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Straw and food as reinforcers for prepartal sows
Applied.4nimal Behaviour Science, 33 ( 1992 ) 217-226
217
Elsevier Science Publishers B.V., A m s t e r d a m
Straw and food as reinforcers for prepartal sows D.S. Arey Centre for Rural Building, Craibstone, Bucksburn, Aberdeen, AB2 9TR, UK (Accepted 23 September 1991 )
ABSTRACT Arey, D.S., 1992. Straw and food as reinforcers for prepartal sows. Appl. Anita. Behav. Sci., 33:217226. In Trial 1, seven Large-While x Landrace sows were initially housed in either stalls (n-4) or straw pens (11=3) during gestation. On Day 107 of pregnancy, each sow was placed inlo a pen in which food was delivered every 2 h and which had operant access to a straw area (S) and a control area (C). Two days before farrowing, sows spent 71% of their time in S and made significantly more entries into S than C ( 19.6 vs. 4.4). On the day before farrowing, entries into S increased to 37.4 and all the sows built nests and farrowed in S. Straw was reinforcing but did not appear to be as important as feed. In Trial 2, five sows inilially housed in straw pens, were each placed, on their Day 100 of pregnancy, into a pen which had operant access to a straw area (S) and a feed area (F). The number of entries made into S and F were, respectively, 17 and 21.4 when cost of entry was low (one panel press) and 2.6 and 11.4 when the cost was high (a mean of 150 panel presses) 2 days before farrowing and 16.4 and 17 on the day before farrowing when the cost was also high. It was concluded that the importance of straw approached that of feed, particularly during the 24 h before farrowing when sows were motivaled to nest-build.
INTRODUCTION
Prior to giving birth, domesticated sows are highly motivated to perform nest-building behaviour (Baxter, 1982). Pre-parturient sows show a strong preference for farrowing in a bedded area and will gather large amounts of straw from dispensers to form a nest (Arey et al., 1991 ). Although these observations indicate that nesting material is important to sows at this time, preference for a commodity such as straw cannot be equated with need for that commodity (Duncan, 1978 ). If it can be shown that sows need material to build a nest - - such as straw - - then it follows that their welfare will suffer if it is not provided. According to Dawkins ( 1988 ), need can be determined by measuring how strong an animal is motivated to obtain something. Operant conditioning techniques can be used to measure the strength o f an animal's motivation for a reinforcement (Teitelbaum, 1966). If an animal
© 1992 Elsevier Science Publishers B.V. All rights reserved 0 1 6 8 - 1 5 9 1 / 9 2 / $ 0 5 . 0 0
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cannot be trained to work to obtain something then its motivation to obtain it cannot be very great (Beilharz and Zeeb, 1981 ) or the c o m m o d i t y is not a reinforcer. Once an animal has been trained to work for some c o m m o d i t y , the strength o f reinforcement for that c o m m o d i t y can be c o m p a r e d with some yardstick (Dawkins, 1983 ). Food provides a convenient yardstick because it is obviously essential for animals to survive. The motivation to obtain two commodities, such as food and straw, can be c o m p a r e d by measuring their d e m a n d curves (Dawkins, 1988 ). D e m a n d curves describe the rate at which d e m a n d falls as 'cost' increases and are calculated by measuring the a m o u n t of work an animal is prepared to do for a c o m m o d i t y as its cost increases. The cost of a c o m m o d i t y can be manipulated in a n u m b e r of ways, one of which is to alter the n u m b e r o f operant responses required for reinforcement. The m e a s u r e m e n t of d e m a n d curves thus provides a useful m e t h o d of getting animals to show, through their behaviour, how important different c o m m o d i ties are to them. Hutson ( 1988 ) found that prepartal sows were not prepared to lift a lever 10 times for a 1 kg straw reward and concluded that they were therefore not strongly motivated to obtain straw. However, the ability to train animals to work for something depends greatly on the kind of operant response and reward used (Dawkins, 1988). In the present experiment, the operant conditioning technique was modified to re-examine the importance of straw to sows during the days leading up to farrowing. The first part was designed to compare the reinforcing properties o f a straw bedded pen and an unbedded pen; the second part was aimed at comparing the d e m a n d curves for straw and food. ANIMALS, MATERIALS A N D M E T H O D S
The experimental animals were multiparous Landrace X Large White sows which normally have a gestation period o f 115 days. In Trial 1, four sows had initially been housed in sow stalls without straw ( c o n f i n e d ) and four had been group-housed in straw pens ( u n c o n f i n e d ) . In Trial 2, all six sows came from straw pens. The sows were normally fed a daily ration of 2.0-2.5 kg o f a cereal-based sow meal. In Trial 1, the experimental pen was divided into three equally sized areas: a straw area (S) which contained 18 kg straw; a central feed area ( F ) which contained an automatic feeder and an ad libitum supply of water; an unbedded control area (C) (Fig. 1 ). The two areas S and C were connected to F via two swing doors. The doors each had a microswitch that was activated when the door opened and a pressure pad 170 m m X 2 5 0 m m m o u n t e d on the side within F. The doors each had a lock mechanism. When the doors were locked, they could only swing one way, into F, by being pushed from the other side, either S or C. When the locks were released, the doors could swing both ways and could thus be pushed open from F. Release of the lock m e c h a n i s m was contingent on the sow pressing the pressure pad, on the relevant door, the
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Fig. 1. Plans of experimental pens used in Trial 1 (above) and Trial 2. required n u m b e r o f times ('cost'). There was no time limit set for the sow to attain the cost. On attaining the cost, a 5 W bulb was illuminated above the door, the lock mechanism opened within 2 s and closed after 30 s. The system was controlled by a BBC B microcomputer, fitted with a S P I D E R control board and a T E R M I T E external interface (Paul Fray Ltd., Cambridge). The pens were continuously observed with a video camera connected to a timelapse video recorder. C o n t i n u o u s artificial light was provided to allow video recording. The temperature of the pens was maintained between 15 and 20°C. In Trial 2, the experimental pen was modified so that it comprised a straw area (S), a central area ( C ) and a feed area ( F ) (Fig. 1 ). Access to either S or F from C was contingent on the sow pressing the pad on the respective swing door to release the lock. In Trial 1, the sows were introduced individually into the pen on Day 107 of pregnancy. The location o f S and C was alternated for each individual. The
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sows were trained to open the swing doors using food rewards provided in S and C during four 10-min daily sessions. To begin with, the swing doors remained unlocked, then the number of presses required to open the lock was increased by one on successive sessions. After training, the cost of entry into S and C was set at 10 panel presses. The sows were offered a daily ration of 3.5 kg sow meal at 09:00 h in F. A further amount of meal (approximately 150 g) was automatically dropped into F every 2 h so that each sow was offered a total of 5.25 kg over a 24-h period, which approaches appetite limit (Whittemore and Elsley, 1976 ). The purpose of the 2-h deliveries of feed was to attract the sows out of S and C at periodic intervals. The video recordings and the data logged by the computer were used to determine: the number of times the sows entered and the amount of time spent in S and C: the number of times the sows fed and the general activity of the sows. Data were compared for the 24 h before farrowing (Day - 1 ) and for the previous 24 h (Day 2 ). Data were compared using M a n n - W h i t n e y U-tests. In Trial 2, the sows were introduced individually into the pen on Day 100 of pregnancy. The swing doors remained unlocked for the first 24 h and were then locked for four 30-rain daily sessions over four days, during which the sow was required to press the panel once to open the lock. This was repeated until each sow was consistently able to open both swing doors. After training, a portion (approximately 110 g) of a daily ration of 3.5 kg of feed was delivered into F every 45 rain. The sows were therefore not fed to their appetite limit in order to maintain their interest in food. The cost of entry into S and F for the first 24 h (Day - n) was set at I. The cost was then increased daily for the two swing doors simultaneously until Day 113 of pregnancy. The rate at which cost was increased was calculated individually for each sow such that entry into the straw area was almost but not completely extinguished by Day 113. The cost was then kept constant until the sow farrowed so that it was the same for the 24 h before farrowing (Day - 1 ) as the previous day (Day - 2 ) . The demand curves for straw and food were determined from the difference in the number of entries made into the respective areas S and F on Day - n (when the cost was lowest) and Day - 2 (when the cost was highest). The data were analysed as modified randomised blocks with the animals as blocks using a regression analysis. The number of entries made into S and F was also compared for Day - 2 and Day - 1 (when cost was constant) to determine any difference in the demand for straw and food, respectively, as the sows approached farrowing. This was determined using an analysis of variance. -
RESULTS
In Trial 1, one straw-housed sow did not respond to training and was therefore omitted from the trial. All seven remaining sows were trained to operate the swing doors by Day I 11 of pregnancy.
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
221
Table 1 shows the mean n u m b e r of entries into the straw and control areas on Day - 1 and Day - 2 for the sows which had been confined and unconfined during pregnancy in Trial 1. All the sows entered and spent more time in the straw area (S) than the control area (C) on Days - 2 and - 1. On both days, the m e a n n u m b e r o f entries into S was significantly greater than the n u m b e r into C ( P < 0 . 0 5 ) . The mean n u m b e r of entries into S significantly increased from 19.6 on Day - 2 to 37.4 on Day - 1. There was no significant difference in the m e a n n u m b e r of entries into C (4.4 on Day - 2 and 8.7 on Day - 1 ). Two sows did not enter C on Day - 2 and one did not enter on Day - 1 . On both days, the sows spent significantly more time in S than C ( P < 0 . 0 0 1 ) . The mean time spent in S was 71% on Day - 2 and 69% on Day - 1. The m e a n time spent in C was 2% on both days. The sows quickly became conditioned to the automatic feeder and usually c o n s u m e d all the feed within a few minutes after it was delivered. On Day -2, none of the 2-h feeds were missed. On Day - 1, one sow missed the last three feeds which were delivered before farrowing, two sows missed two feeds, three sows missed one feed and one sow c o n s u m e d all the feeds delivered. Food was not ignored during the main phase of nest-building behaviour but TABLE 1 T h e difference in lhe m e a n n u m b e r o f entries m a d e into the Straw a n d Control areas by the three u n c o n f i n e d a n d the four c o n f i n e d sows on D a y - 2 a n d Day - 1 in Trial I Group
Unconfined Confined
Day
Day Day Day Day
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-
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3 3 4 4
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Difference
5
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12.7 25.0 24.8 46.8
0.7 1.2 4.4 5.2
3.7 5.3 5.0 12.0
1.9 0.3 2.4 5.0
P < 0.05 P<0.01 P < 0.05 P < 0.01
TABLE 2 N e s t - b u i l d i n g b e h a v i o u r o f the three u n c o n f i n e d a n d the four confined sows in Trial 1 Sows
Bouts o f lying (No.)
Nest-building
Duration (h)
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9.5 13.5
0.5 3.3
22.7 42.8
0.5 4.8
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SE
5.7 18.5
1.0 3.8
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Fig. 2. The number of entries made into (line graph) and the percentage time spent in (bar chart) the Straw and Feed areas between Day - n and Day - 2 (unshaded area) and between Day - 2 and Day - 1 (shaded area) by the five Sows in Trial 2.
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
223
appeared to be less attractive once the sow was lying prostrate and labour had begun. Table 2 shows the s u m m a r y o f nest-building b e h a v i o u r for the confined and unconfined sows. All the sows were observed to perform nest-building b e h a v i o u r and to farrow in the straw area. The mean duration of nest-building was 11.5 h, the mean n u m b e r of nest-building bouts was 32.7, and the mean n u m b e r of lying incidences was 12.1. The confined sows tended to make a greater n u m b e r of entries into the straw area and tended to display more nest-building b e h a v i o u r (non-significant). In Trial 2, one sow farrowed 3 days before its expected date and was therefore omitted from the trial. The remaining five sows farrowed within 36 h of their expected dates. Figure 2 shows the n u m b e r of entries m a d e into and the a m o u n t of time spent in the straw and feed areas on the days prior to farrowing. On day - n , the n u m b e r o f panel presses required to open the gates (cost) was one, and the mean n u m b e r s o f entries into S and F were 17 and 21.4, respectively. The sows spent more time in S ( m e a n 65%) than they did in F ( m e a n 28%) on Day - n. As the cost was progressively increased, the sows m a d e fewer entries into both S and F. By D a y - 2, the cost was increased to between 50 and 300 depending on the individual sows ability/willingness to operate the swing doors. On Day - 2 , the mean n u m b e r s o f entries into S and F had fallen to 2.6 and 11.4, respectively. The a m o u n t of time spent in S was significantly reduced ( m e a n 25%) ( P > 0.05 ), whereas time spent in F remained approximately the same ( m e a n 23%). The rates at which entry into the two areas declined between D a y - n and D a y - 2 were both significantly different from zero ( P > 0.05 ) but were not significantly different form each other ( P < 0.05 ). This shows that as the cost increased, the sows m a d e a similar reduction in panel presses for feed as they did for straw. The cost o f entry into the straw and feeds areas on D a y - 2 and D a y - 1 was kept the same. The mean n u m b e r of entries into the straw area (S) increased significantly from 2.6 to 16.4 on D a y - 1 ( P > 0 . 0 0 1 ) . The mean a m o u n t o f time in S increased from 25% on Day - 2 to 52% on D a y - i, but this difference was not significant. The mean n u m b e r o f entries into F also increased from 11.4 to 17, whereas the mean a m o u n t of time in F was reduced from 23% to 16% (both non-significant). These findings show that there was a marked increase in the d e m a n d for straw during the 24 h prior to farrowing. All the sows were observed to perform nest-building b e h a v i o u r during Day 1 and to farrow in the straw area. -
DISCUSSION AND CONCLUSIONS
In Trial 1, sows were given operant access ( 10 panel presses) to two identical pens, one o f which contained 18 kg straw, the other no straw. On the
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second day before farrowing (Day - 2 ), sows made significantly more entries into the pen containing straw ( 19.6 vs. 4.4) and spent significantly more time in this pen (71% vs. 2%). This shows that the straw positively reinforced the behaviour of the sows. On the day before farrowing (Day - 1 ), the number of entries into the straw area significantly increased from 19.6 to 37.4 whereas there was no difference in entries into the control. The increased entries into the straw area coincided with observations of nest-building behaviour which began 11.5 h before farrowing and included 32.7 bouts of nest-building and 12.1 bouts of lying. There was no difference between these observations and those reported for sows which had free access to a straw area (Arey et al., 1992a) or with sows housed together in pairs (Arey et al., 1992b). This suggests that, although the performance of nesting behaviour can vary, its occurrence is innately typical and relatively unnaffected by environmental and social constraints. In accordance with other authors, the greater activity on Day - 1 indicated that there was an increase in motivation for locomotor behaviour (Hafez and Signoret, 1969; Baxter, 1982; Jensen 1986). In pens, domestic sows increase their activity 24-36 h before farrowing (Vestergaard, 1984), the initial function of which is to search for a suitable nest site away from the normal home range (Jensen et al., 1987). Sows which had previously been confined without straw prior to the experiment appeared to be more active than sows which had been housed in straw pens. The confined sows tended to make more entries into the straw area and show higher levels of nest-building behaviour. Although the amount of data was limited and non-significant, these findings agree with Taylor and Friend ( 1987 ), who showed that activity in an enriched environment is increased in gilts previously kept with greater housing deprivation. In Trial 1, the straw and no straw pens were connected via a feed pen in which food was presented every 2 h so that the sows were fed amounts close to appetite limit. Even so, the sows invariably fed as soon as food was delivered throughout Day - 2 and Day - I. Food therefore appeared to be more important to the sows during the nest-building phase than straw. However, the design of the experiment meant that the sows could leave the straw area, feed and return to building a nest within a very short period of time. Feeding did not therefore represent a significant constraint to time allocated for nestbuilding. The only food deliveries which were missed were those which occurred immediately prior to farrowing during the period of labour which lasts 1-3 h (English et al., 1979). In Trial 2, the experimental pen was modified so that the sows had to work for access to both feed and straw. The results showed that the 'work done' (panel presses) for the two commodities was reduced as their relative cost was increased. The change in the number of entries into each area from a low cost (one panel press) to a high cost (a mean of 150 panel presses) was 17.0
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
225
to 2.6 for the straw area and 21.4 to 11.4 for the feed. The rate at which the number of entries declined was not significantly different for the two commodities, which suggests some degree of similarity between the demand curves for straw and food. According to Dawkins ( 1988 ), commodities which have a similar elasticity of demand as food must be highly important because food is obviously an essential commodity. The cost of the commodities was kept high and constant over the 48 h before farrowing and the number of entries made into the straw area increased significantly from 2.6 on Day - 2 to 16.4 on Day - 1 . The increase in the number of entries into the food area on the same days, from 11.4 to 17, was not significant. This shows that as farrowing approached, demand for straw was greatly increased and observations showed that this increase in demand was associated with the sows motivation to build a nest. All the sows showed nest-building behaviour and farrowed in the straw area. It is suggested that straw did not reinforce the operant of lever lifting in Hutson's (1988) experiment because the reward amount of 1 kg may have been functionally insignificant. In the present experiment, sows were observed to press a panel up to 300 times for access to 18 kg straw and were therefore prepared to do a lot of 'work' for a substantial reward. Similarly, sows can be trained to work for access to earth floors (Van Rooijen, 1982) but training would probably be more difficult if the earth was presented in 1 kg rewards. Even so, earth floors do not appear to be strongly reinforcing for sows which are selecting a farrowing site (Hutson and Haskell, 1990 ). Again, this finding may have been caused by problems with the design of the experiment, as stated by the authors. However, evidence also suggests that earth alone may not be sufficient for building a nest. In semi-natural environments, maternal nests also comprise nesting material such as grass, straw and twigs (Stolba and Wood-Gush, 1984; Jensen, 1989). In enriched pens, sows gathered 23 kg of straw even though they were able to root out a nest in sand floors (Arey et al., 1991 ). If nest material such as cloth tassel is fixed, sows will pull and tear at it, but less so if straw is also available (Widowski and Curtis, 1990). Nesting material which the sows can manipulate with their mouths therefore appears to be a highly valued commodity because it has important role in nest-building behaviour. ACKNOWLEDGEMENTS
I wish to acknowledge the help and advice of M.R. Baxter, A.M. Petchey and V.R. Fowler and thank the Cruden Foundation for a research scholarship. REFERENCES Arey, D.S., Petchey, A.M. and Fowler, V.R., 1991. The pre-parturient behaviour of sows in enriched pens and the effect of pre-formed nests. Appl. Anim. Behav. Sci., 31: 61-68.
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Arey. D.S., Petchey, A.M. and Fowler, V.R., 1992a. The effect of straw on farrowing site choice and nest building bebaviour in sows. Anim. Prod., 54: 129-134. Arey, D.S., Petchey, A,M. and Fowler, V.R., 1992b. The peri-parturient behaviour of sows housed in pairs. Appl. Anim. Behav. Sci., in press. Baxter. M.R., 1982. The nesting behaviour of sows and its disturbance by confinement at farrowing. In: W. Bessai (Editor), Disturbed Behaviour in Farm Animals. Eugen Ulmer, Stuttgart, pp. 101-114. Beilharz, R.G. and Zeeb, K., 1981. Applied ethology and animal welfare. Appl. Anim. Ethol., 7: 3-10. Dawkins, M.S., 1983. Battery hens name their price: consumer demand theory and the measurement of ethological needs. Anim. Behav., 31:1195-1205. Dawkins. M.S., 1988. Behavioural deprivation: a central problem in animal welfare. Appl. Anim. Behav. Sci., 20: 209-225. Duncan, I.J.H., 1978. The interpretation of preference tests in animal behaviour. Appl. Anita. Ethol., 4:197-200. English. P.R., Smith, W.J. and MacLean, A., 1979. Tile S o w - Improving Her Efficiency. Farming Press Ltd., Ipswich, LI.K. Hafez. E.S.E. and Signoret, J.P., 1969. The behaviour of swine. In: E.S.E. Hafez (Editor), The Behaviour of Domestic Animals. Baillibre Tindall, London, pp. 349-390. Hutson, G.D., 1988. Do sows need straw for nest-building? Aust. J. Exp. Agric., 28:187-194. 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. ,lensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anita. Behav. Sci., 16: 131-142. ,lensen, P., Floren, K. and Hobroh, B., 1987. Peri-parturient changes in behaviour in free-ranging domestic pigs. Appl. Anita. Behav. Sci., 17: 69-76. ,Icnsen, P., 1989. Nest site choice and nest building of free-ranging domestic pigs due to farrow. Appl. Anim. Behav, Sci., 22: 13-21. Stolba, A. and Wood-Gush, D.G.M., 1984. Thc identification of bcbavioural key features and their incorporation into a housing design for pigs. Ann. Rech. Vet., 15: 287-298. Taylor. L. and Friend, T.H., 1987. Effect of housing on open-field behaviour of gestating gilts. Appl. Anim. Behav. Sci., 17: 83-93. Tcitclbaum, P., 1966. The use of operant methods in the assessment and control of motivational states. In: W.K. Honig (Editor), Operant Bchaviour. Appleton-Century-Crofts. New York, pp. 565-608. Van Rooijen, J., 1982. Operant preference tests with pigs. Appl. Anita. Ethol., 9: 87-88. (Abstract). Vcstcrgaard, K., 1984. An evaluation of ethological criteria and methods in the assessment of well-being in sows. Ann. Rech. Vet,, 15: 227-235. Whiltcmorc C.T. and Elsley, F.W.H., 1976. Practical Pig Nutrition. Farming Press Ltd., London. Widowski, T.M. and Curtis, S.E., 1990. The influence of straw, cloth tassel or both on the prcparlum bchaviour of sows. Appl. Anita. Behav. Sci., 27: 53-71.
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Straw and food as reinforcers for prepartal sows D.S. Arey Centre for Rural Building, Craibstone, Bucksburn, Aberdeen, AB2 9TR, UK (Accepted 23 September 1991 )
ABSTRACT Arey, D.S., 1992. Straw and food as reinforcers for prepartal sows. Appl. Anita. Behav. Sci., 33:217226. In Trial 1, seven Large-While x Landrace sows were initially housed in either stalls (n-4) or straw pens (11=3) during gestation. On Day 107 of pregnancy, each sow was placed inlo a pen in which food was delivered every 2 h and which had operant access to a straw area (S) and a control area (C). Two days before farrowing, sows spent 71% of their time in S and made significantly more entries into S than C ( 19.6 vs. 4.4). On the day before farrowing, entries into S increased to 37.4 and all the sows built nests and farrowed in S. Straw was reinforcing but did not appear to be as important as feed. In Trial 2, five sows inilially housed in straw pens, were each placed, on their Day 100 of pregnancy, into a pen which had operant access to a straw area (S) and a feed area (F). The number of entries made into S and F were, respectively, 17 and 21.4 when cost of entry was low (one panel press) and 2.6 and 11.4 when the cost was high (a mean of 150 panel presses) 2 days before farrowing and 16.4 and 17 on the day before farrowing when the cost was also high. It was concluded that the importance of straw approached that of feed, particularly during the 24 h before farrowing when sows were motivaled to nest-build.
INTRODUCTION
Prior to giving birth, domesticated sows are highly motivated to perform nest-building behaviour (Baxter, 1982). Pre-parturient sows show a strong preference for farrowing in a bedded area and will gather large amounts of straw from dispensers to form a nest (Arey et al., 1991 ). Although these observations indicate that nesting material is important to sows at this time, preference for a commodity such as straw cannot be equated with need for that commodity (Duncan, 1978 ). If it can be shown that sows need material to build a nest - - such as straw - - then it follows that their welfare will suffer if it is not provided. According to Dawkins ( 1988 ), need can be determined by measuring how strong an animal is motivated to obtain something. Operant conditioning techniques can be used to measure the strength o f an animal's motivation for a reinforcement (Teitelbaum, 1966). If an animal
© 1992 Elsevier Science Publishers B.V. All rights reserved 0 1 6 8 - 1 5 9 1 / 9 2 / $ 0 5 . 0 0
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cannot be trained to work to obtain something then its motivation to obtain it cannot be very great (Beilharz and Zeeb, 1981 ) or the c o m m o d i t y is not a reinforcer. Once an animal has been trained to work for some c o m m o d i t y , the strength o f reinforcement for that c o m m o d i t y can be c o m p a r e d with some yardstick (Dawkins, 1983 ). Food provides a convenient yardstick because it is obviously essential for animals to survive. The motivation to obtain two commodities, such as food and straw, can be c o m p a r e d by measuring their d e m a n d curves (Dawkins, 1988 ). D e m a n d curves describe the rate at which d e m a n d falls as 'cost' increases and are calculated by measuring the a m o u n t of work an animal is prepared to do for a c o m m o d i t y as its cost increases. The cost of a c o m m o d i t y can be manipulated in a n u m b e r of ways, one of which is to alter the n u m b e r o f operant responses required for reinforcement. The m e a s u r e m e n t of d e m a n d curves thus provides a useful m e t h o d of getting animals to show, through their behaviour, how important different c o m m o d i ties are to them. Hutson ( 1988 ) found that prepartal sows were not prepared to lift a lever 10 times for a 1 kg straw reward and concluded that they were therefore not strongly motivated to obtain straw. However, the ability to train animals to work for something depends greatly on the kind of operant response and reward used (Dawkins, 1988). In the present experiment, the operant conditioning technique was modified to re-examine the importance of straw to sows during the days leading up to farrowing. The first part was designed to compare the reinforcing properties o f a straw bedded pen and an unbedded pen; the second part was aimed at comparing the d e m a n d curves for straw and food. ANIMALS, MATERIALS A N D M E T H O D S
The experimental animals were multiparous Landrace X Large White sows which normally have a gestation period o f 115 days. In Trial 1, four sows had initially been housed in sow stalls without straw ( c o n f i n e d ) and four had been group-housed in straw pens ( u n c o n f i n e d ) . In Trial 2, all six sows came from straw pens. The sows were normally fed a daily ration of 2.0-2.5 kg o f a cereal-based sow meal. In Trial 1, the experimental pen was divided into three equally sized areas: a straw area (S) which contained 18 kg straw; a central feed area ( F ) which contained an automatic feeder and an ad libitum supply of water; an unbedded control area (C) (Fig. 1 ). The two areas S and C were connected to F via two swing doors. The doors each had a microswitch that was activated when the door opened and a pressure pad 170 m m X 2 5 0 m m m o u n t e d on the side within F. The doors each had a lock mechanism. When the doors were locked, they could only swing one way, into F, by being pushed from the other side, either S or C. When the locks were released, the doors could swing both ways and could thus be pushed open from F. Release of the lock m e c h a n i s m was contingent on the sow pressing the pressure pad, on the relevant door, the
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Fig. 1. Plans of experimental pens used in Trial 1 (above) and Trial 2. required n u m b e r o f times ('cost'). There was no time limit set for the sow to attain the cost. On attaining the cost, a 5 W bulb was illuminated above the door, the lock mechanism opened within 2 s and closed after 30 s. The system was controlled by a BBC B microcomputer, fitted with a S P I D E R control board and a T E R M I T E external interface (Paul Fray Ltd., Cambridge). The pens were continuously observed with a video camera connected to a timelapse video recorder. C o n t i n u o u s artificial light was provided to allow video recording. The temperature of the pens was maintained between 15 and 20°C. In Trial 2, the experimental pen was modified so that it comprised a straw area (S), a central area ( C ) and a feed area ( F ) (Fig. 1 ). Access to either S or F from C was contingent on the sow pressing the pad on the respective swing door to release the lock. In Trial 1, the sows were introduced individually into the pen on Day 107 of pregnancy. The location o f S and C was alternated for each individual. The
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D.S. AREY
sows were trained to open the swing doors using food rewards provided in S and C during four 10-min daily sessions. To begin with, the swing doors remained unlocked, then the number of presses required to open the lock was increased by one on successive sessions. After training, the cost of entry into S and C was set at 10 panel presses. The sows were offered a daily ration of 3.5 kg sow meal at 09:00 h in F. A further amount of meal (approximately 150 g) was automatically dropped into F every 2 h so that each sow was offered a total of 5.25 kg over a 24-h period, which approaches appetite limit (Whittemore and Elsley, 1976 ). The purpose of the 2-h deliveries of feed was to attract the sows out of S and C at periodic intervals. The video recordings and the data logged by the computer were used to determine: the number of times the sows entered and the amount of time spent in S and C: the number of times the sows fed and the general activity of the sows. Data were compared for the 24 h before farrowing (Day - 1 ) and for the previous 24 h (Day 2 ). Data were compared using M a n n - W h i t n e y U-tests. In Trial 2, the sows were introduced individually into the pen on Day 100 of pregnancy. The swing doors remained unlocked for the first 24 h and were then locked for four 30-rain daily sessions over four days, during which the sow was required to press the panel once to open the lock. This was repeated until each sow was consistently able to open both swing doors. After training, a portion (approximately 110 g) of a daily ration of 3.5 kg of feed was delivered into F every 45 rain. The sows were therefore not fed to their appetite limit in order to maintain their interest in food. The cost of entry into S and F for the first 24 h (Day - n) was set at I. The cost was then increased daily for the two swing doors simultaneously until Day 113 of pregnancy. The rate at which cost was increased was calculated individually for each sow such that entry into the straw area was almost but not completely extinguished by Day 113. The cost was then kept constant until the sow farrowed so that it was the same for the 24 h before farrowing (Day - 1 ) as the previous day (Day - 2 ) . The demand curves for straw and food were determined from the difference in the number of entries made into the respective areas S and F on Day - n (when the cost was lowest) and Day - 2 (when the cost was highest). The data were analysed as modified randomised blocks with the animals as blocks using a regression analysis. The number of entries made into S and F was also compared for Day - 2 and Day - 1 (when cost was constant) to determine any difference in the demand for straw and food, respectively, as the sows approached farrowing. This was determined using an analysis of variance. -
RESULTS
In Trial 1, one straw-housed sow did not respond to training and was therefore omitted from the trial. All seven remaining sows were trained to operate the swing doors by Day I 11 of pregnancy.
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
221
Table 1 shows the mean n u m b e r of entries into the straw and control areas on Day - 1 and Day - 2 for the sows which had been confined and unconfined during pregnancy in Trial 1. All the sows entered and spent more time in the straw area (S) than the control area (C) on Days - 2 and - 1. On both days, the m e a n n u m b e r o f entries into S was significantly greater than the n u m b e r into C ( P < 0 . 0 5 ) . The mean n u m b e r of entries into S significantly increased from 19.6 on Day - 2 to 37.4 on Day - 1. There was no significant difference in the m e a n n u m b e r of entries into C (4.4 on Day - 2 and 8.7 on Day - 1 ). Two sows did not enter C on Day - 2 and one did not enter on Day - 1 . On both days, the sows spent significantly more time in S than C ( P < 0 . 0 0 1 ) . The mean time spent in S was 71% on Day - 2 and 69% on Day - 1. The m e a n time spent in C was 2% on both days. The sows quickly became conditioned to the automatic feeder and usually c o n s u m e d all the feed within a few minutes after it was delivered. On Day -2, none of the 2-h feeds were missed. On Day - 1, one sow missed the last three feeds which were delivered before farrowing, two sows missed two feeds, three sows missed one feed and one sow c o n s u m e d all the feeds delivered. Food was not ignored during the main phase of nest-building behaviour but TABLE 1 T h e difference in lhe m e a n n u m b e r o f entries m a d e into the Straw a n d Control areas by the three u n c o n f i n e d a n d the four c o n f i n e d sows on D a y - 2 a n d Day - 1 in Trial I Group
Unconfined Confined
Day
Day Day Day Day
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3 3 4 4
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Difference
5
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12.7 25.0 24.8 46.8
0.7 1.2 4.4 5.2
3.7 5.3 5.0 12.0
1.9 0.3 2.4 5.0
P < 0.05 P<0.01 P < 0.05 P < 0.01
TABLE 2 N e s t - b u i l d i n g b e h a v i o u r o f the three u n c o n f i n e d a n d the four confined sows in Trial 1 Sows
Bouts o f lying (No.)
Nest-building
Duration (h)
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9.5 13.5
0.5 3.3
22.7 42.8
0.5 4.8
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SE
5.7 18.5
1.0 3.8
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Fig. 2. The number of entries made into (line graph) and the percentage time spent in (bar chart) the Straw and Feed areas between Day - n and Day - 2 (unshaded area) and between Day - 2 and Day - 1 (shaded area) by the five Sows in Trial 2.
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
223
appeared to be less attractive once the sow was lying prostrate and labour had begun. Table 2 shows the s u m m a r y o f nest-building b e h a v i o u r for the confined and unconfined sows. All the sows were observed to perform nest-building b e h a v i o u r and to farrow in the straw area. The mean duration of nest-building was 11.5 h, the mean n u m b e r of nest-building bouts was 32.7, and the mean n u m b e r of lying incidences was 12.1. The confined sows tended to make a greater n u m b e r of entries into the straw area and tended to display more nest-building b e h a v i o u r (non-significant). In Trial 2, one sow farrowed 3 days before its expected date and was therefore omitted from the trial. The remaining five sows farrowed within 36 h of their expected dates. Figure 2 shows the n u m b e r of entries m a d e into and the a m o u n t of time spent in the straw and feed areas on the days prior to farrowing. On day - n , the n u m b e r o f panel presses required to open the gates (cost) was one, and the mean n u m b e r s o f entries into S and F were 17 and 21.4, respectively. The sows spent more time in S ( m e a n 65%) than they did in F ( m e a n 28%) on Day - n. As the cost was progressively increased, the sows m a d e fewer entries into both S and F. By D a y - 2, the cost was increased to between 50 and 300 depending on the individual sows ability/willingness to operate the swing doors. On Day - 2 , the mean n u m b e r s o f entries into S and F had fallen to 2.6 and 11.4, respectively. The a m o u n t of time spent in S was significantly reduced ( m e a n 25%) ( P > 0.05 ), whereas time spent in F remained approximately the same ( m e a n 23%). The rates at which entry into the two areas declined between D a y - n and D a y - 2 were both significantly different from zero ( P > 0.05 ) but were not significantly different form each other ( P < 0.05 ). This shows that as the cost increased, the sows m a d e a similar reduction in panel presses for feed as they did for straw. The cost o f entry into the straw and feeds areas on D a y - 2 and D a y - 1 was kept the same. The mean n u m b e r of entries into the straw area (S) increased significantly from 2.6 to 16.4 on D a y - 1 ( P > 0 . 0 0 1 ) . The mean a m o u n t o f time in S increased from 25% on Day - 2 to 52% on D a y - i, but this difference was not significant. The mean n u m b e r o f entries into F also increased from 11.4 to 17, whereas the mean a m o u n t of time in F was reduced from 23% to 16% (both non-significant). These findings show that there was a marked increase in the d e m a n d for straw during the 24 h prior to farrowing. All the sows were observed to perform nest-building b e h a v i o u r during Day 1 and to farrow in the straw area. -
DISCUSSION AND CONCLUSIONS
In Trial 1, sows were given operant access ( 10 panel presses) to two identical pens, one o f which contained 18 kg straw, the other no straw. On the
224
D.S.AREY
second day before farrowing (Day - 2 ), sows made significantly more entries into the pen containing straw ( 19.6 vs. 4.4) and spent significantly more time in this pen (71% vs. 2%). This shows that the straw positively reinforced the behaviour of the sows. On the day before farrowing (Day - 1 ), the number of entries into the straw area significantly increased from 19.6 to 37.4 whereas there was no difference in entries into the control. The increased entries into the straw area coincided with observations of nest-building behaviour which began 11.5 h before farrowing and included 32.7 bouts of nest-building and 12.1 bouts of lying. There was no difference between these observations and those reported for sows which had free access to a straw area (Arey et al., 1992a) or with sows housed together in pairs (Arey et al., 1992b). This suggests that, although the performance of nesting behaviour can vary, its occurrence is innately typical and relatively unnaffected by environmental and social constraints. In accordance with other authors, the greater activity on Day - 1 indicated that there was an increase in motivation for locomotor behaviour (Hafez and Signoret, 1969; Baxter, 1982; Jensen 1986). In pens, domestic sows increase their activity 24-36 h before farrowing (Vestergaard, 1984), the initial function of which is to search for a suitable nest site away from the normal home range (Jensen et al., 1987). Sows which had previously been confined without straw prior to the experiment appeared to be more active than sows which had been housed in straw pens. The confined sows tended to make more entries into the straw area and show higher levels of nest-building behaviour. Although the amount of data was limited and non-significant, these findings agree with Taylor and Friend ( 1987 ), who showed that activity in an enriched environment is increased in gilts previously kept with greater housing deprivation. In Trial 1, the straw and no straw pens were connected via a feed pen in which food was presented every 2 h so that the sows were fed amounts close to appetite limit. Even so, the sows invariably fed as soon as food was delivered throughout Day - 2 and Day - I. Food therefore appeared to be more important to the sows during the nest-building phase than straw. However, the design of the experiment meant that the sows could leave the straw area, feed and return to building a nest within a very short period of time. Feeding did not therefore represent a significant constraint to time allocated for nestbuilding. The only food deliveries which were missed were those which occurred immediately prior to farrowing during the period of labour which lasts 1-3 h (English et al., 1979). In Trial 2, the experimental pen was modified so that the sows had to work for access to both feed and straw. The results showed that the 'work done' (panel presses) for the two commodities was reduced as their relative cost was increased. The change in the number of entries into each area from a low cost (one panel press) to a high cost (a mean of 150 panel presses) was 17.0
STRAW AND FOOD AS REINFORCERS FOR PREPARTAL SOWS
225
to 2.6 for the straw area and 21.4 to 11.4 for the feed. The rate at which the number of entries declined was not significantly different for the two commodities, which suggests some degree of similarity between the demand curves for straw and food. According to Dawkins ( 1988 ), commodities which have a similar elasticity of demand as food must be highly important because food is obviously an essential commodity. The cost of the commodities was kept high and constant over the 48 h before farrowing and the number of entries made into the straw area increased significantly from 2.6 on Day - 2 to 16.4 on Day - 1 . The increase in the number of entries into the food area on the same days, from 11.4 to 17, was not significant. This shows that as farrowing approached, demand for straw was greatly increased and observations showed that this increase in demand was associated with the sows motivation to build a nest. All the sows showed nest-building behaviour and farrowed in the straw area. It is suggested that straw did not reinforce the operant of lever lifting in Hutson's (1988) experiment because the reward amount of 1 kg may have been functionally insignificant. In the present experiment, sows were observed to press a panel up to 300 times for access to 18 kg straw and were therefore prepared to do a lot of 'work' for a substantial reward. Similarly, sows can be trained to work for access to earth floors (Van Rooijen, 1982) but training would probably be more difficult if the earth was presented in 1 kg rewards. Even so, earth floors do not appear to be strongly reinforcing for sows which are selecting a farrowing site (Hutson and Haskell, 1990 ). Again, this finding may have been caused by problems with the design of the experiment, as stated by the authors. However, evidence also suggests that earth alone may not be sufficient for building a nest. In semi-natural environments, maternal nests also comprise nesting material such as grass, straw and twigs (Stolba and Wood-Gush, 1984; Jensen, 1989). In enriched pens, sows gathered 23 kg of straw even though they were able to root out a nest in sand floors (Arey et al., 1991 ). If nest material such as cloth tassel is fixed, sows will pull and tear at it, but less so if straw is also available (Widowski and Curtis, 1990). Nesting material which the sows can manipulate with their mouths therefore appears to be a highly valued commodity because it has important role in nest-building behaviour. ACKNOWLEDGEMENTS
I wish to acknowledge the help and advice of M.R. Baxter, A.M. Petchey and V.R. Fowler and thank the Cruden Foundation for a research scholarship. REFERENCES Arey, D.S., Petchey, A.M. and Fowler, V.R., 1991. The pre-parturient behaviour of sows in enriched pens and the effect of pre-formed nests. Appl. Anim. Behav. Sci., 31: 61-68.
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Arey. D.S., Petchey, A.M. and Fowler, V.R., 1992a. The effect of straw on farrowing site choice and nest building bebaviour in sows. Anim. Prod., 54: 129-134. Arey, D.S., Petchey, A,M. and Fowler, V.R., 1992b. The peri-parturient behaviour of sows housed in pairs. Appl. Anim. Behav. Sci., in press. Baxter. M.R., 1982. The nesting behaviour of sows and its disturbance by confinement at farrowing. In: W. Bessai (Editor), Disturbed Behaviour in Farm Animals. Eugen Ulmer, Stuttgart, pp. 101-114. Beilharz, R.G. and Zeeb, K., 1981. Applied ethology and animal welfare. Appl. Anim. Ethol., 7: 3-10. Dawkins, M.S., 1983. Battery hens name their price: consumer demand theory and the measurement of ethological needs. Anim. Behav., 31:1195-1205. Dawkins. M.S., 1988. Behavioural deprivation: a central problem in animal welfare. Appl. Anim. Behav. Sci., 20: 209-225. Duncan, I.J.H., 1978. The interpretation of preference tests in animal behaviour. Appl. Anita. Ethol., 4:197-200. English. P.R., Smith, W.J. and MacLean, A., 1979. Tile S o w - Improving Her Efficiency. Farming Press Ltd., Ipswich, LI.K. Hafez. E.S.E. and Signoret, J.P., 1969. The behaviour of swine. In: E.S.E. Hafez (Editor), The Behaviour of Domestic Animals. Baillibre Tindall, London, pp. 349-390. Hutson, G.D., 1988. Do sows need straw for nest-building? Aust. J. Exp. Agric., 28:187-194. 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. ,lensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anita. Behav. Sci., 16: 131-142. ,lensen, P., Floren, K. and Hobroh, B., 1987. Peri-parturient changes in behaviour in free-ranging domestic pigs. Appl. Anita. Behav. Sci., 17: 69-76. ,Icnsen, P., 1989. Nest site choice and nest building of free-ranging domestic pigs due to farrow. Appl. Anim. Behav, Sci., 22: 13-21. Stolba, A. and Wood-Gush, D.G.M., 1984. Thc identification of bcbavioural key features and their incorporation into a housing design for pigs. Ann. Rech. Vet., 15: 287-298. Taylor. L. and Friend, T.H., 1987. Effect of housing on open-field behaviour of gestating gilts. Appl. Anim. Behav. Sci., 17: 83-93. Tcitclbaum, P., 1966. The use of operant methods in the assessment and control of motivational states. In: W.K. Honig (Editor), Operant Bchaviour. Appleton-Century-Crofts. New York, pp. 565-608. Van Rooijen, J., 1982. Operant preference tests with pigs. Appl. Anita. Ethol., 9: 87-88. (Abstract). Vcstcrgaard, K., 1984. An evaluation of ethological criteria and methods in the assessment of well-being in sows. Ann. Rech. Vet,, 15: 227-235. Whiltcmorc C.T. and Elsley, F.W.H., 1976. Practical Pig Nutrition. Farming Press Ltd., London. Widowski, T.M. and Curtis, S.E., 1990. The influence of straw, cloth tassel or both on the prcparlum bchaviour of sows. Appl. Anita. Behav. Sci., 27: 53-71.