Ž penned counterparts given access to straw, despite initial attempts to do so Boulton
. et al., 1997; Burne et al., 1999 . It is possible that nest building seen using the
PGF -induced nesting model is affected by the availability of suitable substrates, such
2 a
as an earth floor, straw, twigs and branches. However, PGF -treated gilts show similar
2 a
patterns of nesting behaviours, such as an increase in locomotion followed by increased pawing and rooting at straw, when housed on a concrete floor in a pen with straw
Ž .
Burne et al., 1999, in press , as they do when housed outdoors with access to an earth Ž
. floor, straw and other vegetation Gilbert et al., 2000 . Therefore, it may be that the
differences we have observed in PGF -induced nesting as a result of environmental
2 a
Ž .
disturbance confinement in a crate without straw are due to the complete absence of any nesting substrate.
The aim of this experiment is to investigate PGF -induced nesting behaviour in pigs
2 a
housed under the same conditions but with or without access to straw. We chose to use straw as a nesting substrate, rather than an earthen floor for example, because it is
inexpensive, readily available and widely used in commercial husbandry systems. Moreover, because most late pregnant sows in the UK are housed on concrete floors, the
provision of a wide range of substrates other than straw is simply not practical. A balanced design to test the hypothesis that straw has an effect on nesting behaviour
would require selecting pigs that have either been housed for long periods on a bare floor or provided with daily access to straw. However, we restricted this study to pigs,
which had been given daily access to straw. This experiment tested the hypothesis that acute removal of straw would alter the expression of PGF -induced nesting behaviour.
2 a
This would establish whether the PGF -induced nesting model is sensitive to environ-
2 a
mental feedback.
2. Methods
2.1. Animals and housing Large White gilts were selected from the Babraham herd after their first oestrus cycle
Ž at ca. 6 months of age. Trials were run in three separate batches in April, August and
. Ž
. December of 1998 and animals housed in groups of 10 in a large covered pen 4 = 8 m
Ž for the first 3 weeks of the experiment. Twenty-four gilts showing signs of oestrus see
. below were selected and transferred in three sequential batches of eight to individual
Ž .
pens in a large enclosed fan-ventilated barn 40 days before the test day, see below . Ž
. Each pen 2.8 = 1.7 m was constructed with solid walls and a concrete floor subdivided
Ž .
by a step into a raised lying area with under floor insulation 1.8 = 1.7 m draining onto Ž
. a dunging area at the rear of the pen 1.0 = 1.7 m . Gilts were floor fed 1.5 kg pelleted
Ž .
ration Dalgety Agricultural Food, Bury St Edmunds, UK and given 2 kg fresh straw in Ž
. the lying area once a day after their pen was cleaned 0800–0830 h . Water was
available ad libitum from a bite drinker on the wall above the dunging area. Animals Ž
. were kept under artificial light from fluorescent strip lights 0800–1800 h in addition to
natural daylight and the temperature varied between 108C and 258C. The gilts were
handled for 10 min a day while they were housed individually to permit familiarisation with the experimenters.
2.2. Pseudopregnancy Ž
. Each gilt received an oral dose 20 mgrday of the synthetic progesterone Al-
Ž .
trenogest Regumate Porcine, Hoechst, Milton Keynes, UK for 18 days to synchronise oestrus. The gilts were then run with a teaser boar for 7 days to monitor for signs of
oestrus. The first day of standing oestrus is referred to as day 0 of the oestrous cycle. Pseudopregnancy was induced with five daily intramuscular injections of 5 mg oestra-
Ž .
diol valerate Sigma, Poole, UK in 0.5 ml sesame oil on days 11–15 of the oestrous cycle. On days 39–41 of pseudopregnancy, each gilt was fitted with an indwelling
jugular catheter as part of a larger experiment. At the end of the experiment, the gilts were given a lethal dose of sodium pentobarbitone into the catheter exactly 65 min after
Ž .
treatment with saline or PGF see below and the brains removed for future histochem-
2 a
ical analysis. Post-mortem inspection on the test day revealed that two gilts had an unenlarged uterus and no corpora lutea and were deemed not to be pseudopregnant. In
addition, one gilt had corpora albicana present and was deemed to have broken pseudopregnancy several days prior to the test day. However, the behavioural data from
Ž .
these animals n s 1 PGF -treated, n s 2 saline-treated did not vary significantly from
2 a
that of the remaining animals and the full data set obtained from 24 animals was analysed together.
2.3. Experimental protocol Ž
. Ž
. Nest building was induced during the morning 1030 h or afternoon 1500 h on day
46 or 47 of pseudopregnancy and this day is referred to as the test day. The pens were cleaned out at 0900 or 1330 h. Half of the gilts had 2 kg fresh straw added to the pen
lying area and the remaining gilts were left in a bare pen. This was the first day that gilts tested in a bare pen had been without straw in the experiment. All gilts received an
Ž .
intramuscular injection randomly into either the left or right side of the neck of 15 mg Ž
. PGF
Lutalyse, Upjohn, Crawley, UK or 3 ml saline at either 1030 or 1500 h. Each
2 a
animal was tested once only. All treatments were allocated in a Latin-square design Ž
. treatment, substrate, time of day to give n s 6 animals in each of the following groups;
saline-treated without straw, saline-treated with straw, PGF -treated without straw and
2 a
PGF -treated with straw.
2 a
2.4. BehaÕioural obserÕations Ž
. The gilts behaviour was recorded for 1 h before pre-treatment to 1 h after treatment
Ž .
with saline or PGF post-treatment on the test day by video cameras attached to
2 a
time-lapse video recorders recording at 24 framesrs. We decided to observe behaviour for only 1 h post-treatment as this period of time has been shown previously to include
Ž peak levels of nesting activity in pigs given PGF
Blackshaw, 1983; Widowski and
2 a
. Curtis, 1989; Burne et al., 1999, in press . Two cameras were positioned at the front
corners of the pen and a third camera was situated 2 m directly above the pen, unlike
Ž .
previous studies, in which a single overhead camera was used e.g. Boulton et al., 1997 . The additional cameras at the corners of the pen permitted more detailed observation of
the gilts’ behaviour. A microphone was also positioned above the pen to record the gilts’ vocalisations, which were scored as one of three different types of call: grunt, squeal or
woof. The onset and duration of each behaviour was scored using the Observer
Ž .
computer package Noldus, 1991 and they are defined in Table 1. 2.5. Statistical analyses
The behavioural data were quantified using the elementary statistics option of the Ž
. Observer computer package
Noldus, 1991 . The behaviours were pooled into the following categories for analysis; stand, lie, change posture, inactive, root, paw, gather,
Ž .
scratch, essential and vocalise see Table 1 . Based on previous studies, the key nesting Ž
behaviours measured included root, paw and gather Widowski and Curtis, 1989; Jensen, .
1993; Burne et al., 1999 . We chose to analyse the post-treatment behavioural data in
Table 1 Behavioural ethogram
Posture Ž
. Stand duration : standing on all four legs
Ž .
Lie duration : lying on the belly Ž
. Change posture frequency : moving between postures — sit, kneel, lie and stand
Behaviour Ž
. Inactive duration : no part of the pig is moving
Ž .
Root duration Forage: oro-nasal contact with straw whilst chewing
Root straw: oro-nasal contact with straw and head-movement but without chewing Root floor: oro-nasal contact with floor and head-movement
Root wall: oro-nasal contact with wall and head-movement Ž
. Chew fixture: chewing at any of the fixtures within the pen apart from the drinker
Ž .
Paw frequency Paw straw: raking movement of either foreleg at an area of floor covered in straw
Paw floor: raking movement of either foreleg at an area of floor devoid of straw Paw wall: raking movement of either foreleg at the walls of the pen
Ž .
Gather duration Lift straw: grasping straw in the mouth and raising the head without locomotion
Carry straw: grasping straw in the mouth and taking at least two steps Ž
. Scratch frequency
Object scratch: scratch or rub any part of the body against another object Rear leg scratch: scratch or attempt to scratch, any part of the body with the rear leg
Ž .
Essential frequency Defaecate
Urinate Drink: oro-nasal contact with drinker
Ž .
Vocalise frequency Grunt, low-pitched call
Squeal, high-pitched call Woof, distinctive alarm call
detail. The data were non-normally distributed and non-parametric statistical procedures Ž
. were used Siegel and Castellan, 1988 . The data sets for frequency per hour and
Ž .
percentage duration were analysed using a Kruskal–Wallis test H
and, where this indicated significant differences between groups, was followed by post-hoc Mann
Ž Whitney tests. Behaviours which were only possible in animals supplied with straw e.g.
. gather were analysed with Mann Whitney tests alone.
Ž Preliminary analysis of the data for two measures of activity proportion of time
. inactive and proportion of time standing in the hour pre-treatment indicated that the
Ž .
Ž time of the injection morning or afternoon was not a significant factor U 49,
. Ž
P 0.2 . Thus, the data were pooled for time of day n s 12 tested in the morning and .
n s 12 tested in the afternoon . Variation was seen in environmental temperature between the test day for each batch of pigs. The temperature within the barn was
measured at the time of injection and there was a significant difference in the mean Ž
Ž .
temperature between the separate batches of pigs mean temperature SEM 8C ; batch 1: 15.5 0.5; batch 2: 23.5 1.3; batch 3: 11.1 0.5; F
s 48.8, P - 0.001; one-way
2,23
. analysis of variance . However, there was no overall significant difference between
Ž groups salinerno straw: 16.8 2.08C; salinerstraw: 16.8 2.98C; PGF rno straw:
2 a
. 15.2 2.08C; PGF rstraw: 18.0 2.78C; F
s 1.3, P s 0.3 and so temperature was
2 a 3,23
not included as a variable in the analysis.
wŽ . Ž .
Ž . x
Ž . Fig. 1. Median scores for nesting behaviour, a gather, b paw and c root and duration of time inactive d
by pigs housed in a bare or a strawed pen of the same size. The error bars indicate the interquartile range Ž
. lower bar: 25th percentile, upper bar: 75th percentile . Data are presented for the hour post-treatment with
Ž .
Ž .
Ž .
saline open bars or PGF hatched bars . Bars with different letters a,b,c,d within each histogram are
2 a
significantly different P - 0.05, post-hoc Mann Whitney test.
3. Results
