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Observations on the behavioural development of suckling and early-weaned piglets during the first six weeks after birth
Anim. Behav ., 1978, 26, 22-30
OBSERVATIONS ON THE BEHAVIOURAL DEVELOPMENT OF SUCKLING AND EARLY-WEANED PIGLETS DURING THE FIRST SIX WEEKS AFTER BIRTH By D . FRASER* School of Agriculture, University of Edinburgh
Abstract . Piglet behaviour was studied during the first 6 weeks after birth using litters weaned at 3 and 6 weeks. The main changes with age in suckling animals involved increases in overall activity and in behaviour associated with solid food ingestion. Newly-weaned animals were particularly active and aggressive, and appeared to have difficulty lying together comfortably . Most animals accepted the new diet in the first day ; frequency of defecation increased over the 4 days after weaning . Unlike suckling piglets, the early-weaned animals often nosed the bellies of pen-mates, and frequently pawed the bedding in conjunction with defecation and before lying down. Consistent individual differences in the incidence of biting litter-mates, feeding, and belly-nosing correlated with either body weight or weight gain . Unusual behaviour associated with early weaning is discussed in terms of digestive upset leading to discomfort, restlessness and fatigue . In recent years pig producers have begun weaning piglets at progressively earlier ages in an effort to increase the efficiency of their breeding stock . Typical weaning age has declined from 8 weeks to 6 or often 5 weeks . Some producers with specialized facilities wean the young during the first week of life, but this can lead to problems in piglet health and behaviour, and in the reproductive performance of the sows . A more common trend is toward 3-week weaning, but even at this age abnormal behaviour and other problems can occur . Behavioural problems which have been observed among early-weaned piglets include unusually high levels of general activity and aggressiveness toward pen-mates, suckling activities directed at other piglets, and faulty regulation of food intake, including both failure to eat and excessive eating which may predispose the animals to digestive disorders (Pittaway & Brown 1974 ; but see also Haythornthwaite & Shaw 1974) . There is much variation between production units in the type and severity of the problems seen, but little systematic work has been done to establish the reasons for such variation . Previous behavioural studies of early-weaned piglets have commonly been limited to measures derived from time-lapse filming ; and the animals have generally been housed in special earlyweaning cages, making it difficult to separate the
effects of weaning from those of the change of environment and management (Marx 1973) . In the following study, piglets were observed in the same situation before and after weaning at 3 weeks of age. In addition, comparable observations were made on the behavioural development of suckling piglets in a similar environment . Methods Eighty piglets were studied during the first 6 weeks after birth. The animals were drawn from 10 litters, each the offspring of a Large White or Large White x Landrace sow in its second or subsequent parity. The litters consisted of between eight and 11 piglets, but observations were limited to eight marked piglets in each litter in order to standardize the procedure . The 10 litters were studied in pairs, and were chosen so that the two litters comprising each pair were born within the same 2 days . One litter of each pair was weaned by removing the sow on one of days 21 and 23 after parturition ('early-weaned litters') . The others were weaned at 6 weeks of age ('normally-weaned litters') after the experimental observations had ended . About 4 days before parturition the dams were moved into farrowing crates (a metal framework which restricts the sow's movement during parturition and lactation to reduce the likelihood of the piglets being crushed) in pens measuring approximately 2 x 3 m . Each pen was
*Author's present address : Ontario Ministry of Natural Resources, Fish and Wildlife Research Branch, Box 50, Maple, Ontario, Canada, LOJ 1EO . 22
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
equipped with two troughs containing water and dry supplementary feed for the young . A low food trough was used for each litter initially, and was replaced by a hopper with three feeding spaces about 3 weeks after parturition . Wood shavings were provided as bedding, and were normally replaced daily at 10 .00 hours. The sows were fed a concentrated ration at 08 .00 and 16 .00 hours . The animals of each pair occupied adjacent pens in a room which contained no other animals . The piglets were marked for easy identification by coloured numbers on their backs, and were weighed during the first day after birth and at about 21 and 42 days of age . For the periods of observation the observer sat to the rear of the sows until one nursed its young successfully as judged by the criteria of Whittemore & Fraser (1974) . A stop clock was started during the period of milk flow (the phase of rapid sucking by the piglets), and the observer made a written record of the activities performed by each of the eight piglets in each successive minute until the period of milk flow of the next successful nursing. The following behavioural categories were used : (i) suckling ; when most or all the young were active on the udder and the sow was giving the characteristic nursing grunts ; (ii) sleeping on the udder ; which sometimes followed suckling when the young slept without leaving their suckling positions ; (iii) nosing the teats when not suckling ; when individual piglets approached and nosed the udder between sucklings ; (iv) active; which included standing, sitting and moving about; (v) lying ; (vi) feeding on supplementary food ; (vii) drinking water ; (viii) defecating ; (ix) urinating ; (x) aggressive biting at litter-mates ; (xi) scratching the body with a hind leg or by rubbing against a fixed object ; (xii) scampering about the pen ; (xiii) rooting the floor with the snout ; (xiv) pawing the floor with a front hoof ; (xv) belly-nosing ; a distinctive sequence in which one piglet rubbed another's belly with rhythmic, up-and-down movements of the snout ; (xvi) nosing and chewing the body of a littermate when the distinctive belly-nosing behaviour was not seen .
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Written notes were also made of other behavioural observations as the occasion arose, and of the colour and firmness of the piglets' faeces. Each litter was typically observed sometime between 12.00 and 15.00 hours on three separate days during each of the first 3 weeks post partum. After the sow was removed, the earlyweaned piglets were observed in a similar way during a 2-h period on each of the first 5 days after weaning, and on 3 days during each of weeks 5 and 6. Observations on the normallyweaned litters continued three times per week throughout the study. In analysing the records a count was made of the number of minutes of observation in which a piglet was scored for each activity . For the earlyweaned litters a separate count was made for each litter-mate, thus permitting a comparison of individual differences among animals . For the normally-weaned litters a separate count was made for successive minutes after suckling in order to show the pattern of behavioural change between one suckling and the next . In both cases the analysis gave an overall score for a litter representing the percentage of 'piglet-minutes' for which each activity was scored during the observation period. Since the number of observation periods was not the same for all weeks, the results of each litter were combined to give a weekly percentage score which, after arcsine square root transformation, was treated by two-way analysis of variance with repeated measures . Results The analysis of variance for groups (normallyweaned and early-weaned) and weeks of age is summarized in Table I which shows all effects reaching the 10 % level of statistical significance . The means of the weekly percentage scores for these activities are shown in Figs . 1 to 3 . Two activities, scampering and urinating, showed no significant effects in the analysis and are not illustrated in the figures . On the basis of this analysis, the activities given in Table I can be divided roughly into four main groups (1) The categories `active', `lying' and `rooting' (Fig. 1) showed a progressive change with age which was similar for both groups. (2) Feeding, defecating and drinking (Fig. 2) showed an increase with age for both groups but an especially large increase after weaning . Scheffe's test (Hicks 1973, p . 36), applied at the
24
ANIMAL BEHAVIOUR, 26, 1
5 % level of significance, showed that feeding scores were higher in weeks 4 to 6 combined than in weeks 1 to 3 combined for both early-weaned and normally-weaned piglets, and that the earlyweaned group exceeded the normally-weaned group during the second 3-week period . The same was true of drinking . Defecation scores of the early-weaned group exceeded those of the normally-weaned group in weeks 4 to 6, but only
the early-weaned animals showed a significant increase with age when weeks I to 3 and weeks 4 to 6 were compared . (3) Pawing and belly-nosing (Fig . 3) were seen with substantial frequency only after weaning . For both activities the scores of the earlyweaned piglets in weeks 4 to 6 exceeded those of weeks 1 to 3, and also exceeded those of the
Table I. Summary of the Analysis of Variance of the Behavioural Categories, for Groups (normally- or early-weaned), Weeks, and Groups x Weeks Interaction Category Active Lying Rooting Feeding Drinking } Defecating Pawing Belly-nosing Nosing/chewing litter-mate Biting litter-mate Scratching
Factor
df
F
P
Weeks Weeks Weeks Group Weeks GxW Weeks GxW Group Weeks GxW Group Weeks GxW Group Weeks GxW Weeks GxW G x W Group
5,40 5,40 5,40 1, 8 5,40 5,40 5,40 5,40 1, 8 5,40 5,40 1, 8 5,40 5,40 1, 8 5,40 5,40 5,40 5,40 5,40 1, 8
11 .92 4.76 23 .99 8 .56 46.06 3 .70 29.42 4.33 4. 67 12. 28 2. 90 18 . 66 9 .41 3 .95 9 . 32 10 . 36 7 . 86 5 . 00 2 . 80 2 . 84 3 . 79
<0 .001 <0 .005 <0-001 <0 .025 <0 .001 <0 .01 <0 .001 <0 .005 <0 . 10 <0 .001 <0 .05 <0 .005 <0 .001 <0 .01 <0 .025 <0.001 <0. 001 <0-005 <0. 05 <0. 05 <0. 10
(c)
(b) 50
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I
2 3
4
5
6
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2 3 5 4 Age (weeks)
I
I
I
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6
2
3
4
5
Fig . 1 . The means of the litters' weekly percentage scores for categories (a) active, (b) lying, and (c) rooting, shown separately for the early-weaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth .
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
normally-weaned group for both periods (P<0.05 by Scheffe's test in all cases) . (4) The biting and the chewing and nosing of litter-mates (Fig . 3) showed complex changes with time, suggesting a peak of both activities during the middle weeks of the experiment for the normally-weaned piglets . However, the effect was not statistically significant by Scheffe's test . Between one nursing and the next, the behaviour of the normally-weaned piglets generally followed a typical pattern of change which is illustrated in Figs . 4 and 5, with results shown separately for weeks 1 to 3 combined and weeks 4 to 6 combined. The results are given for only the first 40 min after milk ejection because the sows frequently resumed nursing by the end of this interval . Of special interest is the behaviour of the early-weaned piglets during the first few days after weaning . Some of the trends are shown day by day in Figs . 6 and 7 . On the first day after removal of the sow, the piglets' behaviour was markedly altered . In addition to the higher level of overall activity (Fig . 6(a)), it was noted that the piglets of all five litters appeared to have difficulty lying down without disruption . When they huddled together there was much shifting of position, and piglets lying beneath others frequently pulled away, often squawking and sometimes biting or thrusting the head at a litter-mate. Biting frequently led to a prolonged fight in the shoulder-to-shoulder stance which often disrupted the entire litter, driving sleeping piglets to their feet . This restlessness sometimes
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persisted for 15 min or longer from the time the huddle first formed. Fighting and the attacking of litter-mates also occurred at the food trough and generally throughout the pen . The postweaning increase in biting litter-mates, and the decreases in scampering and scratching during the same period are illustrated in Fig . 7 . For most animals the amount of time spent at the food trough increased within the first day to its stable post-weaning level (Fig . 6(b)), while scores for defecation increased gradually during the 4 days after weaning (Fig . 6(c)). With some exceptions the faeces generally changed from yellowish (typical of a milk diet) to brown (typical of the solid diet) by the first day . Some diarrhoea was seen in all five litters, particularly the two litters with the lowest 3-week body weight. Nonetheless, there was considerable variation in patterns of feeding and defecating . Three piglets were not seen to eat on the first day . They had loose yellow faeces and attacked littermates frequently . Two of these had begun eating at the food trough by the second day, but the third began obtaining its food by rooting on the floor, and continued to do so until the sixth day . Another piglet had a score for feeding on day 1 which was four times higher than the average of its litter-mates . On day 2 this animal had dark, watery faeces, spent little time eating, and accounted for 14 of the litter's 18 instances of biting litter-mates . Two of the most striking behavioural changes after weaning were in pawing the bedding and in belly-nosing . Pawing, which was rare in piglets
Fig. 2. The means of the litters' weekly percentage scores for categories (a) feeding, (b) drinking, and (c) defecating, shown separately for the early-weaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth .
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ANIMAL BEHAVIOUR, 26, 1 (c) -1 . 0 0
05
1 0 --o
-a
-o
(d)
(b) 0 '
6
2 0 0
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/ 0
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Age (weeks) Fig. 3 . The means of the litters' weekly percentage scores for categories (a) pawing, (b) belly-nosing, (c) biting litter-mates, (d) chewing and nosing litter-mates, and (e) scratching the body, shown separately for the earlyweaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth . before weaning, rose sharply for all litters during the 3 days after the sow was removed . It had declined again by week 6 for most piglets . Pawing was usually accompanied by rooting with the snout, which was very common in both early-weaned and normally-weaned animals . However, changes in the incidence of pawing and rooting followed different patterns (Figs . 1 and 3) . The pawing of bedding by the earlyweaned piglets was observed particularly in two contexts : (i) just before or after a piglet defecated, usually near the place of defecation, and (ii) when a piglet was about to lie down, usually near
the place of lying . Fig. 8 shows the mean percentage of cases in which piglets were seen defecating or lying during the several minutes before and after pawing occurred . Belly-nosing was virtually never seen before weaning, but it was common in all litters after the sow was removed . The onset of belly-nosing was generally sudden, beginning on the same day for several members of the same litter . The activity broke out on the first day after weaning in two litters, and after 6, 12 and 17 days in the others . The percentage of minutes in which the behaviour was seen ranged from 0-9 for one
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
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Fig . 4 . Mean of the mean percentage scores of the five normally-weaned litters for lying (L), being active (A) and for suckling (S) during the 40 min after the period of milk flow of a successful nursing, shown separately for weeks 1 to 3 combined and for weeks 4 to 6 combined .
litter to 8 .0 for another, over weeks 4 to 6 combined . There was also great variation within litters (average coefficient of variation, 106 %), with some piglets of each litter consistently performing the behaviour a great deal while others totally refrained. Like feeding, belly-nosing appeared to be stimulated by the sound of the neighbouring sow nursing its young . Piglets which were feeding, lying down or defecating often stopped these activities and moved to another place when litter-mates began nosing their bellies . Fighting occasionally appeared to result from belly-nosing, since the recipient piglet sometimes turned and bit the performer . (a)
(c)
3
2
1
8
16 24 32 40
8 1 6 24 32 40
8 1 6 24 32 40
Time (min) Fig. 5 . Mean of the mean percentage scores of the five normally-weaned litters for (a) urinating and defecating combined, (b) feeding on supplementary food, and (c) scampering, during the 40 min after the period of milk flow of a successful nursing, shown separately for weeks 1 to 3 combined (open circles) and weeks 4 to 6 combined (closed circles).
Weights of the piglets at 3 weeks of age, taken when the sow was first removed from the earlyweaned animals, showed no significant difference between the two groups . The mean +SE weight of the early-weaned group was 4. 84+0 . 26 kg as compared with 5-31±0-21 (t = 1 .33, Ns) . By 6 weeks of age, however, the early-weaned animals were distinctly lighter (8 .86+0 . 51 kg compared with 10 .75+0 .44 kg, t = 2 . 81, P<0 . 01) . Among the early-weaned animals there were obvious behavioural differences between piglets of the same litter . Correlations were used to test whether the idiosyncratic differences seen just after weaning (in week 4) persisted over weeks 5 and 6 as well . The individual piglets' scores from week 4 for overall activity, feeding, and biting litter-mates correlated highly with their scores for the same activities from weeks 5 and 6 combined (means of the correlation coefficients for the different litters = +0 .54, +0 . 47, and +0.61 ; P<0. 001, 0 . 01, and 0 . 001 respectively) . Bellynosing was not seen during week 4 in three of the litters, but the individual animals' scores from week 5 correlated highly with those from week 6 (r _ + 0.59, P<0.001) . Some of the behavioural differences among litter-mates correlated with differences in the animals' weights at 3 and 6 weeks of age, as summarized in Table II . Discussion The normally-weaned litters provide basic information on the behaviour of suckling piglets
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ANIMAL BEHAVIOUR, 26, 1 (a) Q)
(b)
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(c)
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1 .5
10
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5
1 11 11 4
3
i
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4
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5
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5
Piglet age (weeks) Fig. 6 . The mean percentage of minutes in which early-weaned piglets were scored as (a) active, (b) feeding, and (c) defecating, during weeks 3, 4 and 5 of life . Piglets were weaned at the end of the third week . The results are shown separately for the first 5 days after weaning . (a)
(b)
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Piglet age (weeks) Fig. 7 . The mean percentage of minutes in which early-weaned piglets were scored as (a) biting litter-mates, (b) scratching their bodies, and (c) scampering, during weeks 3, 4 and 5 after birth, expressed as a percentage of the number of minutes in which the animals were scored as active . Piglets were weaned at the end of the third week. The results are shown separately for the first 5 days after weaning. and its development . Over the first 6 weeks after birth, the main behavioural changes consist of an increase in overall activity and in behaviour associated with the ingestion of solid food (feeding, drinking, rooting and defecating) . Similar steady increases with age in overall activity and feeding behaviour have been noted
by Schalbert (1972) . Marx (1973) found no consistent increases in activity among suckling piglets, but his results, like the present study, do indicate that interest in solid food begins to become obvious at about three weeks of age . Many of the behavioural categories showed little consistent change in incidence over the 6 weeks,
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS reflecting the relative precocity of week-old piglets . A detailed study of the development of much of the pig's species-typical behaviour would presumably have to concentrate on the early hours or days of life (cf. Gundlach 1968) . The pattern of behavioural change between successive nursings was also little modified with age . Suckling was generally followed by a period of activity and then lying . Most defecation and urination, and much of the feeding, occurred soon after suckling, while vigorous activity
6 5 4 3 2 Before
1 1 2 3 4 5 After Time (min)
Fig. 8 . Mean percentage of minutes in which piglets were scored for lying (above) and defecating (below), before, during and after a minute in which the same animal began pawing the bedding . Instances of pawing were included only if the record was complete for the full 12-min interval shown, and if pawing had not occurred during the initial 6 min . Lest any link between defecation and lying confound the results, the analysis of scores for lying excluded instances in which defecation occurred during the 12 min. This gave 398 records for the calculation of the lower line and 266 for the upper . Points show the mean (±sE) of the percentage scores of the individual litters.
including scampering was more common later in the interval, especially for the older piglets . The sudden post-weaning increases in general activity and aggression, coupled with the restless behaviour when the animals lay down together, gave the impression that the piglets were for some reason uncomfortable during the first day or more after weaning . Such discomfort may account for the marked increase in pawing the bedding which is apparently a form of nestbuilding (Gundlach 1968), and which frequently occurred in the lying area just before a piglet lay down. In a time-lapse photographic study a relatively small percentage of early-weaned piglets in battery cages were seen sleeping during the first observation period after weaning, compared with suckling piglets of the same age (Marx 1973, Abb . 14) . The very rapid increase in feeding behaviour during the first day after weaning was accompanied by a much slower rise in the frequency of defecation . This may reflect some difficulty in the animals' physiological adaptation to the solid food, perhaps indicated in extreme cases by diarrhoea . Discomfort from this source might account for the animals' restlessness and increased aggression . This hypothesis is supported by the association between loose faeces, aggressiveness and feeding behaviour in the few piglets which displayed anomalous feeding during the first day after weaning . The decreases in scampering and scratching may be related to the greater amount of aggression, as is observed among older pigs (Fraser 1974) . Increased susceptibility to infectious disease is one of the most characteristic features of the post-weaning period (e .g. Fraser, Ritchie & Fraser 1975). Perhaps the restless activity and difficulty in lying together lead the animals to a state of fatigue which contributes to this high susceptibility. It would be of interest to know to what extent the restlessness and related behaviour
Table IL Mean Within-Utter Correlation Coefficients between W at 3 and 6 Weeks and Weight Gain During this Period, and the Animals' Total Scores on Five Behavioural Categories During the Same Period Behaviour Active Feeding Defecating Biting litter-mates Belly-nosing
3-week weight
6-week weight
Weight gain
+0 .23 +0 . 10 +0 . 25 +0. 56*** -0. 03
+0. 20 +024 +0.32* +0.50** -0 . 33*
+0. 15 +0. 37* +0 .28* +0 . 36* -0. 36*
*P<0 .05 ; **P<0 . 01 ; ***P<0.001 .
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ANIMAL BEHAVIOUR, 2 6 , 1
could be influenced by environmental factors . The importance of high, consistent ambient temperature for early-weaned piglets is widely recognized (Pittaway & Brown 1974) . Perhaps a more comfortable lying surface would also be of value. In addition to its possible function as rudimentary bed-making before lying down, the pawing of the floor was also common in the context of defecation . It may be analogous to the perfunctory digging movements of domesticated dogs at the time of defecation, although it is not clear why it should increase so strikingly upon weaning. With the change in diet and frequency of defecating, and with the higher incidence of diarrhoea, the sensation accompanying defecation may be increased beyond a threshold level for eliciting pawing . It is unclear whether the amount of pawing associated with defecation is independent of the amount associated with lying down, or whether some common factors influence the incidence in both contexts . The behaviour is puzzling, but it might repay study since it constitutes one of the most consistent behavioural changes with early weaning. Belly-nosing, like the navel-sucking performed by some early-weaned calves and lambs, closely resembles a principal component of normal suckling behaviour . Despite the clear association with early weaning, the immediate causes of belly-nosing are obscure . Particularly puzzling are the large differences in incidence between members of the same litter, and the variation between litters in the number of days which elapse after weaning before the behaviour begins . Some of the variation within litters might possibly be associated with the animals' teat choice and suckling habits before weaning . Like other behavioural abnormalities such as the featherpecking of fowls and the tail-biting of growing pigs, belly-nosing may be `contagious' . This would help to explain the near synchronous onset of the behaviour by members of the same litter. Some of the practical significance of bellynosing is suggested by the negative correlation with weight-gain within litters. The performance of belly-nosing may have retarded growth, as some piglets persisted in the behaviour for much time which might otherwise have been spent in feeding or resting. Alternatively the correlation might reflect some tendency for piglets to perform belly-nosing more if they were having difficulty in adapting to the conditions of weaning, as indicated by poor growth . Belly-nosing
may also exert an undesirable influence on the recipient animal or on the litter as a whole if it causes outbreaks of fighting . Other correlations showed that there were strong differences between members of the same litter in the incidence of feeding, biting littermates, and in overall activity. Biting litter-mates was performed mainly by the animals which were relatively heavy at the time of weaning . Individual variation in the amount of feeding is probably of commercial significance, as indicated by the correlation with the animals' live-weight gain during the study period . Feeding scores showed particularly large variation during the first days after weaning, probably because the ability to regulate intake of solid food is not fully developed in all animals at this age. Variation among individuals in behavioural reactions to weaning are probably of considerable importance for the health and productivity of the animals, but the causes of the variation largely remain obscure . Acknowledgments This work was supported by the Agricultural Research Council (U.K.) with the co-operation of Professor F . W. H . Elsley, Dr D . G . M . WoodGush and the pig unit staff . Mrs D . K. Ferguson and Mrs M . Thompson kindly assisted with the analysis . REFERENCES Fraser, D . 1974. The behaviour of growing pigs during experimental social encounters . J. agric. Sci., Camb ., 82, 147-163 . Fraser, D ., Ritchie, J . S. D . & Fraser, A. F. 1975 . The term `stress' in a veterinary context . Br . vet. J., 131, 653-663 . Gundlach, H. 1968 . Brutfursorge, Brutpfiege, Verhaltensontogenese and Tagesperiodik beim Europaischen Wildschwein (Sus scrota L.). Z. Tierpsychol., 25,955-995 . Haythornthwaite, A. & Shaw, M . 1974 . The case for cage rearing . Pig Farming, 22 (May), 81-83 . Hicks, C. R . 1973 . Fundamental Concepts In the Design of Experiments, 2nd edn. New York : Holt, Rinehart & Winston . Marx, D . 1973 . Vergleichende Untersuchungen liber das Verhalten von Saugferkeln and friihabgesetzten Ferkeln in K .dfiggruppenhaltung (Batteriehaltung) . Berl. Munch. Tierarztl. Wschr., 86, 289-295. Pittaway, M. J . & Brown, P. L. 1974. Early weaning and cage rearing . Pig Farming, 22 (April), 26-29. Schalbert, J. 1972. A malacok magatartisa az iparszeru sert6startasi rendszerben . Allattenyesztes, 21, 267-277. Whittemore, C. T. & Fraser, D . 1974 . The nursing and suckling behaviour of pigs . II. Vocalization of the sow in relation to suckling behaviour and milk ejection. Br. vet. J., 130, 346-356. (Received 10 June 1975 ; revised 11 May 1976 ; MS. number : A1732)
OBSERVATIONS ON THE BEHAVIOURAL DEVELOPMENT OF SUCKLING AND EARLY-WEANED PIGLETS DURING THE FIRST SIX WEEKS AFTER BIRTH By D . FRASER* School of Agriculture, University of Edinburgh
Abstract . Piglet behaviour was studied during the first 6 weeks after birth using litters weaned at 3 and 6 weeks. The main changes with age in suckling animals involved increases in overall activity and in behaviour associated with solid food ingestion. Newly-weaned animals were particularly active and aggressive, and appeared to have difficulty lying together comfortably . Most animals accepted the new diet in the first day ; frequency of defecation increased over the 4 days after weaning . Unlike suckling piglets, the early-weaned animals often nosed the bellies of pen-mates, and frequently pawed the bedding in conjunction with defecation and before lying down. Consistent individual differences in the incidence of biting litter-mates, feeding, and belly-nosing correlated with either body weight or weight gain . Unusual behaviour associated with early weaning is discussed in terms of digestive upset leading to discomfort, restlessness and fatigue . In recent years pig producers have begun weaning piglets at progressively earlier ages in an effort to increase the efficiency of their breeding stock . Typical weaning age has declined from 8 weeks to 6 or often 5 weeks . Some producers with specialized facilities wean the young during the first week of life, but this can lead to problems in piglet health and behaviour, and in the reproductive performance of the sows . A more common trend is toward 3-week weaning, but even at this age abnormal behaviour and other problems can occur . Behavioural problems which have been observed among early-weaned piglets include unusually high levels of general activity and aggressiveness toward pen-mates, suckling activities directed at other piglets, and faulty regulation of food intake, including both failure to eat and excessive eating which may predispose the animals to digestive disorders (Pittaway & Brown 1974 ; but see also Haythornthwaite & Shaw 1974) . There is much variation between production units in the type and severity of the problems seen, but little systematic work has been done to establish the reasons for such variation . Previous behavioural studies of early-weaned piglets have commonly been limited to measures derived from time-lapse filming ; and the animals have generally been housed in special earlyweaning cages, making it difficult to separate the
effects of weaning from those of the change of environment and management (Marx 1973) . In the following study, piglets were observed in the same situation before and after weaning at 3 weeks of age. In addition, comparable observations were made on the behavioural development of suckling piglets in a similar environment . Methods Eighty piglets were studied during the first 6 weeks after birth. The animals were drawn from 10 litters, each the offspring of a Large White or Large White x Landrace sow in its second or subsequent parity. The litters consisted of between eight and 11 piglets, but observations were limited to eight marked piglets in each litter in order to standardize the procedure . The 10 litters were studied in pairs, and were chosen so that the two litters comprising each pair were born within the same 2 days . One litter of each pair was weaned by removing the sow on one of days 21 and 23 after parturition ('early-weaned litters') . The others were weaned at 6 weeks of age ('normally-weaned litters') after the experimental observations had ended . About 4 days before parturition the dams were moved into farrowing crates (a metal framework which restricts the sow's movement during parturition and lactation to reduce the likelihood of the piglets being crushed) in pens measuring approximately 2 x 3 m . Each pen was
*Author's present address : Ontario Ministry of Natural Resources, Fish and Wildlife Research Branch, Box 50, Maple, Ontario, Canada, LOJ 1EO . 22
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
equipped with two troughs containing water and dry supplementary feed for the young . A low food trough was used for each litter initially, and was replaced by a hopper with three feeding spaces about 3 weeks after parturition . Wood shavings were provided as bedding, and were normally replaced daily at 10 .00 hours. The sows were fed a concentrated ration at 08 .00 and 16 .00 hours . The animals of each pair occupied adjacent pens in a room which contained no other animals . The piglets were marked for easy identification by coloured numbers on their backs, and were weighed during the first day after birth and at about 21 and 42 days of age . For the periods of observation the observer sat to the rear of the sows until one nursed its young successfully as judged by the criteria of Whittemore & Fraser (1974) . A stop clock was started during the period of milk flow (the phase of rapid sucking by the piglets), and the observer made a written record of the activities performed by each of the eight piglets in each successive minute until the period of milk flow of the next successful nursing. The following behavioural categories were used : (i) suckling ; when most or all the young were active on the udder and the sow was giving the characteristic nursing grunts ; (ii) sleeping on the udder ; which sometimes followed suckling when the young slept without leaving their suckling positions ; (iii) nosing the teats when not suckling ; when individual piglets approached and nosed the udder between sucklings ; (iv) active; which included standing, sitting and moving about; (v) lying ; (vi) feeding on supplementary food ; (vii) drinking water ; (viii) defecating ; (ix) urinating ; (x) aggressive biting at litter-mates ; (xi) scratching the body with a hind leg or by rubbing against a fixed object ; (xii) scampering about the pen ; (xiii) rooting the floor with the snout ; (xiv) pawing the floor with a front hoof ; (xv) belly-nosing ; a distinctive sequence in which one piglet rubbed another's belly with rhythmic, up-and-down movements of the snout ; (xvi) nosing and chewing the body of a littermate when the distinctive belly-nosing behaviour was not seen .
23
Written notes were also made of other behavioural observations as the occasion arose, and of the colour and firmness of the piglets' faeces. Each litter was typically observed sometime between 12.00 and 15.00 hours on three separate days during each of the first 3 weeks post partum. After the sow was removed, the earlyweaned piglets were observed in a similar way during a 2-h period on each of the first 5 days after weaning, and on 3 days during each of weeks 5 and 6. Observations on the normallyweaned litters continued three times per week throughout the study. In analysing the records a count was made of the number of minutes of observation in which a piglet was scored for each activity . For the earlyweaned litters a separate count was made for each litter-mate, thus permitting a comparison of individual differences among animals . For the normally-weaned litters a separate count was made for successive minutes after suckling in order to show the pattern of behavioural change between one suckling and the next . In both cases the analysis gave an overall score for a litter representing the percentage of 'piglet-minutes' for which each activity was scored during the observation period. Since the number of observation periods was not the same for all weeks, the results of each litter were combined to give a weekly percentage score which, after arcsine square root transformation, was treated by two-way analysis of variance with repeated measures . Results The analysis of variance for groups (normallyweaned and early-weaned) and weeks of age is summarized in Table I which shows all effects reaching the 10 % level of statistical significance . The means of the weekly percentage scores for these activities are shown in Figs . 1 to 3 . Two activities, scampering and urinating, showed no significant effects in the analysis and are not illustrated in the figures . On the basis of this analysis, the activities given in Table I can be divided roughly into four main groups (1) The categories `active', `lying' and `rooting' (Fig. 1) showed a progressive change with age which was similar for both groups. (2) Feeding, defecating and drinking (Fig. 2) showed an increase with age for both groups but an especially large increase after weaning . Scheffe's test (Hicks 1973, p . 36), applied at the
24
ANIMAL BEHAVIOUR, 26, 1
5 % level of significance, showed that feeding scores were higher in weeks 4 to 6 combined than in weeks 1 to 3 combined for both early-weaned and normally-weaned piglets, and that the earlyweaned group exceeded the normally-weaned group during the second 3-week period . The same was true of drinking . Defecation scores of the early-weaned group exceeded those of the normally-weaned group in weeks 4 to 6, but only
the early-weaned animals showed a significant increase with age when weeks I to 3 and weeks 4 to 6 were compared . (3) Pawing and belly-nosing (Fig . 3) were seen with substantial frequency only after weaning . For both activities the scores of the earlyweaned piglets in weeks 4 to 6 exceeded those of weeks 1 to 3, and also exceeded those of the
Table I. Summary of the Analysis of Variance of the Behavioural Categories, for Groups (normally- or early-weaned), Weeks, and Groups x Weeks Interaction Category Active Lying Rooting Feeding Drinking } Defecating Pawing Belly-nosing Nosing/chewing litter-mate Biting litter-mate Scratching
Factor
df
F
P
Weeks Weeks Weeks Group Weeks GxW Weeks GxW Group Weeks GxW Group Weeks GxW Group Weeks GxW Weeks GxW G x W Group
5,40 5,40 5,40 1, 8 5,40 5,40 5,40 5,40 1, 8 5,40 5,40 1, 8 5,40 5,40 1, 8 5,40 5,40 5,40 5,40 5,40 1, 8
11 .92 4.76 23 .99 8 .56 46.06 3 .70 29.42 4.33 4. 67 12. 28 2. 90 18 . 66 9 .41 3 .95 9 . 32 10 . 36 7 . 86 5 . 00 2 . 80 2 . 84 3 . 79
<0 .001 <0 .005 <0-001 <0 .025 <0 .001 <0 .01 <0 .001 <0 .005 <0 . 10 <0 .001 <0 .05 <0 .005 <0 .001 <0 .01 <0 .025 <0.001 <0. 001 <0-005 <0. 05 <0. 05 <0. 10
(c)
(b) 50
32-
40-
24-
30-
16-
20-
8-
d
UN o) (O 5, V
a 35 2
I
2 3
4
5
6
1
2 3 5 4 Age (weeks)
I
I
I
i
I
6
2
3
4
5
Fig . 1 . The means of the litters' weekly percentage scores for categories (a) active, (b) lying, and (c) rooting, shown separately for the early-weaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth .
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
normally-weaned group for both periods (P<0.05 by Scheffe's test in all cases) . (4) The biting and the chewing and nosing of litter-mates (Fig . 3) showed complex changes with time, suggesting a peak of both activities during the middle weeks of the experiment for the normally-weaned piglets . However, the effect was not statistically significant by Scheffe's test . Between one nursing and the next, the behaviour of the normally-weaned piglets generally followed a typical pattern of change which is illustrated in Figs . 4 and 5, with results shown separately for weeks 1 to 3 combined and weeks 4 to 6 combined. The results are given for only the first 40 min after milk ejection because the sows frequently resumed nursing by the end of this interval . Of special interest is the behaviour of the early-weaned piglets during the first few days after weaning . Some of the trends are shown day by day in Figs . 6 and 7 . On the first day after removal of the sow, the piglets' behaviour was markedly altered . In addition to the higher level of overall activity (Fig . 6(a)), it was noted that the piglets of all five litters appeared to have difficulty lying down without disruption . When they huddled together there was much shifting of position, and piglets lying beneath others frequently pulled away, often squawking and sometimes biting or thrusting the head at a litter-mate. Biting frequently led to a prolonged fight in the shoulder-to-shoulder stance which often disrupted the entire litter, driving sleeping piglets to their feet . This restlessness sometimes
25
persisted for 15 min or longer from the time the huddle first formed. Fighting and the attacking of litter-mates also occurred at the food trough and generally throughout the pen . The postweaning increase in biting litter-mates, and the decreases in scampering and scratching during the same period are illustrated in Fig . 7 . For most animals the amount of time spent at the food trough increased within the first day to its stable post-weaning level (Fig . 6(b)), while scores for defecation increased gradually during the 4 days after weaning (Fig . 6(c)). With some exceptions the faeces generally changed from yellowish (typical of a milk diet) to brown (typical of the solid diet) by the first day . Some diarrhoea was seen in all five litters, particularly the two litters with the lowest 3-week body weight. Nonetheless, there was considerable variation in patterns of feeding and defecating . Three piglets were not seen to eat on the first day . They had loose yellow faeces and attacked littermates frequently . Two of these had begun eating at the food trough by the second day, but the third began obtaining its food by rooting on the floor, and continued to do so until the sixth day . Another piglet had a score for feeding on day 1 which was four times higher than the average of its litter-mates . On day 2 this animal had dark, watery faeces, spent little time eating, and accounted for 14 of the litter's 18 instances of biting litter-mates . Two of the most striking behavioural changes after weaning were in pawing the bedding and in belly-nosing . Pawing, which was rare in piglets
Fig. 2. The means of the litters' weekly percentage scores for categories (a) feeding, (b) drinking, and (c) defecating, shown separately for the early-weaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth .
26
ANIMAL BEHAVIOUR, 26, 1 (c) -1 . 0 0
05
1 0 --o
-a
-o
(d)
(b) 0 '
6
2 0 0
10
E-W
o-o N-W
/ 0
05
N o> m c
5 / 0
U 0
(e)
o. 4
20
C
m
I
2
15
l
3
/
2
.\/ 0 o
10
/
\ 1
05
1
2
3
4
5
6
1
2
3
6
Age (weeks) Fig. 3 . The means of the litters' weekly percentage scores for categories (a) pawing, (b) belly-nosing, (c) biting litter-mates, (d) chewing and nosing litter-mates, and (e) scratching the body, shown separately for the earlyweaned (closed circles) and normally-weaned (open circles) piglets over the first 6 weeks after birth . before weaning, rose sharply for all litters during the 3 days after the sow was removed . It had declined again by week 6 for most piglets . Pawing was usually accompanied by rooting with the snout, which was very common in both early-weaned and normally-weaned animals . However, changes in the incidence of pawing and rooting followed different patterns (Figs . 1 and 3) . The pawing of bedding by the earlyweaned piglets was observed particularly in two contexts : (i) just before or after a piglet defecated, usually near the place of defecation, and (ii) when a piglet was about to lie down, usually near
the place of lying . Fig. 8 shows the mean percentage of cases in which piglets were seen defecating or lying during the several minutes before and after pawing occurred . Belly-nosing was virtually never seen before weaning, but it was common in all litters after the sow was removed . The onset of belly-nosing was generally sudden, beginning on the same day for several members of the same litter . The activity broke out on the first day after weaning in two litters, and after 6, 12 and 17 days in the others . The percentage of minutes in which the behaviour was seen ranged from 0-9 for one
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS
27
Fig . 4 . Mean of the mean percentage scores of the five normally-weaned litters for lying (L), being active (A) and for suckling (S) during the 40 min after the period of milk flow of a successful nursing, shown separately for weeks 1 to 3 combined and for weeks 4 to 6 combined .
litter to 8 .0 for another, over weeks 4 to 6 combined . There was also great variation within litters (average coefficient of variation, 106 %), with some piglets of each litter consistently performing the behaviour a great deal while others totally refrained. Like feeding, belly-nosing appeared to be stimulated by the sound of the neighbouring sow nursing its young . Piglets which were feeding, lying down or defecating often stopped these activities and moved to another place when litter-mates began nosing their bellies . Fighting occasionally appeared to result from belly-nosing, since the recipient piglet sometimes turned and bit the performer . (a)
(c)
3
2
1
8
16 24 32 40
8 1 6 24 32 40
8 1 6 24 32 40
Time (min) Fig. 5 . Mean of the mean percentage scores of the five normally-weaned litters for (a) urinating and defecating combined, (b) feeding on supplementary food, and (c) scampering, during the 40 min after the period of milk flow of a successful nursing, shown separately for weeks 1 to 3 combined (open circles) and weeks 4 to 6 combined (closed circles).
Weights of the piglets at 3 weeks of age, taken when the sow was first removed from the earlyweaned animals, showed no significant difference between the two groups . The mean +SE weight of the early-weaned group was 4. 84+0 . 26 kg as compared with 5-31±0-21 (t = 1 .33, Ns) . By 6 weeks of age, however, the early-weaned animals were distinctly lighter (8 .86+0 . 51 kg compared with 10 .75+0 .44 kg, t = 2 . 81, P<0 . 01) . Among the early-weaned animals there were obvious behavioural differences between piglets of the same litter . Correlations were used to test whether the idiosyncratic differences seen just after weaning (in week 4) persisted over weeks 5 and 6 as well . The individual piglets' scores from week 4 for overall activity, feeding, and biting litter-mates correlated highly with their scores for the same activities from weeks 5 and 6 combined (means of the correlation coefficients for the different litters = +0 .54, +0 . 47, and +0.61 ; P<0. 001, 0 . 01, and 0 . 001 respectively) . Bellynosing was not seen during week 4 in three of the litters, but the individual animals' scores from week 5 correlated highly with those from week 6 (r _ + 0.59, P<0.001) . Some of the behavioural differences among litter-mates correlated with differences in the animals' weights at 3 and 6 weeks of age, as summarized in Table II . Discussion The normally-weaned litters provide basic information on the behaviour of suckling piglets
28
ANIMAL BEHAVIOUR, 26, 1 (a) Q)
(b)
50^
(c)
15
1 .5
10
1 . 0-
5-
0-5-
5
1 11 11 4
3
i
I
5
3
4
I 3
5
4
5
Piglet age (weeks) Fig. 6 . The mean percentage of minutes in which early-weaned piglets were scored as (a) active, (b) feeding, and (c) defecating, during weeks 3, 4 and 5 of life . Piglets were weaned at the end of the third week . The results are shown separately for the first 5 days after weaning . (a)
(b)
(c) I 1 I l
4
5 0 U
I 3
1C
f
c
I
Iv
CL C 4)
2
r
r
r
I
i
I I 1 I
1
2
1 1
3
1 1 1 1, 4
I 5
3
I
I 4
5
3
1 1, 1 1 4
5
Piglet age (weeks) Fig. 7 . The mean percentage of minutes in which early-weaned piglets were scored as (a) biting litter-mates, (b) scratching their bodies, and (c) scampering, during weeks 3, 4 and 5 after birth, expressed as a percentage of the number of minutes in which the animals were scored as active . Piglets were weaned at the end of the third week. The results are shown separately for the first 5 days after weaning. and its development . Over the first 6 weeks after birth, the main behavioural changes consist of an increase in overall activity and in behaviour associated with the ingestion of solid food (feeding, drinking, rooting and defecating) . Similar steady increases with age in overall activity and feeding behaviour have been noted
by Schalbert (1972) . Marx (1973) found no consistent increases in activity among suckling piglets, but his results, like the present study, do indicate that interest in solid food begins to become obvious at about three weeks of age . Many of the behavioural categories showed little consistent change in incidence over the 6 weeks,
FRASER : BEHAVIOUR OF SUCKLING AND EARLY-WEANED PIGLETS reflecting the relative precocity of week-old piglets . A detailed study of the development of much of the pig's species-typical behaviour would presumably have to concentrate on the early hours or days of life (cf. Gundlach 1968) . The pattern of behavioural change between successive nursings was also little modified with age . Suckling was generally followed by a period of activity and then lying . Most defecation and urination, and much of the feeding, occurred soon after suckling, while vigorous activity
6 5 4 3 2 Before
1 1 2 3 4 5 After Time (min)
Fig. 8 . Mean percentage of minutes in which piglets were scored for lying (above) and defecating (below), before, during and after a minute in which the same animal began pawing the bedding . Instances of pawing were included only if the record was complete for the full 12-min interval shown, and if pawing had not occurred during the initial 6 min . Lest any link between defecation and lying confound the results, the analysis of scores for lying excluded instances in which defecation occurred during the 12 min. This gave 398 records for the calculation of the lower line and 266 for the upper . Points show the mean (±sE) of the percentage scores of the individual litters.
including scampering was more common later in the interval, especially for the older piglets . The sudden post-weaning increases in general activity and aggression, coupled with the restless behaviour when the animals lay down together, gave the impression that the piglets were for some reason uncomfortable during the first day or more after weaning . Such discomfort may account for the marked increase in pawing the bedding which is apparently a form of nestbuilding (Gundlach 1968), and which frequently occurred in the lying area just before a piglet lay down. In a time-lapse photographic study a relatively small percentage of early-weaned piglets in battery cages were seen sleeping during the first observation period after weaning, compared with suckling piglets of the same age (Marx 1973, Abb . 14) . The very rapid increase in feeding behaviour during the first day after weaning was accompanied by a much slower rise in the frequency of defecation . This may reflect some difficulty in the animals' physiological adaptation to the solid food, perhaps indicated in extreme cases by diarrhoea . Discomfort from this source might account for the animals' restlessness and increased aggression . This hypothesis is supported by the association between loose faeces, aggressiveness and feeding behaviour in the few piglets which displayed anomalous feeding during the first day after weaning . The decreases in scampering and scratching may be related to the greater amount of aggression, as is observed among older pigs (Fraser 1974) . Increased susceptibility to infectious disease is one of the most characteristic features of the post-weaning period (e .g. Fraser, Ritchie & Fraser 1975). Perhaps the restless activity and difficulty in lying together lead the animals to a state of fatigue which contributes to this high susceptibility. It would be of interest to know to what extent the restlessness and related behaviour
Table IL Mean Within-Utter Correlation Coefficients between W at 3 and 6 Weeks and Weight Gain During this Period, and the Animals' Total Scores on Five Behavioural Categories During the Same Period Behaviour Active Feeding Defecating Biting litter-mates Belly-nosing
3-week weight
6-week weight
Weight gain
+0 .23 +0 . 10 +0 . 25 +0. 56*** -0. 03
+0. 20 +024 +0.32* +0.50** -0 . 33*
+0. 15 +0. 37* +0 .28* +0 . 36* -0. 36*
*P<0 .05 ; **P<0 . 01 ; ***P<0.001 .
29
30
ANIMAL BEHAVIOUR, 2 6 , 1
could be influenced by environmental factors . The importance of high, consistent ambient temperature for early-weaned piglets is widely recognized (Pittaway & Brown 1974) . Perhaps a more comfortable lying surface would also be of value. In addition to its possible function as rudimentary bed-making before lying down, the pawing of the floor was also common in the context of defecation . It may be analogous to the perfunctory digging movements of domesticated dogs at the time of defecation, although it is not clear why it should increase so strikingly upon weaning. With the change in diet and frequency of defecating, and with the higher incidence of diarrhoea, the sensation accompanying defecation may be increased beyond a threshold level for eliciting pawing . It is unclear whether the amount of pawing associated with defecation is independent of the amount associated with lying down, or whether some common factors influence the incidence in both contexts . The behaviour is puzzling, but it might repay study since it constitutes one of the most consistent behavioural changes with early weaning. Belly-nosing, like the navel-sucking performed by some early-weaned calves and lambs, closely resembles a principal component of normal suckling behaviour . Despite the clear association with early weaning, the immediate causes of belly-nosing are obscure . Particularly puzzling are the large differences in incidence between members of the same litter, and the variation between litters in the number of days which elapse after weaning before the behaviour begins . Some of the variation within litters might possibly be associated with the animals' teat choice and suckling habits before weaning . Like other behavioural abnormalities such as the featherpecking of fowls and the tail-biting of growing pigs, belly-nosing may be `contagious' . This would help to explain the near synchronous onset of the behaviour by members of the same litter. Some of the practical significance of bellynosing is suggested by the negative correlation with weight-gain within litters. The performance of belly-nosing may have retarded growth, as some piglets persisted in the behaviour for much time which might otherwise have been spent in feeding or resting. Alternatively the correlation might reflect some tendency for piglets to perform belly-nosing more if they were having difficulty in adapting to the conditions of weaning, as indicated by poor growth . Belly-nosing
may also exert an undesirable influence on the recipient animal or on the litter as a whole if it causes outbreaks of fighting . Other correlations showed that there were strong differences between members of the same litter in the incidence of feeding, biting littermates, and in overall activity. Biting litter-mates was performed mainly by the animals which were relatively heavy at the time of weaning . Individual variation in the amount of feeding is probably of commercial significance, as indicated by the correlation with the animals' live-weight gain during the study period . Feeding scores showed particularly large variation during the first days after weaning, probably because the ability to regulate intake of solid food is not fully developed in all animals at this age. Variation among individuals in behavioural reactions to weaning are probably of considerable importance for the health and productivity of the animals, but the causes of the variation largely remain obscure . Acknowledgments This work was supported by the Agricultural Research Council (U.K.) with the co-operation of Professor F . W. H . Elsley, Dr D . G . M . WoodGush and the pig unit staff . Mrs D . K. Ferguson and Mrs M . Thompson kindly assisted with the analysis . REFERENCES Fraser, D . 1974. The behaviour of growing pigs during experimental social encounters . J. agric. Sci., Camb ., 82, 147-163 . Fraser, D ., Ritchie, J . S. D . & Fraser, A. F. 1975 . The term `stress' in a veterinary context . Br . vet. J., 131, 653-663 . Gundlach, H. 1968 . Brutfursorge, Brutpfiege, Verhaltensontogenese and Tagesperiodik beim Europaischen Wildschwein (Sus scrota L.). Z. Tierpsychol., 25,955-995 . Haythornthwaite, A. & Shaw, M . 1974 . The case for cage rearing . Pig Farming, 22 (May), 81-83 . Hicks, C. R . 1973 . Fundamental Concepts In the Design of Experiments, 2nd edn. New York : Holt, Rinehart & Winston . Marx, D . 1973 . Vergleichende Untersuchungen liber das Verhalten von Saugferkeln and friihabgesetzten Ferkeln in K .dfiggruppenhaltung (Batteriehaltung) . Berl. Munch. Tierarztl. Wschr., 86, 289-295. Pittaway, M. J . & Brown, P. L. 1974. Early weaning and cage rearing . Pig Farming, 22 (April), 26-29. Schalbert, J. 1972. A malacok magatartisa az iparszeru sert6startasi rendszerben . Allattenyesztes, 21, 267-277. Whittemore, C. T. & Fraser, D . 1974 . The nursing and suckling behaviour of pigs . II. Vocalization of the sow in relation to suckling behaviour and milk ejection. Br. vet. J., 130, 346-356. (Received 10 June 1975 ; revised 11 May 1976 ; MS. number : A1732)