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ENVIRONMENT, WELL-BEING, AND BEHAVIOR |
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* Swiss Federal Veterinary Office, Centre for Proper Housing: Poultry and Rabbits, Burgerweg 22, CH-3052 Zollikofen, Switzerland; Federal Veterinary Research Office Aulendorf, Löwenbreitestr. 18/20, 88326 Aulendorf, Germany; Swiss College of Agriculture, Länggasse 85, CH-3052 Zollikofen, Switzerland; and University of Ljubljana, Biotechnical Faculty, Department of Animal Science, Groblje 3, 1230 Dom
ale, Slovenia
1 Corresponding author: manjazupan{at}hotmail.com
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: laying hen • nest choice • prelaying behavior • nest layer • litter layer
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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From an evolutionary perspective, nesting and laying are important forms of behavior in laying hens. After domestication and intensive selection for nonbroodiness and high egg production, hens from modern commercial laying strains are reported to produce, on average, 326 eggs in a laying period (Damme, 2006). Each time a hen lays an egg, she seeks out potential nest sites (Hughes et al., 1989). Studies have shown that the prelaying activity level by hens increases in the hour or so before oviposition, which may facilitate reaching a suitable nest site such as a nest box. Hens are prepared to overcome different barriers, such as an unfamiliar bird (Freire et al., 1997), narrow gaps (Bubier, 1996), or push doors (Cooper and Appleby, 2003). From these and other studies, it has been concluded that hens are highly motivated to reach a nest box for laying. The majority of hens in commercial flocks lay in the nest boxes provided. Apparently, these hens perceive the nest boxes as suitable nesting places. However, at the onset of lay, the percentage of eggs laid on the floor is high, with hens laying the first several eggs outside the nests (Appleby and Smith, 1991). After 4 to 6 wk, the percentage drops to 1 to 2% (Häne, 1999).
If the nests that are provided are not used, it is possible that the hens do not perceive them as appropriate nest sites. Hens that do not have access to suitable nest sites may display elaborate sequences of nest-seeking and nest-building behavior during the hour preceding oviposition, showing signs of apparent frustration. Behaviors suggestive of frustration in laying hens include excessive locomotion or exploring activities (Cooper and Appleby, 1996), stereotyped pacing (Sherwin and Nicol, 1993; Yue and Duncan, 2003), and the occurrence of a specific vocalization, the gackel-call (Meijsser and Hughes, 1989; Zimmerman et al., 2000). In addition, a hen may respond physiologically in such a frustrating situation, retaining her egg in the shell gland (Hughes et al., 1986), which may result in an extracuticle layer of calcium on the eggshell (Reynard and Savory, 1999). All these signs indicate that the welfare of a hen may be compromised by lack of a nest site perceived to be suitable (Keeling, 2004).
Cooper and Appleby (1996) and Cronin et al. (2005, 2006) reported that particular hens do not use the nest boxes provided. Cooper and Appleby (1996) observed that these birds showed an increase in locomotion, inspections, and nest entries, and they interpreted these to mean that the birds behaved as if they perceived the nest box on offer to be less attractive than the other birds did. Cronin et al. (2005, 2006) concluded that these hens perceived the wire cage floor as a suitable location for laying in the same way that other hens perceived the provided nest boxes as suitable. This would mean that there were at least 2 perceptions of suitable nest sites within a flock of laying hens. Thus, a flock of commercial laying hens may consist of "nest layers" and "floor layers," as suggested in previous studies by McGibbon (1976) and Rietveld-Piepers et al. (1985).
To verify that there are different types of layers that both perceive their chosen nest site as appropriate, we conducted the following investigation. Individually housed laying hens were provided with 2 nest sites (a nest box and a litter tray) representing potential nest sites as available in the noncage systems. Because of its seclusion (Appleby and Smith, 1991), a nest box fulfills the needs of a hen to a high degree, so we expected the majority of hens to choose the nest box consistently after laying in the litter tray a few times. However, because of different perceptions, we expected some of the hens to use the litter tray consistently. On the basis of the results shown by Cooper and Appleby (1996), we formulated the hypothesis that nest layers would perform more settled prelaying behavior compared with litter-tray layers.
Furthermore, Cooper and Appleby (1995) reported that prelaying behavior changed with experience, whereas the motivation toward nesting remained unchanged. We also focused on the impact that laying experience has on the behavior. We predicted that once both nest sites were familiar to the hen and she was laying, the hen would show less restlessness and stay in the nest site for a longer time, but with fewer visits. The aim of this study was to investigate whether the choice of different nest locations entailed different prelaying behavior and whether this would have any implications for welfare.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Twenty-four non-beak-trimmed hens of a commercial hybrid strain (Lohmann Selected Leghorn) were litter-reared under commercial conditions until the age of 17 wk. Birds were then placed in a laying house, where they were observed from the beginning of the laying period in wk 20 until they reached the age of 26 wk.
Housing
At the age of 17 wk, birds were randomly selected and singly housed in test pens, each measuring 2 x 2 x 2.5 m (length x width x height), within a laying house. Test pens were arranged in 4 rows of 6. The front side of each test pen including the entrance door (88 x 238 cm) was made of spruce laths covered with wire mesh and reinforced with plywood board (height: 94 cm). The pens were separated by plywood walls. A net was attached above the pens, preventing birds from escaping. The floor consisted of plastic slats with integrated perches. Each pen was provided with a polystyrene block (25 x 25 x 15 cm) to stimulate the hens.
Each test pen had a nest-site area separated from the rest of the pen by a partition (2 m x 40 cm x 2.5 cm; Figure 1
) made of wooden faceplates. The partition contained 2 openings, each measuring 60 cm in length and 40 cm in height, whereas the rest was furnished with wire mesh. The activity area (i.e., the area between the entrance and the partition) contained a suspended trough, 30 cm in diameter, and a round metal perch 2 m long, 3.5 cm wide, and 60 cm above the floor, with 4 nipple drinkers with cups installed beneath. Access to water and commercial layers’ mash feed was ad libitum. Every alternate test pen had a window covered with wire mesh, 15 cm above the floor and 50 cm wide x 35 cm high, allowing acoustic as well as visual contact between 2 birds. In the nest-site area (approximately 1 m2), 2 equally sized nest sites were provided. In each corner, a plastic tray (40 x 40 x 10 cm) was placed, with either wood shavings (litter tray) or with a single nest box plus wood shavings (nest box). The nest box was constructed from wood and measured 28.5 x 32 x 36.5 cm. To prevent hens from seeing both nest sites at the same time when behind the partition, a 72-cm-high plywood board was placed in the middle of the nest-site area. In addition, above the partition and the plywood board, a net was hung to force the birds to use the openings and not to jump over the partition. During data collection, wood shavings were added to the plastic trays whenever necessary.
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Procedure and Behavioral Observations
During the experiment, the nest site where an egg had been laid was registered. Individual observations started after detection of the first egg laid. The behavior of each hen was videotaped for 24 h on 3 occasions: during the laying of the second or third, sixth or seventh, and 19th or 20th egg. These occasions were then taken as the 3 stages of laying experience at which data were collected. From the video recordings, the time of oviposition was identified for each hen, either by seeing an egg laid or by observing the transition from egg-laying posture (the hen stands up with raised head, bends her neck and moves her head toward the thorax, the tail feathers are bent backward) to normal posture. This was possible for all hens laying in the litter tray and for 12 of the 17 hens laying in the nest box. It was impossible to detect the time of oviposition of 5 nest layers because their laying position was in a well-covered corner of the nest so that the time of oviposition of these hens could not exactly be seen inside the nest box on the video recordings. The average time between oviposition and leaving the nest box for the 12 hens for which oviposition could be seen was taken to set the time of oviposition of the 5 hens for which the observation of oviposition was not possible. From the videotapes, prelaying behavior was collated for the hour before oviposition by using The Observer 3.0 software (Noldus Information Technology, Wageningen, the Netherlands). The behavior was recorded every 15 s by means of scan sampling and was classified by using the following categories: 1) foraging: ingestion (drinking; feeding—the head is above the feeder) and standing or locomotion with head down (the head is below the level of the highest point of the shoulder) in the activity area except on the perch; 2) resting: sitting or standing with grooming or retracted head and neck in the activity area; 3) exploring: standing or locomotion with head up (the head is above the level of the highest point of the shoulder) in the activity area, pecking at the polystyrene block, and standing or locomotion on the perch; 4) nest seeking: all behavior performed in the nest-site area and inspection of the partition from outside the nest-site area; and 5) nesting: staying in the nest site (both feet inside). Additionally, the number of nest-site visits (both feet in the nest site) and the time spent at the nest site (until exiting it with both feet out) during the final visit (when the egg was laid) were noted.
Statistical Analysis
Although the experiment was carried out with 24 hens, the statistical analysis included data from 15 hens (11 nest layers and 4 litter layers) fulfilling 2 criteria. First, at the 3 predetermined stages of laying experience, eggs were laid in either the nest box or the litter tray. Second, oviposition occurred either an hour after the twilight lights went on or later. The mean frequency of each behavior, the number of nest-site visits, and their duration were calculated for the 60 min preceding oviposition per hen per observed day. Two hens were excluded from the analysis because their third egg was laid on the floor slats, although the following collected eggs were found in the nest box. One hen was omitted because the behavior could not be observed for 60 min. Finally, a video recording failure was responsible for the omission of 6 hens.
The data residuals were tested for normality (PROC UNIVARIATE) and, when necessary, data were transformed to meet parametric requirements. The influence of the 2 fixed factors (type of layer with 2 levels, and laying experience with 3 stages) as well as of their interaction on prelaying behavior, the duration of the final nest visit, and the number of nest-site visits was analyzed by using the MIXED model procedure in SAS, version 9.1 (SAS Institute, 2002). The individual hens presented the random factor. When a significant effect in laying experience was found, the LSMEANS and ESTIMATE statements were used to estimate the contrasts between the stages of laying experience and to compare the means of the factor levels. Results are presented as mean ± SD, and all reported P-values are 2-tailed.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Seventeen of the 24 hens revealed themselves as nest layers (laying in the nest box) and 7 were litter layers (laying in the litter tray; i.e., 71 and 29%, respectively). The choice of a nest site was constant during data collection because no individual laid in both nest sites provided. Of the 504 eggs collected (21 per hen), 7 were found on the slats, with either a thin shell or none at all, or they were laid in the dark from the perch.
Laying Type
During the hour prior to oviposition, nest layers spent significantly less time exploring than did litter layers (nest layers: 13.0 ± 7.9%; litter layers: 22.8 ± 11.0%; F1,45 = 5.22, P = 0.04; Figure 2). However, nest layers tended to spend a higher proportion of time nesting than did litter layers (47.7 ± 16.5% and 32.8 ± 16.0%, respectively; F1,45 = 3.75, P = 0.07). No significant differences were found in the time performing foraging (14.0 ± 8.9%; F1,45 = 1.80, P = 0.20), resting (15.3 ± 12.5%; F1,45 = 0.00, P = 0.97), and nest seeking (11.4 ± 6.7%; F1,45 = 0.02, P = 0.90).
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The time spent in the nest site after the final entry and until leaving it again after oviposition was significantly different for the 2 layer types (F1,45 = 5.86, P = 0.03). Nest layers remained longer in the nest box than litter layers stayed in the litter tray (Figure 2
). When analyzed further, it was revealed that nest layers spent more time in the nest site after oviposition than litter layers did at their nest site (8 ± 8 min and 5 ± 3 min, respectively; F1,45 = 5.27, P = 0.04).
Laying Experience
There was a significant effect of laying experience on foraging (F2,45 = 4.42, P = 0.02), resting (F2,45 = 4.51, P = 0.02), and nest seeking (F2,45 = 7.97, P < 0.01). With increasing laying experience, hens performed more foraging and resting behavior (Figure 3). Additionally, hens showed a tendency to spend less time on exploring (F2,45 = 3.10, P = 0.06). On the other hand, time spent on nest seeking decreased with increasing laying experience. Laying experience affected neither nesting (F2,45 = 1.42, P = 0.28) nor the duration of the final nest-site visit (F2,45 = 0.85, P = 0.45).
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). The highest rate of visits was recorded with the second or third egg being laid, and the lowest was recorded with the 19th to 20th egg. |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The hens tested exhibited a strong conservatism in nest-site selection. Although some of the hens visited both nest sites, the eggs from each hen were exclusively found in either the nest box or the litter tray. The results suggest that hens were highly motivated to lay eggs in the chosen nest site. This suggestion was affirmed by Kruschwitz et al. (2007) in their studies requiring hens to push a door to obtain access to the chosen nest site. Hence, we concluded that laying hen flocks consist of at least 2 types, which consistently lay either in closed nest sites such as nests or in more open nest sites such as litter.
Assuming that the 2 types of layers experienced the same rearing environment and exhibited a similar level of motivation (Kruschwitz et al., 2007), it may be reasonable to suppose that floor layers do not lay in nest boxes, not because they are prohibited from doing so (Sherwin and Nicol, 1993), but because they simply do not want to. They may possibly behave so because of genetic differences among layers (McGibbon, 1976).
At the beginning of lay, litter layers behaved in a different manner from nest layers in the hour prior to oviposition. Even though they continuously chose the nest site and entered the litter tray as often as nest layers entered the nest box, they were, as expected, more unsettled in their activities. They performed more exploring behavior and less nesting behavior than did nest layers. This coincides with the recently presented findings of grouped-housed birds in furnished cages (Cronin et al., 2005, 2006) showing that nest layers behaved less actively than floor layers. Consequently, the observed increased performance of exploring in floor layers could be interpreted as an indication of frustrated behavior (Zimmerman et al., 2000). If this were true, we may presume that litter layers perceive their nest site as less appropriate than nest layers do the nest box. It is possible that the "desired" image laid down in the brains of litter layers matched the actual image of the nest site to a lesser degree than did that of nest layers (Hughes and Duncan, 1988). Although such an interpretation might be generally well accepted, we do not believe this argument.
Using the consumer demand theory approach, Kruschwitz et al. (2007) reported that the motivation to gain access to the preferred nest site did not vary between the 2 types of layers. Litter layers pushed a weighted door leading to the litter tray to the same degree as nest layers pushed a weighted door leading to the nest box. This led us to hypothesize that the increased prelaying locomotion seen in litter layers does not necessarily reflect enhanced frustration and poorer welfare, but a stronger motivation to reach the nest site.
Nevertheless, the observed variation in behavioral responses could be explained by a behavioral strategy that is thought to vary among individuals (Krebs and Kacelnik, 1991). It could be that with a choice of strategy, our hens behaved differently depending on the features of the nest site. In an open nest site, as in the litter tray, a hen has to be very attentive to detect predators or other disturbances. In the case of a threat, the hen is able to escape immediately and is not restricted. On the other hand, in a covered nest site, such as the nest box, a hen is better protected from external dangers, but her movement is restricted and she may have more difficulty in trying to escape a potential danger. The shorter time litter layers stayed in the nest site after laying could be explained by this argument. Other studies (Appleby et al., 1993; Struelens et al., 2005) have shown that the design of a chosen nest site may affect the behavior of hens.
As expected, with increasing laying experience, a greater frequency of foraging and resting behavior, paralleled by a lower frequency of nest seeking, was seen in the hens when approaching the point of lay. According to the motivational model of Hughes and Duncan (1988), this may be in response to an increase in a feeling of certainty and contentment when laying. The observed decline in the number of nest-site visits also supports this presumption. Furthermore, we found a change in neither the frequency of nesting nor the duration of the last nest-site visit with laying experience. It can be assumed that every time a hen lays an egg, a certain amount of time is needed to perform specific behavior patterns.
In commercial poultry houses where only one type of nest box is installed, some hens choose to lay on the floor. Assuming the belief that animals will choose environments in which they experience more contentment and less pain, fear, or other negative states (Duncan and Fraser, 1997), we suggest that the long-term preference for the litter tray can be interpreted to mean that our litter layers seemed to perceive the litter tray as a better place to lay than the nest box. If our litter layers resemble the floor layers in commercial housing systems, we suggest providing various types of nest boxes, corresponding to both types of layers, the floor layers and the nest layers. This may lead to a reduction in the problems with floor laying. In view of this, more work is needed, first to establish a nest-site design for floor layers, and second, to investigate our suggestion in practice.
In conclusion, we demonstrated the existence of different types of layers within a white commercial hybrid of laying hens with regard to nest-site preference. Although one view may be that the behavioral needs of the nest layers regarding nesting are fulfilled to a greater extent compared with the litter layers, we think that there is a varied behavioral strategy in hens, accompanied by a similar motivational level.
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ACKNOWLEDGMENTS |
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Received for publication October 6, 2006. Accepted for publication December 3, 2007.
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REFERENCES |
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