Directory UMM :Data Elmu:jurnal:A:Applied Animal Behaviour Science:Vol69.Issue2.Sept2000:
Applied Animal Behaviour Science 69 Ž2000. 169–173
www.elsevier.comrlocaterapplanim
Short communication
No effect of variation in handling on behaviour in a
porcine elevated plus-maze — a brief report
Andrew M. Janczak a,) , Lene J. Pedersen b, Karin H. Jensen b,
Inger Lise Andersen c , Knut Egil Bøe c , Morten Bakken a
a
Department of Animal Science, Agricultural UniÕersity of Norway, P.O. BOX 5025, N-1432 Aas, Norway
b
Department of Animal Health and Welfare, Danish Institute of Agricultural Science, P.O. BOX 50,
D-8830 Tjele, Denmark
c
Department of Agricultural Engineering, Agricultural UniÕersity of Norway, P.O. BOX 5065,
N-1432 Aas, Norway
Accepted 31 January 2000
Abstract
The elevated plus-maze is a widely used model of anxiety in rodents and has recently been
suggested as a putative model of anxiety or fear in swine. The aim of the present experiment was
to examine the effects of a pretest blood sampling procedure on the behaviour of weaned pigs in
an elevated plus-maze. Animals in the control group were lifted one-by-one into a transport trolley
and moved to the test apparatus, where they were observed for a 5-min period. The treatment
group differed from the control group in that these animals were immobilized with a nose snare
and a blood sample was extracted from the jugular vein prior to transport to the test room.
Behaviour in the porcine elevated plus-maze did not differ significantly between the two handling
procedures. q 2000 Published by Elsevier Science B.V. All rights reserved.
Keywords: Pig — fearful behaviour; Fear; Anxiety; Human–animal relationship; Elevated plus-maze; Blood
sampling
1. Introduction
The elevated plus-maze is widely used and well validated as a model of anxiety in
rodents ŽLister, 1987; File, 1992; Rodgers and Cole, 1993; Cruz et al., 1994; Pellow et
)
Corresponding author. Tel.: q47-649-48000; fax: q47-649-47960.
E-mail address: andrew.janczak@ihf.nlh.no ŽA.M. Janczak..
0168-1591r00r$ - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 8 - 1 5 9 1 Ž 0 0 . 0 0 1 1 1 - 8
170
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
al., 1995; Hogg, 1996.. The apparatus is composed of four elevated arms of equal size
radiating from a central platform. Exterior walls enclose two opposite arms, while the
other two are open. Animals are free to enter all arms from the central platform, but
avoid open arms. Avoidance of open arms is measured as the number of open entries
ŽOE. and amount of time ŽOT. spent on open arms. OE and OT are the primary
measures of anxiety in rodents. Our research group recently showed that pigs also avoid
open arms and that avoidance is reduced by treatment with the anxiolytic drug
Diazepam ŽAndersen et al., 2000.. These findings indicate that OE and OT may be
related to anxiety or fear in swine, a possibility that should be investigated by further
studies. However, to better understand the model, it is also important to know which
methodological factors lead to variation in behaviour. For rats, repeated gentle handling
prior to testing leads to reduced avoidance of open arms in the elevated plus-maze, while
more acute stress in the form of injections with saline prior to testing increases
avoidance ŽAdamec et al., 1991; Schmitt and Hiemke, 1998.. The aim of the present
experiment was therefore to illuminate whether a blood sampling procedure prior to
testing would affect behaviour in a porcine elevated plus-maze as suggested by the
above findings in rats.
2. Materials and methods
2.1. Animals
The experiment was conducted using animals from the National Institute of Animal
Science in Foulum, Denmark. The animals were 8-week-old female pigs ŽYorkshire=
Danish Landrace.. All animals were born in standard crates where they lived until
weaning at the age of 28 days without access to food except milk from the sow. At
weaning, animals were moved to weaning pens measuring 170 = 180 cm with 2r3
slatted floors. They lived in these cages in stable litter groups of F 7 animals per cage
throughout the period of testing. After weaning the piglets had ad libitum access to
concentrated dry pig feed and water. Two animals from each of 10 litters Ž20 pigs in
total. were randomly assigned to either the control or treatment group and tested in the
PEPM. Experienced technicians weighed the experimental pigs once each week from
weaning until 8 weeks of age.
2.2. The porcine eleÕated plus-maze
The PEPM was a modification of the apparatus described by Andersen et al. Ž2000.,
adjusted to the size of pigs at 8 weeks of age. The apparatus was composed of two
opposite, open arms without walls Ž160 = 80 cm. and two closed arms with walls
Ž160 = 80 = 60 cm3 . that radiated from a central platform Ž80 = 80 cm2 . to form a plus
sign. The floor surface of the apparatus was elevated to a height of 90 cm above the
concrete floor of the test room by four 1 = 2-in. wooden supports under each arm. The
maze floor was built in 1-in. water-resistant plywood, covered by sand, which was glued
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
171
to the plywood with transparent acrylic paint. The side and end walls of the enclosed
arms were made of transparent 5-mm plexiglas, supported along all edges with 1 = 2-in.
planks. The apparatus was set up in a test room measuring 4.4 = 5.6 m2 . The test room
was totally isolated, having concrete walls, iron sliding doors, and had no windows. The
room was lit by neon lamps mounted on the ceiling.
2.3. Treatments
All testing was performed on 5 days over a 5-week period between 1400 and 1600 h
with the 10 litters distributed over test days according to age. Pigs from the treatment
group were removed singly from their home pen. Each test animal was lifted by two
arms under its body and placed onto the floor outside the home cage. It was then led
through a door to the hallway, the technician gripping the animal’s ear with one hand,
the other hand placed behind its rump. Upon entering the hallway, a second technician
fitted a nose snare on the animal. The nose snare circled over the test animal’s snout and
passed through the mouth Žbehind the incisor teeth.. After this the technician took a
blood sample from the jugular vein by vena puncture, while another technician held the
animal firmly in the nose snare, effectively limiting its movement. From the time the
technician entered the home pen until the needle was removed from the animal took
55 " 33 s Žmean " s.d... After taking the blood sample, the nose snare was immediately
removed. The pigs were then lifted into a transport trolley and moved to the door outside
of the test room before being placed into the center of the PEPM facing an open arm.
The time from when the technician entered the home pen to catch the animal until it was
placed onto the PEPM apparatus was always 5 min for the treatment group. After
placing the animal onto the apparatus, the technician immediately exited the room and
closed the door.
Animals in the control group were caught, transported and placed onto the test
apparatus in the shortest possible time to minimize handling-related stress. Because of
this attempt to minimize handling duration, the time from when the technician entered
the home cage of animals in the control group until they were placed onto the maze was
194 " 111 s Žmean " s.d... Behaviour was filmed by a video camera mounted above the
plus-maze apparatus and connected to a monitor and VCR in an adjacent observation
room. Observations were made from film using a hand-held computer ŽPsion Workabout; Noldus Information Technology, 1997. and The Observer software package
ŽNoldus Information Technology, 1995.. Behaviour was observed for a period of 5 min
from the time that the laboratory technician removed her hands from the pig after
placing it into the centre of the test apparatus facing an open arm.
Measures included the number of open- and closed-arm entries and the time spent in
the various sections of the maze, including the central platform, as well as the latency to
enter an open arm. An arm entry was defined as all four feet being over a line separating
the central platform from a maze arm. In addition to these spatiotemporal measures,
frequency of the following behaviours were also observed: ‘‘rooting’’ Ždefined as a
scraping of the snout against the floor and walls of the apparatus., ‘‘standing’’ Žwhen
the animal stood still with no locomotive movement of the feet. and ‘‘dipping’’
172
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
Table 1
Differences in porcine elevated plus-maze behavior between a treatment group Žsubject to blood sampling
prior to testing. and a control group Žno blood sampling. were not significant. The percent of variation in
behavior for which group accounted is given by the variable r 2 , derived from linear analysis of variance.
There were 10 weaned female pigs in each group
Behavior
Open entries Žtotal.
Open time Žtotal.
Closed entries Žtotal.
Closed time Žtotal.
Center time Žtotal.
Total entries Žtotal.
Latency to enter open arm
Standing Žfrequency.
Rooting Žfrequency.
Dipping Žfrequency.
Defecation Žfrequency.
Treatment group
r2
Control group
Mean
SE
Range
Mean
SE
Range
2.4
69.5
2.5
86.7
143.8
4.9
98.0
8.4
8.4
4.1
0.1
0.7
17.6
0.5
21.2
30.1
1.1
30.0
1.4
1.4
1.2
0.1
0–6
0–160
0–6
0–166
36–300
0–10
0–279
3–18
1–15
0–10
0–1
2.2
63.8
2.2
98.8
137.4
4.4
61.2
7.9
6.1
3.6
0.4
0.6
17.6
0.5
25.8
24.6
1.0
25.9
0.8
1.3
1.0
0.2
0–5
0–139
0–4
0–218
61–300
0–9
0–248
5–14
0–13
0–9
0–1
0.003
0.003
0.009
0.008
0.002
0.007
0.05
0.005
0.07
0.006
0.12
Žplacement of the snout over the edge of open arms at floor level, the pig standing either
in open arms or the central square of the apparatus..
3. Statistics
The Wilcoxon signed ranks test was used to test for differences in location between
the two groups and r 2 , derived from linear analysis of variance, was used to estimate
the percent of variation in behaviour for which the treatments accounted. Nonparametric
methods were used, as some of the data did not conform to the assumption of parametric
statistics. All tests were double sided.
4. Results
There were no significant differences in location between the mean values of
behaviour for the two treatments ŽTable 1. and treatment accounted for very little of the
variation in behaviour between groups Žsee r 2 values in Table 1..
5. Discussion and conclusion
The treatment had no effects on behaviour. This result is counterintuitive; any
reasonable experimenter should expect such aversive handling to affect motivation and
behaviour in an ensuing test. The results indicate that the test is not sensitive to variation
in the described handling and is thus reasonably robust. Fear of humans is important in
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
173
pig production Žsee Gonyou et al., 1986; Hemsworth et al., 1990; Tanida et al., 1995.
and subjective observations indicate that handling is aversive to animals in our experimental herd. A high level of fear towards humans in the transport situation may have
reduced the behavioural differences between the groups through ceiling effects. In the
present experiment it is therefore concluded that differences in the treatment, blood
sampling followed by transport or ‘‘mere’’ transport, were not important in determining
the plus-maze behaviour of the pigs tested. However, before any conclusive statement
can be made, similar experiments should be performed on pigs that are less fearful of
humans.
References
Adamec, R.E., Sayin, U., Brown, A., 1991. The effects of corticotropin releasing factor ŽCRF. and handling
stress on behavior in the elevated plus-maze test of anxiety. J. Psychopharmacol. 5, 175–186.
Andersen, I.L., Færevik, G., Bøe, K.E., Janczak, A.M., Bakken, M., 2000. Effects of diazepam on the
behaviour of weaned pigs in three putative models of anxiety. Appl. Anim. Behav. Sci. 68, 121–130.
Cruz, A.P.M., Frei, F., Graeff, F.G., 1994. Ethopharmacological analysis of rat behavior on the elevated
plus-maze. Pharmacol. Biochem. Behav. 49, 171–176.
File, S.E., 1992. Behavioural detection of anxiolytic action. In: Elliott, J.M., Heal, D.J. ŽEds.., Experimental
approaches to anxiety and depression. Wiley, Chichester, UK, pp. 25–44.
Gonyou, H.W., Hemsworth, P.H., Barnett, J.L., 1986. Effects of frequent interactions with humans on growing
pigs. Appl. Anim. Behav. Sci. 16, 269–278.
Hemsworth, P.H., Barnett, J.L., Treacy, D., Madgwick, P., 1990. The heritability of the trait fear of humans
and the association between this trait and subsequent reproductive performance of gilts. Appl. Anim.
Behav. Sci. 25, 85–95.
Hogg, S., 1996. A review of the validity and variability of the elevated plus-maze as an animal model of
anxiety. Pharmacol. Biochem. Behav. 54, 21–30.
Lister, R.G., 1987. The use of a plus-maze to measure anxiety in the mouse. Psychopharmacology 92, 80–185.
Noldus Information Technology, 1995. The Observer system for collection and analysis of observational data,
Base Package for Windows, Reference Manual, Version 3.0. Noldus Information Technology,
Wageningen, Netherlands.
Noldus Information Technology, 1997. The Observer system for collection and analysis of observational data,
Base Package for the Psion Workabout, Users Manual, Version 3.0. Noldus Information Technology,
Wageningen, Netherlands.
Pellow, S., Chopin, P., File, S.E., Briley, M., 1995. Validation of open:closed arm entries in an elevated
plus-maze as a measure of anxiety in the rat. J. Neurosci. Methods 14, 147–167.
Rodgers, R.J., Cole, J.C., 1993. Influence of social isolation, gender, strain, and prior novelty on plus-maze
behavior in mice. Physiol. Behav. 54, 729–736.
Schmitt, U., Hiemke, C., 1998. A combination of open field and elevated plus-maze: a suitable test battery to
assess strain as well as treatment differences in rat behavior. Prog. Neuro-Psychopharmacol. Biol.
Psychiatry 22, 1197–1215.
Tanida, H., Miura, A., Tanaka, T., Yoshimoto, T., 1995. Behavioral responses to humans in individually
handled weanling pigs. Appl. Anim. Behav. Sci. 42, 249–259.
www.elsevier.comrlocaterapplanim
Short communication
No effect of variation in handling on behaviour in a
porcine elevated plus-maze — a brief report
Andrew M. Janczak a,) , Lene J. Pedersen b, Karin H. Jensen b,
Inger Lise Andersen c , Knut Egil Bøe c , Morten Bakken a
a
Department of Animal Science, Agricultural UniÕersity of Norway, P.O. BOX 5025, N-1432 Aas, Norway
b
Department of Animal Health and Welfare, Danish Institute of Agricultural Science, P.O. BOX 50,
D-8830 Tjele, Denmark
c
Department of Agricultural Engineering, Agricultural UniÕersity of Norway, P.O. BOX 5065,
N-1432 Aas, Norway
Accepted 31 January 2000
Abstract
The elevated plus-maze is a widely used model of anxiety in rodents and has recently been
suggested as a putative model of anxiety or fear in swine. The aim of the present experiment was
to examine the effects of a pretest blood sampling procedure on the behaviour of weaned pigs in
an elevated plus-maze. Animals in the control group were lifted one-by-one into a transport trolley
and moved to the test apparatus, where they were observed for a 5-min period. The treatment
group differed from the control group in that these animals were immobilized with a nose snare
and a blood sample was extracted from the jugular vein prior to transport to the test room.
Behaviour in the porcine elevated plus-maze did not differ significantly between the two handling
procedures. q 2000 Published by Elsevier Science B.V. All rights reserved.
Keywords: Pig — fearful behaviour; Fear; Anxiety; Human–animal relationship; Elevated plus-maze; Blood
sampling
1. Introduction
The elevated plus-maze is widely used and well validated as a model of anxiety in
rodents ŽLister, 1987; File, 1992; Rodgers and Cole, 1993; Cruz et al., 1994; Pellow et
)
Corresponding author. Tel.: q47-649-48000; fax: q47-649-47960.
E-mail address: andrew.janczak@ihf.nlh.no ŽA.M. Janczak..
0168-1591r00r$ - see front matter q 2000 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 8 - 1 5 9 1 Ž 0 0 . 0 0 1 1 1 - 8
170
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
al., 1995; Hogg, 1996.. The apparatus is composed of four elevated arms of equal size
radiating from a central platform. Exterior walls enclose two opposite arms, while the
other two are open. Animals are free to enter all arms from the central platform, but
avoid open arms. Avoidance of open arms is measured as the number of open entries
ŽOE. and amount of time ŽOT. spent on open arms. OE and OT are the primary
measures of anxiety in rodents. Our research group recently showed that pigs also avoid
open arms and that avoidance is reduced by treatment with the anxiolytic drug
Diazepam ŽAndersen et al., 2000.. These findings indicate that OE and OT may be
related to anxiety or fear in swine, a possibility that should be investigated by further
studies. However, to better understand the model, it is also important to know which
methodological factors lead to variation in behaviour. For rats, repeated gentle handling
prior to testing leads to reduced avoidance of open arms in the elevated plus-maze, while
more acute stress in the form of injections with saline prior to testing increases
avoidance ŽAdamec et al., 1991; Schmitt and Hiemke, 1998.. The aim of the present
experiment was therefore to illuminate whether a blood sampling procedure prior to
testing would affect behaviour in a porcine elevated plus-maze as suggested by the
above findings in rats.
2. Materials and methods
2.1. Animals
The experiment was conducted using animals from the National Institute of Animal
Science in Foulum, Denmark. The animals were 8-week-old female pigs ŽYorkshire=
Danish Landrace.. All animals were born in standard crates where they lived until
weaning at the age of 28 days without access to food except milk from the sow. At
weaning, animals were moved to weaning pens measuring 170 = 180 cm with 2r3
slatted floors. They lived in these cages in stable litter groups of F 7 animals per cage
throughout the period of testing. After weaning the piglets had ad libitum access to
concentrated dry pig feed and water. Two animals from each of 10 litters Ž20 pigs in
total. were randomly assigned to either the control or treatment group and tested in the
PEPM. Experienced technicians weighed the experimental pigs once each week from
weaning until 8 weeks of age.
2.2. The porcine eleÕated plus-maze
The PEPM was a modification of the apparatus described by Andersen et al. Ž2000.,
adjusted to the size of pigs at 8 weeks of age. The apparatus was composed of two
opposite, open arms without walls Ž160 = 80 cm. and two closed arms with walls
Ž160 = 80 = 60 cm3 . that radiated from a central platform Ž80 = 80 cm2 . to form a plus
sign. The floor surface of the apparatus was elevated to a height of 90 cm above the
concrete floor of the test room by four 1 = 2-in. wooden supports under each arm. The
maze floor was built in 1-in. water-resistant plywood, covered by sand, which was glued
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
171
to the plywood with transparent acrylic paint. The side and end walls of the enclosed
arms were made of transparent 5-mm plexiglas, supported along all edges with 1 = 2-in.
planks. The apparatus was set up in a test room measuring 4.4 = 5.6 m2 . The test room
was totally isolated, having concrete walls, iron sliding doors, and had no windows. The
room was lit by neon lamps mounted on the ceiling.
2.3. Treatments
All testing was performed on 5 days over a 5-week period between 1400 and 1600 h
with the 10 litters distributed over test days according to age. Pigs from the treatment
group were removed singly from their home pen. Each test animal was lifted by two
arms under its body and placed onto the floor outside the home cage. It was then led
through a door to the hallway, the technician gripping the animal’s ear with one hand,
the other hand placed behind its rump. Upon entering the hallway, a second technician
fitted a nose snare on the animal. The nose snare circled over the test animal’s snout and
passed through the mouth Žbehind the incisor teeth.. After this the technician took a
blood sample from the jugular vein by vena puncture, while another technician held the
animal firmly in the nose snare, effectively limiting its movement. From the time the
technician entered the home pen until the needle was removed from the animal took
55 " 33 s Žmean " s.d... After taking the blood sample, the nose snare was immediately
removed. The pigs were then lifted into a transport trolley and moved to the door outside
of the test room before being placed into the center of the PEPM facing an open arm.
The time from when the technician entered the home pen to catch the animal until it was
placed onto the PEPM apparatus was always 5 min for the treatment group. After
placing the animal onto the apparatus, the technician immediately exited the room and
closed the door.
Animals in the control group were caught, transported and placed onto the test
apparatus in the shortest possible time to minimize handling-related stress. Because of
this attempt to minimize handling duration, the time from when the technician entered
the home cage of animals in the control group until they were placed onto the maze was
194 " 111 s Žmean " s.d... Behaviour was filmed by a video camera mounted above the
plus-maze apparatus and connected to a monitor and VCR in an adjacent observation
room. Observations were made from film using a hand-held computer ŽPsion Workabout; Noldus Information Technology, 1997. and The Observer software package
ŽNoldus Information Technology, 1995.. Behaviour was observed for a period of 5 min
from the time that the laboratory technician removed her hands from the pig after
placing it into the centre of the test apparatus facing an open arm.
Measures included the number of open- and closed-arm entries and the time spent in
the various sections of the maze, including the central platform, as well as the latency to
enter an open arm. An arm entry was defined as all four feet being over a line separating
the central platform from a maze arm. In addition to these spatiotemporal measures,
frequency of the following behaviours were also observed: ‘‘rooting’’ Ždefined as a
scraping of the snout against the floor and walls of the apparatus., ‘‘standing’’ Žwhen
the animal stood still with no locomotive movement of the feet. and ‘‘dipping’’
172
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
Table 1
Differences in porcine elevated plus-maze behavior between a treatment group Žsubject to blood sampling
prior to testing. and a control group Žno blood sampling. were not significant. The percent of variation in
behavior for which group accounted is given by the variable r 2 , derived from linear analysis of variance.
There were 10 weaned female pigs in each group
Behavior
Open entries Žtotal.
Open time Žtotal.
Closed entries Žtotal.
Closed time Žtotal.
Center time Žtotal.
Total entries Žtotal.
Latency to enter open arm
Standing Žfrequency.
Rooting Žfrequency.
Dipping Žfrequency.
Defecation Žfrequency.
Treatment group
r2
Control group
Mean
SE
Range
Mean
SE
Range
2.4
69.5
2.5
86.7
143.8
4.9
98.0
8.4
8.4
4.1
0.1
0.7
17.6
0.5
21.2
30.1
1.1
30.0
1.4
1.4
1.2
0.1
0–6
0–160
0–6
0–166
36–300
0–10
0–279
3–18
1–15
0–10
0–1
2.2
63.8
2.2
98.8
137.4
4.4
61.2
7.9
6.1
3.6
0.4
0.6
17.6
0.5
25.8
24.6
1.0
25.9
0.8
1.3
1.0
0.2
0–5
0–139
0–4
0–218
61–300
0–9
0–248
5–14
0–13
0–9
0–1
0.003
0.003
0.009
0.008
0.002
0.007
0.05
0.005
0.07
0.006
0.12
Žplacement of the snout over the edge of open arms at floor level, the pig standing either
in open arms or the central square of the apparatus..
3. Statistics
The Wilcoxon signed ranks test was used to test for differences in location between
the two groups and r 2 , derived from linear analysis of variance, was used to estimate
the percent of variation in behaviour for which the treatments accounted. Nonparametric
methods were used, as some of the data did not conform to the assumption of parametric
statistics. All tests were double sided.
4. Results
There were no significant differences in location between the mean values of
behaviour for the two treatments ŽTable 1. and treatment accounted for very little of the
variation in behaviour between groups Žsee r 2 values in Table 1..
5. Discussion and conclusion
The treatment had no effects on behaviour. This result is counterintuitive; any
reasonable experimenter should expect such aversive handling to affect motivation and
behaviour in an ensuing test. The results indicate that the test is not sensitive to variation
in the described handling and is thus reasonably robust. Fear of humans is important in
A.M. Janczak et al.r Applied Animal BehaÕiour Science 69 (2000) 169–173
173
pig production Žsee Gonyou et al., 1986; Hemsworth et al., 1990; Tanida et al., 1995.
and subjective observations indicate that handling is aversive to animals in our experimental herd. A high level of fear towards humans in the transport situation may have
reduced the behavioural differences between the groups through ceiling effects. In the
present experiment it is therefore concluded that differences in the treatment, blood
sampling followed by transport or ‘‘mere’’ transport, were not important in determining
the plus-maze behaviour of the pigs tested. However, before any conclusive statement
can be made, similar experiments should be performed on pigs that are less fearful of
humans.
References
Adamec, R.E., Sayin, U., Brown, A., 1991. The effects of corticotropin releasing factor ŽCRF. and handling
stress on behavior in the elevated plus-maze test of anxiety. J. Psychopharmacol. 5, 175–186.
Andersen, I.L., Færevik, G., Bøe, K.E., Janczak, A.M., Bakken, M., 2000. Effects of diazepam on the
behaviour of weaned pigs in three putative models of anxiety. Appl. Anim. Behav. Sci. 68, 121–130.
Cruz, A.P.M., Frei, F., Graeff, F.G., 1994. Ethopharmacological analysis of rat behavior on the elevated
plus-maze. Pharmacol. Biochem. Behav. 49, 171–176.
File, S.E., 1992. Behavioural detection of anxiolytic action. In: Elliott, J.M., Heal, D.J. ŽEds.., Experimental
approaches to anxiety and depression. Wiley, Chichester, UK, pp. 25–44.
Gonyou, H.W., Hemsworth, P.H., Barnett, J.L., 1986. Effects of frequent interactions with humans on growing
pigs. Appl. Anim. Behav. Sci. 16, 269–278.
Hemsworth, P.H., Barnett, J.L., Treacy, D., Madgwick, P., 1990. The heritability of the trait fear of humans
and the association between this trait and subsequent reproductive performance of gilts. Appl. Anim.
Behav. Sci. 25, 85–95.
Hogg, S., 1996. A review of the validity and variability of the elevated plus-maze as an animal model of
anxiety. Pharmacol. Biochem. Behav. 54, 21–30.
Lister, R.G., 1987. The use of a plus-maze to measure anxiety in the mouse. Psychopharmacology 92, 80–185.
Noldus Information Technology, 1995. The Observer system for collection and analysis of observational data,
Base Package for Windows, Reference Manual, Version 3.0. Noldus Information Technology,
Wageningen, Netherlands.
Noldus Information Technology, 1997. The Observer system for collection and analysis of observational data,
Base Package for the Psion Workabout, Users Manual, Version 3.0. Noldus Information Technology,
Wageningen, Netherlands.
Pellow, S., Chopin, P., File, S.E., Briley, M., 1995. Validation of open:closed arm entries in an elevated
plus-maze as a measure of anxiety in the rat. J. Neurosci. Methods 14, 147–167.
Rodgers, R.J., Cole, J.C., 1993. Influence of social isolation, gender, strain, and prior novelty on plus-maze
behavior in mice. Physiol. Behav. 54, 729–736.
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