L.J. WILKINS2
F. SHORT3
C.J. NICOL2
1Univ New South Wales, School Biol Sci, Armidale, NSW 2351, Australia
2Univ Bristol, Dept Vet Clin Sci, Bristol, Avon England, Australia
3ADAS Gleadthorpe, Mansfield, Notts England, Australia
In recent times, market forces, public attitudes and legislation have all lead to a largely worldwide decrease in the use of conventional cages for laying hens and a trend towards housing in large group systems. We investigated whether a large group system provided good welfare standards for all birds. By tagging birds with transponders, we found that a minority of hens in a large group were victimised; they were smaller than other birds, stayed under the perches where it was relatively dark, and showed extensive feather damage. The range in use of the area under the perches suggests that there are degrees of victimisation, rather than an all or nothing phenomenon. The design of large group systems should provide resources that allow successful social avoidance.
I. Introduction
In recent times, the use of conventional cages for laying hens has attracted public attention and, in Europe at least, legislative measures which have questioned their suitability as a type of housing which safeguards animal welfare. The result is that there is in Europe a present trend towards housing of laying hens in large group systems. Driving this trend has been the opinion that welfare is not safeguarded in battery cages. The latter view has largely been supported by scientific evidence- laying hens in conventional cages are prevented from expressing normal dust bathing, foraging, nesting and perching (Baxter, 1994).
Many large group systems for housing laying hens, in contrast, cater for the limitations imposed by cages by providing a large area, litter, nest boxes and perches. This has lead to the assumption, in our opinion unfounded, that laying hen welfare is protected in large group systems.
One of the most obvious causes for concern for the welfare of laying hens in large group systems is the unnaturally large group sizes. It is clear that hens do not try and establish a peck order in large groups (Hughes et al., 1997), resulting in low levels of aggression. However, in large groups there is the potential for a few individuals to receive disproportionate amounts of aggression, sometimes these birds are referred to as victimised birds, and these individuals could experience very poor levels of welfare. Research into the problem of victimised birds has been limited, mainly because it is very difficult to obtain detailed information on individual birds within a large group.
Our initial observations of hens in a perchery pen containing 1000 birds suggested that some birds remained under the perches and appeared to be repeatedly pecked by other birds, suggesting that these were victimised birds. In the present experiment we aimed to learn more about these particular birds. We developed a novel technique using a transponder system that automatically recorded the presence of tagged birds at various sites. This allowed continuous long-term measurement of the time that birds of known identity spent at particular areas of a perchery system. Subsequent recapture of the birds fitted with transponders also provided the opportunity to perform behavioural tests and measure physical condition thereby providing, as far as we are aware, a hitherto unattained level of information on the association between individual behaviour and location and condition in a large flock.
II. Methods
One thousand, non-beak-trimmed ISA Brown laying hens reared in large groups on litter were housed at 16 weeks of age in a perchery pen measuring 11.0 x 5.0 m which contained central 3-tier vertical wood perches (measuring 5 x 5 cm and providing 19.4 cm of perch per bird) up to a height of 1.8 m over wooden slats. The slatted area (175 cm wide) was the darkest part of the perchery and was relatively well delineated with two longitudinally placed feed troughs; eight support beams (approximately 40 x 30 cm) and the perch frame. Individual rollaway nest boxes lined with Astroturf (one nest box per 5 birds) were also provided.
A leg-band containing a transponder [MID Trovan®, Weymouth, U.K.] (approximately 10 g and a diameter of 2 cm) that emitted a unique identification number was placed on the leg of 80 birds at 33 weeks of age. Only birds on the floor were caught for tagging in an attempt to increase the likelihood of tagging victimised birds. Eight antennae measuring 50 x 50 cm were placed on the slats for 3 weeks and on the litter for a further 3 weeks. Antennae were placed about 1 m apart and 10 cm from the divider between the litter and slats so as to provide a reasonable spread in location. The bird identity, antenna location, date and time on the antenna were recorded each time a tagged bird walked on an antenna by a 486 PC running specialist software [Fingerprint®, Bristol, U.K.].
At 39 weeks of age birds were caught and each individual, of known identity, undertook a social avoidance test. The test involved placing the tagged bird at one end of a corridor measuring 2 x 0.5 m located in an adjacent room to the perchery. The bird was positioned with the body oriented at and as close to the side as possible. Next to the bird and outside the corridor was a wire cage (1.5 x 1.0 m) containing 5 birds from the same pen. The latency to move away from the group of birds and furthest distance reached in one minute were recorded.
Following the social avoidance test each bird was weighed. Feather scores were then taken for the head, neck, back and tail regions. These regions were chosen, as they were most likely to be pecked by other birds. One experienced experimenter assessed feather score on a scale of 1 (complete feather cover) to 5 (mostly devoid of feathers).
III. Results and discussion
There was a large variation in the daily duration recorded on the slats (i.e. the area under the perches) with eight birds never recorded on the slats and other birds recorded for up to three hours. On average birds spent 22.9±5.3 min/day on the slats from 11.6±2.5 observations. A median duration on the slats of 2.2 min/day from 2.5 observations indicated an exponential distribution as shown in Figure 1. This distribution suggests that some birds are spending disproportionate amounts of time on the slats, and support our initial observations that some birds use this area considerably.
On average birds spent 11.3±1.9 min/day on the litter from 6.2±2.0 observations. The time spent on litter was less variable than time spent on the slats, with maximum durations of 118.7 and 188.4 min/day respectively (Bartlett's variance test, F=15.2, P<0.0001). A significant positive correlation was found between time on the litter and slats (Spearman rank order correlation coefficient, r = +0.23, N=77, P<0.05), indicating that there was individual variation in use of floor areas as a whole irrespective of whether it was litter or slats.
The social avoidance test was undertaken to investigate if birds that spent considerable amounts of time on the slats were more likely to avoid other birds. On average birds took 30.6±2.6 s to move a maximum of 26.9±1.2 cm away from a group of hens in the avoidance test. Birds that moved sooner reached a further distance away from the group of birds (Pearson correlation coefficient, r =-0.48, N=69, P<0.001). However, the duration on the slats was not related to either the latency to move away from a group of hens (Pearson correlation coefficient, r =-0.01, N=69, NS) or the maximum distance reached (Pearson correlation coefficient, r =0.14, N=69, NS). Thus we found no evidence that birds that used the slats did so as a means of avoiding other birds, though it is unclear whether avoidance may be specific to the perchery, and hence not observable in our test.
In general, feather cover for the back and tail regions was very poor, with about half the birds displaying a score of 5 (mostly devoid of feathers). No birds showed complete feather cover for any region. As some body areas recorded few good scores, grouping of scores was undertaken to provide appropriate sample size for analyses. Birds with the worst feather cover for the back, tail and head regions spent significantly more time (P<0.05) on the slats than birds with better feather scores (Table 1), consistent with the idea that the former birds may have been receiving more pecks than the latter.
Birds that spent little or considerable amounts of time on the slats were lighter than birds that spent an intermediate amount of time on the slats (third order polynomial fitted line, regression analysis F1,68= 6.6, P<0.0001). A third order polynomial fitted line was also predicted bird weight following depopulation (regression analysis, F1,36 = 2.7, P<0.01). Thus birds that were recorded for little (or no) time on the slats and birds that spent large proportions of time on the slats weighed less than birds that spent intermediate amounts of time on the slats, and this was observed both at 39 weeks and at 72 weeks of age.
IV. Conclusion
A minority of hens in a large group stayed on the slats under the perches where it was relatively dark for a considerable amount of time. These birds were also smaller than other birds and showed extensive feather loss to the back and head regions suggesting that they may have been pecked repeatedly. Combined, the distribution, weight and feather cover of these birds suggests that they may be recipients of repeated aggressive acts, and show characteristics of victimised birds.
The range in use of the area under the perches suggests that there are degrees of victimisation, rather than an all or nothing phenomenon. Since this study was restricted to one housing system (perchery) at one farm, it would be worthwhile to further examine the phenomenon of victimisation in other systems.
References
Baxter, M.R. (1994). Veterinary Record, 134 (24): 614-619.
Hughes, B.O., Carmichael, N.L., Walker, A.W. and Grigor, P.N. (1997). Applied Animal Behaviour Science, 54: 215-234.
From Proceedings of the "17th Australian Poultry Science Symposium", New South Wales, Australia.
