The behaviour of farrowing sows with free and operant access to an earth floor

Applied Animal Behaviour Science, 26 (1990) 363-372

363

Elsevier Science Publishers B.V., Amsterdam

T h e B e h a v i o u r of F a r r o w i n g S o w s w i t h F r e e and O p e r a n t A c c e s s to an E a r t h Floor G.D. H U T S O N and M.J. H A S K E L L

School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria, 3052 (Australia) (Accepted for publication 20 February 1990 )

ABSTRACT Hutson, G.D. and Haskell, M.J., 1990. The behaviour of farrowing sows with free and operant access to an earth floor. Appl. Anim. Behav. Sci., 26: 363-372. The motivation of sows to utilize an earth floor for farrowing was measured in two experiments. In the first experiment, 6 sows housed individually in a concrete-floored pen had free access for 8 h per day to an earth-floored pen. The sows made regular visits to the pen each day and an increased number of visits on the day prior to farrowing. About 8 h before the birth of the first piglet, the sows commenced excavation of an earth nest, primarily by rooting movements of the snout. All sows dug a nest and farrowed in it. In the second experiment, an operant requirement was introduced so that the sows had to lift a lever to open a vertically sliding gate to gain access to the earth pen. This requirement interfered with the pattern of earth pen use. Three sows dug a nest hole and only one sow farrowed entirely within the nest. It appears that the operant requirement itself (lifts on a progressive fixed ratio) does not interfere with pen use, but that the uncertainty created by the opening and closing of the gate may affect nest site selection and nest use by the SOWS.

INTRODUCTION

One of the main arguments in the animal welfare debate is whether animals in intensive environments are suffering if they are unable to perform behaviour patterns that they would normally carry out in a more natural environment (Dawkins, 1988). A frequently cited example is that of the farrowing sow (Baxter, 1982; Vestergaard, 1983 ). In the period prior to parturition she would normally gather grass or straw to build a nest, but in an intensive piggery she is unable to do this. So the questions can be asked: Does this matter? Is it important for the welfare of confined animals that they are able to express their normal behaviour? Are they deprived in some way if they are unable to do so? Do they suffer? One way of approaching this problem is to measure the motivation of the

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G.D. HUTSON AND M,J. HASKELL

sow to perform normal nest-building behaviour. Motivation, or the internal readiness of an animal to respond, can be measured simply by recording responsiveness over time towards a constant external stimulus (e.g. straw for nest building), or by using more elaborate means, such as an operant conditioning technique, to determine whether a pig is prepared to work to gain access to nest-building materials. T h u s the first method will tell us if there is variation in motivation and hence the potential for deprivation, and the second may tell us what value the animal places on it. The nest-building behaviour of wild sows and free-ranging domestic sows is complex and involves a number of behaviour patterns, including digging with rooting movements of the snout, pawing with the forelegs, and gathering, carrying and manipulating nest-building materials with the mouth (Gundlach, 1968; Jensen, 1986 ). However, in previous experiments with farrowing sows in our laboratory, a low responsiveness towards straw at the time of farrowing was found, although the motivation of sows to perform a nest-building behaviour pattern such as pawing was high (Hutson, 1988). One possible interpretation of this result is that straw may not be a key external stimulus for nesting in the sow; another possibility is that nest building may be a chain response so that sows are unresponsive to straw until a depression in the ground has been dug. In this study, we investigated whether confined sows would dig a nesting hole prior to farrowing if they had the opportunity to do so. The motivation of farrowing sows to utilize earth as a nest-building material was measured by recording visits to an earth-floored pen when they had free access to it. In a second experiment, we attempted to measure what value sows placed on access to an earth floor. An operant requirement was introduced so that the rows had to make an increasing number of lifts on a lever to gain access to the earthfloored pen. MATERIALS AND METHODS

Experiment 1 Six sows (Large White or Large White × Landrace) were selected to represent a range of parities (1, 4, 4, 4, 6 and 9). The sows were normally neck tethered in partial stalls on a concrete floor in a dry sow shed accommodating 75 sows. The sows had no previous experience of earth floors. On Day 107 of gestation, a sow was introduced into the experimental pen. Observations commenced on Day 108, 5 days before the expected day (113) of parturition, and continued for 5 days after the day of actual farrowing. The pen was in a separate laboratory and consisted of a concrete-floored pen containing the feeder and drinker, joined by a short passage and timber ramp to an earth-floored pen (Fig. 1 ). The earth was a red clay loam and was thor-

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Experiment 2 The gate between the two pens was modified so that it could slide vertically, and be opened and closed by an electric motor and winch. Sows could open the

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gate by lifting a lever adjacent to the race entrance. The motor and gate were controlled by relay equipment in an adjacent room. A progressive fixed-ratio schedule of reinforcement was used with the ratio increasing by an increment of one with each reinforcement. Thus, the sow was required to make one lift to open the gate the first time, two for the second, three for the third, and so on. The gate took 5.4 s to open and remained open until the sow had entered and then departed from the earth-floored pen, when it was closed by remote control immediately she re-entered the concrete-floored pen. A progressive fixed-ratio schedule was chosen so that the level of responding reached could be used as a measure of the motivation of the sows to gain access to earth. Presumably, when the ratio of lifts to reinforcements is too high the pig will stop responding and that point can be used as a measure of the strength of that reinforcement (Hodos, 1961; Hutson and van Mourik, 1981). The lever was placed in the pen for the 8-h observation period each day and then removed at night and the gate closed. If farrowing was imminent, then the lever was left in the pen and observations continued. The ratio was reset to one at the start of each observation day. Six sows (parities 1, 2, 3, 4, 5 and 6) were observed in the pen. RESULTS Experiment

I: F r e e access

Each of the 6 pigs dug a hole in the floor of the earth pen and farrowed in it. These depressions varied considerably in shape and size (Fig. 2), and were dug primarily by the sows using rooting movements of the snout. Rooting of the earth floor commenced suddenly ~ 8 h before the birth of the first piglet (median 8.3 h, range 6.6-11.5 h, n = 5). Sows also performed pawing behaviour, but this appeared to be largely ineffective in excavating earth. A typical example of the frequency of occurrence of nest-building behaviour patterns performed by one sow is given in Fig. 3. Rooting and pawing behaviour were not confined solely to the earth pen, but were also performed in the concrete pen and connecting passageway, although at reduced frequencies. Prior to farrowing most rooting occurred in the concrete-floored pen, whereas post-farrowing the sow continued to dig in the nest with regular bouts of rooting and occasional pawing. The 6 pigs showed a similar pattern of visits to the earth-floored pen (Fig. 4). A small number of regular visits was made each day until the day prior to farrowing, when the number of visits increased. The median number of visits to the earth pen on observation day 4 was 7 (range 4-13, n-- 6) compared with a median of 27 visits (range 23-44, n = 5 ) in the 8 h immediately prior to farrowing. Following farrowing, a similar pattern of occasional visits was resumed, although the use of the pen had changed (Fig. 5 ). Prior to farrowing,

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Experiment 2: Operant access The insertion of an operant requirement changed the pattern of use of the earth pen by some pigs. Three sows showed a similar increase in visits prior to parturition and excavated a nest (Fig. 6: 054, 0569, R42). One of these sows

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BEHAVIOUR OF FARROWING SOWS WITH ACCESS TO EARTH FLOOR

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(P>0.05, Mann-Whitney U test) in the number of visits made to the earth pen with free and operant access in the 8 h immediately prior to farrowing. DISCUSSION

It is clear that the change from free to operant access disrupted normal farrowing behaviour in the experimental pen. The pigs no longer farrowed exclusively on the earth floor and not all pigs excavated a nesting hole. However, it is important to pinpoint exactly the cause of the interference with normal farrowing behaviour. There are two aspects of the experimental pen which were altered in the transition from free to operant access: firstly, the introduction of a gate which opened vertically; secondly, the introduction of operant control over the gate. We think that the operant requirement did not affect the sows' use of the earth-floored pen. In other words, the pigs did not reach the point on the progressive fixed-ratio schedule where they gave up responding. Our evidence in support of this conclusion is that the sows which did not excavate a hole continued to lift the lever both before and after farrowing. These sows had the opportunity to begin nest construction, but did not do so. Furthermore, the sows which utilized the earth floor visited the pen on a similar number of occasions to those with free access. If the operant requirement was not interfering with nesting behaviour on the earth floor, then what was? We suggest that the most likely explanation may be the uncertainty created by the opening and closing of the gate. The contingency of the gate opening in response to a certain number of lever lifts was learnt quickly by all sows (median latency to second entry to the pen on test Day 1 was 37 min, range 17-80). However, the contingency for closing of the gate may be less easily learnt by the sow as it depended solely on their locomotory response back into the earth pen. Dawkins and Beardsley (1986) reported that when hens had to perform a locomotory response and break a photoelectric beam to gain access to a goal box, a large number of trials was necessary to distinguish between preferred and non-preferred boxes. Other possible explanations for the results are that other factors apart from the type of substrate may influence nest site selection by the sow, e.g. the position of the pen in relation to the laboratory door, or the view out of the pen, or the perceived amount of protection provided by the pen. Also, the location of the feed trough and drinker may influence nest location, although this was not the case when sows had free access. It is quite conceivable that both these factors, nest site selection and access to food and water, could interact with the uncertainty created by the gate. It is clear that we need to design more sophisticated experiments to measure the motivation of sows to farrow on an earth floor. The experiment with free access to earth shows that there is variation in the motivation of sows to utilize earth and hence the potential for deprivation. However, we cannot yet say what

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G.D. HUTSON AND M.J. HASKELL

v a l u e t h e sow p l a c e s o n b e i n g able to use a n e a r t h floor for farrowing. S e v e r a l possibilities for f u t u r e w o r k include r e v e r s i n g t h e p e n s so t h a t t h e sow is conf i n e d in t h e h o m e p e n on a n e a r t h floor a n d m u s t w o r k to get out, or t h e i n t r o d u c t i o n of a s e c o n d o p e r a n t r e q u i r e m e n t on d e p a r t u r e f r o m t h e pen. I f t h e pig h a s i m m e d i a t e c o n t r o l of e n t r y a n d exit f r o m t h e pen, we m a y t h e n be able to i n t r o d u c e m o r e d e m a n d i n g o p e r a n t s c h e d u l e s to m e a s u r e t h e s t r e n g t h of m o t i v a t i o n to f a r r o w o n e a r t h . ACKNOWLEDGEMENTS T h i s s t u d y w a s f u n d e d b y a g r a n t f r o m t h e A u s t r a l i a n P i g R e s e a r c h Council. W e are i n d e b t e d to M r s . L y n n e D i c k e n s o n for h e r tireless a s s i s t a n c e w i t h t h e o b s e r v a t i o n s a n d a n a l y s i s o f video t a p e s .

REFERENCES Baxter, M.R., 1982. The nesting behaviour of sows and its disturbance by confinement at farrowing. In: W. Bessei (Editor), Disturbed Behaviour in Farm Animals. Eugen Ulmer, Stuttgart. Dawkins, M.S., 1988. Behavioural deprivation: a central problem in animal welfare. Appl. Anim. Behav. Sci., 20: 209-225. Dawkins, M.S. and Beardsley, T., 1986. Reinforcing properties of access to litter in hens. Appl. Anim. Behav. Sci., 15: 351-364. Gundlach, H., 1968. Brutfiirsorge, Brutpflege, Verhaltensontogenese und Tagesperiodik beim Europ~iischen Wildschwein (Sus scro[a L.). Z. Tierpsychol., 25: 955-995. Hodos, W., 1961. Progressive ratio as a measure of reward strength. Science, 134: 943-944. Hutson, G.D., 1988. Do sows need straw for nest-building? Aust. J. Exp. Agric., 28: 187-194. Hutson, G.D. and van Mourik, S.C., 1981. Food preferences of sheep. Aust. J. Exp. Agric. Anim. Husb., 21: 575-582. Jensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anim. Behav. Sci., 16: 131-142. Phillips, P.A., Thompson, B.K. and Fraser, D., 1988. Preference tests of ramp designs for young pigs. Can. J. Anim. Sci., 68: 41-48. Vestergaard, K., 1983. Are tethered sows stressed? A behavioral comparison of tethered and loose sows. Appl. Anim. Ethol., 11: 81-82.