Dimensions of maternal behaviour characteristics in
domestic and wild
domestic crossbred sows
Marek SÏpinka
a,*, Gudrun Illmann
a, Francien de Jonge
b,
Maria Andersson
c, Teun Schuurman
d, Per Jensen
caGroup of Ethology, Research Institute of Animal Production, CZ-104 01 Prague-UhrÏõÂneÏves, Czech Republic bDepartment of Ecological Agriculture and Society, Wageningen University and Research Centre,
Haarweg 333, 6709 RZ Wageningen, Netherlands
cDepartment of Animal Environment and Health, Faculty of Veterinary Medicine, Section of Ethology,
Swedish University of Agricultural Sciences, POB 234, S-532 23 Skara, Sweden
dHuman and Animal Physiology Group, Wageningen Institute of Animal Sciences, Wageningen University,
Haarweg 10, 6709 PJ Wageningen, Netherlands
Accepted 29 May 2000
Abstract
We examined the maternal behaviour of seven domestic and seven wilddomestic primiparous
sows during 10 days post partum to investigate two questions: (1) Did maternal behaviour change during domestication? (2) Can the interindividual variability of maternal behaviour be subsumed into a few dimensions of maternal temperament? We recorded: (a) willingness to leave the nest for food on Day 2; (b) reaction to a playback of squeezed piglet distress vocalisation on Day 2; (c) spontaneous nursing behaviour and spontaneous lying-down behaviour on Day 5 (from an overnight video recording); (d) reactions to playbacks of various piglet distress vocalisations on Day 6 and (e) reactions to a human in the `nest' with piglets on Day 9. Moreover, data on baseline cortisol saliva concentration and its increase during a brief transportation period and novel environment challenge at the age of 5 months were available. Crossbred sows did not differ from domestic ones in any aspect of maternal behaviour except for a higher tendency to terminate ®nal massage during nursings and a higher frequency of changing posture from lying to standing and back during the night. Factor analysis (based on correlation matrix of 11 behaviour and cortisol variables calculated for all 14 sows after removing the effect of breed) indicated that 82% of the variability in the data could be explained by three factors: ®rst, `calmness' on which low night time frequency of major posture changes, carefulness of lying-down behaviour and high propensity to remain in nursing position after milk ejection loaded positively while cortisol concentrations during challenge loaded negatively; second, `protectiveness' with high loadings of the reaction scores to the playbacks of piglet distress calls and the human presence near the piglets; and third, `nursing activity' which was
*Corresponding author. Tel.:420-2-6771-0713; fax:420-2-6771-0779.
E-mail address: spinka@vuzv.cz (M. SÏpinka).
strongly positively associated with nursing frequency, and negatively with the proportion of nutritive nursings and baseline cortisol values. The results indicate that most aspects of pig maternal behaviour have not been signi®cantly changed by domestication and that substantial variability in maternal behaviour exists between sows, perhaps in the form of several behaviour characteristics
which encompass both behaviour and endocrine pro®les of the sows.#2000 Elsevier Science B.V.
All rights reserved.
Keywords: Maternal behaviour; Pigs; Domestication; Nursing; Cortisol; Vocalisation; Temperament
1. Introduction
Maternal behaviour is important for pig husbandry since it partly determines mortality and growth of the piglets. About 15% of the live born piglets die before weaning (McKay, 1993; Blackshaw et al., 1994), and among them 70±80% is attributable to the sow behaviour, directly or indirectly. During the ®rst day of life, piglets get trapped under the sow while she is lying-down or rolling from her belly to her side (Dyck and Swiestra, 1987; Weary et al., 1996a; Herskin et al., 1998). Individual dams differ in the frequency of postural changes, and in how often they change posture in a way that is dangerous for the piglets (i.e. ¯opping straight down to one side versus descending to lying posture in a vertical plane; lying down when piglets are nearby). Even after a piglet is trapped, the sow's behaviour is important. Just 20% of piglets trapped under the sow's body are actually crushed. If a trapped piglet starts screaming, the sow may stand up immediately and release it. In cases when the sow stood up within 1 min, only 5% of piglets died; in contrast, 67% of the piglets trapped for longer than 4 min were lost (Weary et al., 1996a). Two aspects of the sow's behaviour, thus, affect the probability of crushing: ®rst, the sow's general restlessness and her lying-down behaviour; second, the sow's individual reactivity to a screaming piglet (Wechsler and Hegglin, 1997).
Another problem in piglet production is low milk intake in some piglets or in whole litters which results in low or too variable weaning weights. This may even lead to piglet losses, either directly due to starvation or indirectly due to the weak piglets being crushed by the sow (Hutson et al., 1993; Weary et al., 1996b). Low frequency of nursings (SÏpinka et al., 1997; SÏpinka et al., 1999), and a high proportion of non-nutritive nursings (nursings without milk ejection, CastreÂn et al., 1989; Illmann and Madlafousek, 1995; Illmann et al., 1999) are probably the aspects of nursing behaviour which can most signi®cantly reduce milk intake. A tendency to terminate the udder massage by the piglets soon after milk ejection might also suppress future milk production in the glands, although the evidence is equivocal (Algers and Jensen, 1991; SÏpinka and Algers, 1995; Jensen et al., 1998; Illmann et al., 1998).
stock vary in biologically signi®cant aspects of maternal behaviour. In order to answer this question, we collected data on maternal behaviour in seven domestic and seven crossbred
wilddomestic primiparous sows. During the data analysis, we found that the breeding
effect could explain only a small proportion of the variation in the data. Therefore, we investigated the interindividual variation through a post-hoc correlational and factor analysis. We focused on questions of how various aspects of maternal behaviour relate to each other and whether they could be subsumed into a few `maternal behaviour traits'.
2. Methods
2.1. Animals
We used 14 primiparous sows which were born to YorkshireDutch Landrace mothers.
Seven of them were sired by various Yorkshire fathers (`domestic' sows) and seven by one male wild boar (`crossbred' sows). The sows were born and reared in the outdoor housing system described below. At the age of 20±21 months, all experimental sows were inseminated with Great Yorkshire sperm. Hence, the offspring interacting with the experimental mothers in the current study were either 100% domestic or 25% wild boar.
2.2. Housing conditions
The experiment was carried out at the Wageningen Agricultural University, The Netherlands in April±June 1997. All sows were loose housed during pregnancy. Two days before the scheduled farrowing induction, the sows were locked in half-covered
concrete-¯oored rectangular outdoor pens (2.2 m4.5 m). About 5 kg of straw was
provided in the covered half of the farrowing pen, the open half was provided with drinking nipples for both the sows and the piglets and also served as dunging area. At the back of the farrowing pens, half-open doors allowed behavioural observations, without disturbances to sow or litter. At 8 a.m. and 1:30 p.m., sows were allowed to leave the pens in order to feed in separate feeding crates positioned about 20 m from the pens. Sows which were to be tested in the same batch (see below) were not housed in adjacent pens in order to reduce the possibility of habituation to acoustic stimuli in the playbacks tests.
2.3. Procedure
2.3.1. Farrowing and cross-fostering
In order to enable early and balanced cross-fostering between litters, farrowings were
induced on about Day 112 of pregnancy by a prostaglandin analogue (PGF2a) injection.
ratio (in that order of priority). The resulting litter sizes varied between seven and nine piglets among which two±four piglets were the sow's own progeny while the rest originated from the other litters in the batch. Mortality of the piglets was assessed by noting any losses occurring between cross-fostering and video recording 4 days later (see below).
2.3.2. Nest-leaving and playback experiment on Day 2
On Day 2 after parturition (Day 2), each sow was tested for her willingness to leave the nest and the young for food and also for her reactivity to squeezed piglet distress vocalisation. At the time of the morning feeding, the non-tested sows were ®rst allowed to feed in a normal way. After they were locked back again in their farrowing pens, the pen of the ®rst sow to be tested was opened and the latency of her emergence from the farrowing pen was noted. If she did not leave the pen within 5 min, the gate was closed and latency was set equal to 300 s. We then waited for the moment when the sow was lying down in the farrowing pen for the ®rst time. When her body touched the ground, a 30 s recording of piglet distress vocalisation was played (at about natural volume) from a loudspeaker through an expanded-metal-covered opening in the outer wall of the farrowing pen. The recording was the vocalisation of a 2-days-old piglet, unrelated to any animal in the experiment. During the recording, vocalisations were stimulated by restraining the piglet on the ground by an experimenter using both hands. The reaction of the sow to the playback was video recorded and later scored using the following scale: 0 Ð no reaction, 1 Ð head movement, 2 Ð body movement, 3 Ð sits, 4 Ð stands up, 5 Ð makes contact with the expanded metal covering the loudspeaker, 6 Ð bites or paws at the expanded metal. Two extra points were added if the sow stood up within 5 s since the beginning of the playback or one point if she did so within 30 s. After the testing of the ®rst sow was ®nished, we continued with testing of the next sow until all sows from a batch (up to four) were tested. The same vocal stimulus was used for all sows.
2.3.3. Undisturbed nursing behaviour
During the night between Days 4 and 5 (or between Days 5 and 6) post partum, each sow was video recorded either between 18:00 and 24:00 or between 00:00 and 06:00 h while there were no people present near the animal facilities. The videotapes were later analysed to quantify the following parameters of the undisturbed nursing behaviour: intervals between nursings, proportion non-nutritive nursings, duration of pre-ejection and post-ejection udder massage, and proportion of nursings terminated by the sow. Non-nutritive nursings (nursings without milk ejection) were identi®ed by the absence of synchronised rapid sucking activity of the litter (Illmann and Madlafousek, 1995). A nursing was classi®ed as terminated by the sow if she rolled over onto her belly or stood up while some of the piglets were still active at the udder.
2.3.4. Undisturbed lying-down behaviour
point if the sow descended in a vertical plane (as opposed to ¯opping over to one side), one point if there were, at that moment, no piglets near her on the side on which she lay down.
2.3.5. Playback experiment on Day 5 or 6
These tests were conducted on Day 5 or 6 post partum either in the morning or in the afternoon. The behaviour of the sow was videotaped in her pen while she was subjected to three different tests of her reactivity to piglet distress vocalisations. The tests were:
Trapped piglet call± A 35 s playback of a piglet's distress vocalisation which had been recorded as described in the section on playback experiment on Day 2. However, different recordings were used from those on Day 2. The playback was started while the sow was descending to a lying posture at the moment her body touched the ground.
Isolated piglet call± A 60 s playback of a piglet's grunting and squeaking which had been recorded when a 7-day old piglet had been isolated from her mother and littermates. The playback was started at any moment between 20 and 35 min after the last milk ejection when both the sow and the litter was resting.
Teat fighting calls± A 50 s playback of loud vocalisations recorded while two piglets had been fighting for a teat during nursing. The playback was started during a nursing about 15 s after the pre-ejection udder massage by the piglets had begun.
Each of the three tests was repeated twice using vocalisations from different piglets to those used for the playback stimuli. Hence, each sow was presented with a total of six playback stimuli during the experimental session. The playbacks were always separated by at least 15 min. The order of the tests was variable in individual sows as it was dependent on the spontaneous nursing and resting behaviour of the animals. The behavioural reactions of the sow were scored using the same scale as in the playback experiment on Day 2. A preliminary analysis showed that the scores from the three types of tests were highly intercorrelated and displayed similar results in the domestic-crossbred comparison. There-fore, the score reactions from the six tests (reactions to trapped-piglet, isolated-piglet and teat-®ghting calls, each tested twice) were combined into a ®nal score.
2.3.6. The human-in-the-nest test
jumped on it with her front legs. The average number of points for a 20 s interval was taken as a measure of the sow's reaction to the human presence near her young.
2.4. Comparison with daytime nursing behaviour data
In order to see whether the individual characteristics of nursing behaviour were stable over the diurnal period, we compared the nursing data with the data collected on the same animals at 4±7 days post partum through direct daytime 4 h observations by Gustafsson et al. (1999).
2.5. Cortisol data
In the post-hoc analysis (see Section 2.6), the set of behavioural scores was comple-mented with data on cortisol baseline concentration and cortisol concentrations under a complex challenge in the same sows. These data were collected about 15 months earlier, when the animals were 5 months old. The gilts were housed in pairs in small pens and trained to chew on cottonwool plugs for saliva collection. The ®rst saliva sample was
collected in the gilt's home pen just before the test started (t0 min). Att10 min, the gilt
was loaded to a carrier cage and, using a tractor, transported to another building. At the end of transportation, 20 min after the ®rst sample, a second sample was taken and the gilt was
released to a 3 m7 m pen with concrete ¯ooring. At 40 min, the third saliva sample was
taken and a gate was opened which connected this pen to a second pen provided richly with straw. The fourth to sixth samples were collected at 55, 65 and 75 min after the ®rst one. All tests were performed between 8:00 and 11:30 h in the morning in order to reduce cortisol concentration differences caused by the circadian rhythm (Ekkel et al., 1996; Ruis et al., 1997).
The saliva samples were immediately put on ice and centrifuged after the ®nal one was
collected. Plasma was stored atÿ208C until the assay. 0.5 ml of the thawn, undiluted saliva
sample was extracted with 2.5 ml dichloromethane. After evaporation of the solvent the extract was subjected to a cortisol assay described by Janssens et al. (1994). The cortisol-antibody used was a rabbit antiserum (K7348) raised against a cortisol-bovine-serum-albumin-conjugate. Sensitivity of the assay was 0.5 ng/ml. The intra- and inter-assay variances were 8 and 15%, respectively.
Two variables were extracted from the cortisol data. The ®rst was equalled to the pre-test sample at time 0 and was labelled `cortisol baseline' concentration. The second was an average of the second to sixth sample and was named `cortisol under challenge' concentration.
2.6. Statistical analysis
2.6.1. Domesticcrossbred differences
Data on nest-leaving on Day 2 were treated as a binary variable (sow left the nest within
5 min or did not), and the domesticcrossbred comparison was made using the Fisher
exact probability test. In all other comparisons between the domestic and crossbred sows,
2.6.2. Nightdaytime nursing behaviour comparison
In order to see whether the nursing behaviour was different over night compared to daytime, and whether the sows kept their individual nursing style over the diurnal period, we pooled the data from daytime direct observation (Gustafsson et al., 1999) and night video recording. The data set was then subjected to an ANOVA with breed, time (day versus
night), breedtime interaction, and sow nested within breed as the main effects. For the
breed effect, the between-pig MS was used as the error term.
2.6.3. Association of piglet mortality with maternal traits
The dependence of piglet mortality on maternal characteristics was assessed by computing the Spearman rank correlation between the proportion of piglets dying from Days 0 to 4 within a given `litter' (the group of piglets composed through cross fostering and suckled by the given sow) and the scores of their foster mother in the tests and observations. The breed effect was removed prior to computing the correlations.
2.6.4. Post-hoc correlational and factor analysis
Correlational post-hoc analysis was used to investigate whether the results from the three tests, nursing and posture change behaviour scores from the night time video recording and the cortisol data (11 variables in total) related to each other. A factor analysis was carried out in an attempt to describe the complex results in terms of a few factors. In order to make the results easier to interpret and present in a ®gure, we inverted some of the variables such that the higher the level of the variable, the better (presumably) the survival and growth of the piglets. Instead of proportion of nursings terminated by the sow, we took the proportion
of nursing not terminated by the sow and labelled it `massage allowance'; instead of
nursing interval, the nursing frequency (mean number of nursings per hour) was used; and instead of proportion of non-nutritive nursings, the proportion of nutritive nursings was used. The duration of pre-ejection udder massage was changed to `speed of milk ejection' by converting the number of seconds into negative values. Similarly, the night time number of standing-up acts was rendered negative and labelled `night time inactivity'. The effect of breed (domestic versus crossbred) was removed from this modi®ed set of variables by a GLM procedure with breed as the only main effect. Next, the residual values were used to construct a matrix of product-moment correlations between the variables. Finally, the matrix was subjected to factor analysis with the procedure Factor of the SAS software. Squared multiple correlations were used for the prior communality estimates. Factors with eigenvalues larger than 1 were retained and subjected to orthogonal varimax prerotation followed by promax oblique rotation. This procedure was chosen in order to separate out original variables on the resulting factors as well as possible, and, at the same time, show whether the factors are correlated to each other or not.
3. Results
3.1. Crossbreddomestic differences
Crossbred sows were more likely to terminate the post-ejection massage during nursings
shorter post-ejection udder massage (268 versus 428 s, Mann±Whitney U-test, U6,
p<0.05). Second, the crossbred sows tended to stand up, on average, three times as often
during the 6 h of night time video recording than the domestic ones (4.7 versus 1.7 times,
Mann±WhitneyU-test,U9,p<0.1). There were no other signi®cant differences between
the two breeds in any of the recorded aspects of maternal reactivity, posture changing behaviour or nursing behaviour.
No difference was detected in the saliva unbound cortisol baseline concentrations at 5 months of age (Fig. 1: crossbred sows 2.2 ng/ml versus domestic sows 1.8 ng/ml, Mann±
WhitneyU-test,U15, NS). However, the `cortisol under challenge' concentration, i.e. the
average concentration in ®ve samples collected after the transport and during the new environment challenge (Fig. 1) was more than twice higher in the crossbred sows (5.5
versus 2.7 ng/ml, Mann±WhitneyU-test,U4,p<0.01).
The mortality of piglets during the 4 days following cross-fostering was not different between those suckled by the crossbred and domestic mothers (10% versus 13%, Mann±
WhitneyU-test,U20, NS; Table 1).
3.2. Comparison with daytime nursing behaviour data
Of the ®ve variables in the pooled day-and-night data set (duration of pre- and post-ejection udder massage, nursing interval, proportion of non-nutritive nursings, and proportion of nursings terminated by the sow), the ANOVA model with time, breed,
timebreed interaction and the sow identity as main effects was not signi®cant for the
nursing interval and the proportion of non-nutritive nursings. The proportion of nursings
terminated by the sow was lower (ANOVA,F1, 1210.67,p<0.01) and post-ejection udder
massage was longer (ANOVA, F1, 1213.49, p<0.01) in the night than during daytime
(Table 2). Crossbred sows terminated more nursings (ANOVA,F1, 1286.37,p<0.0001),
and allowed shorter post-ejection massage (ANOVA,F1, 127.97,p<0.05). The interaction
between time of day and breed was not signi®cant for any variable. Sow identity in¯uenced
the proportion of sow-terminated nursings (ANOVA, F12, 124.55, p<0.01) and the
duration of pre-ejection massage (ANOVA, F12, 123.02, p<0.05) but not the nursing interval, percentage of non-nutritive nursings or the post-ejection massaging duration.
3.3. Piglet losses and maternal traits
Piglet mortality within a given litter between Days 0 and 4 tended to be correlated negatively with the number of lying-down acts during the 6 h night time recording
(rSÿ0.51,p<0.1). Mortality did not correlate signi®cantly with the carefulness of the
sow's lying-down behaviour (rSÿ0.41, p0.15) or with any other of the recorded
maternal behaviours or reaction scores (allrSbetween ±0.30 and 0.30,p>0.20). Neither
was mortality related to any of the Factors 1±3 (rS±0.23, 0.36, and ±0.07, respectively).
3.4. Post-hoc correlational and factor analysis of maternal traits
In the correlational matrix of the 11 quantitative behaviour and cortisol variables, there were 11 signi®cant and three marginally signi®cant correlations, which formed three interconnected groups of behaviours (Fig. 2). The factor analysis based on the correlation matrix revealed that ®rst the three factors had eigenvalues of 3.19, 2.98 and 2.06, explaining 32, 30 and 20% (82% in total) of the variation in the matrix. The fourth factor had an eigenvalue of only 0.64 and hence, the ®rst three were extracted and subjected to varimax orthogonal and then promax oblique rotation (Fig. 3). After promax rotation, the
Table 1
Maternal reactivity, posture changing behaviour and nursing behaviour in domestic and crossbred sowsa Variable Breed Uvalue Significance
Domestic Crossbred Nest leaving on Day 2 (number of
sows with latency <300 s) Reaction to three types of piglet call
on Day 5 (arbitrary score)
27.67.2 31.97.6 19 NS Reaction to a human in the piglet
nest on Day 8 (arbitrary score)
22.85.0 19.64.1 22 NS Internursing interval (min) 39.72.5 35.41.6 15 NS Non-nutritive nursings (%) 13.75.4 17.03.0 22 NS Nursings terminated by the sow (%) 16.72.7 56.919.6 1 *** Pre-ejection massage duration (s) 9612 11110 18 NS Post-ejection massage duration (s) 42853 26832 6 ** Number of standing-ups during six night time hours 1.70.6 4.71.2 9 * Carefulness of lying-down (arbitrary score) 3.50.3 3.10.1 12 NS Piglet mortality (% of pigs dying between Days 0 and 4) 9.92.9 12.93.8 20 NS
aWith the exception of the variable `nest leaving' on Day 2, meansS.E. are given. Significances as
Table 2
The effects of diurnal period, breed and sow identity on nursing behavioura
Variable Time of day Breed Interaction between time of day and breed
Sow identify
Day Night Significance Domestic Crossbred Significance Significance Significance Internursing interval (min) 36.51.8 37.61.5 NS 37.41.7 36.71.7 NS NS NS Non-nutritive nursings (%) 113 153 NS 122 143 NS NS NS Nursings terminated by the sow (%) 519 377 ** 234 657 *** NS ** Pre-ejection massage duration (s) 10211 1048 NS 959 11010 NS NS * Post-ejection massage duration (s) 20222 34837 ** 33139 21927 ** NS NS
aMeansS.E. and significances as resulting from the F-tests within are given: NS;P>0.1; *P<0.05; **P<0.01; ***P<0.001.
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Fig. 2. Clusters of correlated variables from the correlational matrix of 11 behavioural and cortisol variables. Pearson correlation values are given. Dotted arrows: p<0.1; hatched arrows:p<0.05; solid arrows:p<0.01. Variable labels: LY, carefulness of lying-down; AM, allow massage, i.e. proportion of nursings which the sows did not terminate; NI, night inactivity, i.e. negatively taken number of body position changes during 6 h; CC, cortisol concentration during challenge; RH, reaction to human near piglets; RT, reaction to trapped piglet screaming on Day 2; RC, reaction of various distress calls by the piglets on Day 6; ES, ejection speed, i.e. the briefness of pre-ejection massage; NF, nursing frequency; CB, cortisol baseline; %N, proportion of nutritive nursings.
three factors remained almost orthogonal (uncorrelated) with the correlations between the
factors being at ÿ0.03, 0.01 and ÿ0.16. Three groups of behaviour variables were
suggested by the factor pattern. High propensity to allow post-ejection udder massage, carefulness of lying-down behaviour and night time inactivity loaded highly on Factor 1. Reaction scores in the three stimuli tests (to trapped piglet vocalisation on Day 2, to piglet distress vocalisations on Day 5 or 6, and to human intrusion into the `nest' on Day 8 or 9) and the speed of milk release loaded highly on Factor 2. Finally, nursing frequency was strongly positively, and the proportion of nutritive nursings strongly negatively, associated with Factor 3. Cortisol concentration under challenge loaded highly negatively on Factor 1, and cortisol baseline negatively on Factor 3. Factor 2 was not associated with cortisol concentrations at all.
4. Discussion
In this study, we documented striking similarities in maternal behaviour of domestic and
wild boardomestic pigs. This study complements a previous paper by Gustafsson et al.
(1999) which was based on parallel observations on the same animals and which focused on prefarrowing nest building behaviour and on daytime nursing and general proximity behaviours. Since all 14 experimental sows were born to and raised by mothers of the same breed and kept until testing in the same type of environment, we have controlled for other than genetic factors. The studies were performed on the assumption that behavioural traits, especially the quantitative ones like frequency and duration of behaviours, are in¯uenced by many genes. For such traits, the behavioural phenotype of a hybrid should be about halfway between that of the two parental genotypes (Price, 1998). A lack of difference between one of the parental genotypes and the hybrid suggests that the other parent's genotype is not differing grossly from the hybrid either. This is exactly what was found in the two studies. The results thus might suggest that domestic sows retain the maternal behaviour which has evolved under natural selection. This conclusion is in agreement with previous observations of semi-naturally kept domestic sows (Jensen, 1986, 1988) and female wild boar (Horrell, 1997). However, our conclusion must be regarded as pre-liminary for two reasons. First, the sample size was small. Second, all seven crossbred sows were sired by the same wild boar. The sows within this group were, thus, half-siblings which may somewhat weaken the genetic comparison.
(Gustafsson et al., 1999) and in less frequent interruptions of the night time rest through standing-up acts (this study). Lower activity saves energy and might, thus, be a result of the intense selection for fast growth, ef®cient food conversion, heavier live weight and larger body size (Robert et al., 1987). As a side effect, the less active domestic sows may remain in the nursing position longer after milk ejection. A third interpretation is that higher agility of crossbred sows is due to hybrid vigour, since, presumably, a higher heterozygosity was
achieved in the wild boarLandrace hybrids than in the YorkshireLandrace crosses.
We found a close similarity in the duration of pre-ejection udder massage, nursing interval, and the proportion of non-nutritive nursings observed by a human observer during the day and the same variables scored from the night time video recordings. This demonstrates, ®rst, that these aspects of nursing behaviour were not in¯uenced by daytime human activity, and second, that the nursing effort was evenly distributed over the diurnal period. Equal nursing frequency over day and night was also found in domestic sows by Hartman et al. (1962). During the night, sows terminated fewer nursings and, consequently, post-ejection udder massage lasted longer than during the day. This was probably connected to the fact that sows rested in a recumbent posture for most of the night, as reported previously by Bùe (1991, 1994).
In the ANOVA analysis of the pooled day-and-night nursing data, the sows' identity as a factor signi®cantly in¯uenced the proportion of nursings terminated by the sow and the pre-ejection massage duration (Table 2). This documents that these nursing characteristics were retained in their nursing behaviour throughout the diurnal period. On the other hand, the internursing interval and the proportion of non-nutritive nursings were not signi®cantly affected by sow identity, showing that the frequency of nursing and the related frequency of failures to release milk were not stable over the diurnal period.
Several previous studies found piglet mortality to be in¯uenced by sow reactivity to piglet distress calls, and to carefulness and frequency of postural changes (McGlone and Blecha, 1987; Hutson et al., 1993; Wechsler and Hegglin, 1997). In our study, the frequency of postural changes was moderately related to piglet mortality, but carefulness of lying-down and the reactivity to vocal stimuli was not. This failure to con®rm the previously reported relationships may be due to the fact that we followed the mortality only starting with the moment of cross-fostering, about 12±36 h after the birth of the piglets. Since more than a half of the live-born piglet mortality occurs during the parturition and within 24 h after birth (Weary et al., 1996a), we probably missed the period when the maternal behaviour is most in¯uential on piglets' survival.
sows' reactions to any piglet-related signals including tactile ones. Factor 3 could be labelled `nursing activity' as it is associated with high nursing frequency which is, in turn, known to be connected with high proportion of non-nutritive nursings (this study; Fraser, 1975; CastreÂn et al., 1989; SÏpinka et al., 1997).
The three factors remained almost orthogonal after the oblique promax rotation, demonstrating that they are independent of each other. This excludes the possibility that differences in pig maternal style scale along just one dimension of `emotionality' or `temperament' in the narrow sense (Wilson et al., 1994; Clarke and Boinski, 1995; Gosling and John, 1999). An important area of future research is how sows' maternal behaviour characteristics relate to their emotionality in other biologically signi®cant situations, such as food competition, meeting strangers, novel environment, or behaviour towards humans (Lawrence et al., 1991; Forkman et al., 1995; Erhard and Mendl, 1999; Erhard et al., 1999; Thodberg et al., 1999).
The factor analysis also indicated that corticosteroid pro®les of individual sows were related to their maternal behaviour. Speci®cally, cortisol concentrations under challenge loaded strongly negatively on Factor 1. This may suggest a common factor underlying `calm care' behaviour towards the piglets and `calm' physiological reaction to a challenge (low adrenal cortex reactivity). Factor 3, describing `nursing activity', was negatively related to cortisol baseline values. However, high or low cortisol pro®les at 5 months were not predictive for protective reactions to piglets in danger as revealed in Factor 2. The cortisol data were collected in juvenile animals long before the maternal behaviour was expressed. However, it is known that cortisol pro®les remain individually stable during ontogeny for periods of months in pigs (von Borell and Ladewig, 1992; Ladewig et al., 1993). We, therefore, assume that the correlations between cortisol concentrations and later maternal behaviour re¯ect a real relationship. To our knowledge, there are no other data on the relationship between sows' pituitary-adrenocortical (PAC) pro®les and their styles of maternal behaviour. It would be important to know whether exogenous ACTH or cortisol will alter maternal behaviour or vice versa, whether maternal experience has an effect on PAC functioning.
5. Conclusions
Two main conclusions follow from this study.
First, we found no differences in most aspects of maternal behaviour between domestic
and crossbred domesticwild boar sows. This might indicate that maternal behaviour has
not changed signi®cantly during domestication and/or under modern breeding pro-grammes.
Acknowledgements
This study was funded by grants No. 523/98/0789 and 523/99/0985 from the grant Agency of the Czech Republic and grant No. M02/99/03 from the Czech Ministry of Agriculture. Suzanne Held kindly helped with the English in two versions of the text.
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