title / Importance of dustbathing in laying hens - is there a need to perform this behaviour?
/ MAFF
project code / AW0217
ministry of agriculture, fisheries and food CSG 15
Research and Development
Final Project Report
(Not to be used for LINK projects)
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Project title / Importance of dustbathing in laying hens - is there a need to perform this behaviour?
MAFF project code / AW0217
Contractor organisation and location / University of Bristol, Department of Clinical Veterinary Science, Langford House, Langford BS40 5DU
Total MAFF project costs / £ 151,363
Project start date / 01/04/97 / Project end date / 31/3/00
Executive summary (maximum 2 sides A4)
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CSG 15 (1/00) 2
Projecttitle / Importance of dustbathing in laying hens - is there a need to perform this behaviour?
/ MAFF
project code / AW0217
An experiment was conducted to examine the extent to which dustbathing on a litter substrate and dustbathing on concrete reduced underlying dustbathing motivation. The work showed that sham dustbathing behaviour did not reduce dustbathing motivation to the same degree after dustbathing in a more appropriate substrate. This shows that sham dustbathing cannot be considered an adequate substitute for real dustbathing.
Dustbathing behaviour was extremely rare when birds were transferred from familiar home pen environments into less familiar test pen environments. No modifications designed to increase the attractiveness of the test pens were totally successful. This demonstrates that dustbathing behaviour is highly affected by the familiarity of the environment. Other important factors that inhibited dustbathing were the absence of familiar conspecifics, and dustbaths that were smaller than the facilities that hens were accustomed to in their home pens.
Although birds must be familiar with the environment and substrate on which they dustbathe it was shown that there is considerable flexibility as to when such familiarity can develop and influence later adult behaviour. Young birds exposed to shavings litter at almost any stage of development (excluding the first 20 days of life) accepted and used litter shavings to dustbathe on as adults.
Individual differences in dustbathing behaviour are consistent over time, but depend upon the continued presence of social companions for their expression. Birds separated from companions are unlikely to dustbathe. However, if stocking density is too high then dustbathing behaviour can be disrupted.
The implications of these results for the design of dustbathing facilities in furnished cages and alternative systems are discussed.
CSG 15 (1/00) 2
Projecttitle / Importance of dustbathing in laying hens - is there a need to perform this behaviour?
/ MAFF
project code / AW0217
Scientific report (maximum 20 sides A4)
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CSG 15 (1/00) 2
Projecttitle / Importance of dustbathing in laying hens - is there a need to perform this behaviour?
/ MAFF
project code / AW0217
The aims of this programme were to investigate the importance of dustbathing as a behaviour of laying hens. The issue is of high strategic relevance as dustbathing is a behaviour that cannot be performed satisfactorily in a conventional battery cage. Recent developments in furnished cage design tend to incorporate a 'dustbath' although there is evidence that this is sometimes poorly used by the hens. Dustbathing behaviour is frequently observed on the cage floor (sham dustbathing), even when a separate 'dustbath' is provided within the cage. The provision of a dustbath within a furnished cage is controversial as it substantially increases the management effort required in comparison with furnished cages that provide only perches and nesting facilities. The new European Directive does not specify that birds must have a dustbath only that they should have satisfactory 'pecking and scratching' facilities. In alternative systems it is clear that not all birds are able to access the litter areas provided. In project AW0218 where birds were fitted with transponders, subsets of birds were identified that did not move far from slatted areas. Against this background it is crucial to determine just how important dustbathing behaviour is to the laying hen, and to consider the factors that influence the design of appropriate dustbathing facilities.
The aims of this project were:
1. To determine whether sham dustbathing is an adequate substitute for real dustbathing
2. To determine qualitative and quantitative differences in behavioural components of dustbathing bouts performed on litter or non-litter substrates. This objective was modified when very low levels of dustbathing behaviour were observed.
3. To obtain information on the birds' requirements for dustbathing performance.
4. To study the effects of litter versus non-litter rearing on subsequent dustbathing motivation
5. To investigate whether sham dustbathing occurs in an environment where no dusty of loose substrate is available. It was not possible to achieve this objective.
6. To study individual variation in motivational states in relation to the birds' reactions on gaining access to dust.
7. To examine the effects of bird density: are sham dustbaths necessarily short or is this feature of sham dustbaths an artefact of the ease with which they are disrupted?
8. To build a predictive motivational model and test it.
1. Is Sham-Dustbathing an Adequate Substitute for Real Dustbathing ?
This issue is of great importance given that hens in commercial systems are frequently observed to perform sham dustbathing. If sham dustbathing reduces dustbathing motivation to the same degree observed after dustbathing in an appropriate substrate then it may be considered an adequate substitute. However, if sham dustbathing does not reduce motivation sufficiently then the welfare of hens without access to appropriate substrates may be compromised. This questions was addressed by allowing hens to perform dustbathing on either litter or concrete areas, and then transferring them to litter pens to investigate the extent to which dustbathing motivation had been reduced.
The factors that influence dustbathing have been studied intensively in recent decades, revealing that a combination of internal and external factors affect a hen’s motivation to dustbathe. Dustbathing occurs on a cyclic pattern under normal conditions, but is not totally fixed and is affected by, for example, environmental temperature, radiant heat, light and social stimulation (Duncan et al. 1998). Dustbathing occurs as a vacuum (or sham) behaviour even in the apparent absence of salient stimuli such as dust or feathers. A vacuum behaviour is defined as “a clearly recognisable, usually stereotyped, behaviour, performed in the absence of those external stimuli normally associated with it” (Hughes & Duncan 1988). Vacuum behaviours are similar to many stereotyped fixated responses in that they are driven by internal factors and appear not to be dependent on feedback from the environment. The finding that hens in furnished cages vacuum dustbath on the wire floor even when substrate was available (Lindberg & Nicol 1997) led to the hypothesis that sham dustbathing might be an adequate substitute for real dustbathing.
The lack of clear cut results in studies of preference and demand for a dustbathing substrate (e.g.Widowski and Duncan, 1998) may be because fowl use litter not just for dustbathing but also for foraging and pecking (Petherick et al. 1995), which under some circumstances may override dustbathing. Several functional consequences of dustbathing have been proposed, such as control of feather lipids (van Liere & Bokma 1987), maintenance of plumage thermoregulatory function (van Liere 1992) and removal of ectoparasites (Borchelt et al. 1973). However, the persistent performance of vacuum dustbathing by litter-deprived hens shows that such functional consequences are not essential to elicit or maintain the behaviour.
Previous studies have shown a positive correlation between amount of dustbathing and the duration of the preceding litter deprivation. This suggests that deprivation of a dusty substrate increases the motivation to dustbathe and performance of dustbathing acts to reduce the motivation. Van Liere & Wiepkema (1992) kept hens in litter-free conditions while also preventing them from sham dustbathing. This was achieved by having a floor constructed from a frame work of wooden sticks, so that there was no level surface. Thwarting of sham dustbathing resulted in a significant increase in the daily total time spent sham dustbathing when deprivation ended. The question we set out to answer in this experiment was whether dustbathing motivation was reduced by performance of sham dustbathing. Our approach was to test birds at specific times after performance of sham or real dustbathing. We hypothesised that dustbathing motivation would be reduced during the period following the behaviour and would then gradually rise until its next occurrence. There are several possible scenarios, with different predictions:
1. Vacuum dustbathing does not reduce motivation at all. The only reason the bird does not express continuous dustbathing is because other motivations (e.g. feeding) compete with that of dustbathing. This means that the bird is in a state of permanent high motivation.
2. Vacuum dustbathing reduces motivation but not to the same extent as real dustbathing. The bird is frequently in a state of high motivation.
3. A third possibility is that vacuum dustbathing reduces motivation to the same extent as real dustbathing. In this case, the bird’s motivation returns to baseline when performing the vacuum or real dustbathing and then gradually rises to the level where the behaviour is again performed.
When a bird is transferred from an environment where only vacuum dustbathing is possible, to a litter surface where real dustbathing can be performed, the above hypotheses would lead to the following predictions:
1. Constant high motivation means that the bird will show almost instant dustbathing on transfer.
2. There would be a strong possibility that the bird dustbathes with a short latency.
3. The bird would be no more likely to perform real dustbathing than a bird kept on litter pre-testing.
However, there may also be additional effects of external causal factors, such as a substrate with high incentive value. Efficient external causal factors act by lowering the threshold for performance and could affect these predictions. Therefore, even under condition 3, a bird transferred from litter-free conditions to a litter substrate is expected to dustbathe with a shorter latency than a bird kept on litter throughout, although not as quickly as under conditions 1 and 2.
METHODS
This experiment used forty ISA Brown hens, obtained from a commercial supplier, which were 41 weeks old at the beginning of the experiment and had been reared and kept on woodshavings deep litter. They were placed in groups of 5 in eight home pens of 1.5 x 2 m (6000 cm2 per hen or 1.7 hens per m2). All birds were legbanded and had a small notch cut into the back or tail plumage (this had been shown in a pilot study to have no observable effect on the hens’ behaviour) for individual identification on the black and white videos. Each pen was equipped with one bell drinker and one ad libitum tube feeder with layers' mash. The light regimen was 12L:12D (lights on 0630 hours, lights off 1830 hours) and the temperature 17-20oC. Four of the pens had 5 cm depth of woodshavings litter on the concrete floor (‘litter-kept’ hens) and four pens had 1.5 x 1.8 m wire floors (raised approximately 25 cm above the floor) with an area of 1.5 x 0.2 m of solid concrete floor, giving 600 cm2 per hen of non-wire floor (‘wire-kept’ hens). Two test pens in an adjacent room were provided with fresh woodshavings litter on the floor but were otherwise identical to the home pens in construction, size, lighting, temperature, feeders and drinkers. Fresh woodshavings were used in this experiment for practical reasons and to ensure the substrate was similar in all home and test pens. Large woodshavings are not the most preferred substrate for dustbathing behaviour (see e.g. van Liere 1992) but these woodshavings were relatively fine, allowing some penetration of the plumage. Wood shavings are also the most commonly available substrate in deep litter systems. All observations were by 24 hour time lapse video recording.
A dustbathing bout was defined as commencing at the first vertical wingshake and ending in the minute in which the last dustbathing element occurred without more than a ten minute lapse between it and the preceding element (Kruijt 1964, Vestergaard et al. 1990). During a bout, hens also showed rubbing, pecking and billraking behaviour. Behavioural sequences consisting only of sitting with billraking and pecking were not scored as dustbaths, while bouts of rubbing were not observed to occur without preceding vertical wingshakes.
During the 10 days preceding testing, we recorded the ‘baseline’ levels of dustbathing in the home pens, observing the frequency of real dustbathing bouts performed by the litter-kept hens and vacuum dustbathing bouts by the wire-kept hens. There was strong diurnal rhythm to the birds' home pen dustbathing behaviour (Fig 1), and the behaviour was strongly socially facilitated. In 85% of observations 3 or more of the 5 hens in a group dustbathed simultaneously, and only one session of group dustbathing was observed per day. Birds that did not join in group dustbathing generally did not dustbathe at all that day. The hens were given four tests over a 24 day period. Two tests were given approximately 24 hours after hens had performed dustbathing in their home pen. Each test lasted 2 hours, and began between 1100 and 1300h. The other two tests were given approximately 4 hours after hens had performed dustbathing in their home pen. Each test lasted 2 hours and began at approximately 1500h. As the behaviour of hens within the group was not independent, all tests were conducted at the group level, although hens could be individually identified.
Figure 1
Each group to be tested was transferred from its home pen to the test pen by opening the appropriate doors and slowly walking behind the flock from one pen to the other. Birds were not caught or carried, to avoid alarming them during the transfer. Tests ended at 1715 hours since no dustbaths were observed to commence after 1700 hours, although if a dustbath was in progress at this time, return was delayed until dustbathing had ceased.