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Some relations between stereotyped suckling in piglets and exploratory behaviour and discrimination reversal learning in adult swine
Applied Animal Ethology, 4 (1978) 223-233 o Elsevier Scientific Publishing Company, Amsterdam
223 -
Printed
in The Netherlands
SOME RELATIONS BETWEEN STEREOTYPED SUCKLING IN PIGLETS AND EXPLORATORY BEHAVIOUR AND DISCRIMINATION REVERSAL LEARNING IN ADULT SWINE
J. LIEN
and F.D. KLOPFER’
Animal Behavior Laboratory, Memorial University of Newfoundland, St. John’s, Newfoundland (Canada) ’Comparative Behavior Laboratory, Washington State University, WA (U.S.A.) (Received
4 April
1977)
ABSTRACT Lien, J. and Klopfer, F.D., 1978. Some relations and exploratory behaviour and discrimination
Anim. Ethol.,
between stereotyped suckling in piglets reversal learning in adult swine. Appl.
4: 223-233.
The relationship of stereotyped suckling positions in artificially fed and sow-fed infant swine to the behaviour of adult animals was investigated. Suckling behaviour was observed, and four animals from each feeding condition exhibiting low suckling stereotypy and four from each feeding condition exhibiting high suckling stereotypy were selected. Animals were tested at five months of age in exploratory situations and on a two-window position discrimination and reversals. Low suckling stereotypy and artificially reared animals made fewer errors on the first discrimination reversals than high stereotypy and sow-fed animals. They were also less emotional on the first reversals. Over nine reversals artificially reared animals made significantly fewer errors than sow-fed subjects and low stereotype sow-fed animals made fewer errors than high stereotypy sow-reared animals. Low stereotypy subjects explored more objects and over a longer period of time than high stereotypy subjects. It was concluded that stereotyped suckling in piglets is related to behaviour exhibited by the adult in problem-solving situations.
INTRODUCTION
Previous work with swine suggests that response stereotypy in the infant’s feeding behaviour may be related to behavioural characteristics of the adult animal (Klopfer, 1961; Wesley and Klopfer, 1962). Piglets typically develop strong teat preferences, although some exhibit position variability in their suckling behaviour (McBride, 1963; Hemsworth et al., 1976). Piglets that develop suckling stereotypy are strongly reinforced for this positional orientation. Attempts to change feeding position are punished by agonistic behaviour by littermates or result in loss of milk. However, animals that succeed in varying their suckling position receive food reinforcement both for varying position orientations and for approaching novel positions. If these response
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characteristics generalize to other situations, they may be only partially adaptive. This partial adaptiveness may place the animal on a partial reinforcement schedule, thereby making extinction more difficult and allowing the behaviour to persist. Thus, in situations where positional flexibility is required, animals with stereotyped suckling positions earlier in life may have relatively greater difficulty in learning the required variability of spatial orientation. In situations where novel stimulation is present, such stereotyped animals should approach novel stimulus situations less readily. Conversely, animals with variable suckling positions should more readily approach novel stimuli. Additionally, animals less flexible in suckling should be relatively more stressed when placed in novel situations and those requiring positional flexibility. METHODS
Subjects Subjects were selected from 34 healthy neonatal swine obtained from four primiparous matings farrowing within a four-day period. Litters were a cross X cross mating, a purebred Poland China mating, a purebred Berkshire mating, and a Hampshire X cross mating. These thirty-four neonates were marked with identification letters and randomly assigned to either troughfed or sow-fed feeding conditions. Sow-fed subjects were fostered to one of two sows. Teat positions on each sow were numbered from 1 (anterior) to 8 (posterior) on her right and left side. Trough-fed piglets were fed via a Nurs-ette automatic piglet feeder. The Nurs-ette feeder automatically dispensed a predetermined portion of sow’s milk replacer powder and water which was heated, mixed and pumped into a 1.4 m long double trough and available ad libitum. Each side of the trough was divided into 8 positions by means of a wire divider. Piglets were maintained under these feeding conditions until the age of 35 days, at which time they were weaned. During the 35-day rearing period, nursingsuckling behaviour was watched daily by an observer through a one-way window located in the roof of each vivarium. Observation periods were of 5 min duration at 2-3 h intervals during the day and night. After the first week postpartum, these observations were restricted to the daytime. Numerical position of suckling and within-bout position shifts were recorded by the observer. The mean numerical position of suckling in all observation periods until weaning, and the variability around this position, were calculated. Piglets were then rank-ordered on the basis of position variability and sixteen animals were selected; eight from each feeding condition, four exhibiting high variability in suckling position, and four exhibiting low variability in suckling position. No patterns in teat or trough positions and weight, litter, or sex were detected across groups. Trough-fed animals failed to exhibit the extreme
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position stereotypy of some sow-fed piglets, however. Mean standard deviations of suckling position for high stereotypy groups were 0.70 in sow-fed animals, and 1.54 in trough-fed animals. Mean standard deviations of suckling positions in low stereotypy animals were 1.53 for sow-fed animals, and 1.78 for trough-fed animals. High stereotypy animals in both feeding conditions had significantly fewer shifts of position within suckling bouts than low sterotypy animals; however, variability was significantly higher in the trough-fed animals. After weaning at 35 days postpartum, each animal was housed witn other animals in the same feeding condition group until the age of five months, when exploratory and discrimination tests were administered. Throughout this postweaning period, animals were floor-fed on a pelleted growing ration for swine (Wesley and Klopfer, 1962) and standard hog-rearing practices were followed. Apparatus
The two exploration test situations were located within two 2.5 m X 3 m concrete block rooms located 6 m distance from the living pens. Each contained a holding box and an open field area with stimulus objects or alleys. The holding box of each room was 1.5 m X 0.8 m X 1 m high with a 0.5 m wide guillotine door, centred in the distal end, which permitted access to the test chamber. The guillotine door could be raised or lowered by the experimenter in the adjacent observation room. In the first exploratory test room (A), four stimulus objects were placed in the open field area. Stimulus objects were constructed from 10 cm X 10 cm X 4 cm black and grey wooden blocks mounted on hinges and then bolted into position on steel angles, 15 cm from the floor. At the distal end of the open field area of thessecond exploratory test room (B) were three alleys, 1 m deep, broadening in width from 0.5 m at the entrance to 0.8 m at the rear. The 1 m high alleys were constructed of 1 cm plywood and painted grey. Inside each alley, a variety of geometric forms were stencilled on the walls, rough-cut wooden laths were fastened to the floor and roof of each alley in various diagonal patterns and each alley was rubbed with orange peel, fecal material and soap. Viewing windows in the wall permitted continuous observation of the animals during the test periods. The discrimination test situation was a 2.5 m X 3.0 m concrete block room containing a response apparatus in the distal corner of the room and an automatic feeder in the near corner of the room. Directly adjacent to the test room was a control room with a one-way observation window. The response apparatus consisted of a housing, two response panels, and a retracting mechanism. This apparatus has previously been described by Wesley and Klopfer (1962). In the near corner of the test room was a solenoid operated feeder which delivered lo-12 g of standard hog pellets when activated. The pellets were scattered on approximately 0.8 m2 of floor area accompanied by a ioud solenoid sound.
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Procedures
Exploratory situation adaptation and test trials were completed first. Then discrimination situation pretraining and testing were done. Each individual was given two 5 min adaptation periods in the holding pens of each exploration situation. During each of these four adaptation sessions, the amount of vocalization, squealing, defecation, urination and jumping were noted by the experimenter on a five point scale (where 1 = no emotionality and 5 = extremely emotional). Exploratory testing was started the day following completion of the adaptation trials. During testing, an animal was placed into the holding pen of the exploratory situation and after 45 s the door was opened. A trial consisted of 5 min from the time the door was opened and the animal entered the pen field area. The first exploratory trial was given randomly in either exploratory situation (A or B). After this initial trial assignment, the four trials in the two situations were given on alternate consecutive days. Random trial order within days was observed in assigning trials for each animal and group. The duration of open field activity started when a holding pen exit occurred and ended when the head and front two feet of the animal were again in the holding pen. In exploratory situation A, frequency and duration of snout contact with the desig nated stimulus objects and snout contact with other objects were recorded. In exploratory situation B, an alley entry was recorded when the head and front two feet of the animal were in the alley, and the duration of alley activity was scored from this point until the head and front two feet of the subject were behind the alley entrance line. Head entry without feet entry was recorded as a partial entry. Frequency of defecation, urination, and jumping were recorded, and the amount of vocalization and squealing were rated by the experimenter on a five point scale, while the animal was in the holding pen and in the open field area during the 5 min exploratory trials. The discrimination pretraining followed completion of exploratory test trials. Two days prior to initial experience in the discrimination situation, the typical food ration was reduced by one-third. The initial pretraining trial consisted of allowing pen mates a total of 15 min of ad libitum feeding under the feeder and in front of the stimulus windows. In the second pretraining trial the animals were taken singly to the discrimination situation and were trained to respond to sound cues for food and to press the stimulus-response plates with their snouts after the method of successive approximations (Wesley and Klopfer, 1962). Once plate-pressing was closely approximated on either plate, the right window was exposed until the animal had made ten responses which were followed by food reinforcement. Then the left window was exposed and the subject was trained to the same criterion. Duration of pretraining, number of food reinforcements during shaping, and emotionality were recorded for each pretraining session. The pretraining food deprivation schedule continued through the position discrimination trials. After the assignment of initial problem position, each
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animal was given twenty trials per day until it reached the criterion. Criterion of learning was a response probability greater than the 0.01 level of significance within a day, with a minimum of fifteen responses, or the same response probability level in twenty consecutive trials, in two days. Random trial order within days was observed in assigning the time of test trials for each subject, and brightness cues were randomized for each of twenty trials. In each test period, the animal was placed in the discrimination situation. After 30 s, the stimulus lights were turned on according to that animal’s problem and 15 s later the apparatus was lowered into the response position. After the animal responded, the stimulus apparatus was immediately retracted, the response recorded, brightness cues were reset and after 15 s the stimulus apparatus was again lowered into the response position. This procedure was followed for each of the twenty daily trials. If an animal failed to respond within 5 min, or for two successive trials within a day, testing was discontinued for that day. When the animal achieved the criterion of learning on the original problem, it then received the reversal of this problem, was trained to criterion, and so on for nine successive reversals. Throughout the reversal trials, the same procedures were utilized as on the original problem. Throughout the discrimination tests, the one-way observation window was kept closed to prevent the animal’s behaviour from influencing experimenter procedure. RESULTS
The two feeding conditions and the two levels of stereotypy were incorporated into a 2 X 2 factorial design, with errors to criterion in reversal learning, frequency and duration of open field activity, object contact, compartment entrances in exploration, and emotionality as dependent variables. The results will be presented in the following order: (1) emotionality, (2) exploratory behaviour, and (3) discrimination learning and reversal performance. Emotionality Typically, the highest emotionality scores were achieved the first day of the adaptation trials with a gradual decrease in scores for most subjects as trials progressed. Individual animals in all groups showed wide variation in the several measures utilized in the emotionality scores. While some animals attained high scores primarily through high vocalization rates, others achieved them as a function of frequent urination and defecation. Since there were no apparent differences among the groups on patterns of emotionality, these were not tested. Emotionality scores during adaptation trials in the exploratory situations were significantly higher for trough-fed than for sow-fed animals
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(F = 6.20, d.f. = 12, P < 0.01). Significant interaction between feeding condition and level of stereotypy occurred during tests in the exploratory situations (F = 17.51, d.f. = 12, P < 0.01). Simple effects were then tested. In the stimulus object situation, sow-fed low stereotypy animals attained a much lower mean total emotionality score than high stereotypy subjects (P < O.Ol), hut this was not so in trough-fed animals. Comparison of the two feeding conditions indicated sow-fed animals achieved lower emotionality scores than trough-fed subjects (P < 0.01). No significant over-all differences were apparent among emotionality scores during pretraining procedures on the discrimination apparatus, and dif. ferences in total emotionality scores for the original problem, and over the series of reversals, were also not significant. On the first position reversal problem, however, sow-fed animals achieved significantly higher emotionality scores (F = 26.78, d.f. = 12, P < 0.01) than trough-fed animals, and low stereotypy subjects were significantly lower in the scores that they attained than high stereotypy subjects (F = 4.54, d.f. = 12, P < 0.05). Exploratory
behaviours
Mean total frequency and duration of activities in the exploratory situation are presented in Table I. Trough-fed animals had a higher mean total entry frequency into the open field of the two exploratory situations than sow-fed animals (F = 4.83, d.f. = 12, P < O.Ol), which reflects a generally higher locomotor activity. No significant differences between feeding conditions or levels or stereotypy were found in duration of open field activity in either exploratory situation, and interaction effects between feeding condition and level of stereotypy were not significant. Significant interaction effects in frequency of stimulus object contact (Test A) (F = 3.65, d.f. = 12, P < 0.05) and duration of contact (F = 15.06, d.f. = 12, P < 0.01) were found, and simple effects were then tested. In frequency of contact, low stereotypy sow-fed animals had significantly higher scores than high stereotypy sow-fed animals (P < 0.01). Low stereotypy sow-fed animals spent a mean total duration of 158.0 s in contact with the four stimulus objects while high stereotypy sow-fed subjects spent a mean total duration of only 47.3 s in such contact (P < 0.001). Differences between levels of stereotypy in the trough-fed animals in frequency and duration of contact were slight (F = 1.24. d.f. = 12, P > 0.05). Objects which were not among the four designated stimulus objects were contacted by the subjects, including the holding pen walls and door edges and the steel angle fastened to the wall perimeters. Significant interaction between feeding conditions and level of stereotypy was found in both frequency (8’= 6.59, d.f. = 12, P < 0.01). and duration (8’= 17.53, d.f. = 12, P < 0.01) of contact with nondesignated stimulus objects. The simple effects were then tested. Low stereotypy sow-fed animals more often contacted
Frequency at stimulus objects Frequency of contact with other objects Duration of contact with stimulus objects (s) Duration of contact with other objects (s) Frequency of alley entrance Duration of alley entries (s)
Measure
2.3 1.48
65.3 29.46
13.5 8.65 9.0 1.58 145.8 23.42
_X SD
_X SD
_X SD _X SD w SD
~_
19.8 4.66
X SD
6.3 5.70 6.8 4.49 101.5 104.64
43.3 19.75
1.3 0.83
17.3 5.58
9.9 8.11 7.9 3.51 123.6 78.99
59.3 27.39
1.8 1.30
18.5 5.29
1.3 1.30 8.0 3.39 99.8 56.81
47.3 1.09
0.5 0.22
17.0 1.26
24.8 7.19 8.3 1.09 307.0 91.32
158.0 8.87
3.8 1.92
23.0 2.00
stereotypy
LOW
High stereotypy
Total
High stereotypy Low stereotypy
Sow-fed animals
Trough-fed animals
_
Mean total frequency and duration of behaviour in the exploration tests
TABLE I
13.0 12.85 8.1 2.52 203.4 128.50
79.0 33.27
2.10 2.15
20.0 3.40
Total
7.4 8.60 8.5 2.69 122.8 48.16
56.3 23.96
1.4 1.41
18.4 3.64
High stereotypy
Totals
15.5 11.34 7.5 3.36 209.3 142.09
77.0 36.07
2.5 1.94
20.1 5.09
Low stereotypy
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these objects in the exploratory situations than did high stereotypy sow-fed animals (P < 0.01). Variability within feeding conditions and within stereotypy levels around the mean total duration inside the alleys of exploratory test B was rather large. Interaction effects between level of stereotypy and feeding condition were significant (F = 8.23, d.f. = 12, P < 0.01). Simple effects were then tested and low stereotypy sow-fed animals spent a significantly longer duration in the compartments than did high stereotypy animals (P < 0.01). Differences between low and high stereotypy trough-fed animals were not significant. Discrimination
learning and reversals
Errors to criterion in standard scores on the original problem and reversals are presented in Table II. During the pretraining procedures, total duration of pretraining, number of pretraining periods, and number of food reinforcements through pretraining criterion were recorded. Differences between feeding condition and stereotypy level were slight and nonsignificant. Differences between feeding conditions and levels of stereotypy and the interaction effects were not significant on errors to criterion on the initial position problem. On the first reversal, high stereotypy animals made significantly more errors to criterion than low stereotypy animals (F = 5.41, d.f. = 12, P < 0.01). Sow-fed subjects made significantly more errors than troughfed animals (F = 4.10, d.f. = 12, P < 0.05). On the second reversal to the ninth reversal, differences between feeding conditions and stereotypy levels on errors to criterion on individual reversals were not significant. The sum of errors to criterion on the first to the ninth reversals was not significantly different between levels of stereotypy (F = 2.20, d.f. = 12, P < 0.05). Differences between feeding conditions in mean total errors to criterion on the sum of all reversals were significant (F = 4.21, d.f. = 12, P < 0.05). Sow-fed animals made more errors than trough-fed animals. High stereotypy animals, however, made more errors on the first reversals than low stereotypy animals. The effect of level of stereotypy on the first two reversals was significant (F = 11.75, d.f. = 12, P < 0.01). On the sum of the first to the fourth reversals, differences between feeding conditions (F = 3.91, d.f. = 12, P < 0.05) and levels of stereotypy (F = 4.42, d.f. = 12, P < 0.05) were significant. The analysis of variance on differences between levels of stereotypy (F = 0.30, d.f. = 12, P > 0.05) and feeding condition (F = 2.20, d.f. = 12, P > 0.05) on the sum of errors to criterion on reversals five to nine were not significant. DISCUSSION
Reversal learning was relatively more difficult for animals with stereotyped suckling positions early in life. The significantly fewer errors to
Original learning First reversal Total: First to fourth reversals Total: Fifth to ninth reversals Ninth reversal Total: First to ninth reversals
Measure
_~
x SD 8 SD x SD x SD B SD x SD
17.75 14.04 15.75 6.10 58IOO 13.21 48.75 14.74 6.25 3.96 106.75 21.73 14.25 9.04 10.00 2.45 41.00 9.57 48.25 16.68 10.25 9.65 89.25 26.15
16.00 12.18 12.87 5.39 49.50 14.35 48.50 15.75 8.25 7.64 98.00 25.59
12.75 6.14 28.00 10.49 73.75 20.25 68.25 23.93 16.75 12.97 142.00 37.87 9.75 3.96 14.50 7.23 57.00 9.li 58.00 9.87 8.50 5.59 115.00 9.99
stereotypy
LOW
High stereotypy
High stereotypy
Low stereotypy
Sow-fed animals
Trough-fed animals Total
Errors through criterion on original problem and discrimination reversal problems
TABLE II
11.25 5.38 21.25 11.23 65.37 17.97 63.12 19.00 12.62 10.78 128.50 30.81
Total
15.25 11.45 21.88 10:54 65.87 19.03 58.50 22.14 11.50 10.91 124.37 35.55
High stereotypy
Totals LOW
12.00 7.33 12.25 5.85 49.00 12.30 53.12 14.56 9.37 7.94 102.12 23.60
stereotypy
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criterion made by low stereotypy animals on the first reversal, on the total errors in the first and second and on the first to the fourth reversals confirm this hypothesis. However, in errors to criterion on later reversals, high and low stereotypy animals were not significantly different. This indicates that effects of stereotypy may not persist if sufficient training on reversal learning tasks is given to the adult animal. Differences in performance by high and low stereotypy animals were relatively greater in the sow-fed conditions than in the trough-fed group. This may be influenced by the relatively greater flexibility in feeding positions in the trough-fed animals and the greater difference between high and low stereotypy levels in sow-fed animals. These findings are in agreement with the previous studies of discrimination reversals in swine (Wesley and Klopfer, 1962; Klopfer, 1961) where patterns of sensory contingencies relevant to food acquisition by the piglet were related to relative difficulty of later reversal learning. As the artificially reared animals exhibited greater flexibility in feeding positions, it was expected they would do relatively better than sow-reared subjects on discrimination reversals. High stereotypy trough-fed animals were more variable in feeding position than low stereotypy sow-fed animals. Positional orientations on the trough were less marked and feeding position was varied more frequently than in the sow-feeding condition. Significantly fewer errors through criterion were made by trough-fed animals on the first reversal, first two reversals, first to fourth reversals, and the sum of all nine reversals. This finding is in agreement with unpublished data by Klopfer and Lien in which animals fed on synthetic diets in shallow pans did relatively better on reversal performance than sow-fed animals. Contributing factors in this difference may be: (1) the differences in variability of feeding; (2) differential reinforcement for wider variety of sensory cues. In the trough-feeding conditions, visual cues were directly relevant to milk acquisition, whereas in sow-fed animals, visual cues relevant to the presence of milk were minimal. Animals were not observed to root or suck at the trough when milk was absent, but sow-reared animals frequently sucked between periods of milk let-down. When milk was pumped into the trough, feeding behaviour would again resume. The differential reinforcement for attentiveness to these and perhaps other visual cues may account partially for the superior ability of trough animals to vary their responses in the discrimination reversal problems. It was hypothesized that low feeding stereotypy animals would engage in relatively more exploratory behaviour than high stereotypy animals. However, significant interaction effects in both frequency and duration of the stimulus object contact and other object contact were obtained. Simple effects of level of stereotypy in the sow-fed animals indicate that low stereotypy animals explore more frequently and were in contact with objects longer. In the trough-fed animals, simple effects of stereotypy were not significant. In the compartment situation, main effects of stereotypy were not significant in frequency of compartment entrances. For duration scores,
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interaction effects were significant. In analyzing the simple effects of stereotypy, again low stereotypy sow-fed animals explored more than high, but this difference was not found in trough-fed animals. The finding of greater exploration in low stereotypy sow-fed animals is consistent with the hypothesis. In general, there is a non-significant trend in trough-fed animals for high stereotypy animals to explore more than low stereotypy animals. The failure to obtain differences between stereotypy levels with trough-fed animals may be attributable to the lesser difference in stereotypy levels in these animals. There was also a general non-significant tendency for artificially fed animals to explore less than the sow-fed group. The failure to find overall differences between artificial and sow-feeding conditions also indicates that factors other than feeding position stereotypy in the two feeding conditions may influence the adult animals. In rearing pens, trough-fed animals were more excitable and more readily frightened, and this trait persisted into adulthood. In early testing, trough-fed animals continued to be more emotional than sow-fed animals. After a period of handling they became more quiescent. This greater emotionality during early handling and tests, in spite of extensive adaptation handling, could account for the failure to find the predicted exploration levels in trough-fed animals. The results of this investigation are consistent with the hypothesis that differential reinforcement patterns in nursing-suckling interactions may develop rather general perceptual orientations and motor characteristics, which may persist and be representative of, or modify, behaviour in mature organisms. The logic of this investigation does not allow the conclusion that stereotypy in suckling affects later learning and exploration. The under-performing adult swine may have been more stereotyped in suckling during infancy because they were poor learners or explorers. They were, with practice, rather quickly able to match performances of less stereotyped animals in discrimination reversal learning at least. The results, however, are consistent with the hypothsis that ability of the adult animal to adapt to new and changing environmental patterns has roots in infantile development and response patterns acquired there.
REFERENCES Hemsworth, P.H., Winfield, C.G. and Mullaney, P.D., 1976. A study of the development of the teat order of piglets. Appl. Anim. Ethol., 2: 225-233. Klopfer, F.D., 1961. Early experience and discrimination learning in swine. Am. Zool., 1: 366 (abstract). McBride, G., 1963. The “teat order” and communication in young pigs. Anim. Behav., 11: 53-56. Wesley, F. and Klopfer, F.D., 1962. Visual discrimination learning in swine. Z. Tierpsychol., 19: 93-104.
223 -
Printed
in The Netherlands
SOME RELATIONS BETWEEN STEREOTYPED SUCKLING IN PIGLETS AND EXPLORATORY BEHAVIOUR AND DISCRIMINATION REVERSAL LEARNING IN ADULT SWINE
J. LIEN
and F.D. KLOPFER’
Animal Behavior Laboratory, Memorial University of Newfoundland, St. John’s, Newfoundland (Canada) ’Comparative Behavior Laboratory, Washington State University, WA (U.S.A.) (Received
4 April
1977)
ABSTRACT Lien, J. and Klopfer, F.D., 1978. Some relations and exploratory behaviour and discrimination
Anim. Ethol.,
between stereotyped suckling in piglets reversal learning in adult swine. Appl.
4: 223-233.
The relationship of stereotyped suckling positions in artificially fed and sow-fed infant swine to the behaviour of adult animals was investigated. Suckling behaviour was observed, and four animals from each feeding condition exhibiting low suckling stereotypy and four from each feeding condition exhibiting high suckling stereotypy were selected. Animals were tested at five months of age in exploratory situations and on a two-window position discrimination and reversals. Low suckling stereotypy and artificially reared animals made fewer errors on the first discrimination reversals than high stereotypy and sow-fed animals. They were also less emotional on the first reversals. Over nine reversals artificially reared animals made significantly fewer errors than sow-fed subjects and low stereotype sow-fed animals made fewer errors than high stereotypy sow-reared animals. Low stereotypy subjects explored more objects and over a longer period of time than high stereotypy subjects. It was concluded that stereotyped suckling in piglets is related to behaviour exhibited by the adult in problem-solving situations.
INTRODUCTION
Previous work with swine suggests that response stereotypy in the infant’s feeding behaviour may be related to behavioural characteristics of the adult animal (Klopfer, 1961; Wesley and Klopfer, 1962). Piglets typically develop strong teat preferences, although some exhibit position variability in their suckling behaviour (McBride, 1963; Hemsworth et al., 1976). Piglets that develop suckling stereotypy are strongly reinforced for this positional orientation. Attempts to change feeding position are punished by agonistic behaviour by littermates or result in loss of milk. However, animals that succeed in varying their suckling position receive food reinforcement both for varying position orientations and for approaching novel positions. If these response
224
characteristics generalize to other situations, they may be only partially adaptive. This partial adaptiveness may place the animal on a partial reinforcement schedule, thereby making extinction more difficult and allowing the behaviour to persist. Thus, in situations where positional flexibility is required, animals with stereotyped suckling positions earlier in life may have relatively greater difficulty in learning the required variability of spatial orientation. In situations where novel stimulation is present, such stereotyped animals should approach novel stimulus situations less readily. Conversely, animals with variable suckling positions should more readily approach novel stimuli. Additionally, animals less flexible in suckling should be relatively more stressed when placed in novel situations and those requiring positional flexibility. METHODS
Subjects Subjects were selected from 34 healthy neonatal swine obtained from four primiparous matings farrowing within a four-day period. Litters were a cross X cross mating, a purebred Poland China mating, a purebred Berkshire mating, and a Hampshire X cross mating. These thirty-four neonates were marked with identification letters and randomly assigned to either troughfed or sow-fed feeding conditions. Sow-fed subjects were fostered to one of two sows. Teat positions on each sow were numbered from 1 (anterior) to 8 (posterior) on her right and left side. Trough-fed piglets were fed via a Nurs-ette automatic piglet feeder. The Nurs-ette feeder automatically dispensed a predetermined portion of sow’s milk replacer powder and water which was heated, mixed and pumped into a 1.4 m long double trough and available ad libitum. Each side of the trough was divided into 8 positions by means of a wire divider. Piglets were maintained under these feeding conditions until the age of 35 days, at which time they were weaned. During the 35-day rearing period, nursingsuckling behaviour was watched daily by an observer through a one-way window located in the roof of each vivarium. Observation periods were of 5 min duration at 2-3 h intervals during the day and night. After the first week postpartum, these observations were restricted to the daytime. Numerical position of suckling and within-bout position shifts were recorded by the observer. The mean numerical position of suckling in all observation periods until weaning, and the variability around this position, were calculated. Piglets were then rank-ordered on the basis of position variability and sixteen animals were selected; eight from each feeding condition, four exhibiting high variability in suckling position, and four exhibiting low variability in suckling position. No patterns in teat or trough positions and weight, litter, or sex were detected across groups. Trough-fed animals failed to exhibit the extreme
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position stereotypy of some sow-fed piglets, however. Mean standard deviations of suckling position for high stereotypy groups were 0.70 in sow-fed animals, and 1.54 in trough-fed animals. Mean standard deviations of suckling positions in low stereotypy animals were 1.53 for sow-fed animals, and 1.78 for trough-fed animals. High stereotypy animals in both feeding conditions had significantly fewer shifts of position within suckling bouts than low sterotypy animals; however, variability was significantly higher in the trough-fed animals. After weaning at 35 days postpartum, each animal was housed witn other animals in the same feeding condition group until the age of five months, when exploratory and discrimination tests were administered. Throughout this postweaning period, animals were floor-fed on a pelleted growing ration for swine (Wesley and Klopfer, 1962) and standard hog-rearing practices were followed. Apparatus
The two exploration test situations were located within two 2.5 m X 3 m concrete block rooms located 6 m distance from the living pens. Each contained a holding box and an open field area with stimulus objects or alleys. The holding box of each room was 1.5 m X 0.8 m X 1 m high with a 0.5 m wide guillotine door, centred in the distal end, which permitted access to the test chamber. The guillotine door could be raised or lowered by the experimenter in the adjacent observation room. In the first exploratory test room (A), four stimulus objects were placed in the open field area. Stimulus objects were constructed from 10 cm X 10 cm X 4 cm black and grey wooden blocks mounted on hinges and then bolted into position on steel angles, 15 cm from the floor. At the distal end of the open field area of thessecond exploratory test room (B) were three alleys, 1 m deep, broadening in width from 0.5 m at the entrance to 0.8 m at the rear. The 1 m high alleys were constructed of 1 cm plywood and painted grey. Inside each alley, a variety of geometric forms were stencilled on the walls, rough-cut wooden laths were fastened to the floor and roof of each alley in various diagonal patterns and each alley was rubbed with orange peel, fecal material and soap. Viewing windows in the wall permitted continuous observation of the animals during the test periods. The discrimination test situation was a 2.5 m X 3.0 m concrete block room containing a response apparatus in the distal corner of the room and an automatic feeder in the near corner of the room. Directly adjacent to the test room was a control room with a one-way observation window. The response apparatus consisted of a housing, two response panels, and a retracting mechanism. This apparatus has previously been described by Wesley and Klopfer (1962). In the near corner of the test room was a solenoid operated feeder which delivered lo-12 g of standard hog pellets when activated. The pellets were scattered on approximately 0.8 m2 of floor area accompanied by a ioud solenoid sound.
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Procedures
Exploratory situation adaptation and test trials were completed first. Then discrimination situation pretraining and testing were done. Each individual was given two 5 min adaptation periods in the holding pens of each exploration situation. During each of these four adaptation sessions, the amount of vocalization, squealing, defecation, urination and jumping were noted by the experimenter on a five point scale (where 1 = no emotionality and 5 = extremely emotional). Exploratory testing was started the day following completion of the adaptation trials. During testing, an animal was placed into the holding pen of the exploratory situation and after 45 s the door was opened. A trial consisted of 5 min from the time the door was opened and the animal entered the pen field area. The first exploratory trial was given randomly in either exploratory situation (A or B). After this initial trial assignment, the four trials in the two situations were given on alternate consecutive days. Random trial order within days was observed in assigning trials for each animal and group. The duration of open field activity started when a holding pen exit occurred and ended when the head and front two feet of the animal were again in the holding pen. In exploratory situation A, frequency and duration of snout contact with the desig nated stimulus objects and snout contact with other objects were recorded. In exploratory situation B, an alley entry was recorded when the head and front two feet of the animal were in the alley, and the duration of alley activity was scored from this point until the head and front two feet of the subject were behind the alley entrance line. Head entry without feet entry was recorded as a partial entry. Frequency of defecation, urination, and jumping were recorded, and the amount of vocalization and squealing were rated by the experimenter on a five point scale, while the animal was in the holding pen and in the open field area during the 5 min exploratory trials. The discrimination pretraining followed completion of exploratory test trials. Two days prior to initial experience in the discrimination situation, the typical food ration was reduced by one-third. The initial pretraining trial consisted of allowing pen mates a total of 15 min of ad libitum feeding under the feeder and in front of the stimulus windows. In the second pretraining trial the animals were taken singly to the discrimination situation and were trained to respond to sound cues for food and to press the stimulus-response plates with their snouts after the method of successive approximations (Wesley and Klopfer, 1962). Once plate-pressing was closely approximated on either plate, the right window was exposed until the animal had made ten responses which were followed by food reinforcement. Then the left window was exposed and the subject was trained to the same criterion. Duration of pretraining, number of food reinforcements during shaping, and emotionality were recorded for each pretraining session. The pretraining food deprivation schedule continued through the position discrimination trials. After the assignment of initial problem position, each
227
animal was given twenty trials per day until it reached the criterion. Criterion of learning was a response probability greater than the 0.01 level of significance within a day, with a minimum of fifteen responses, or the same response probability level in twenty consecutive trials, in two days. Random trial order within days was observed in assigning the time of test trials for each subject, and brightness cues were randomized for each of twenty trials. In each test period, the animal was placed in the discrimination situation. After 30 s, the stimulus lights were turned on according to that animal’s problem and 15 s later the apparatus was lowered into the response position. After the animal responded, the stimulus apparatus was immediately retracted, the response recorded, brightness cues were reset and after 15 s the stimulus apparatus was again lowered into the response position. This procedure was followed for each of the twenty daily trials. If an animal failed to respond within 5 min, or for two successive trials within a day, testing was discontinued for that day. When the animal achieved the criterion of learning on the original problem, it then received the reversal of this problem, was trained to criterion, and so on for nine successive reversals. Throughout the reversal trials, the same procedures were utilized as on the original problem. Throughout the discrimination tests, the one-way observation window was kept closed to prevent the animal’s behaviour from influencing experimenter procedure. RESULTS
The two feeding conditions and the two levels of stereotypy were incorporated into a 2 X 2 factorial design, with errors to criterion in reversal learning, frequency and duration of open field activity, object contact, compartment entrances in exploration, and emotionality as dependent variables. The results will be presented in the following order: (1) emotionality, (2) exploratory behaviour, and (3) discrimination learning and reversal performance. Emotionality Typically, the highest emotionality scores were achieved the first day of the adaptation trials with a gradual decrease in scores for most subjects as trials progressed. Individual animals in all groups showed wide variation in the several measures utilized in the emotionality scores. While some animals attained high scores primarily through high vocalization rates, others achieved them as a function of frequent urination and defecation. Since there were no apparent differences among the groups on patterns of emotionality, these were not tested. Emotionality scores during adaptation trials in the exploratory situations were significantly higher for trough-fed than for sow-fed animals
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(F = 6.20, d.f. = 12, P < 0.01). Significant interaction between feeding condition and level of stereotypy occurred during tests in the exploratory situations (F = 17.51, d.f. = 12, P < 0.01). Simple effects were then tested. In the stimulus object situation, sow-fed low stereotypy animals attained a much lower mean total emotionality score than high stereotypy subjects (P < O.Ol), hut this was not so in trough-fed animals. Comparison of the two feeding conditions indicated sow-fed animals achieved lower emotionality scores than trough-fed subjects (P < 0.01). No significant over-all differences were apparent among emotionality scores during pretraining procedures on the discrimination apparatus, and dif. ferences in total emotionality scores for the original problem, and over the series of reversals, were also not significant. On the first position reversal problem, however, sow-fed animals achieved significantly higher emotionality scores (F = 26.78, d.f. = 12, P < 0.01) than trough-fed animals, and low stereotypy subjects were significantly lower in the scores that they attained than high stereotypy subjects (F = 4.54, d.f. = 12, P < 0.05). Exploratory
behaviours
Mean total frequency and duration of activities in the exploratory situation are presented in Table I. Trough-fed animals had a higher mean total entry frequency into the open field of the two exploratory situations than sow-fed animals (F = 4.83, d.f. = 12, P < O.Ol), which reflects a generally higher locomotor activity. No significant differences between feeding conditions or levels or stereotypy were found in duration of open field activity in either exploratory situation, and interaction effects between feeding condition and level of stereotypy were not significant. Significant interaction effects in frequency of stimulus object contact (Test A) (F = 3.65, d.f. = 12, P < 0.05) and duration of contact (F = 15.06, d.f. = 12, P < 0.01) were found, and simple effects were then tested. In frequency of contact, low stereotypy sow-fed animals had significantly higher scores than high stereotypy sow-fed animals (P < 0.01). Low stereotypy sow-fed animals spent a mean total duration of 158.0 s in contact with the four stimulus objects while high stereotypy sow-fed subjects spent a mean total duration of only 47.3 s in such contact (P < 0.001). Differences between levels of stereotypy in the trough-fed animals in frequency and duration of contact were slight (F = 1.24. d.f. = 12, P > 0.05). Objects which were not among the four designated stimulus objects were contacted by the subjects, including the holding pen walls and door edges and the steel angle fastened to the wall perimeters. Significant interaction between feeding conditions and level of stereotypy was found in both frequency (8’= 6.59, d.f. = 12, P < 0.01). and duration (8’= 17.53, d.f. = 12, P < 0.01) of contact with nondesignated stimulus objects. The simple effects were then tested. Low stereotypy sow-fed animals more often contacted
Frequency at stimulus objects Frequency of contact with other objects Duration of contact with stimulus objects (s) Duration of contact with other objects (s) Frequency of alley entrance Duration of alley entries (s)
Measure
2.3 1.48
65.3 29.46
13.5 8.65 9.0 1.58 145.8 23.42
_X SD
_X SD
_X SD _X SD w SD
~_
19.8 4.66
X SD
6.3 5.70 6.8 4.49 101.5 104.64
43.3 19.75
1.3 0.83
17.3 5.58
9.9 8.11 7.9 3.51 123.6 78.99
59.3 27.39
1.8 1.30
18.5 5.29
1.3 1.30 8.0 3.39 99.8 56.81
47.3 1.09
0.5 0.22
17.0 1.26
24.8 7.19 8.3 1.09 307.0 91.32
158.0 8.87
3.8 1.92
23.0 2.00
stereotypy
LOW
High stereotypy
Total
High stereotypy Low stereotypy
Sow-fed animals
Trough-fed animals
_
Mean total frequency and duration of behaviour in the exploration tests
TABLE I
13.0 12.85 8.1 2.52 203.4 128.50
79.0 33.27
2.10 2.15
20.0 3.40
Total
7.4 8.60 8.5 2.69 122.8 48.16
56.3 23.96
1.4 1.41
18.4 3.64
High stereotypy
Totals
15.5 11.34 7.5 3.36 209.3 142.09
77.0 36.07
2.5 1.94
20.1 5.09
Low stereotypy
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these objects in the exploratory situations than did high stereotypy sow-fed animals (P < 0.01). Variability within feeding conditions and within stereotypy levels around the mean total duration inside the alleys of exploratory test B was rather large. Interaction effects between level of stereotypy and feeding condition were significant (F = 8.23, d.f. = 12, P < 0.01). Simple effects were then tested and low stereotypy sow-fed animals spent a significantly longer duration in the compartments than did high stereotypy animals (P < 0.01). Differences between low and high stereotypy trough-fed animals were not significant. Discrimination
learning and reversals
Errors to criterion in standard scores on the original problem and reversals are presented in Table II. During the pretraining procedures, total duration of pretraining, number of pretraining periods, and number of food reinforcements through pretraining criterion were recorded. Differences between feeding condition and stereotypy level were slight and nonsignificant. Differences between feeding conditions and levels of stereotypy and the interaction effects were not significant on errors to criterion on the initial position problem. On the first reversal, high stereotypy animals made significantly more errors to criterion than low stereotypy animals (F = 5.41, d.f. = 12, P < 0.01). Sow-fed subjects made significantly more errors than troughfed animals (F = 4.10, d.f. = 12, P < 0.05). On the second reversal to the ninth reversal, differences between feeding conditions and stereotypy levels on errors to criterion on individual reversals were not significant. The sum of errors to criterion on the first to the ninth reversals was not significantly different between levels of stereotypy (F = 2.20, d.f. = 12, P < 0.05). Differences between feeding conditions in mean total errors to criterion on the sum of all reversals were significant (F = 4.21, d.f. = 12, P < 0.05). Sow-fed animals made more errors than trough-fed animals. High stereotypy animals, however, made more errors on the first reversals than low stereotypy animals. The effect of level of stereotypy on the first two reversals was significant (F = 11.75, d.f. = 12, P < 0.01). On the sum of the first to the fourth reversals, differences between feeding conditions (F = 3.91, d.f. = 12, P < 0.05) and levels of stereotypy (F = 4.42, d.f. = 12, P < 0.05) were significant. The analysis of variance on differences between levels of stereotypy (F = 0.30, d.f. = 12, P > 0.05) and feeding condition (F = 2.20, d.f. = 12, P > 0.05) on the sum of errors to criterion on reversals five to nine were not significant. DISCUSSION
Reversal learning was relatively more difficult for animals with stereotyped suckling positions early in life. The significantly fewer errors to
Original learning First reversal Total: First to fourth reversals Total: Fifth to ninth reversals Ninth reversal Total: First to ninth reversals
Measure
_~
x SD 8 SD x SD x SD B SD x SD
17.75 14.04 15.75 6.10 58IOO 13.21 48.75 14.74 6.25 3.96 106.75 21.73 14.25 9.04 10.00 2.45 41.00 9.57 48.25 16.68 10.25 9.65 89.25 26.15
16.00 12.18 12.87 5.39 49.50 14.35 48.50 15.75 8.25 7.64 98.00 25.59
12.75 6.14 28.00 10.49 73.75 20.25 68.25 23.93 16.75 12.97 142.00 37.87 9.75 3.96 14.50 7.23 57.00 9.li 58.00 9.87 8.50 5.59 115.00 9.99
stereotypy
LOW
High stereotypy
High stereotypy
Low stereotypy
Sow-fed animals
Trough-fed animals Total
Errors through criterion on original problem and discrimination reversal problems
TABLE II
11.25 5.38 21.25 11.23 65.37 17.97 63.12 19.00 12.62 10.78 128.50 30.81
Total
15.25 11.45 21.88 10:54 65.87 19.03 58.50 22.14 11.50 10.91 124.37 35.55
High stereotypy
Totals LOW
12.00 7.33 12.25 5.85 49.00 12.30 53.12 14.56 9.37 7.94 102.12 23.60
stereotypy
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criterion made by low stereotypy animals on the first reversal, on the total errors in the first and second and on the first to the fourth reversals confirm this hypothesis. However, in errors to criterion on later reversals, high and low stereotypy animals were not significantly different. This indicates that effects of stereotypy may not persist if sufficient training on reversal learning tasks is given to the adult animal. Differences in performance by high and low stereotypy animals were relatively greater in the sow-fed conditions than in the trough-fed group. This may be influenced by the relatively greater flexibility in feeding positions in the trough-fed animals and the greater difference between high and low stereotypy levels in sow-fed animals. These findings are in agreement with the previous studies of discrimination reversals in swine (Wesley and Klopfer, 1962; Klopfer, 1961) where patterns of sensory contingencies relevant to food acquisition by the piglet were related to relative difficulty of later reversal learning. As the artificially reared animals exhibited greater flexibility in feeding positions, it was expected they would do relatively better than sow-reared subjects on discrimination reversals. High stereotypy trough-fed animals were more variable in feeding position than low stereotypy sow-fed animals. Positional orientations on the trough were less marked and feeding position was varied more frequently than in the sow-feeding condition. Significantly fewer errors through criterion were made by trough-fed animals on the first reversal, first two reversals, first to fourth reversals, and the sum of all nine reversals. This finding is in agreement with unpublished data by Klopfer and Lien in which animals fed on synthetic diets in shallow pans did relatively better on reversal performance than sow-fed animals. Contributing factors in this difference may be: (1) the differences in variability of feeding; (2) differential reinforcement for wider variety of sensory cues. In the trough-feeding conditions, visual cues were directly relevant to milk acquisition, whereas in sow-fed animals, visual cues relevant to the presence of milk were minimal. Animals were not observed to root or suck at the trough when milk was absent, but sow-reared animals frequently sucked between periods of milk let-down. When milk was pumped into the trough, feeding behaviour would again resume. The differential reinforcement for attentiveness to these and perhaps other visual cues may account partially for the superior ability of trough animals to vary their responses in the discrimination reversal problems. It was hypothesized that low feeding stereotypy animals would engage in relatively more exploratory behaviour than high stereotypy animals. However, significant interaction effects in both frequency and duration of the stimulus object contact and other object contact were obtained. Simple effects of level of stereotypy in the sow-fed animals indicate that low stereotypy animals explore more frequently and were in contact with objects longer. In the trough-fed animals, simple effects of stereotypy were not significant. In the compartment situation, main effects of stereotypy were not significant in frequency of compartment entrances. For duration scores,
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interaction effects were significant. In analyzing the simple effects of stereotypy, again low stereotypy sow-fed animals explored more than high, but this difference was not found in trough-fed animals. The finding of greater exploration in low stereotypy sow-fed animals is consistent with the hypothesis. In general, there is a non-significant trend in trough-fed animals for high stereotypy animals to explore more than low stereotypy animals. The failure to obtain differences between stereotypy levels with trough-fed animals may be attributable to the lesser difference in stereotypy levels in these animals. There was also a general non-significant tendency for artificially fed animals to explore less than the sow-fed group. The failure to find overall differences between artificial and sow-feeding conditions also indicates that factors other than feeding position stereotypy in the two feeding conditions may influence the adult animals. In rearing pens, trough-fed animals were more excitable and more readily frightened, and this trait persisted into adulthood. In early testing, trough-fed animals continued to be more emotional than sow-fed animals. After a period of handling they became more quiescent. This greater emotionality during early handling and tests, in spite of extensive adaptation handling, could account for the failure to find the predicted exploration levels in trough-fed animals. The results of this investigation are consistent with the hypothesis that differential reinforcement patterns in nursing-suckling interactions may develop rather general perceptual orientations and motor characteristics, which may persist and be representative of, or modify, behaviour in mature organisms. The logic of this investigation does not allow the conclusion that stereotypy in suckling affects later learning and exploration. The under-performing adult swine may have been more stereotyped in suckling during infancy because they were poor learners or explorers. They were, with practice, rather quickly able to match performances of less stereotyped animals in discrimination reversal learning at least. The results, however, are consistent with the hypothsis that ability of the adult animal to adapt to new and changing environmental patterns has roots in infantile development and response patterns acquired there.
REFERENCES Hemsworth, P.H., Winfield, C.G. and Mullaney, P.D., 1976. A study of the development of the teat order of piglets. Appl. Anim. Ethol., 2: 225-233. Klopfer, F.D., 1961. Early experience and discrimination learning in swine. Am. Zool., 1: 366 (abstract). McBride, G., 1963. The “teat order” and communication in young pigs. Anim. Behav., 11: 53-56. Wesley, F. and Klopfer, F.D., 1962. Visual discrimination learning in swine. Z. Tierpsychol., 19: 93-104.