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The effects of branches on prepartum nest building
in gilts with access to straw
B.I. Damm
), K.S. Vestergaard, D.L. Schrøder-Petersen, J. Ladewig
The Royal Veterinary and Agricultural UniÕersity, DiÕision of Ethology and Health, GroennegaardsÕej 8,1870 Frederiksberg C, Denmark
Accepted 27 March 2000
Abstract
Sows farrowing in a semi-natural environment terminate nest building 1–7 h prior to parturition after having built a nest for which a variety of materials are used. No nest-building behaviour occurs during parturition and the sows remain lying in the nest throughout most of the farrowing. In contrast, many intensively housed sows are restless during farrowing. To investigate whether gilts housed indoors would use branches for nest building and whether access to branches would affect the termination of nest building and parturient behaviour, we studied gilts housed
Ž .
individually in pens designed to stimulate natural nest building. The control group ns21 had
Ž .
unlimited access to straw and the experimental group ns21 had unlimited access to straw and branches. During nest building all the gilts used straw and all the experimental gilts also used branches. In the experimental group the interval from termination of nest building to birth of the
Ž . Ž
first piglet BFP was significantly longer than in the control group 132 versus 58 min,
.
Ps0.04 . In the experimental group, nest-building behaviour was also performed by fewer Ž
individuals during the interval from BFP until 2 h after than in the control group 38% versus 71% .
of the gilts, Ps0.03 . Gilts that performed nest building during this interval carried out more
Ž . Ž .
postural changes P-0.001 and spent less time in lateral recumbency Ps0.001 than gilts
which did not perform nest building. On average, gilts that performed nest building behaviour
Ž .
after BFP ns26 spent 54% of the first 2 h of parturition in lateral recumbency and carried out 16 postural changes. Gilts that did not perform nest building behaviour during this interval Žns16 spent 85% of the time in lateral recumbency and carried out five postural changes. In 10. gilts that were selected randomly from the experimental group nest building was studied in more detail. In these gilts nest building peaked between 17 and 6 h prepartum. There was no difference in amount of behaviour directed towards straw and amount of behaviour directed towards branches.
)Corresponding author. Tel.:q45-35-28-30-36; fax:q45-35-28-30-22.
Ž .
E-mail address: [email protected] B.I. Damm .
0168-1591r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved. Ž .
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The results indicate that the termination of nest building in sows is under environmental feedback control. When only straw was provided the nests did not have much of a lasting structure. However, when gilts had access to straw and branches more structured and functional nests could be built. These nests may have been more effective in reducing the motivation for nest
building prior to the onset of parturition.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Nest building behaviour; Parturition; Environmental enrichment; Sows; Swine
1. Introduction
In recent years welfare considerations have resulted in increased interest in loose housing systems for parturient and lactating sows. However, piglet mortality in these
Ž
systems tends to be higher than in systems with farrowing crates Nielsen, 1996; Arey,
. Ž
1997 . Maternal behaviour can greatly affect piglet health and survival Wechsler and .
Hegglin, 1997 , and therefore a detailed understanding of the regulation of periparturient behaviour is necessary in order to apply these systems successfully.
Within the last 24 h prior to parturition sows are motivated for building a nest ŽJensen, 1986; Castren et al., 1993 . Wild boar sows as well as domesticated sows in
´
. semi-natural environment build a nest by excavating a hollow, and pawing and ripping grass or straw into the hollow. They then collect grass, straw, twigs and branches, whichŽ .
are carried to and arranged at the nest site Gundlach, 1968; Jensen, 1986 . In a semi-natural environment nest building was terminated 1 to 7 h prior to farrowing ŽJensen, 1986; Stolba and Wood-Gush, 1989 and no nest building was performed after.
Ž .
parturition had begun Petersen et al., 1990 . In contrast, it has been found that under Ž
intensive housing conditions some sows remain restless during parturition Fraser et al., .
1995; Cronin et al., 1998 . Some of this restlessness may be due to nest building behaviour still being performed. Nest building during parturition has been observed in
Ž .
confined and loose housed sows Baxter, 1982; Vestergaard and Hansen, 1984 , as well Ž as in sows given access to nest materials and sows given no materials at all Baxter,
. 1982; Thodberg et al., 1999 .
Ž
Nest building appears to be both internally and externally controlled Jensen, 1988, .
1993; Arey et al., 1991; Boulton et al., 1997a,b . Thus, the termination of the behaviour may depend not only on physiological changes associated with the impending parturition
Ž .
but also on feedback from the nest Jensen et al., 1993 . Contrary to the variety of nest materials used in semi-natural environment, commercial housing and many experimental studies have provided sows with only straw, wood shavings or other materials of which
Ž .
little more than a pile can be constructed Castren et al., 1993; Nielsen, 1996 . If it is
´
impossible for the sow to build a functional nest the motivation for nest building may be sustained longer than in semi-natural environment. It may even be sustained beyond the onset of parturition.
The objective of our experiment was to investigate whether the construction of a nest of greater resemblance to nests built in a natural environment would have a positive effect on the behaviour of gilts before and during parturition. It was hypothesised that Ž .1 gilts housed indoors would use branches for nest building, 2 gilts with access toŽ .
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Ž .
straw and branches would terminate nest building sooner and 3 they would be calmer during parturition than gilts with access to straw only.
2. Materials and methods
2.1. Animals, housing and care
Forty-two primiparous Danish Landrace Yorkshire crossbred sows were used. During gestation the animals were housed in stalls, in which they had access to cut straw. By random selection the gilts were designated to either an experimental group with straw and branches or a control group with only straw. Five to seven days prior to the
Ž .
expected date of parturition the gilts were moved to individual farrowing pens Fig. 1 which were situated in the same room. The pens were designed to stimulate and allow
Ž .
natural nest-building behaviour Schmid, 1991, 1993 . A 2.6=2.7 m pen was divided
Ž 2.
into a resting area 2.86 m covered by 20 kg of long cut straw and a solid floor Ž 2.
activity area 4.16 m . A piglet box was situated in the centre of the pen. A nipple drinker, a feed trough, a straw rack and a branch rack were placed in the activity area. The racks were filled regularly and the gilts thus had unlimited access to nest building material. The materials were bare branches of 2–4 cm in diameter and 40–75 cm in
Ž . Ž .
length experimental group and long cut straw experimental and control group . The gilts were fed standard sow rations twice daily. If, however, nest building was apparently terminated and parturition was pre-eminent the ration was withheld until 2 h
Ž .
after birth of the first piglet BFP . This was done to prevent disturbance of gilts, which had possibly completed nest building and might remain in their nests if undisturbed. The
Ž
Fig. 1. Schematic drawing of the farrowing pen, which is slightly modified form the design of Schmid 1991,
. Ž .
1993 . In the experimental group ns21 both straw and branch racks were filled regularly. In the control
Ž .
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activity area was cleaned daily and the straw-bedded area was cleaned if soiled. When Ž
signs of nest building nest building behaviour, materials removed from the racks or .
materials arranged in the resting area had been observed the pen was no longer entered. Room temperature was kept at 17"38C and recorded every morning throughout the experiment. The room was ventilated by fans and lit both by natural daylight and artificial lighting switched on at 07.00 h and off at 15.00 h. At all hours infrared lamps switched on automatically when light became too dim for video recording to take place. 2.2. BehaÕioural obserÕations
The gilts were video recorded from day 113 in gestation until parturition was
Ž .
completed using 24 h time lapse recording three frames per second . The period from 24 h prior to BFP until 2 h after BFP was observed and analysed.
2.2.1. Prepartum nest building behaÕiour
For all gilts it was recorded whether the provided materials were used for nest building during the last 24 h prior to BFP. The criterion for use of materials was that the gilt collected and arranged straw or both straw and branches when these were provided. Furthermore, the time of termination of nest building was recorded. The prepartum phase was divided into 5-min intervals. Termination of nest building was then defined as the end of the last 5-min interval in which rooting had occurred in more than two successive intervals or the end of the last interval in which collecting or arranging straw or branches had been performed.
In order to describe the use of branches, 10 gilts were selected randomly from the experimental group. Detailed behavioural analysis was carried out from 24 h prior to parturition until 2 h after BFP. Nest building was recorded by onerzero sampling in 5-min intervals. The behaviours recorded were rooting, pawing, collecting strawrbranches, arranging strawrbranches, and biting the pen equipment.
2.2.2. Parturient behaÕiour
For all gilts it was recorded whether or not nest building occurred during the first 2 h of parturition. Nest building during parturition was defined as occurrence of pawing, collecting or arranging straw or at least 4 min of standing in the nest rooting. The 4-min criterion was chosen on the basis of observations from semi-natural environment ŽPetersen et al., 1990 . Here sows were observed to get up to sniff their piglets during. farrowing, but this usually lasted less than 1 min and never more than 3 min. Additionally, number of minutes spent in lateral recumbency with the udder exposed and number of postural changes were recorded. Number of postural changes included all changes between lying, sitting and standing. Definitions of nest building behaviours can be seen in Table 1.
2.3. Statistical methods
When analyses which require normality of data were used, the distribution was tested
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Table 1
Behaviour recorded by 1r0 sampling in 5-min intervals in 10 gilts with branches from 24 h prepartum until 2 h after BFP
Behaviour Definition
Rooting Snout movements directed at the straw bedding or at branches in the bedding Pawing Moving a foreleg back and forth in the straw bedding
Collecting straw Taking straw from the rack or floor and carrying it in the mouth while taking at least two steps
Collecting branches Taking branches from the rack or floor and carrying it in the mouth while taking at least two steps
Arranging straw All other straw-directed behaviour than rooting and collecting straw that occurred in the resting area
Arranging branches All other branch-directed behaviour than rooting and collecting branches that occurred in the resting area
Biting pen equipment Biting and chewing pen equipment
termination of nest building to BFP in gilts with branches and gilts with no branches was compared by survival analysis using a Log-Rank test in the Proc Lifetest of SAS ŽAllison, 1995 . The association between provision of branches and frequency of. animals performing nest building during parturition was analysed by a x2
test in the
Ž .
Proc Freq of SAS Delwiche and Slaughter, 1995 . Wilcoxon 2-sample tests using the
Ž . Ž .
Proc Npar1way of SAS 1989 were carried out to compare the 1 number of postural Ž . changes and time spent in lateral recumbency between the two treatment groups, 2 number of postural changes and time spent in lateral recumbency between gilts that did
Ž .
perform nest building during parturition and gilts that did not, and 3 the room temperatures for the two treatment groups. Use of branches and straw in the 10 gilts that were studied in detail was analysed by paired t-tests using the Proc Means of SAS ŽDelwiche and Slaughter, 1995 ..
3. Results
3.1. Prepartum nest building behaÕiour
All gilts farrowed in the straw-bedded area after having used straw or both straw and branches when these were provided. Gilts with access to branches had a significantly longer interval from termination of nest building to BFP than gilts with no access to
Ž .
branches Ps0.04 . On average, gilts with access to branches terminated nest building
Ž .
132 S.E.s33.1 min prior to parturition, whereas gilts with no access to branches
Ž . Ž .
terminated nest building 58 S.E.s21.1 min prior to parturition Table 2 . Ž In the 10 gilts observed in detail, nest building peaked from 17 to 6 h prepartum Fig. .
2 . Total number of 5-min intervals in which straw and branches were collected
Ž . Ž .
averaged 21.3 S.E.s5.6 and 14.2 S.E.s3.9 , respectively. This correspond to 5.1% Žstraw collection and 3.4% branch collection of all the 5-min intervals from 24 h prior. Ž .
Ž .
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Table 2
Termination of nest building and parturient behaviour in gilts. Numbers with different superscripts differ at the 0.05 level
Variable Branches No branches
Žns21. Žns21.
a b
Interval from termination of nest building to parturition"S.E. 131.8"33.1 57.7"21.1
a b
Percentage of gilts performing nest building during the first 2 h of parturition 38 71 Number of postural changes during first 2 h of parturition"S.E. 9.2"2.1 9.7"2.4 Minutes spent in lateral recumbency during first 2 h of parturition"S.E. 95.3"5.7 80.1"9.2
Ž .
23.8 S.E.s9.1 intervals, respectively, which corresponds to 8.1% and 5.9% of all the 5-min intervals. There was no overall difference between number of intervals with
Ž .
collecting straw and number of intervals with collecting branches Ps0.16 . Nor was there a difference between number of intervals with arranging straw and number of
Ž .
intervals with arranging branches Ps0.32 . The data indicated that the greatest difference between amount of straw- and amount of branch-directed behaviour might
Ž .
have occurred in the interval from 11 to 6 h prepartum Fig. 2 and therefore this period was analysed separately. A tendency for more intervals with collecting straw than
Ž .
collecting branches Ps0.07 was found, but there was no difference in number of
Ž .
intervals with arranging straw or branches Ps0.17 . The differences between straw-and branch-directed behaviour were normally distributed. Biting the pen equipment occurred in 9 of the 10 gilts and it was always directed at the wooden piglet box in the
Ž .
centre of the pen. On average the gilts were biting the box in 5.5 S.E.s1.6 5-min
Ž .
intervals 1.3% of all intervals and this took place from 24 to 3 h prepartum. Room
Ž .
temperature did not vary between groups Ps0.48 . 3.2. Parturient behaÕiour
In the group of gilts that had access to branches there were significantly fewer individuals that performed nest building behaviour during parturition than in the group
Ž .
which did not have access to branches Ps0.03 . Seventy-one percent of the gilts with no access to branches performed nest building during the first 2 h of parturition, whereas
Ž .
only 38% of the gilts with access to branches did so Table 2 . Nest building behaviours performed during parturition were rooting, pawing and arranging straw or branches.
Ž .
There were no effects of treatment on number of postural changes Ps1.00 or on time
Ž . Ž .
spent in lateral recumbency Ps0.47 Table 2 . However, when these parameters were tested with occurrence of nest building as the independent variable, it was found that gilts, which performed nest building during parturition carried out significantly more
Ž .
postural changes P-0.001 and spent significantly less time in lateral recumbency ŽPs0.001 than gilts which did not perform nest building during parturition. On.
Ž .
average, gilts that performed nest building behaviour during parturition ns26 spent
Ž . Ž
65 S.E.s9.6 min of the first 2 h of parturition in lateral recumbency 54% of the
. Ž .
time and carried out 16 S.E.s2.9 postural changes. Gilts that did not perform nest
Ž . Ž .
building behaviour during this interval ns16 spent 102 S.E.s5.0 min of the time
Ž . Ž .
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Fig. 2. Branch-directed behaviour, straw-directed behaviour and total nest building during the 24 h preceding parturition until 2 h after BFP. BFP is indicated as 0. Behaviours are shown as mean number of 5-min intervals per hour in which the behaviours were performed.
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4. Discussion
In the group of gilts that had access to branches, fewer individuals performed nest building during parturition and they terminated nest building earlier prior to parturition. Several investigations have shown that nest building in sows is a complex set of
Ž .
behaviours with an element of internal Widowski et al., 1990; Blackshaw, 1983 as well
Ž .
as external control Jensen, 1988, 1993; Arey et al., 1991 . However, the exact
Ž .
regulation is still not known in detail. Jensen 1988, 1993 has proposed a model in which the behaviour is divided into an initial internally controlled phase of rooting and pawing and a subsequent phase of gathering and arranging nest material that depends more on environmental feedback. The results of our experiment support the contention that the later stage and in particular the termination of nest building is under environ-mental feedback control. Nests that were built of straw only did not seem to have much of a lasting structure, but when gilts were provided with both straw and branches more functional nests could be built. These nests may have been more effective in reducing the motivation for nest building prior to parturition. In some behaviours the motivation may be reduced primarily via performance of the behaviour, whereas the function or
Ž .
result of the behaviour is of less importance Vestergaard et al., 1999 . In the present experiment, it cannot be completely excluded that it was not the nest as such that had an effect, but rather the mere performance of nest-building behaviour. However, this seems unlikely because the behaviours directed towards straw were very similar to those directed towards branches and they occurred concurrently during the nest building phase. Therefore, branch-directed behaviour did not seem to be a certain class of behaviours that was never elicited in gilts with only straw. Although the results show that the termination of nest building was affected by environmental factors, internal factors may also have been involved. Changes in internal factors may increase
sensitiv-Ž . Ž .
ity to external stimuli Haskell and Hutson, 1996 . Castren et al.
´
1993 found a correlation between the termination of nest building and plasma concentrations ofŽ
oxytocin, which begin to rise 7 to 3 h prior to parturition Castren et al., 1993; Lawrence
´
. Ž
et al., 1995 leading to frequent uterine contractions Forsling et al., 1979; Gilbert et al., .
1994 . Feedback from the completed nest in combination with increased uterine muscular activity and possibly other physiological changes may cause the termination of nest building. It is also likely that strong frequent contractions can bring about the termination of nest building in the absence of a completed nest, but this termination may occur later than the one mediated by both internal factors and adequate feedback from the nest.
All the gilts in the present experiment used the available nest materials. In semi-natu-ral environments not all sows used branches, although this was more common in the
Ž .
winter season Jensen, 1989 . The reason may be that it was colder in winter and that this stimulated the sows to build larger, more thermostable nest or that in summer other
Ž Ž ..
materials e.g. fern leaves, Vestergaard, personal communication substituted branches by giving structure to the nest. Similarly, in the present experiment branches may have been used by all gilts that had access to them because the room temperature was cool enough to stimulate the use of branches or because the nest materials were limited to
Ž
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.
neighbouring pens, management routines or the pen design may also have increased the use of branches relative to the descriptions of nest building in semi-natural environment. In the 10 gilts observed in detail, nest building peaked between 17 and 6 h prepartum,
Ž
which is in accordance with nest building observed in other studies Vestergaard and .
Hansen, 1984; Thodberg et al., 1999 . The nest building behaviour observed before 17 h Ž
prepartum is, however, not a common finding e.g. Arey et al., 1991; Haskell and .
Hutson, 1996 . The relatively early performance of collecting and arranging materials
Ž .
does not support the model proposed by Jensen 1988, 1993 . According to the model, collecting and arranging materials belong to phase two and should not occur from the onset of nest building. An explanation could be that the materials acted as eliciting
Ž .
stimuli for phase two behaviours. Arey et al. 1991 found that nest building generally occurred earlier when pre-formed nests were presented to sows, and carrying materials was observed as early as 24 h prepartum. This indicates that the availability of nest
Ž .
materials can affect the timing of nest building Arey et al., 1991 , an effect that may Ž
operate at the level of elicitation of behaviour directed towards straw Thodberg et al., .
1999 and in our experiment, also towards branches.
Biting the pen equipment was observed in 9 of the 10 gilts at a low frequency from 24 to 3 h prior to parturition. It has previously been suggested that biting pen equipment may be vacuum-like gathering of material or behaviour derived from the motor pattern
Ž .
for tearing twigs and branches from trees and bushes Jensen, 1993 . The gilts in our experiment had unlimited access to straw and branches in racks, so it is unlikely that they performed vacuum-like gathering behaviour. However, the branches were presented in the rack as a loose pile, so they could merely be collected, not torn. This may have resulted in vacuum-like tearing or in tearing elicited by the box and performed with the purpose of using the box material for nest building or removing it from the preferred nest site.
Both in the experimental and in the control group several gilts performed nest building during parturition. Individual gilts may differ in their requirements for a satisfactory nest and the continued behaviour indicates that the sows’ motivation was not satisfied during the prepartum phase normally designated to this behaviour. Nest building is energy consuming for the parturient animal and risky for the offspring and therefore it can hardly be viewed as a successful adaptation to the environment. Overall, branches and straw as nest materials appeared to be better than straw alone, but in some cases straw was sufficient and in others even straw and branches were insufficient. In a semi-natural environment sows sought isolation and selected a nest site before nest
Ž .
building was commenced Jensen, 1986 . In the present experiment the animals were only given the limited isolation that was provided by the pen design, they had little choice of nest site and they also could not excavate a lasting hollow in the straw bedding. Possibly, the results of these initial behaviours are important in the later feedback-regulated phase of nest building. Feedback from an appropriate nest site andror a hollow may have been inadequate in our experiment and have led to the continued nest building in gilts from both groups.
Nest building during parturition was associated with increased number of postural changes. Domestic sows in a semi-natural environment stood up an average of 3.3 times
Ž .
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piglets and they also frequently turned around either to lie on the other side or to face in
Ž .
the opposite direction Jensen, 1986 . Thus, both the average of 16 postural changes found in gilts that performed nest building during parturition and the average of five in gilts that did not may be a part of the normal parturient behaviour of sows. However, wild boar sows in a natural environment gave birth in lateral recumbency, changing only
Ž .
from one side to another Gundlach, 1968 . Samples sizes were small in the studies done on wild sows and domestic sows in semi-natural environments and further studies are needed to quantify the normal restlessness of parturient sows.
Postural changes and time spent in lateral recumbency are likely to have implications
Ž .
for the piglets as they are born Fraser et al., 1995 . The piglets can only find and remain near the udder if the sow is lying down in lateral recumbency and if the sow carries out many postural changes there is a risk of piglet crushing. A risk that may be further
Ž
increased if the piglets have consumed little or no colostrum English and Smith, 1975; .
Weary et al., 1996 .
It has to be kept in mind that the results of our experiment may be particular to
Ž .
primiparous sows. Age or experience modifies nest-building behaviour Jensen, 1989
Ž .
and parity can interact with farrowing environment Thodberg et al., 1999 . Gilts may
Ž .
also be more fearful or agitated at parturition than experienced sows Baxter, 1982 . Therefore, extrapolation of these results to older, more experienced animals should be done with caution.
In conclusion, indoor gilts used branches for nest building. When gilts had access to branches, fewer individuals performed nest building during parturition and they also terminated nest building sooner. The results indicate that the termination of nest building is under environmental feedback control. Nest building during parturition was positively correlated with number of postural changes and negatively correlated with time spent in lateral recumbency. Therefore, providing preparturient sows with relevant nest materials may potentially improve sow welfare and piglet health and survival.
Acknowledgements
We are grateful to The Federation of Danish Pig Producers and Slaughterhouses for supplying animals, facilities and care of the animals. We also thank L. Lawson for statistical advice and Dr. P.F. Johnsen and Dr. L. Alban for useful comments on an earlier draft of this manuscript. The study was supported by a grant from the Danish Academy of Sciences.
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Stolba, A., Wood-Gush, D.G.M., 1989. The behaviour of pigs in a semi-natural environment. Anim. Prod. 48, 419–425.
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Thodberg, K., Jensen, K.H., Herskin, M.S., Jørgensen, E., 1999. Influence of environmental stimuli on nest building and farrowing behaviour in domestic sows. Appl. Anim. Behav. Sci. 63, 131–144.
Vestergaard, K., Hansen, L.L., 1984. Tethered versus loose sows: ethological observations and measures of productivity: I. Ethological observations during pregnancy and farrowing. Ann. Rech. Vet. 15, 245–256. Vestergaard, K.S., Damm, B.I., Abbott, U., Bildsøe, M., 1999. Regulation of dustbathing in feathered and
featherless domestic chicks. Anim. Behav. 58, 1017–1025.
Weary, D.M., Pajor, E.A., Thompson, B.K., Fraser, D., 1996. The relationship between piglet body condition and proximity to the sow: a trade-off between feeding and the risk of mortality by maternal crushing?. Anim. Behav. 51, 619–624.
Wechsler, B., Hegglin, D., 1997. Individual differences in the behaviour of sows at the nest-site and the crushing of piglets. Appl. Anim. Behav. Sci. 51, 39–49.
Widowski, T.M., Curtis, S.E., Dziuk, P.J., Wagner, W.C., Sherwood, O.D., 1990. Behavioural and endocrine
Ž .
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Fig. 2. Branch-directed behaviour, straw-directed behaviour and total nest building during the 24 h preceding parturition until 2 h after BFP. BFP is indicated as 0. Behaviours are shown as mean number of 5-min intervals per hour in which the behaviours were performed.
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4. Discussion
In the group of gilts that had access to branches, fewer individuals performed nest building during parturition and they terminated nest building earlier prior to parturition. Several investigations have shown that nest building in sows is a complex set of
Ž .
behaviours with an element of internal Widowski et al., 1990; Blackshaw, 1983 as well
Ž .
as external control Jensen, 1988, 1993; Arey et al., 1991 . However, the exact
Ž .
regulation is still not known in detail. Jensen 1988, 1993 has proposed a model in which the behaviour is divided into an initial internally controlled phase of rooting and pawing and a subsequent phase of gathering and arranging nest material that depends more on environmental feedback. The results of our experiment support the contention that the later stage and in particular the termination of nest building is under environ-mental feedback control. Nests that were built of straw only did not seem to have much of a lasting structure, but when gilts were provided with both straw and branches more functional nests could be built. These nests may have been more effective in reducing the motivation for nest building prior to parturition. In some behaviours the motivation may be reduced primarily via performance of the behaviour, whereas the function or
Ž .
result of the behaviour is of less importance Vestergaard et al., 1999 . In the present experiment, it cannot be completely excluded that it was not the nest as such that had an effect, but rather the mere performance of nest-building behaviour. However, this seems unlikely because the behaviours directed towards straw were very similar to those directed towards branches and they occurred concurrently during the nest building phase. Therefore, branch-directed behaviour did not seem to be a certain class of behaviours that was never elicited in gilts with only straw. Although the results show that the termination of nest building was affected by environmental factors, internal factors may also have been involved. Changes in internal factors may increase
sensitiv-Ž . Ž .
ity to external stimuli Haskell and Hutson, 1996 . Castren et al.
´
1993 found acorrelation between the termination of nest building and plasma concentrations of Ž
oxytocin, which begin to rise 7 to 3 h prior to parturition Castren et al., 1993; Lawrence
´
. Ž
et al., 1995 leading to frequent uterine contractions Forsling et al., 1979; Gilbert et al., .
1994 . Feedback from the completed nest in combination with increased uterine muscular activity and possibly other physiological changes may cause the termination of nest building. It is also likely that strong frequent contractions can bring about the termination of nest building in the absence of a completed nest, but this termination may occur later than the one mediated by both internal factors and adequate feedback from the nest.
All the gilts in the present experiment used the available nest materials. In semi-natu-ral environments not all sows used branches, although this was more common in the
Ž .
winter season Jensen, 1989 . The reason may be that it was colder in winter and that this stimulated the sows to build larger, more thermostable nest or that in summer other
Ž Ž ..
materials e.g. fern leaves, Vestergaard, personal communication substituted branches by giving structure to the nest. Similarly, in the present experiment branches may have been used by all gilts that had access to them because the room temperature was cool enough to stimulate the use of branches or because the nest materials were limited to
Ž
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.
neighbouring pens, management routines or the pen design may also have increased the use of branches relative to the descriptions of nest building in semi-natural environment. In the 10 gilts observed in detail, nest building peaked between 17 and 6 h prepartum,
Ž
which is in accordance with nest building observed in other studies Vestergaard and .
Hansen, 1984; Thodberg et al., 1999 . The nest building behaviour observed before 17 h Ž
prepartum is, however, not a common finding e.g. Arey et al., 1991; Haskell and .
Hutson, 1996 . The relatively early performance of collecting and arranging materials
Ž .
does not support the model proposed by Jensen 1988, 1993 . According to the model, collecting and arranging materials belong to phase two and should not occur from the onset of nest building. An explanation could be that the materials acted as eliciting
Ž .
stimuli for phase two behaviours. Arey et al. 1991 found that nest building generally occurred earlier when pre-formed nests were presented to sows, and carrying materials was observed as early as 24 h prepartum. This indicates that the availability of nest
Ž .
materials can affect the timing of nest building Arey et al., 1991 , an effect that may Ž
operate at the level of elicitation of behaviour directed towards straw Thodberg et al., .
1999 and in our experiment, also towards branches.
Biting the pen equipment was observed in 9 of the 10 gilts at a low frequency from 24 to 3 h prior to parturition. It has previously been suggested that biting pen equipment may be vacuum-like gathering of material or behaviour derived from the motor pattern
Ž .
for tearing twigs and branches from trees and bushes Jensen, 1993 . The gilts in our experiment had unlimited access to straw and branches in racks, so it is unlikely that they performed vacuum-like gathering behaviour. However, the branches were presented in the rack as a loose pile, so they could merely be collected, not torn. This may have resulted in vacuum-like tearing or in tearing elicited by the box and performed with the purpose of using the box material for nest building or removing it from the preferred nest site.
Both in the experimental and in the control group several gilts performed nest building during parturition. Individual gilts may differ in their requirements for a satisfactory nest and the continued behaviour indicates that the sows’ motivation was not satisfied during the prepartum phase normally designated to this behaviour. Nest building is energy consuming for the parturient animal and risky for the offspring and therefore it can hardly be viewed as a successful adaptation to the environment. Overall, branches and straw as nest materials appeared to be better than straw alone, but in some cases straw was sufficient and in others even straw and branches were insufficient. In a semi-natural environment sows sought isolation and selected a nest site before nest
Ž .
building was commenced Jensen, 1986 . In the present experiment the animals were only given the limited isolation that was provided by the pen design, they had little choice of nest site and they also could not excavate a lasting hollow in the straw bedding. Possibly, the results of these initial behaviours are important in the later feedback-regulated phase of nest building. Feedback from an appropriate nest site andror a hollow may have been inadequate in our experiment and have led to the continued nest building in gilts from both groups.
Nest building during parturition was associated with increased number of postural changes. Domestic sows in a semi-natural environment stood up an average of 3.3 times
Ž .
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piglets and they also frequently turned around either to lie on the other side or to face in
Ž .
the opposite direction Jensen, 1986 . Thus, both the average of 16 postural changes found in gilts that performed nest building during parturition and the average of five in gilts that did not may be a part of the normal parturient behaviour of sows. However, wild boar sows in a natural environment gave birth in lateral recumbency, changing only
Ž .
from one side to another Gundlach, 1968 . Samples sizes were small in the studies done on wild sows and domestic sows in semi-natural environments and further studies are needed to quantify the normal restlessness of parturient sows.
Postural changes and time spent in lateral recumbency are likely to have implications
Ž .
for the piglets as they are born Fraser et al., 1995 . The piglets can only find and remain near the udder if the sow is lying down in lateral recumbency and if the sow carries out many postural changes there is a risk of piglet crushing. A risk that may be further
Ž
increased if the piglets have consumed little or no colostrum English and Smith, 1975; .
Weary et al., 1996 .
It has to be kept in mind that the results of our experiment may be particular to
Ž .
primiparous sows. Age or experience modifies nest-building behaviour Jensen, 1989
Ž .
and parity can interact with farrowing environment Thodberg et al., 1999 . Gilts may
Ž .
also be more fearful or agitated at parturition than experienced sows Baxter, 1982 . Therefore, extrapolation of these results to older, more experienced animals should be done with caution.
In conclusion, indoor gilts used branches for nest building. When gilts had access to branches, fewer individuals performed nest building during parturition and they also terminated nest building sooner. The results indicate that the termination of nest building is under environmental feedback control. Nest building during parturition was positively correlated with number of postural changes and negatively correlated with time spent in lateral recumbency. Therefore, providing preparturient sows with relevant nest materials may potentially improve sow welfare and piglet health and survival.
Acknowledgements
We are grateful to The Federation of Danish Pig Producers and Slaughterhouses for supplying animals, facilities and care of the animals. We also thank L. Lawson for statistical advice and Dr. P.F. Johnsen and Dr. L. Alban for useful comments on an earlier draft of this manuscript. The study was supported by a grant from the Danish Academy of Sciences.
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