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The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests
Applied Animal Behaviour Science, 31 ( 1991 ) 6 1 - 6 8
61
Elsevier Science Publishers B.V., A m s t e r d a m
The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests D.S. Arey a, A.M. Petchey a and V.R.
Fowler u
aCentre for Rural Building, Craibstone, Bucksburn, Aberdeen, AB2 9TR, UK bNorth of Scotland College of Agriculture, 581, King Street, Aberdeen, AB9 1 LID, UK (Accepted 26 November 1990)
ABSTRACT Arey, D.S., Petchey, A.M. and Fowler, V.R., 199 I. The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests. Appl. Anim. Behav. Sci., 31: 61-68. The nest building behaviour of 12 preparturient sows was studied in enriched pens. Four categories ofbehaviour were observed: rooting, straw carrying, pawing and lying. In the 24 h before farrowing, six sows excavated hollows in sand floors and removed straw from dispensers to construct nests similar to those reported for sows kept outdoors. When pre-formed nests were presented to six sows on the day before farrowing, straw removal was reduced ( P < 0.05 ), straw carrying and pawing remained the same. Rooting, lying and the duration of nest building increased ( P < 0.05 ). Nest building is highly motivated behaviour in sows and the performance of the activities themselves appears to have a significant role in reducing the motivation. Nesting material appears to be a key factor both in the regulation and performance of the behaviour.
INTRODUCTION
In the intensive pig production industry, sows are normally confined in crates at farrowing time and it has been argued that their welfare suffers because they are unable to perform their normal patterns of behaviour, which include the building of a maternal nest (Baxter, 1982b). Stolba and WoodGush (1984) suggested that farrowing accommodation should therefore enable sows to perform nest building behaviour in a motivationally satisfactory way. They argued that sows should be provided with environmental conditions which allow the performance of the activities which are frequently observed in a more natural environment. Detailed descriptions of sow nest-building behaviour have been documented for the wild sow (Sus scrofa) (Gunlach, 1968; Graves, 1984), for feral sows (Kurz and Marchinton, 1972 ) and for domestic sows in semi-natural enclosures (Stolba and Wood-Gush, 1984; Jensen, 1986 ). Nests are generally built in sheltered locations and usually comprise a scraped hollow, lined 0168-1591/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
62
D.S. AREY ET AL.
with nest material such as leaves and twigs which is then surrounded by earth walls and branches. Similar nesting activities have been reported for sows housed in straw pens (Baxter, 1982b; Vestergaard and Hansen, 1984 ). However, the behaviour may be modified as protection is afforded by the housed environment. Buss ( 1972 ) showed that domestic sows were less inclined to excavate a hollow and performed more nest lining behaviour than wild sows. Furthermore, Hutson (1988) found that sows were not prepared to work for a straw reward, indicating that nesting material is u n i m p o r t a n t to preparturient sows kept inside. According to Baxter (1982a), the identification of the environmental requirements of sows prior to farrowing can be gained from understanding the control mechanisms of nest building behaviour. He speculated that the function of the behaviour is to provide comfort for the udder and that motivation is reduced when the sow can lie down and her udder remains comfortable. Baxter (1982b) suggested that the provision of a soft resilient lying substrate might obviate any need to perform nest building, thereby satisfying that sow's requirements. However, recent work suggests that the control mechanisms of nest building in sows may be more complex, involving several factors (Hutson, 1988; Jensen, 1989). The following experiment was designed to document sow nest building behaviour in enriched pens. The aim was to identify the preferred physical requirements of nesting behaviour in a straightforward choice test which gave sows access to a sand floor and a straw dispenser. The properties of the nests built were recorded and reconstructed for a second group of sows. The nest building behaviour of the two groups was compared to determine whether the behaviour is modified by the presence of a pre-formed nest. ANIMALS, MATERIALS AND M E T H O D S
A total of 12 second or third parity Large White × Landrace sows were used in the experiment; these were divided into two groups of six animals. The sows had previously been housed in straw pens during gestation. The two experimental pens measured 5 m × 2.5 m, and had two floor surfaces (each 2.5 m × 2.5 m ) of sand and concrete (Fig. 1 ). The coarse building sand was 60 cm deep and was at the same floor level as the concrete. A water bowl and feed trough were positioned where the floors abutted. A straw dispenser was m o u n t e d on the wall between the two floors (Fig. 2). The two pens were adjacent and geometrically opposed. The pens were continuously observed with a National Panasonic video camera fitted with an 8.5 m m auto iris lens and a time lapse video cassette recorder. Continuous artificial light was provided to allow video recording. The pens were maintained at a temperature of between 15 and 20°C. The sows were introduced individually into one of the experimental pens
63
PREI°ARTURIENT BEH&VIOUR OF SOWS
2500
2500
--I_
~ - - ] Sand area
Concrete area
Gate L~roug h
Straw
Onnker ~" Drinker
| Straw dispenser
dispense..~.r Yr°ugiqL ~L
--] I
Gate
!
I Sand a r e a
Concrete area
Fig. I. Plan of experimental pens. 700
~
~
450
Wall
Straw
I
S 150
Side elevation
End elevation
Fig. 2. The straw dispenser. on the 109th day of pregnancy. They were offered 3.5 kg of sow meal at 09: 00 h and dung was r e m o v e d during feeding. After farrowing, the location of the nest site, the dimensions of nests constructed and the amount of straw incorporated in the nest was recorded for G r o u p 1. Similar nests were constructed for G r o u p 2 sows on the 113th day of pregnancy using the median values from G r o u p 1. Video recordings were used to compare the nest building behaviour of the t',,o groups. Statistical comparisons were made using M a n n - W h i t n e y U tests.
64
D.S. AREY ET AL.
RESULTS
Figure 3 shows the hourly means for the performance of nest building activities prior to farrowing in the two groups of sows. During the 24 h before farrowing, all the sows displayed nest building behaviour which comprised three activities: rooting, pawing and straw carrying. The onset of nest building behaviour was signified by the repeated performance of these activities. Only rooting was observed prior to nest building but was distinguished by its short duration (less than 30 s) and by the fact that it was always terminated by the animal lying down. The first nesting activities observed in Group 1 were rooting and pawing, Group 1
20
t ---.o---
Rooting Pawing Strawcarrying
15
.___
~-- 10
5
252423222120191817161514131211109
8
7 6 5 4 3 2
1
F
Hours to Farrowing 20
Group 2
°
Rooting Pawing Straw carrying
15
.~
tO
5
0 252423222120191817161514131211109
8 7
6 5 4 3
2
1 F
Hours to farrowing Fig. 3. Hourly means for the performance of nest building activities.
PREPARTURIENT BEHAVIOUROF SOWS
65
these were directed at the sand. Five sows formed elliptical-shaped depressions in the sand, the m e d i a n size was 1.62 m × 1.07 m with a depth of 0.21 m. There was a weak positive correlation between the a m o u n t of rooting and pawing and the size o f the hollow, r=0.21 and r = 0 . 3 8 , respectively. All the sows in Group 1 removed straw from the dispenser, and deposited it in the hollow and around the edge to form a rim. Straw carrying occurred 1-4 h after rooting and pawing had commenced. The median a m o u n t of straw removed was 23 kg. Straw removal (kg) was strongly correlated with the amount of time spent straw carrying (s) r = 0.71. The sows further manipulated the straw by rooting, pawing and carrying. Four of the sows were frequently observed to lie down, this was more pronounced at the beginning and end of nest building. Two sows in Group 1 did not lie down until after the nest building activities had ceased. All the sows farrowed in the sand area. The pre-formed nests constructed for the sows in Group 2 consisted of a 1.62 m × 1.07 mX0.21 m depression in the sand with 23 kg straw placed in and around the hollow. All the sows farrowed in the pre-formed nest between 24 and 48 h after it was formed. Group 2 sows displayed straw carrying at the start of nest building. Five sows removed straw from the dispenser, the median a m o u n t was 9.5 kg. This was significantly less than the a m o u n t of straw removed by Group 1 ( P < 0.05). There was, however, no significant difference in the total amounts of straw found in the pens of the two groups at the end of nest building. The nest building activities did not appear to significantly alter the appearance of the nest. Table 1 shows a s u m m a r y of the nest building behaviour of the sows in Groups 1 and 2. There were several differences in the behaviour of the two groups. Nest building was observed earlier in Group 2. Group 1 sows started at a median time of 9 h 30 min before farrowing, whereas in Group 2 the median time was 14 h 30 mins. This difference was significant ( P < 0 . 0 1 ) . The total amounts of time spent rooting and lying were significantly increased TABLE 1 A summary of the nest building behaviour Bchaviour
Rooting (s) Pawing (s) Straw carrying (s) Lying (s) Total duration (h) Straw removed (kg)
INS, not significant.
Group 1
Group 2
/'-value
Median
Min.
Max.
Median
Min.
Max.
2337 232 2353 6900 9.5 23
1426 63 1139 600 5 14
3282 482 5276 15820 12 51.5
4045 208 2025 19470 14.5 9.5
2657 126 800 15120 12 0
8580 367 5762 33420 25 27
<0.05 NS l NS < 0.05 <0.01 <0.05
66
D.S. AREY ETAL.
in Group 2 ( P < 0.05 ). Rooting was increased from 2337 to 4045 s. Lying was increased from 6900 to 19 470 s. There was no significant difference in the total amounts of time spent pawing or straw carrying. Pawing was 232 s in Group 1 and 208 s in Group 2, straw carrying was 2354 s and 2025 s, respectively. There was no significant difference in rates (activity/total duration of nest building) at which rooting, pawing, straw carrying and lying were performed by the two groups. DISCUSSION
The study demonstrated that domestic sows housed in enriched pens display nest building behaviour which is very similar to that reported for feral sows (Kurz and Marchinton, 1972 ) and for domestic sows kept in semi-natural environments (Stolba and Wood-Gush, 1984; Jensen, 1986). In Group 1, the typical product of the behaviour was a shallow elliptical shaped depression in the sand which was lined with straw and surrounded by a rim of sand and further amounts of straw. The differences in nest building between sows kept indoors and wild sows noted by Buss (1972) may have been a result of the reduced complexity of the internal environment. Hutson's ( 1988 ) claim that nesting material is unimportant to prepartal sows is questioned as the acquisition of nesting material was a major component of the nest building in this study. Nest building behaviour was modified by the presence of a pre-formed nest. In Group 2, sows started nest building earlier, gathered less straw, performed more rooting and spent more time lying. Pawing and straw-carrying activities remained unchanged. The average duration of nest building was increased from 9.5 h (Group 1 ) to 14.5 h (Group 2) which was more consistent with earlier reports of 12-24 h (Vestergaard, 1984). Straw carrying was observed at the start of nest building in Group 2 but was not observed until later in Group 1. These findings suggest that nest building may have been delayed in Group 1 because the straw was not as readily available. Although Blackshaw ( 1983 ) reported that nesting material is not necessary for nest building activities to be performed, Stolba and Wood-Gush (1984) suggest that "high standing stalks" may trigger the behaviour in sows kept outdoors. Thus, once the sow is motivated to build a nest, the presence of nest material might be instrumental in releasing the normal pattern ofbehaviour. Sows are able to adjust their nest building behaviour according to prevailing external conditions such as weather and degree of shelter. This indicates that the behaviour is under feedback regulation (Jensen, 1989). On average, Group 1 sows removed 23 kg of straw from the dispenser. Group 2 sows, which were presented with 23 kg straw in the pre-formed nest, removed significantly less straw from the dispenser (9.5 kg). Similarly therefore, the gathering of nest material appears to be regulated by negative feedback.
PREPARTURIENT BEHAVIOUR OF SOWS
67
Nest building appeared to comprise three stages, the excavation of a hollow, the collection of nest material and the manipulation of the material in the hollow to form the nest. Compared with Group 1, the sows with a preformed nest performed the first two stages less and the third more. During the latter stages of nest building, the wild sow (Sus scrofa) periodically roots through the nest and may lie down (Gunlach, 1968; Fradrich, 1974). The increased rooting and lying in Group 2 appeared to be an accentuation of this behaviour. Motivation for general activity is dramatically increased prior to farrowing (Lammers and de Lange, 1986; Jensen et al., 1987), and sows stand up and lie down repetitively (Hansen and Curtis, 1980). This increased motivation was not reduced by the presence of a nest but was directed into behaviour more typical of the latter stages of nest building. This indicates that the performance of nest building behaviour may itself be important in reducing the high levels of motivation. Other studies have indicated that some nest building behaviours are performed irrespective of any environmental feedback. For example, certain nest building activities in mice are self-sustaining regardless of whether or not they lead to nest formation (Roper, 1976). Similarly, the construction of a nest is not the proximate function of nest building in hens, moreover the behaviour itself is reinforcing (Hughes et al., 1989 ). The sows were observed to lie down between episodes of nest building. This behaviour has been interpreted as part of a feedback mechanism which controls nest building in sows (Baxter, 1982a). However, lying was associated more with the beginning and end of the nest building and not the period when nest activity was greatest. Furthermore, two sows in Group 1 did not lie down at all during nest building and could not have used udder comfort as a controlling factor of the behaviour. Baxter's (1982b) hypothesis, which suggests that nest building motivation in sows should be reduced by the presence of a pre-formed nest, seems to be an oversimplification. Nest building in sows is very complex behaviour (Vestergaard, 1984) and would seem to involve both internal and external causal factors (Jensen, 1989), not just the specific external motivation reducing factors suggested by Baxter (1982b). Farrowing accommodation should therefore enable sows to perform nest building to reduce the high levels of motivation. Nest material is essential to the behaviour and therefore to the environmental requirements of the sow at this time.
ACKNOWLEDGEMENTS
We wish to thank Mr. R.K. Howitt, Rowett Research Institute, for providing the experimental animals and the Cruden Foundation for a research scholarship.
68
D.S. AREY ET AL.
REFERENCES Baxter, M.R., 1982a. The nesting behaviour of sows and its disturbance by confinement at farrowing. In: W. Bessair (Editor), Disturbed Behaviour in Farm Animals. Seminar in the EEC Program of Coordination of Research on Animal Welfare at the University of Hohenheim, 1981, Eugen Ulner, Stuttgart, pp. 101-114. Baxter, M.R., 1982b. Ethology in environmental design for animal production. Appl. Anita, Ethol., 9: 207-220. Blackshaw, J.K., 1983. Prostaglandin F2 (alpha) induced nest building behavior in the nonpregnant sow and some welfare considerations. Int. J. Stud. Anita. Probl., 4 (4): 299-304. Buss, K.D., 1972. Ein Vergleich des Nestbauverhaltens beim Wildschwein und Hausschwein. (A comparison of nest-building behaviour with the wild pig and domestic pig.) Inaugural Thesis, Institute for Zoology of the Hannover Veterinary College. Fradrich, H., 1974. A comparison of behaviour in the (Suidae). In: V. Geist and F. Walther (Editors), The Behaviour of Ungulates and its Relation to Management. IUCN, New Series No. 24, Morges, pp. 133-143. Graves, H.B., 1984. Behaviour and ecology of wild and feral swine (Sus scrofa). J. Anita. Sci., 58: 482-492. Gunlach, H., 1968. Brufursorge, Brutpflege, Verhaltensontogenese und Tagesperiodik beim Europaischen Wildschwein (Sus scrofa L). Z. Tierpsychol., 25: 955-995. Hansen, K.E. and Curtis, S.E., 1980. Prepartal activity of sows in stall or pen. J. Anita. Sci., 51: 456-460. Hughes, B.O., Duncan, I.J.H. and Brown, M.F., 1989. The performance of nest-building by domestic hens: is it more important than the construction of a nest? Anita. Behav., 37: 210214. Hutson, G.D., 1988. Do sows need straw for nest-building? Aust. J. Exp. Agric., 28:187-194. Jensen, P., 1986. Observations on the maternal behaviour of free-ranging domestic pigs. Appl. Anim. Behav. Sci., 16: 131-142. Jensen, P., 1989. Nest site choice and nest building of free-ranging domestic pigs due to farrow. Appl. Anim. Behav. Sci., 22: 13-21. Jensen, P., Floren, K. and Hobroh, B., 1987. Peri-parturient changes in behaviour in free-ranging domestic pigs. Appl. Anim. Behav. Sci., 17: 69-76. Kurz, J.C. and Marchinton, R.L., 1972. Radiotelemetry studies of feral hogs in South Carolina. J. Wildl. Manage., 36: 1240-1248. Lammers, G.J. and de Lange, A., 1986. Pre- and post-farrowing behaviour of primiparous domesticated pigs. Appl. Anita. Behav. Sci., 15: 31-43. Roper, T.J., 1976. Self-sustaining activities and reinforcement in the nest building behaviour of mice. Behaviour, 59: 40-58. Stolba, A. and Wood-Gush, D.G.M., 1984. The identification of behavioural key features and their incorporation into a housing design for pigs. Ann. Rech. Vet., 15 (2): 287-299. Vestergaard, K., 1984. An evaluation of ethological criteria and methods in the assessment of wellbeing in sows. Ann. Rech. Vet., 15 (2): 227-235. Vestergaard, K. and Hansen, L.L., 1984. Tethered versus loose sows: ethological observations and measures of productivity. 1. Ethological observations during pregnancy and farrowing. Ann. Rech. Vet., 15 (2): 245-256.
61
Elsevier Science Publishers B.V., A m s t e r d a m
The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests D.S. Arey a, A.M. Petchey a and V.R.
Fowler u
aCentre for Rural Building, Craibstone, Bucksburn, Aberdeen, AB2 9TR, UK bNorth of Scotland College of Agriculture, 581, King Street, Aberdeen, AB9 1 LID, UK (Accepted 26 November 1990)
ABSTRACT Arey, D.S., Petchey, A.M. and Fowler, V.R., 199 I. The preparturient behaviour of sows in enriched pens and the effect of pre-formed nests. Appl. Anim. Behav. Sci., 31: 61-68. The nest building behaviour of 12 preparturient sows was studied in enriched pens. Four categories ofbehaviour were observed: rooting, straw carrying, pawing and lying. In the 24 h before farrowing, six sows excavated hollows in sand floors and removed straw from dispensers to construct nests similar to those reported for sows kept outdoors. When pre-formed nests were presented to six sows on the day before farrowing, straw removal was reduced ( P < 0.05 ), straw carrying and pawing remained the same. Rooting, lying and the duration of nest building increased ( P < 0.05 ). Nest building is highly motivated behaviour in sows and the performance of the activities themselves appears to have a significant role in reducing the motivation. Nesting material appears to be a key factor both in the regulation and performance of the behaviour.
INTRODUCTION
In the intensive pig production industry, sows are normally confined in crates at farrowing time and it has been argued that their welfare suffers because they are unable to perform their normal patterns of behaviour, which include the building of a maternal nest (Baxter, 1982b). Stolba and WoodGush (1984) suggested that farrowing accommodation should therefore enable sows to perform nest building behaviour in a motivationally satisfactory way. They argued that sows should be provided with environmental conditions which allow the performance of the activities which are frequently observed in a more natural environment. Detailed descriptions of sow nest-building behaviour have been documented for the wild sow (Sus scrofa) (Gunlach, 1968; Graves, 1984), for feral sows (Kurz and Marchinton, 1972 ) and for domestic sows in semi-natural enclosures (Stolba and Wood-Gush, 1984; Jensen, 1986 ). Nests are generally built in sheltered locations and usually comprise a scraped hollow, lined 0168-1591/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
62
D.S. AREY ET AL.
with nest material such as leaves and twigs which is then surrounded by earth walls and branches. Similar nesting activities have been reported for sows housed in straw pens (Baxter, 1982b; Vestergaard and Hansen, 1984 ). However, the behaviour may be modified as protection is afforded by the housed environment. Buss ( 1972 ) showed that domestic sows were less inclined to excavate a hollow and performed more nest lining behaviour than wild sows. Furthermore, Hutson (1988) found that sows were not prepared to work for a straw reward, indicating that nesting material is u n i m p o r t a n t to preparturient sows kept inside. According to Baxter (1982a), the identification of the environmental requirements of sows prior to farrowing can be gained from understanding the control mechanisms of nest building behaviour. He speculated that the function of the behaviour is to provide comfort for the udder and that motivation is reduced when the sow can lie down and her udder remains comfortable. Baxter (1982b) suggested that the provision of a soft resilient lying substrate might obviate any need to perform nest building, thereby satisfying that sow's requirements. However, recent work suggests that the control mechanisms of nest building in sows may be more complex, involving several factors (Hutson, 1988; Jensen, 1989). The following experiment was designed to document sow nest building behaviour in enriched pens. The aim was to identify the preferred physical requirements of nesting behaviour in a straightforward choice test which gave sows access to a sand floor and a straw dispenser. The properties of the nests built were recorded and reconstructed for a second group of sows. The nest building behaviour of the two groups was compared to determine whether the behaviour is modified by the presence of a pre-formed nest. ANIMALS, MATERIALS AND M E T H O D S
A total of 12 second or third parity Large White × Landrace sows were used in the experiment; these were divided into two groups of six animals. The sows had previously been housed in straw pens during gestation. The two experimental pens measured 5 m × 2.5 m, and had two floor surfaces (each 2.5 m × 2.5 m ) of sand and concrete (Fig. 1 ). The coarse building sand was 60 cm deep and was at the same floor level as the concrete. A water bowl and feed trough were positioned where the floors abutted. A straw dispenser was m o u n t e d on the wall between the two floors (Fig. 2). The two pens were adjacent and geometrically opposed. The pens were continuously observed with a National Panasonic video camera fitted with an 8.5 m m auto iris lens and a time lapse video cassette recorder. Continuous artificial light was provided to allow video recording. The pens were maintained at a temperature of between 15 and 20°C. The sows were introduced individually into one of the experimental pens
63
PREI°ARTURIENT BEH&VIOUR OF SOWS
2500
2500
--I_
~ - - ] Sand area
Concrete area
Gate L~roug h
Straw
Onnker ~" Drinker
| Straw dispenser
dispense..~.r Yr°ugiqL ~L
--] I
Gate
!
I Sand a r e a
Concrete area
Fig. I. Plan of experimental pens. 700
~
~
450
Wall
Straw
I
S 150
Side elevation
End elevation
Fig. 2. The straw dispenser. on the 109th day of pregnancy. They were offered 3.5 kg of sow meal at 09: 00 h and dung was r e m o v e d during feeding. After farrowing, the location of the nest site, the dimensions of nests constructed and the amount of straw incorporated in the nest was recorded for G r o u p 1. Similar nests were constructed for G r o u p 2 sows on the 113th day of pregnancy using the median values from G r o u p 1. Video recordings were used to compare the nest building behaviour of the t',,o groups. Statistical comparisons were made using M a n n - W h i t n e y U tests.
64
D.S. AREY ET AL.
RESULTS
Figure 3 shows the hourly means for the performance of nest building activities prior to farrowing in the two groups of sows. During the 24 h before farrowing, all the sows displayed nest building behaviour which comprised three activities: rooting, pawing and straw carrying. The onset of nest building behaviour was signified by the repeated performance of these activities. Only rooting was observed prior to nest building but was distinguished by its short duration (less than 30 s) and by the fact that it was always terminated by the animal lying down. The first nesting activities observed in Group 1 were rooting and pawing, Group 1
20
t ---.o---
Rooting Pawing Strawcarrying
15
.___
~-- 10
5
252423222120191817161514131211109
8
7 6 5 4 3 2
1
F
Hours to Farrowing 20
Group 2
°
Rooting Pawing Straw carrying
15
.~
tO
5
0 252423222120191817161514131211109
8 7
6 5 4 3
2
1 F
Hours to farrowing Fig. 3. Hourly means for the performance of nest building activities.
PREPARTURIENT BEHAVIOUROF SOWS
65
these were directed at the sand. Five sows formed elliptical-shaped depressions in the sand, the m e d i a n size was 1.62 m × 1.07 m with a depth of 0.21 m. There was a weak positive correlation between the a m o u n t of rooting and pawing and the size o f the hollow, r=0.21 and r = 0 . 3 8 , respectively. All the sows in Group 1 removed straw from the dispenser, and deposited it in the hollow and around the edge to form a rim. Straw carrying occurred 1-4 h after rooting and pawing had commenced. The median a m o u n t of straw removed was 23 kg. Straw removal (kg) was strongly correlated with the amount of time spent straw carrying (s) r = 0.71. The sows further manipulated the straw by rooting, pawing and carrying. Four of the sows were frequently observed to lie down, this was more pronounced at the beginning and end of nest building. Two sows in Group 1 did not lie down until after the nest building activities had ceased. All the sows farrowed in the sand area. The pre-formed nests constructed for the sows in Group 2 consisted of a 1.62 m × 1.07 mX0.21 m depression in the sand with 23 kg straw placed in and around the hollow. All the sows farrowed in the pre-formed nest between 24 and 48 h after it was formed. Group 2 sows displayed straw carrying at the start of nest building. Five sows removed straw from the dispenser, the median a m o u n t was 9.5 kg. This was significantly less than the a m o u n t of straw removed by Group 1 ( P < 0.05). There was, however, no significant difference in the total amounts of straw found in the pens of the two groups at the end of nest building. The nest building activities did not appear to significantly alter the appearance of the nest. Table 1 shows a s u m m a r y of the nest building behaviour of the sows in Groups 1 and 2. There were several differences in the behaviour of the two groups. Nest building was observed earlier in Group 2. Group 1 sows started at a median time of 9 h 30 min before farrowing, whereas in Group 2 the median time was 14 h 30 mins. This difference was significant ( P < 0 . 0 1 ) . The total amounts of time spent rooting and lying were significantly increased TABLE 1 A summary of the nest building behaviour Bchaviour
Rooting (s) Pawing (s) Straw carrying (s) Lying (s) Total duration (h) Straw removed (kg)
INS, not significant.
Group 1
Group 2
/'-value
Median
Min.
Max.
Median
Min.
Max.
2337 232 2353 6900 9.5 23
1426 63 1139 600 5 14
3282 482 5276 15820 12 51.5
4045 208 2025 19470 14.5 9.5
2657 126 800 15120 12 0
8580 367 5762 33420 25 27
<0.05 NS l NS < 0.05 <0.01 <0.05
66
D.S. AREY ETAL.
in Group 2 ( P < 0.05 ). Rooting was increased from 2337 to 4045 s. Lying was increased from 6900 to 19 470 s. There was no significant difference in the total amounts of time spent pawing or straw carrying. Pawing was 232 s in Group 1 and 208 s in Group 2, straw carrying was 2354 s and 2025 s, respectively. There was no significant difference in rates (activity/total duration of nest building) at which rooting, pawing, straw carrying and lying were performed by the two groups. DISCUSSION
The study demonstrated that domestic sows housed in enriched pens display nest building behaviour which is very similar to that reported for feral sows (Kurz and Marchinton, 1972 ) and for domestic sows kept in semi-natural environments (Stolba and Wood-Gush, 1984; Jensen, 1986). In Group 1, the typical product of the behaviour was a shallow elliptical shaped depression in the sand which was lined with straw and surrounded by a rim of sand and further amounts of straw. The differences in nest building between sows kept indoors and wild sows noted by Buss (1972) may have been a result of the reduced complexity of the internal environment. Hutson's ( 1988 ) claim that nesting material is unimportant to prepartal sows is questioned as the acquisition of nesting material was a major component of the nest building in this study. Nest building behaviour was modified by the presence of a pre-formed nest. In Group 2, sows started nest building earlier, gathered less straw, performed more rooting and spent more time lying. Pawing and straw-carrying activities remained unchanged. The average duration of nest building was increased from 9.5 h (Group 1 ) to 14.5 h (Group 2) which was more consistent with earlier reports of 12-24 h (Vestergaard, 1984). Straw carrying was observed at the start of nest building in Group 2 but was not observed until later in Group 1. These findings suggest that nest building may have been delayed in Group 1 because the straw was not as readily available. Although Blackshaw ( 1983 ) reported that nesting material is not necessary for nest building activities to be performed, Stolba and Wood-Gush (1984) suggest that "high standing stalks" may trigger the behaviour in sows kept outdoors. Thus, once the sow is motivated to build a nest, the presence of nest material might be instrumental in releasing the normal pattern ofbehaviour. Sows are able to adjust their nest building behaviour according to prevailing external conditions such as weather and degree of shelter. This indicates that the behaviour is under feedback regulation (Jensen, 1989). On average, Group 1 sows removed 23 kg of straw from the dispenser. Group 2 sows, which were presented with 23 kg straw in the pre-formed nest, removed significantly less straw from the dispenser (9.5 kg). Similarly therefore, the gathering of nest material appears to be regulated by negative feedback.
PREPARTURIENT BEHAVIOUR OF SOWS
67
Nest building appeared to comprise three stages, the excavation of a hollow, the collection of nest material and the manipulation of the material in the hollow to form the nest. Compared with Group 1, the sows with a preformed nest performed the first two stages less and the third more. During the latter stages of nest building, the wild sow (Sus scrofa) periodically roots through the nest and may lie down (Gunlach, 1968; Fradrich, 1974). The increased rooting and lying in Group 2 appeared to be an accentuation of this behaviour. Motivation for general activity is dramatically increased prior to farrowing (Lammers and de Lange, 1986; Jensen et al., 1987), and sows stand up and lie down repetitively (Hansen and Curtis, 1980). This increased motivation was not reduced by the presence of a nest but was directed into behaviour more typical of the latter stages of nest building. This indicates that the performance of nest building behaviour may itself be important in reducing the high levels of motivation. Other studies have indicated that some nest building behaviours are performed irrespective of any environmental feedback. For example, certain nest building activities in mice are self-sustaining regardless of whether or not they lead to nest formation (Roper, 1976). Similarly, the construction of a nest is not the proximate function of nest building in hens, moreover the behaviour itself is reinforcing (Hughes et al., 1989 ). The sows were observed to lie down between episodes of nest building. This behaviour has been interpreted as part of a feedback mechanism which controls nest building in sows (Baxter, 1982a). However, lying was associated more with the beginning and end of the nest building and not the period when nest activity was greatest. Furthermore, two sows in Group 1 did not lie down at all during nest building and could not have used udder comfort as a controlling factor of the behaviour. Baxter's (1982b) hypothesis, which suggests that nest building motivation in sows should be reduced by the presence of a pre-formed nest, seems to be an oversimplification. Nest building in sows is very complex behaviour (Vestergaard, 1984) and would seem to involve both internal and external causal factors (Jensen, 1989), not just the specific external motivation reducing factors suggested by Baxter (1982b). Farrowing accommodation should therefore enable sows to perform nest building to reduce the high levels of motivation. Nest material is essential to the behaviour and therefore to the environmental requirements of the sow at this time.
ACKNOWLEDGEMENTS
We wish to thank Mr. R.K. Howitt, Rowett Research Institute, for providing the experimental animals and the Cruden Foundation for a research scholarship.
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