Shack Sound Level Meter Model 33-2050 , set to Fast response and A weighting.
Ž .
12 Piglet squeal. A recording of day-old piglet squeals was played back at 92–95 dB. The recording was made from a 6-h-old piglet removed from a sow and litter, held
between two hands, and gently squeezed. Ž
. Ž
Ž .
13 Bell bird song. Manorina melanophrys song recorded by H. Horton 1990 , .
Australian Broadcasting, Sydney was played back at 94–96 dB. Ž
. 14 Buzzer. An electric buzzer was activated at 92 dB.
Ž .
15 Sow grunt. A recording of sow grunts was played back at 92–96 dB. The recording was made from an unfamiliar sow during a nursing bout.
Ž .
16 Cap gun. A toy cap gun was fired seven times at 10 s intervals for 60 s. Peak sound level varied between 80 and 95 dB.
Ž .
17 Smoke alarm. A commercial smoke alarm beep was activated for 60 s. Peak sound level was 106–108 dB.
Ž .
42 Dog bark. A recording of a dog barking was played back at 92–96 dB. Ž
. 43 Pig bark. A recording of pig barks was played back at 100–102 dB. The
recording was made from growing pigs responding to the sudden appearance of an unfamiliar human handler.
Ž .
44 White noise. A recording of white noise was played back at 103 dB. Ž
. Ž
. 45 Siren. A personal alarm siren Intertan Australia was activated at 106–108 dB.
Ž .
46 Compressed air. A recording of the release of compressed air in bursts of 5 s on, 5 s off, was played back at 103 dB.
Ž .
47 Vibrating sheet steel. A recording of a vibrating 1.8 = 1.2-m sheet of 1-mm steel was played back at 104 dB.
2.3.4. Tactile stimuli All tactile stimuli except the hot and control air treatments were delivered by a
human sitting with feet on the floor of the stimulus box. Each stimulus was administered once every 10 s for 60 s if the pig was within range, i.e., standing with head over the
food box. The stimuli were: Ž
. 18 Slap. A firm slap on the neckrshoulder with an open palm.
Ž .
19 Prod. A prod with a rounded 10-cm length of 18-mm diameter wooden dowel. Ž
. 20 Rub. A rub with the open palm on the neckrshoulder
Ž .
21 Clip. A 65-mm spring-action ‘‘Bulldog’’ paper clip was placed on the middle of the leading edge of the pig’s left ear.
Ž .
22 Water. A 100-ml of water was tipped onto the pig’s back by remotely pulling a string which released a container attached 1.0 m above the pig.
Ž .
23 Brush. A soft nylon-bristled 15-cm brush was brushed along the neckrshoulder. Ž
. 48 Feather duster. An emu-feathered duster was applied for about 1 s to the pig’s
snoutrface. Ž
. 49 Aerosol spray. An aerosol spray of low allergen insecticide was applied for about
1 s to the pig’s neckrshoulder. Ž
. 50 Hot air. An electric fan-forced heater was attached to a 18 = 18-cm opening at
the rear of the stimulus box and blew air at 468C towards the pig. Ž
. 51 Control air. The fan was used to blow air towards the pig but the heating element
was turned off. Ž
. 52 Electric prod. A hand-held commercial electric cattle prod was applied to the
shoulderrneck of the pig. Ž
. 53 Control prod. The electric prod was applied to the pig with the current turned off.
2.3.5. Complex stimuli Ž
For stimuli involving novel or control food presentation, 50 g of feed instead of 200 .
g used in other tests was placed in the food box prior to testing. This was done to ensure that the pigs were not satiated prior to presentation of the stimulus. One of two
people was used at random in human tests. They wore identical clean long-sleeved overalls and clean boots.
Ž .
24 Toy robot. An electronic toy ‘‘Talk’n Walk robot’’, which combined movement, Ž
. sound ‘‘Hands up’’, ‘‘Drop your weapon’’ and flashing lights, was operated remotely.
Ž .
25 Standing human. The experimenter stood in the stimulus box, facing the pig. Ž
. 26, 56
Sitting human. The back of the stimulus box was removed and the experimenter sat on a chair with feet in the box and hands clenched, resting on the
knees. Ž
. 27 Sitting human in mask and gloves. As above, except the experimenter wore red
rubber gloves and a Donald Duck-mask. Ž
. 28 Green food. Ten grams of pellets dyed with green food dye were placed in the
middle of the stimulus box. Ž
. 54 Rabbit. A live Dutch dwarf rabbit in a 40 = 28 = 27-cm wire mesh hutch.
Ž .
55 Toy dog. A battery powered 15-cm toy dog which walked, shook its tail and barked.
Ž .
57 Quinine treated food. Ten grams of pellets, which had been soaked in quinine Ž
. hydrochloride 2 gr100 ml and dried were placed in the middle of the stimulus box.
Ž .
58 Blue food. Ten grams of pellets dyed with blue food dye were placed in the middle of the stimulus box.
2.3.6. Control stimuli Ž
. 29, 59 Control empty. The stimulus box was empty.
Ž .
Ž .
30, 60 Control food. Ten grams of pellets normal ration were placed in the middle of the stimulus box.
2.4. Procedure Pigs were fed daily with a commercial pelleted grower ration at 0900 h. If the
previous day’s ration had been completely eaten then the amount was increased by 0.5 kg. After the feeders had been replenished, a cover was placed over each to prevent the
pig from feeding. Each pen was then cleaned by scraping with a shovel. Testing began 2 h after the feeders were replenished and covered, to ensure that each
pig would be motivated to eat in the test pen. The order of testing was determined at random, and the stimulus for each pig was also determined at random. The only
constraint on test order was that only one olfactory stimulus was tested per session and it was the last test done in any session. This procedure was adopted to avoid any possible
carryover effects from the olfactory stimulus. One olfactory stimulus was tested more than once on some occasions when the same stimulus was required for different pigs.
A 200-g of pelleted ration was placed in the food box in front of the stimulus box. The pig was then introduced to the pen through the rear gate. After 2 min, the sliding
door was remotely opened to reveal the stimulus. After 2 min exposure to the stimulus, the door was closed and the pig released from the test pen through the side mesh panel.
On return to its home pen, the cover was removed from the feeder. The stimulus box was wiped with a damp cloth after each test and the food box replaced with 200 g of
fresh pellets. At the completion of the session, the test pen was hosed down and the covers on the home pen feeders were replaced at 1300 h for afternoon testing to
commence at 1500 h.
Prior to testing the experimental stimuli, there was a training period in which each pig had to reach a criterion of commencing to eat from the food box within 5 s of
introduction to the pen, and eating at least 50 g pellets, on two successive days. This criterion ensured that pigs immediately approached the food box on entering the test
pen, readily fed from it, and were familiar with the stimulus box door sliding open after 120 s. The number of sessions to reach criterion ranged from 10 to 18, with a mean of
12.8 in Trial 1 and 13.4 in Trial 2.
2.5. ObserÕations and statistical analysis Videotapes were analysed by recording the location of the tip of the test pig’s snout
in 1 s scans for each of the 120 s before and after stimulus presentation. Location was scored as one of six areas — the stimulus box, the food box, or four 0.5-m sections of
the pen. The average distance of the pig from the food box was then computed before and after stimulus presentation using these frequency distributions of location. The effect
of the stimulus on approachravoidance behaviour could then be assessed by subtracting the average distance before stimulus presentation from the average distance after. Data
Ž were analysed as a randomized block design, with pigs as blocks Genstat 5, Release
. 4.1, Lawes Agricultural Trust, Rothamstead Experimental Station, 1997 . Distance from
the food box before stimulus presentation was used as a covariate to improve precision. In the analysis of variance, the effect of stimuli was divided into the six different groups
described above. Stimuli effects were then tested separately within each of the stimulus
Ž .
groups, but using the overall residual error between pigs Table 1 . Fitted values vs. residual graphs were examined for all of the variates to check for homoscedasticity.
All occurrences of defaecation and urination and the number of 1808 turns away from the stimulus box were recorded. The difference in frequency of elimination and turning
between the 120 s periods before and after stimulus presentation were used as dependent variables in the analysis. The latency to eat after exposure to the stimulus, and the
latency to enter the stimulus box were also recorded. If a pig failed to eat or enter the
Table 1 Structure of the analysis of variance
Effect Degrees of freedom
Pig stratum Covariate
1 Residual
8 Time within pig stratum
Stimulus group 5
Differences within Visual 4
Differences within Olfactory 5
Differences within Auditory 5
Differences within Tactile 5
Differences within Complex 4
Differences within Control 1
Covariate 1
Residual 260
stimulus box it was assigned a latency of 120 s. Latencies were transformed to common logarithms before analysis of variance. Back-transformed means are given in the results.
Table 2 Effect of stimulus presentation on behaviour in Trial 1. Negative mean values for turns and eliminations
indicate a reduction in frequency following presentation; positive mean values indicate an increase. Values for Ž
latencies represent backtransformed means, adjusted for the covariate approachravoidance distance before .
stimulus presentation . SEDs for latencies represent values after log base 10 transformation Stimulus
Mean no. Mean no.
Latency Latency to
Ž . Ž .
turns away eliminations
to eat s stimulus s
Visual stimuli y0.8
y0.1 2.6
7.0 Funnel
y1.9 y0.1
1.9 5.6
Umbrella y1.0
0.1 2.9
10.4 Torch light
0.5 y0.1
2.2 4.3
Mirror y1.1
y0.1 2.9
5.3 Rod
y0.7 y0.1
3.8 12.3
Olfactory stimuli 0.0
0.0 2.3
6.8 Eucalyptus oil
0.0 0.0
2.9 9.0
Triethylamine y0.9
0.1 2.5
5.9 Vanillin
0.3 0.0
1.7 9.7
Oil of wintergreen 0.0
0.0 2.5
5.4 Mineral turpentine
0.3 0.0
2.6 6.5
Aniseed oil 0.5
0.0 1.7
5.6 Auditory stimuli
0.1 0.0
2.8 13.2
Piglet squeal y0.1
0.0 3.6
21.9 Bell bird song
0.2 y0.1
4.0 24.4
Buzzer 0.3
0.0 2.5
14.4 Sow grunt
0.4 y0.1
2.3 7.6
Cap gun 0.3
0.0 1.7
4.5 Smoke alarm
y0.7 0.1
3.3 20.2
Tactile stimuli y0.2
0.0 2.4
14.0 Slap
y0.6 y0.1
1.2 19.0
Prod y0.8
y0.1 2.5
19.4 Rub
y0.3 0.0
2.4 8.0
Clip y0.4
0.0 2.6
7.7 Water
0.5 0.0
3.3 16.7
Brush 0.5
0.0 3.0
19.5 Complex stimuli
y0.2 0.0
3.0 11.7
Toy robot y0.3
y0.1 5.1
36.7 Standing human
y0.2 y0.1
2.4 9.4
Sitting human 0.6
0.2 2.6
8.5 Sitting human with maskrgloves
y0.7 y0.1
2.2 13.5
Green food y0.2
y0.1 3.5
5.7 Control stimuli
0.5 y0.1
2.6 5.4
Control empty 1.3
0.1 2.9
5.5 Control food
y0.3 y0.3
2.3 5.2
SED 0.709
0.127 0.244
0.271
Distance from the food box before stimulus presentation was used as a covariate for the analysis of latencies, but not in the analysis of elimination or turning.
Table 3 Effect of stimulus presentation on behaviour in Trial 2. Negative mean values for turns and eliminations
indicate a reduction in frequency following presentation; positive mean values indicate an increase. Values for Ž
latencies represent backtransformed means, adjusted for the covariate approachravoidance distance before .
stimulus presentation . SEDs for latencies represent values after log base 10 transformation Stimulus
Mean no. Mean no.
Latency Latency to
Ž . Ž .
turns away eliminations
to eat s stimulus s
Visual stimuli y0.5
0.0 15.4
41.0 Dropping ball
y1.4 0.0
7.8 30.5
Standing cross y1.1
0.4 13.3
36.6 Flashing light
y0.9 y0.3
14.5 38.8
Revolving cross 0.6
0.1 92.7
119.9 Moving tail
0.2 y0.2
6.2 22.4
Olfactory stimuli y0.6
y0.1 5.3
12.2 Glacial acetic acid
y1.8 y0.2
3.9 9.4
Almond oil y0.5
y0.1 5.6
16.3 Ethanedithiol
y0.3 0.1
4.8 16.0
Skatole y0.3
0.0 5.4
10.1 Amyl acetate
y0.6 0.0
4.6 6.9
Citronella oil y0.3
y0.4 8.4
19.3 Auditory stimuli
y1.0 0.1
15.6 50.9
Dog bark y2.4
0.0 19.2
35.4 Pig bark
y0.8 0.3
17.6 106.4
White noise 0.2
0.3 11.9
38.0 Siren
y1.4 0.0
32.9 97.1
Compressed air y1.0
y0.1 11.2
35.8 Vibrating steel
y0.4 0.1
9.6 35.1
Tactile stimuli y1.1
y0.1 6.8
15.6 Feather duster
y1.4 0.1
5.1 12.5
Aerosol spray y1.2
y0.1 8.9
8.6 Hot air
y0.8 y0.2
9.6 30.1
Control air y1.1
y0.3 9.3
33.0 Electric prod
y1.0 y0.2
5.6 6.1
Control prod y0.9
0.4 4.3
22.1 Complex stimuli
y1.3 0.0
13.3 22.1
Rabbit y1.6
0.3 12.0
14.6 Toy dog
y1.2 0.0
40.6 49.0
Quinine food y1.1
y0.2 11.3
18.3 Sitting human
y1.8 0.0
8.8 22.3
Blue food y0.6
y0.3 8.6
18.1 Control stimuli
y0.4 y0.2
9.1 21.8
Control empty y0.2
y0.2 5.2
21.8 Control food
y0.5 y0.1
16.0 21.7
SED 0.793
0.299 0.286
0.273
3. Results
