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Feather eating in layer pullets and its possible role in the aetiology of feather pecking damage
Applied Animal Behaviour Science 65 Ž1999. 73–85
Feather eating in layer pullets and its possible role in the aetiology of feather pecking damage Dorothy E.F. McKeegan
a,)
, C.J. Savory
b
a b
EnÕironment and Welfare DiÕision, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK National Centre for Poultry Studies, Scottish Agricultural College, AuchincruiÕe, Ayr, KA6 5HW, UK Accepted 29 April 1999
Abstract Feather pecking and cannibalism remain serious welfare and economic problems in the egg industry. Previous studies have suggested a role for feather eating in the development of pecking damage, but no definite link has been shown. This study examined feather eating and its possible relationship with damaging pecking in pen-housed ISA Brown layer pullets. Collection and measurement of loose feathers in sample plots on pen floors Ža bimodal distribution allowed characterisation of feathers as either ‘short’ or ‘long’., and examination of faecal droppings Žeaten feathers are not digested. were used to assess levels of feather eating. Feather eating was rarely observed directly, but the presence of feather material in a high proportion of droppings Žup to 48%. suggested that the behaviour was common. Pecking damage occurred in 5 out of 12 pens and was related to feather eating as indicated by both depletion of feathers on pen floors and feather material in droppings. Short feathers were eaten preferentially, and an absence of short feathers was associated with an increase in partially eaten long feathers. The 4 pens exhibiting the highest levels of feather eating were those in which severe outbreaks of feather pecking and cannibalism occurred around the onset of lay. A second experiment, examining age-related changes in feather eating behaviour between 6 and 26 weeks of age, showed that feathers cast during a juvenile moult at 9–11 weeks were depleted by varying levels of feather eating over subsequent weeks. Numbers of short feathers available on pen floors decreased with age while numbers of partially eaten feathers increased, as did proportions of droppings containing feathers. Levels of feather eating were lower than in the first experiment, and there was no pecking damage. It is concluded that once feather eating has become established, a low availability of preferred short feathers on pen floors may cause feather eating and pecking to be redirected to other birds. High levels of feather eating by growing birds Žperhaps above a threshold level. may
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D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
be associated with feather pecking and cannibalism around the onset of lay. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Feather eating; Feather pecking; Pica; Domestic fowl; Development
1. Introduction Feather eating has been observed in a few species of birds, namely parrots ŽHollmann, 1997., grebes ŽSimmons, 1956; Piersma and Van Eerden, 1989. and both commercial layer ŽSavory and Mann, 1997a. and bantam ŽSavory and Griffiths, 1997; Savory and Mann, 1997b. strains of domestic fowl. Feather eating in great crested grebes has been studied in detail where the behaviour is known to have a specialized function relating to feeding. The ingested feathers add bulk to the stomach contents, enabling indigestible remains of the fish diet to be ejected as pellets ŽPiersma and Van Eerden, 1989.. The function of feather eating in domestic fowls is unclear, since this granivorous species does not possess the ability to break down keratin in the digestive tract and feathers cannot, therefore, have any nutritive value. This suggests that feather eating in the domestic fowl is a form of pica Žconsumption of non-nutritive material with no apparent function.. Studies of pica in birds have concentrated on inappropriate ingestion of materials with harmful consequences, for example in ostriches ŽStewart, 1994; Samson, 1996. and broiler type chickens ŽHutson, 1978.. It is possible that the likelihood of pica may be increased for species Žsuch as the domestic fowl. in which the ingestion of grit to aid digestion is adaptive. No previous studies have attempted to quantify the extent of feather eating in poultry, a behaviour that may be widespread. Feather eating is examined here in the context of its possible relationship with feather pecking and cannibalism. Earlier work ŽSavory and Mann, 1997a,b. suggested a role for feather eating in the development of feather pecking, although no definite link was shown. Injurious pecking is a serious welfare and economic problem in the egg industry, for which there is currently no reliable solution. The aetiology of pecking damage is not fully understood, and studies have been hampered by the unpredictability of this behaviour, particularly in commercial laying strains. Previous studies strongly suggest that feather pecking represents a redirection of ground pecking, in either foraging or dustbathing contexts ŽSavory, 1995.. Cloacal cannibalism, the most severe form of pecking damage, often occurs around the onset of lay, and may be related to hormonal changes occurring at that time ŽHughes, 1973.. Environmental factors such as stocking density, light intensity and food form ŽSavory et al., 1999. are known to increase the likelihood of damaging pecking, and there is evidence that genetic variation, between both individuals ŽBlokhuis et al., 1993; Kjaer and Sorensen, 1997; Savory and Griffiths, 1997. and strains ŽBlokhuis and Beuving, 1993. is important. This study aimed to determine the extent of feather eating behaviour in both juvenile and adult commercial layer pullets, and investigated any possible relationship between feather eating and damaging pecking. During a large experiment designed to investigate the hormonal basis of behavioural development in pullets, it was noticed that there was wide variation between pens in the availability of loose feathers on the floor. This led to
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
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an experiment designed to estimate the extent of feather eating in juvenile birds by measuring floor feather availability and examining faecal droppings for evidence of feather material. Information from behaviour observations and plumage damage scores, carried out as part of the larger study, allowed the relationship between feather eating and feather pecking to be investigated, yielding the results described in Experiment 1. Experiment 2 was designed to give more comprehensive information about age-related changes in feather eating behaviour, in juvenile birds and also after the onset of lay, by monitoring floor feather availability from 6–26 weeks of age. It was not possible to relate feather eating to feather pecking in Experiment 2, since no damaging pecking occurred in either juveniles or adults.
2. Methods 2.1. Experiment 1: Feather eating and damaging pecking in juÕenile pullets 2.1.1. Subjects and husbandry 144 ISA Brown layer pullets were randomly allocated on the day of hatch to 12 groups of 12 chicks and placed in 12 pens measuring 1.6 m = 1.2 m, allowing approximately 1600 cm2 floor space for each bird. The pens were in a windowless house and each had solid walls, wood shavings litter, one bell-type drinker and one food hopper. Pelleted food and water were provided ad libitum, and all groups received a layer starter diet Ž205 grkg crude protein, 11.5 MJrkg metabolisable energy. for the first 6 weeks of life followed by a layer grower diet Ž164 grkg crude protein, 11.8 MJrkg metabolisable energy.. The photoperiod was 10 h until 14 weeks, and was then increased by 1 h in each of the next 4 weeks until it was 14 h at 18 weeks. An additional 100 W light was present in each pen, average light intensities at floor level ranged from 84 to 144 lx Žoverall mean 116 lx.. Daily temperatures ranged from 10 to 228C Žoverall mean 178C.. Observations were carried out from 5–14 weeks of age. 2.1.2. BehaÕiour obserÕations Detailed observations of bird to bird pecking were carried out weekly. Birds in each group were identified by unique coloured leg rings and were observed individually for one minute, twice weekly Žone morning and one afternoon.. During each minute observation, every peck and feather pull given or received by the subject was recorded on a check sheet. Pecks were defined as either aggressive Žforceful, aimed at the head or back of the recipient, rarely repeated, recipient immediately withdraws. or non-aggressive Žgentle or vigorous, aimed at any part of the body, often repeated, recipient may eventually withdraw.. Feather eating events along with their source Žfor example from the litter floor or another bird. were also recorded. Data from morning and afternoon sessions were combined to give total pecking counts for each pen for each week. 2.1.3. Pecking damage scores The birds were inspected for pecking damage every 2 weeks. The plumage was examined and damage to each body area was scored as follows: 0, no damage; 1, slight
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feather damagerloss with no bare skin; 2, damage with - 1 cm2 bare skin; 3, moderate damage with up to 5 = 5 cm2 bare skin, or - 1 cm2 bare skin with minor haemorrhage; 4, significant damage with ) 5 = 5 cm2 bare skin, or up to 5 = 5 cm2 bare skin with minor haemorrhage; 5, significant Ž1–2 cm2 . haemorrhage, or ) 5 = 5 cm2 bare skin with minor Ž- 1 cm2 . haemorrhage. Each body area was scored separately and the values were summed to give a total for each bird. 2.1.4. Feather aÕailability At 12 weeks of age the availability of loose feathers on the floor of each pen was estimated. All feathers within two 0.5 = 0.5 m quadrats placed at random on the pen floor were collected, counted and measured to the nearest cm. An overall frequency distribution of feather lengths Žtotals across pens. was produced ŽFig. 1.. The bimodal distribution of feather lengths allowed the categorisation of feathers as ‘short’ Žup to 10 cm. or ‘long’ Ž) 10 cm.. It was also noted whether feathers were ‘downy’ Ž) 75% of length downy. and whether they had been partially eaten. This was indicated by a particular type of damage to feathers, with larger primary feathers being most affected. Damage resulting from feather eating was usually seen as one or more notches Žor in some cases large areas. missing from the vane of the feather, with the edges around the missing area appearing rough and uneven. 2.1.5. Faecal feather material At 14 weeks of age, 100 faecal droppings of approximately equal size were collected from the floor of each pen Žmany of these had been trodden on and flattened, and may have been incomplete.. The droppings were broken and examined for evidence of feather material Žwhich is not digested and can be clearly seen within droppings.. Numbers of droppings containing feather material were recorded, no attempt was made to quantify the feather material.
Fig. 1. Overall frequency distribution of feather lengths from loose feathers collected from all pens at 12 weeks of age in Experiment 1.
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
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2.2. Experiment 2: Age-related changes in feather eating and feather aÕailability 2.2.1. Subjects and husbandry A second batch of 144 ISA Brown layer pullets were used, and maintained in the same pens with the same set-up as Experiment 1 to 26 weeks of age. The birds received a layer producer diet Ž158 grkg crude protein, 11.2 MJrkg metabolisable energy. ad libitum from 16 to 26 weeks of age. Ambient temperatures were higher than in Experiment 1 Ždue to the time of year. and ranged from 12 to 318C Žoverall mean 218C.. 2.2.2. BehaÕiour obserÕations These were carried out as in Experiment 1, except non-aggressive pecks were categorised as ‘gentle’ or ‘ vigorous’. 2.2.3. Pecking damage scores These were carried out as in Experiment 1. 2.2.4. Feather aÕailability From 6 to 26 weeks of age, the availability of loose feathers on the floor of each pen was estimated weekly, using the quadrat method described for Experiment 1. At 12, 18, 22 and 26 weeks the feathers were removed from the pen and measured before being returned, in all other weeks they were counted in the pen without being measured. As in Experiment 1, as feathers were being measured it was noted if they were downy or partially eaten. 2.2.5. Faecal feather material At 10, 14, 18 and 22 weeks, the percentage of droppings containing feathers was determined using the method described for Experiment 1. Faecal droppings could not be examined at 26 weeks because poor litter quality made it impossible to collect individual droppings. 2.2.6. Statistical analysis A Spearman rank correlation matrix for the 7 variables measured in Experiment 1 was carried out. In Experiment 2, proportions of droppings containing feather material and available loose feathers on pen floors at the same age were correlated. Student’s t-tests Žpaired and unpaired. were carried out within and between experiments to make comparisons of floor feather counts, percentages of droppings containing feathers Žafter transformation to the logistic scale., and observations of behaviour. All statistical analysis was carried out using Genstat Version 4.1.
3. Results 3.1. Experiment 1: Feather eating and damaging pecking in juÕenile pullets There was much variation between pens in total numbers of non-aggressive pecks observed ŽTable 1., ranging from 36 to 173 Žoverall mean 91.4.. Few aggressive pecks
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Table 1 Numbers of pecks, feather eating events and mean damage scores from 5–14 weeks, and feather material in droppings Ž14 weeks. and floor feather counts Ž12 weeks. in Experiment 1
Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6 Pen 7 Pen 8 Pen 9 Pen 10 Pen 11 Pen 12 Mean
Nonaggressive pecksrpulls
Aggressive pecks
Feather eating events
Pecking damage scores
% Droppings containing feathers
Short feathers
Long feathers
131 57 60 57 98 173 36 133 44 75 82 151 91.4
19 2 2 0 1 7 5 3 2 3 1 0 3.8
9 11 5 4 8 5 17 7 0 2 2 7 6.4
11.7 0 0 0 0 4.1 1.9 0.3 0 1.3 0 0 1.6
41 31 16 9 12 48 22 15 19 29 7 35 23.7
13 31 105 237 192 2 26 92 122 3 192 23 86.5
22 12 43 34 52 26 35 21 34 23 29 21 29.3
were observed, ranging from 0 to 19 Žoverall mean 3.8., accounting for only a small proportion of total pecks Ž3.9% across all pens.. Pecking damage occurred in 5 of the 12 pens, and was greatest in Pen 1, less severe in Pens 6, 7 and 10, and minimal in Pen 8. Overall, the tail was most affected by pecking damage, accounting for 89% of total scores. There was no mortality due to pecking damage in juveniles. Feathers were rarely seen to be eaten, and numbers of observed feather eating events ranged from 0 to 17 Žoverall mean 6.4.. However, feather material was found to be present in faecal droppings collected from all 12 pens sampled at 14 weeks of age, with levels between 7 and 48% Žoverall mean 23.7%.. Numbers of short feathers on the floor, sampled at 12 weeks, varied much more between pens ŽCoefficient of Variation ŽCV. s 0.97. than did numbers of long feathers ŽCV s 0.37.. Thus, the overall variation between pens in numbers of loose feathers was mainly due to variation in the number of short feathers available. Cross correlations ŽSpearman rank. among the 7 variables measured are shown in Table 2. There were 6 significant results. Numbers of short feathers on the floor were highly correlated, negatively, with percentages of droppings containing feathers. No such correlation was found with long feathers. Mean pecking damage scores were correlated negatively with numbers of short feathers on the floor, and positively with percentages of droppings containing feathers. Numbers of aggressive pecks were correlated positively with pecking damage scores and proportions of droppings containing feathers, and negatively with numbers of short feathers on the floor. During behaviour observations, feathers were seen to be eaten in 6 situations. Eating feathers from the pen floor Žlitter. was most common, accounting for 38% of the 77 observed feather eating events. 34% of feathers eaten were caught in the air, while 19%
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Table 2 Spearman rank correlations of measurements made from 5–14 weeks in Experiment 1 r Values
Non-aggressive
Aggressive
Feather eat
Peck damage
Droppings
Short
Aggressive Feather eat Peck damage Droppings Short Long
0.115 0.035 0.289 0.333 y0.411 y0.395
0.292 0.904UUU 0.573U y0.695U y0.165
0.298 0.337 y0.255 y0.173
0.585U y0.750UU y0.203
y0.904UUU y0.498
0.496
U
P - 0.05;
UU
P - 0.01;
UUU
P - 0.001.
were removed from other birds. The drinker, feeder, self Žwhile preening. and stealing from other birds were the rarest sources of eaten feathers accounting for between 1% and 5% of the total. Proportions of downy feathers collected from the floor ranged between 0 and 30% of the total number Žoverall mean 19.3%., all of which were in the short category. Numbers of downy feathers were correlated negatively with numbers of partially eaten feathers Ž P - 0.05, Spearman rank, n s 12.. Partially eaten feathers accounted for between 0 and 57% Žoverall mean 11.6%. of feathers collected, and were present in both long and short categories. 3.2. Experiment 2: Age-related changes in feather eating and feather aÕailability Numbers of non-aggressive pecks observed ranged between 41 and 148 across pens Žoverall mean 65.5., of which an average of 24% were vigorous, while aggressive pecks ranged between 0 and 6 Žoverall mean 1.9.. Observed feather eating events ranged from 1 to 12 Žoverall mean 3.8.. No pecking damage was recorded. Temporal changes in the availability of loose feathers on pen floors varied between pens, but followed a pattern indicated by the mean curve ŽFig. 2a.. Numbers of feathers on the floor were low at 6 weeks of age, ranging from 3 to 15 Žoverall mean 9.5.. Numbers then increased slightly to 9 weeks, after which very large increases were observed with a maximal level of 581 feathers counted in Pen 1 at 12 weeks. Mean numbers of feathers decreased most rapidly between 18 and 22 weeks of age, and by 26 weeks had returned to low levels, ranging from 11 to 48 feathers Žoverall mean 27.8.. Fig. 2b shows mean changes in floor feather counts across all pens and illustrates that the biggest increases in floor feather counts occurred between the ages of 9 and 14 weeks, with a steady decrease in numbers of feathers on the floor between 16 and 26 weeks. Not all pens contributed to means after 18 weeks, a water leak necessitated the changing of litter in 2 pens, and one pen was removed from the experiment as a result of injurious pecking. Proportions of downy feathers tended to decrease with age ŽTable 3., and were significantly lower at 22 weeks Ž9.8% of collected feathers. than at 18 weeks Ž26%, P - 0.01, paired t-test, n s 9.. At 26 weeks only 7.7% of collected feathers were
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Fig. 2. a. Mean floor feather counts in each week from 6 to 26 weeks of age in Experiment 2; b. Mean changes in floor feather counts from week to week, from 6 to 26 weeks of age in Experiment 2.
downy. By contrast, proportions of partially eaten feathers increased with age ŽTable 3., from 1.2% at 12 weeks, to significantly higher levels at 18 Ž8.7%, P - 0.01., 22 Ž43.5%, P - 0.001. and 26 weeks Ž71.7%, P - 0.01.. At 12 weeks of age a bimodal distribution of feather length frequencies similar to that seen in Experiment 1 ŽFig. 1. was apparent. The distribution at 18 weeks ŽFig. 3a. showed a decrease in the availability of short feathers, but there were significantly more long feathers than at 12 weeks of age Ž P - 0.01, paired t-test, n s 11.. By 22 weeks ŽFig. 3b., the availability of feathers was further reduced, with significantly fewer short feathers than at 18 weeks Ž P - 0.01, paired t-test, n s 9.. At 26 weeks ŽFig. 3c. levels
Table 3 Mean percentages of downy and partially eaten feathers collected at ages 12, 18, 22 and 26 weeks in Experiment 2 Mean Ž"SE. % feathers collected
Downy Partially eaten
12 weeks
18 weeks
22 weeks
26 weeks
23.9"2.4 1.2"3.5
26.2"3.9 8.7"14.0
9.8"2.8 43.5"25.9
7.7"1.5 71.7"22.1
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
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Fig. 3. Overall frequency distribution of feather lengths from loose feathers collected from all pens at ages 18, 22 and 26 weeks in Experiment 2; a. 18 weeks; b. 22 weeks; c. 26 weeks.
of both short and long feathers were significantly lower than at 22 weeks Ž P - 0.05 and P - 0.01, respectively, paired t-test, n s 9.. Proportions of droppings containing feathers tended to increase with age ŽTable 4., ranging from 3 to 21% at 10 weeks, 4 to 30% at 14 weeks, 10 to 29% at 18 weeks and 11 to 27% at 22 weeks. Sequential comparisons between the four ages showed that levels of feather material in droppings were significantly higher at 14 weeks than at 10 weeks Ž P - 0.001, paired t-test, n s 12., but not at 18 or 22 weeks. Correlations ŽSpearman rank. between proportions of droppings containing feather material and available loose feathers on pen floors at the same age were negative and significant at all ages, and strongest at 18 weeks ŽTable 4.. 3.3. Comparisons between experiments 1 and 2 There were significantly less total available feathers Ž P - 0.05, t-test, n s 24. and a higher proportion of partially eaten feathers Ž P - 0.05, t-test, n s 24. in Experiment 1 compared to Experiment 2 at 12 weeks of age. At 14 weeks, the mean proportion of
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Table 4 Incidence of feather material in droppings at ages 10, 14, 18 and 22 weeks, and their correlations ŽSpearman rank. with counts of floor feather availability at the same age in Experiment 2. ŽU indicates missing value. % Droppings containing feather material
Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6 Pen 7 Pen 8 Pen 9 Pen 10 Pen 11 Pen 12 Mean"SE Correlation Ž r . P value
10 weeks
14 weeks
18 weeks
22 weeks
3 3 4 5 11 21 14 6 5 13 2 10 8.1"1.7 y0.600 - 0.05
8 9 4 13 27 30 17 7 13 23 8 25 15.3"2.6 y0.821 - 0.01
U
U
10 13 17 23 29 17 15 12 19 13 23 17.4"1.7 y0.925 - 0.001
13 11 24 14 25 23 18 23 U U
27 19.7"2.0 y0.646 - 0.05
droppings containing feathers was greater in Experiment 1 than in Experiment 2 Ž P s 0.084, t-test, n s 24..
4. Discussion In Experiment 1, when pecking damage occurred in 5 of the 12 pens, there was no significant correlation between damage scores and numbers of non-aggressive pecks observed. This is probably because most of the latter are gentle and non-damaging, ŽSavory, 1995.. If gentle pecks and vigorous pecksrpulls had been recorded separately, the damage scored in some pens might have been reflected by higher counts of the vigorous type. Although the behavioural sample for each individual bird was fairly small, care was take to ensure that observations were as representative as possible and analysis was carried out on a per pen basis. The highly significant correlation found between pecking damage scores and numbers of aggressive pecks observed in Experiment 1 was unexpected, and may be misleading. Aggressive pecks accounted for a only small proportion of the total pecks observed in this experiment, and the correlation is strongly influenced by the fact that 2 pens Ž1 and 6. had the highest levels of both pecking damage and aggressive pecking ŽTable 1.. Previous work investigating the relationship between feather pecking and social rank was inconclusive ŽWood-Gush and Rowland, 1973.. Numbers of observed feather eating events were low and variable, and as a result were not correlated significantly with feather material in droppings or floor feather
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counts. Where feather eating was observed, the floor litter was the most common source of eaten feathers, followed by feathers caught in the air as they floated to the ground, particularly after some disturbance in the pen caused them to be thrown into the air. A few birds were seen to eat their own feathers immediately after they were dislodged by preening, and on one occasion a feather was eaten after it had been stolen from a pen-mate. In Experiment 1, variation in numbers of short feathers on pen floors accounted for the observed differences in feather availability, suggesting that short feathers were eaten preferentially. Experiment 2 also showed that in all pens, to a greater or lesser extent, short feathers were depleted by feather eating over several weeks, and that long feathers were partially eaten when short feathers were no longer available. All feather sizes were found to be partially eaten, except very small Ž1–2 cm. and completely downy feathers. There were fewer downy feathers in pens where feather eating was most common, but since downy feathers tended to fall into the ‘short’ category, it is difficult to ascertain whether a preference for downy feathers over other types of short feathers was present. It is possible that downy feathers, which tend to have a softer rachis, were easier to swallow and were therefore preferred. The changes observed in feather length frequency distributions with age in Experiment 2 also support the assertion that short feathers are eaten preferentially, since this was clearly the part of the distribution curve which was most affected over time ŽFig. 3.. The distributions at 22 and 26 weeks also show reductions in the numbers of long feathers available, but this can be explained by the prevalence of partially eaten feathers at these ages Žranging from 33% to 100% of all feathers measured at 26 weeks.. Feathers Žintact or otherwise. were measured as they were collected, with no attempt made to estimate their original size. Long feathers, for example, originally measuring 14–16 cm, could be measured as 8–10 cm fragments, with only the thickest Žand stiffest. part of the quill Žcalamus. and rachis remaining. The rate at which feathers were cast by birds in Experiment 2 could not be measured, making it impossible to determine a rate of feather eating on the basis of floor feather counts. However, it seems reasonable to assume that moulting rate would have been roughly equal across pens containing the same number of birds. The moult resulting in the largest increase of loose feathers was age related Žoccurring between 9 and 11 weeks., but it is possible that slight differences in the rate of development of individuals could have caused variation in feather availability. Numbers of feathers counted could possibly have been affected by litter turnover and bird movement; only feathers on the litter surface were counted. In both experiments, levels of feather material detected in droppings were higher than levels reported previously for bantams ŽSavory and Mann, 1997b.. Feathers that had passed through the digestive system often had a yellow appearance making them distinguishable from uneaten feather material, and care was taken to ensure that only feather material contained within faecal fragments was counted. It is likely that the proportion of droppings containing feathers was an underestimate, since very small feathers were not detectable in droppings. In Experiment 2, levels of feather material in droppings increased with age ŽTable 4., presumably reflecting the cumulative nature of the measurement. Thus, the droppings examined could have been produced at any time
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prior to collection, and would not necessarily reflect the amount of feather eating then. Nevertheless, strong negative correlations between feather material in droppings and floor feather availability were observed at all ages ŽTable 4., suggesting that feather eating continued throughout the experiment and accounted for the observed depletion of feathers on the floor. The pecking damage seen in juveniles was not severe, and occurred mainly between 5 and 10 weeks of age, as reported previously ŽHughes, 1973.. Damaging pecking at this age tends to be directed at the tail and preen gland, and the back region in front of the preen gland is usually the first part of the body to be denuded of feathers ŽSavory and Mann, 1997b.. The feathers there are accessible, easily plucked, of a size preferred for eating Ž2–6 cm., and a liberal supply of preen oil due to their proximity to the preen gland may make them especially attractive. Comparisons between Experiments 1 and 2 can only be done to 14 weeks of age. In Experiment 2, no feather pecking or cannibalism took place, but high levels of aggressive pecking after the onset of lay led to some ‘bullied’ birds being culled Žas a result of pecking injuries to the head, neck or comb or weight loss.. True aggressive pecking is thought to be related more closely to social dominance than to feather eating and will not be discussed here. Feather eating took place in both experiments, but reached higher levels in Experiment 1. In Experiment 2, there were more loose feathers available at 12 weeks of age, less feathers in droppings and less partially eaten feathers than in Experiment 1. This suggests a possible threshold effect, where limited availability of loose feathers to eat at a particular age may redirect attention towards the feathers of pen mates. Recent work ŽJohnsen and Vestergaard, 1997. emphasised the importance of early rearing conditions Žlitter substrate. on the development of feather pecking behaviour, and it is possible that feather availability on litter in early life may affect subsequent pecking behaviour. The notion that feather eating may be a ‘precursor’ to subsequent damaging pecking is supported by the results of Experiment 1, where pens with the highest levels of feather eating and pecking damage as juveniles were also those where outbreaks of feather pecking and cannibalism occurred around the onset of lay. In conclusion, the data presented here show an association between feather eating and feather pecking, but are not sufficient to establish a causal link. In Experiment 1, damaging pecking was related to increased feather eating as indicated by both depletion of short feathers on pen floors and the presence of feather material in droppings. In Experiment 2, a moult at 9–11 weeks of age increased the number of feathers available, which were then depleted by feather eating. Short feathers were eaten preferentially, and long feathers were partially eaten when short feathers became scarce. It is proposed that once feather eating has become established, a low availability of suitably sized feathers may cause feather eating and pecking to be redirected towards other birds. In Experiment 1, high levels of feather eating as juveniles Žperhaps above a threshold level. were associated with outbreaks of feather pecking and cannibalism in adulthood. The relevance of feather eating in development of damaging pecking in commercial situations is unclear. However, since commercial layer pullets are usually reared on litter floors, with access to moulted feathers, the role of feather eating in development of feather pecking merits further study.
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Acknowledgements D.E.F. McKeegan is a British Egg Marketing Board Trust scholar and this work forms part of her thesis for a Ph.D. degree at the University of Edinburgh.
References Blokhuis, H.J., Beuving, G., 1993. Feather pecking and other characteristics in two lines of laying hen. In: Savory, C.J., Hughes, B.O. ŽEds.., Proceedings of the 4th European Symposium on Poultry Welfare, Potters Bar, Universities Federation for Animal Welfare, pp. 145–157. Blokhuis, H.J., Beuving, G., Rommers, J.M., 1993. Individual variation of stereotyped pecking in laying hens. In: Savory, C.J., Hughes, B.O. ŽEds.., Proceedings of the 4th European Symposium on Poultry Welfare, Potters Bar, Universities Federation for Animal Welfare, pp. 266–267. Hollmann, P., 1997. Behaviour disorders in psittacines: 1. Signs and causes. Tierarztliche Praxis 25, 233–240. Hughes, B.O., 1973. The effect of implanted gonadal hormones on feather pecking and cannibalism in pullets. Br. Poult. Sci. 14, 341–348. Hutson, L.R., 1978. Pica in eight-week-old chicken broilers. Vet. Rec. 103, 186–187. Johnsen, P.F., Vestergaard, K.S., 1997. Influence of early rearing conditions on the development of feather pecking and cannibalism in domestic fowl. In: Hemsworth, P.H., Kostal, L. ŽEds.., Proceedings of the 31st International Congress of the ISAE, Prague, 13–16 August, 1997, p. 81. Kjaer, J.B., Sorensen, P., 1997. Feather pecking behaviour in White Leghorns, a genetic study. Br. Poult. Sci. 38, 333–341. Piersma, T., Van Eerden, M.R., 1989. Feather eating in Great Crested Grebes Podiceps cristatus: a unique solution to the problems of debris and gastric parasites in fish-eating birds. Ibis 131 Ž4., 477–486. Samson, J., 1996. Behavioural problems of farmed ostriches in Canada. Can. Vet. J. 37, 412–414. Savory, C.J., 1995. Feather pecking and cannibalism. Worlds Poult. Sci. J. 51, 215–219. Savory, C.J., Griffiths, J.D., 1997. Individual variation in rates of giving and receiving feather pecks in bantams, and some behaviour correlates. In: Koene, P., Blokhuis, H.J. ŽEds.., Proceedings of the 5th European Symposium on Poultry Welfare, pp. 109–110. Savory, C.J., Mann, J.S., 1997a. Behavioural development in groups of pen-housed pullets in relation to genetic strain, age and food form. Br. Poult. Sci. 38, 38–47. Savory, C.J., Mann, J.S., 1997b. Development of pecking damage in growing bantams in relation to floor litter substrate and plumage colour. Br. Poult. Sci., Supplement S13–S14. Savory, C.J., Mann, J.S., McLeod, M.G., 1999. Incidence of pecking damage in growing bantams in relation to food form, group size, stocking density, dietary tryptophan concentration, and dietary protein source. Br. Poult. Sci. Žin press.. Simmons, K.E.L., 1956. Feather eating and pellet-formation in the Great Crested Grebe. Br. Birds 49, 432–435. Stewart, J.S., 1994. Ostrich behaviour and behavioural problems. In: Proceedings of the Association of Avian Veterinarians, pp. 104–109. Wood-Gush, D.G.M., Rowland, C.G., 1973. Allopreening in the domestic fowl. Rev. Comp. Animal 7, 83–91.
Feather eating in layer pullets and its possible role in the aetiology of feather pecking damage Dorothy E.F. McKeegan
a,)
, C.J. Savory
b
a b
EnÕironment and Welfare DiÕision, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK National Centre for Poultry Studies, Scottish Agricultural College, AuchincruiÕe, Ayr, KA6 5HW, UK Accepted 29 April 1999
Abstract Feather pecking and cannibalism remain serious welfare and economic problems in the egg industry. Previous studies have suggested a role for feather eating in the development of pecking damage, but no definite link has been shown. This study examined feather eating and its possible relationship with damaging pecking in pen-housed ISA Brown layer pullets. Collection and measurement of loose feathers in sample plots on pen floors Ža bimodal distribution allowed characterisation of feathers as either ‘short’ or ‘long’., and examination of faecal droppings Žeaten feathers are not digested. were used to assess levels of feather eating. Feather eating was rarely observed directly, but the presence of feather material in a high proportion of droppings Žup to 48%. suggested that the behaviour was common. Pecking damage occurred in 5 out of 12 pens and was related to feather eating as indicated by both depletion of feathers on pen floors and feather material in droppings. Short feathers were eaten preferentially, and an absence of short feathers was associated with an increase in partially eaten long feathers. The 4 pens exhibiting the highest levels of feather eating were those in which severe outbreaks of feather pecking and cannibalism occurred around the onset of lay. A second experiment, examining age-related changes in feather eating behaviour between 6 and 26 weeks of age, showed that feathers cast during a juvenile moult at 9–11 weeks were depleted by varying levels of feather eating over subsequent weeks. Numbers of short feathers available on pen floors decreased with age while numbers of partially eaten feathers increased, as did proportions of droppings containing feathers. Levels of feather eating were lower than in the first experiment, and there was no pecking damage. It is concluded that once feather eating has become established, a low availability of preferred short feathers on pen floors may cause feather eating and pecking to be redirected to other birds. High levels of feather eating by growing birds Žperhaps above a threshold level. may
)
C orresponding author. [email protected]
Tel.:
q 44-131-527-4212;
fax:
q 44-131-440-0434;
0168-1591r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 5 9 1 Ž 9 9 . 0 0 0 5 1 - 9
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D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
be associated with feather pecking and cannibalism around the onset of lay. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Feather eating; Feather pecking; Pica; Domestic fowl; Development
1. Introduction Feather eating has been observed in a few species of birds, namely parrots ŽHollmann, 1997., grebes ŽSimmons, 1956; Piersma and Van Eerden, 1989. and both commercial layer ŽSavory and Mann, 1997a. and bantam ŽSavory and Griffiths, 1997; Savory and Mann, 1997b. strains of domestic fowl. Feather eating in great crested grebes has been studied in detail where the behaviour is known to have a specialized function relating to feeding. The ingested feathers add bulk to the stomach contents, enabling indigestible remains of the fish diet to be ejected as pellets ŽPiersma and Van Eerden, 1989.. The function of feather eating in domestic fowls is unclear, since this granivorous species does not possess the ability to break down keratin in the digestive tract and feathers cannot, therefore, have any nutritive value. This suggests that feather eating in the domestic fowl is a form of pica Žconsumption of non-nutritive material with no apparent function.. Studies of pica in birds have concentrated on inappropriate ingestion of materials with harmful consequences, for example in ostriches ŽStewart, 1994; Samson, 1996. and broiler type chickens ŽHutson, 1978.. It is possible that the likelihood of pica may be increased for species Žsuch as the domestic fowl. in which the ingestion of grit to aid digestion is adaptive. No previous studies have attempted to quantify the extent of feather eating in poultry, a behaviour that may be widespread. Feather eating is examined here in the context of its possible relationship with feather pecking and cannibalism. Earlier work ŽSavory and Mann, 1997a,b. suggested a role for feather eating in the development of feather pecking, although no definite link was shown. Injurious pecking is a serious welfare and economic problem in the egg industry, for which there is currently no reliable solution. The aetiology of pecking damage is not fully understood, and studies have been hampered by the unpredictability of this behaviour, particularly in commercial laying strains. Previous studies strongly suggest that feather pecking represents a redirection of ground pecking, in either foraging or dustbathing contexts ŽSavory, 1995.. Cloacal cannibalism, the most severe form of pecking damage, often occurs around the onset of lay, and may be related to hormonal changes occurring at that time ŽHughes, 1973.. Environmental factors such as stocking density, light intensity and food form ŽSavory et al., 1999. are known to increase the likelihood of damaging pecking, and there is evidence that genetic variation, between both individuals ŽBlokhuis et al., 1993; Kjaer and Sorensen, 1997; Savory and Griffiths, 1997. and strains ŽBlokhuis and Beuving, 1993. is important. This study aimed to determine the extent of feather eating behaviour in both juvenile and adult commercial layer pullets, and investigated any possible relationship between feather eating and damaging pecking. During a large experiment designed to investigate the hormonal basis of behavioural development in pullets, it was noticed that there was wide variation between pens in the availability of loose feathers on the floor. This led to
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
75
an experiment designed to estimate the extent of feather eating in juvenile birds by measuring floor feather availability and examining faecal droppings for evidence of feather material. Information from behaviour observations and plumage damage scores, carried out as part of the larger study, allowed the relationship between feather eating and feather pecking to be investigated, yielding the results described in Experiment 1. Experiment 2 was designed to give more comprehensive information about age-related changes in feather eating behaviour, in juvenile birds and also after the onset of lay, by monitoring floor feather availability from 6–26 weeks of age. It was not possible to relate feather eating to feather pecking in Experiment 2, since no damaging pecking occurred in either juveniles or adults.
2. Methods 2.1. Experiment 1: Feather eating and damaging pecking in juÕenile pullets 2.1.1. Subjects and husbandry 144 ISA Brown layer pullets were randomly allocated on the day of hatch to 12 groups of 12 chicks and placed in 12 pens measuring 1.6 m = 1.2 m, allowing approximately 1600 cm2 floor space for each bird. The pens were in a windowless house and each had solid walls, wood shavings litter, one bell-type drinker and one food hopper. Pelleted food and water were provided ad libitum, and all groups received a layer starter diet Ž205 grkg crude protein, 11.5 MJrkg metabolisable energy. for the first 6 weeks of life followed by a layer grower diet Ž164 grkg crude protein, 11.8 MJrkg metabolisable energy.. The photoperiod was 10 h until 14 weeks, and was then increased by 1 h in each of the next 4 weeks until it was 14 h at 18 weeks. An additional 100 W light was present in each pen, average light intensities at floor level ranged from 84 to 144 lx Žoverall mean 116 lx.. Daily temperatures ranged from 10 to 228C Žoverall mean 178C.. Observations were carried out from 5–14 weeks of age. 2.1.2. BehaÕiour obserÕations Detailed observations of bird to bird pecking were carried out weekly. Birds in each group were identified by unique coloured leg rings and were observed individually for one minute, twice weekly Žone morning and one afternoon.. During each minute observation, every peck and feather pull given or received by the subject was recorded on a check sheet. Pecks were defined as either aggressive Žforceful, aimed at the head or back of the recipient, rarely repeated, recipient immediately withdraws. or non-aggressive Žgentle or vigorous, aimed at any part of the body, often repeated, recipient may eventually withdraw.. Feather eating events along with their source Žfor example from the litter floor or another bird. were also recorded. Data from morning and afternoon sessions were combined to give total pecking counts for each pen for each week. 2.1.3. Pecking damage scores The birds were inspected for pecking damage every 2 weeks. The plumage was examined and damage to each body area was scored as follows: 0, no damage; 1, slight
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D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
feather damagerloss with no bare skin; 2, damage with - 1 cm2 bare skin; 3, moderate damage with up to 5 = 5 cm2 bare skin, or - 1 cm2 bare skin with minor haemorrhage; 4, significant damage with ) 5 = 5 cm2 bare skin, or up to 5 = 5 cm2 bare skin with minor haemorrhage; 5, significant Ž1–2 cm2 . haemorrhage, or ) 5 = 5 cm2 bare skin with minor Ž- 1 cm2 . haemorrhage. Each body area was scored separately and the values were summed to give a total for each bird. 2.1.4. Feather aÕailability At 12 weeks of age the availability of loose feathers on the floor of each pen was estimated. All feathers within two 0.5 = 0.5 m quadrats placed at random on the pen floor were collected, counted and measured to the nearest cm. An overall frequency distribution of feather lengths Žtotals across pens. was produced ŽFig. 1.. The bimodal distribution of feather lengths allowed the categorisation of feathers as ‘short’ Žup to 10 cm. or ‘long’ Ž) 10 cm.. It was also noted whether feathers were ‘downy’ Ž) 75% of length downy. and whether they had been partially eaten. This was indicated by a particular type of damage to feathers, with larger primary feathers being most affected. Damage resulting from feather eating was usually seen as one or more notches Žor in some cases large areas. missing from the vane of the feather, with the edges around the missing area appearing rough and uneven. 2.1.5. Faecal feather material At 14 weeks of age, 100 faecal droppings of approximately equal size were collected from the floor of each pen Žmany of these had been trodden on and flattened, and may have been incomplete.. The droppings were broken and examined for evidence of feather material Žwhich is not digested and can be clearly seen within droppings.. Numbers of droppings containing feather material were recorded, no attempt was made to quantify the feather material.
Fig. 1. Overall frequency distribution of feather lengths from loose feathers collected from all pens at 12 weeks of age in Experiment 1.
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
77
2.2. Experiment 2: Age-related changes in feather eating and feather aÕailability 2.2.1. Subjects and husbandry A second batch of 144 ISA Brown layer pullets were used, and maintained in the same pens with the same set-up as Experiment 1 to 26 weeks of age. The birds received a layer producer diet Ž158 grkg crude protein, 11.2 MJrkg metabolisable energy. ad libitum from 16 to 26 weeks of age. Ambient temperatures were higher than in Experiment 1 Ždue to the time of year. and ranged from 12 to 318C Žoverall mean 218C.. 2.2.2. BehaÕiour obserÕations These were carried out as in Experiment 1, except non-aggressive pecks were categorised as ‘gentle’ or ‘ vigorous’. 2.2.3. Pecking damage scores These were carried out as in Experiment 1. 2.2.4. Feather aÕailability From 6 to 26 weeks of age, the availability of loose feathers on the floor of each pen was estimated weekly, using the quadrat method described for Experiment 1. At 12, 18, 22 and 26 weeks the feathers were removed from the pen and measured before being returned, in all other weeks they were counted in the pen without being measured. As in Experiment 1, as feathers were being measured it was noted if they were downy or partially eaten. 2.2.5. Faecal feather material At 10, 14, 18 and 22 weeks, the percentage of droppings containing feathers was determined using the method described for Experiment 1. Faecal droppings could not be examined at 26 weeks because poor litter quality made it impossible to collect individual droppings. 2.2.6. Statistical analysis A Spearman rank correlation matrix for the 7 variables measured in Experiment 1 was carried out. In Experiment 2, proportions of droppings containing feather material and available loose feathers on pen floors at the same age were correlated. Student’s t-tests Žpaired and unpaired. were carried out within and between experiments to make comparisons of floor feather counts, percentages of droppings containing feathers Žafter transformation to the logistic scale., and observations of behaviour. All statistical analysis was carried out using Genstat Version 4.1.
3. Results 3.1. Experiment 1: Feather eating and damaging pecking in juÕenile pullets There was much variation between pens in total numbers of non-aggressive pecks observed ŽTable 1., ranging from 36 to 173 Žoverall mean 91.4.. Few aggressive pecks
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Table 1 Numbers of pecks, feather eating events and mean damage scores from 5–14 weeks, and feather material in droppings Ž14 weeks. and floor feather counts Ž12 weeks. in Experiment 1
Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6 Pen 7 Pen 8 Pen 9 Pen 10 Pen 11 Pen 12 Mean
Nonaggressive pecksrpulls
Aggressive pecks
Feather eating events
Pecking damage scores
% Droppings containing feathers
Short feathers
Long feathers
131 57 60 57 98 173 36 133 44 75 82 151 91.4
19 2 2 0 1 7 5 3 2 3 1 0 3.8
9 11 5 4 8 5 17 7 0 2 2 7 6.4
11.7 0 0 0 0 4.1 1.9 0.3 0 1.3 0 0 1.6
41 31 16 9 12 48 22 15 19 29 7 35 23.7
13 31 105 237 192 2 26 92 122 3 192 23 86.5
22 12 43 34 52 26 35 21 34 23 29 21 29.3
were observed, ranging from 0 to 19 Žoverall mean 3.8., accounting for only a small proportion of total pecks Ž3.9% across all pens.. Pecking damage occurred in 5 of the 12 pens, and was greatest in Pen 1, less severe in Pens 6, 7 and 10, and minimal in Pen 8. Overall, the tail was most affected by pecking damage, accounting for 89% of total scores. There was no mortality due to pecking damage in juveniles. Feathers were rarely seen to be eaten, and numbers of observed feather eating events ranged from 0 to 17 Žoverall mean 6.4.. However, feather material was found to be present in faecal droppings collected from all 12 pens sampled at 14 weeks of age, with levels between 7 and 48% Žoverall mean 23.7%.. Numbers of short feathers on the floor, sampled at 12 weeks, varied much more between pens ŽCoefficient of Variation ŽCV. s 0.97. than did numbers of long feathers ŽCV s 0.37.. Thus, the overall variation between pens in numbers of loose feathers was mainly due to variation in the number of short feathers available. Cross correlations ŽSpearman rank. among the 7 variables measured are shown in Table 2. There were 6 significant results. Numbers of short feathers on the floor were highly correlated, negatively, with percentages of droppings containing feathers. No such correlation was found with long feathers. Mean pecking damage scores were correlated negatively with numbers of short feathers on the floor, and positively with percentages of droppings containing feathers. Numbers of aggressive pecks were correlated positively with pecking damage scores and proportions of droppings containing feathers, and negatively with numbers of short feathers on the floor. During behaviour observations, feathers were seen to be eaten in 6 situations. Eating feathers from the pen floor Žlitter. was most common, accounting for 38% of the 77 observed feather eating events. 34% of feathers eaten were caught in the air, while 19%
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
79
Table 2 Spearman rank correlations of measurements made from 5–14 weeks in Experiment 1 r Values
Non-aggressive
Aggressive
Feather eat
Peck damage
Droppings
Short
Aggressive Feather eat Peck damage Droppings Short Long
0.115 0.035 0.289 0.333 y0.411 y0.395
0.292 0.904UUU 0.573U y0.695U y0.165
0.298 0.337 y0.255 y0.173
0.585U y0.750UU y0.203
y0.904UUU y0.498
0.496
U
P - 0.05;
UU
P - 0.01;
UUU
P - 0.001.
were removed from other birds. The drinker, feeder, self Žwhile preening. and stealing from other birds were the rarest sources of eaten feathers accounting for between 1% and 5% of the total. Proportions of downy feathers collected from the floor ranged between 0 and 30% of the total number Žoverall mean 19.3%., all of which were in the short category. Numbers of downy feathers were correlated negatively with numbers of partially eaten feathers Ž P - 0.05, Spearman rank, n s 12.. Partially eaten feathers accounted for between 0 and 57% Žoverall mean 11.6%. of feathers collected, and were present in both long and short categories. 3.2. Experiment 2: Age-related changes in feather eating and feather aÕailability Numbers of non-aggressive pecks observed ranged between 41 and 148 across pens Žoverall mean 65.5., of which an average of 24% were vigorous, while aggressive pecks ranged between 0 and 6 Žoverall mean 1.9.. Observed feather eating events ranged from 1 to 12 Žoverall mean 3.8.. No pecking damage was recorded. Temporal changes in the availability of loose feathers on pen floors varied between pens, but followed a pattern indicated by the mean curve ŽFig. 2a.. Numbers of feathers on the floor were low at 6 weeks of age, ranging from 3 to 15 Žoverall mean 9.5.. Numbers then increased slightly to 9 weeks, after which very large increases were observed with a maximal level of 581 feathers counted in Pen 1 at 12 weeks. Mean numbers of feathers decreased most rapidly between 18 and 22 weeks of age, and by 26 weeks had returned to low levels, ranging from 11 to 48 feathers Žoverall mean 27.8.. Fig. 2b shows mean changes in floor feather counts across all pens and illustrates that the biggest increases in floor feather counts occurred between the ages of 9 and 14 weeks, with a steady decrease in numbers of feathers on the floor between 16 and 26 weeks. Not all pens contributed to means after 18 weeks, a water leak necessitated the changing of litter in 2 pens, and one pen was removed from the experiment as a result of injurious pecking. Proportions of downy feathers tended to decrease with age ŽTable 3., and were significantly lower at 22 weeks Ž9.8% of collected feathers. than at 18 weeks Ž26%, P - 0.01, paired t-test, n s 9.. At 26 weeks only 7.7% of collected feathers were
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Fig. 2. a. Mean floor feather counts in each week from 6 to 26 weeks of age in Experiment 2; b. Mean changes in floor feather counts from week to week, from 6 to 26 weeks of age in Experiment 2.
downy. By contrast, proportions of partially eaten feathers increased with age ŽTable 3., from 1.2% at 12 weeks, to significantly higher levels at 18 Ž8.7%, P - 0.01., 22 Ž43.5%, P - 0.001. and 26 weeks Ž71.7%, P - 0.01.. At 12 weeks of age a bimodal distribution of feather length frequencies similar to that seen in Experiment 1 ŽFig. 1. was apparent. The distribution at 18 weeks ŽFig. 3a. showed a decrease in the availability of short feathers, but there were significantly more long feathers than at 12 weeks of age Ž P - 0.01, paired t-test, n s 11.. By 22 weeks ŽFig. 3b., the availability of feathers was further reduced, with significantly fewer short feathers than at 18 weeks Ž P - 0.01, paired t-test, n s 9.. At 26 weeks ŽFig. 3c. levels
Table 3 Mean percentages of downy and partially eaten feathers collected at ages 12, 18, 22 and 26 weeks in Experiment 2 Mean Ž"SE. % feathers collected
Downy Partially eaten
12 weeks
18 weeks
22 weeks
26 weeks
23.9"2.4 1.2"3.5
26.2"3.9 8.7"14.0
9.8"2.8 43.5"25.9
7.7"1.5 71.7"22.1
D.E.F. McKeegan, C.J. SaÕoryr Applied Animal BehaÕiour Science 65 (1999) 73–85
81
Fig. 3. Overall frequency distribution of feather lengths from loose feathers collected from all pens at ages 18, 22 and 26 weeks in Experiment 2; a. 18 weeks; b. 22 weeks; c. 26 weeks.
of both short and long feathers were significantly lower than at 22 weeks Ž P - 0.05 and P - 0.01, respectively, paired t-test, n s 9.. Proportions of droppings containing feathers tended to increase with age ŽTable 4., ranging from 3 to 21% at 10 weeks, 4 to 30% at 14 weeks, 10 to 29% at 18 weeks and 11 to 27% at 22 weeks. Sequential comparisons between the four ages showed that levels of feather material in droppings were significantly higher at 14 weeks than at 10 weeks Ž P - 0.001, paired t-test, n s 12., but not at 18 or 22 weeks. Correlations ŽSpearman rank. between proportions of droppings containing feather material and available loose feathers on pen floors at the same age were negative and significant at all ages, and strongest at 18 weeks ŽTable 4.. 3.3. Comparisons between experiments 1 and 2 There were significantly less total available feathers Ž P - 0.05, t-test, n s 24. and a higher proportion of partially eaten feathers Ž P - 0.05, t-test, n s 24. in Experiment 1 compared to Experiment 2 at 12 weeks of age. At 14 weeks, the mean proportion of
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Table 4 Incidence of feather material in droppings at ages 10, 14, 18 and 22 weeks, and their correlations ŽSpearman rank. with counts of floor feather availability at the same age in Experiment 2. ŽU indicates missing value. % Droppings containing feather material
Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6 Pen 7 Pen 8 Pen 9 Pen 10 Pen 11 Pen 12 Mean"SE Correlation Ž r . P value
10 weeks
14 weeks
18 weeks
22 weeks
3 3 4 5 11 21 14 6 5 13 2 10 8.1"1.7 y0.600 - 0.05
8 9 4 13 27 30 17 7 13 23 8 25 15.3"2.6 y0.821 - 0.01
U
U
10 13 17 23 29 17 15 12 19 13 23 17.4"1.7 y0.925 - 0.001
13 11 24 14 25 23 18 23 U U
27 19.7"2.0 y0.646 - 0.05
droppings containing feathers was greater in Experiment 1 than in Experiment 2 Ž P s 0.084, t-test, n s 24..
4. Discussion In Experiment 1, when pecking damage occurred in 5 of the 12 pens, there was no significant correlation between damage scores and numbers of non-aggressive pecks observed. This is probably because most of the latter are gentle and non-damaging, ŽSavory, 1995.. If gentle pecks and vigorous pecksrpulls had been recorded separately, the damage scored in some pens might have been reflected by higher counts of the vigorous type. Although the behavioural sample for each individual bird was fairly small, care was take to ensure that observations were as representative as possible and analysis was carried out on a per pen basis. The highly significant correlation found between pecking damage scores and numbers of aggressive pecks observed in Experiment 1 was unexpected, and may be misleading. Aggressive pecks accounted for a only small proportion of the total pecks observed in this experiment, and the correlation is strongly influenced by the fact that 2 pens Ž1 and 6. had the highest levels of both pecking damage and aggressive pecking ŽTable 1.. Previous work investigating the relationship between feather pecking and social rank was inconclusive ŽWood-Gush and Rowland, 1973.. Numbers of observed feather eating events were low and variable, and as a result were not correlated significantly with feather material in droppings or floor feather
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counts. Where feather eating was observed, the floor litter was the most common source of eaten feathers, followed by feathers caught in the air as they floated to the ground, particularly after some disturbance in the pen caused them to be thrown into the air. A few birds were seen to eat their own feathers immediately after they were dislodged by preening, and on one occasion a feather was eaten after it had been stolen from a pen-mate. In Experiment 1, variation in numbers of short feathers on pen floors accounted for the observed differences in feather availability, suggesting that short feathers were eaten preferentially. Experiment 2 also showed that in all pens, to a greater or lesser extent, short feathers were depleted by feather eating over several weeks, and that long feathers were partially eaten when short feathers were no longer available. All feather sizes were found to be partially eaten, except very small Ž1–2 cm. and completely downy feathers. There were fewer downy feathers in pens where feather eating was most common, but since downy feathers tended to fall into the ‘short’ category, it is difficult to ascertain whether a preference for downy feathers over other types of short feathers was present. It is possible that downy feathers, which tend to have a softer rachis, were easier to swallow and were therefore preferred. The changes observed in feather length frequency distributions with age in Experiment 2 also support the assertion that short feathers are eaten preferentially, since this was clearly the part of the distribution curve which was most affected over time ŽFig. 3.. The distributions at 22 and 26 weeks also show reductions in the numbers of long feathers available, but this can be explained by the prevalence of partially eaten feathers at these ages Žranging from 33% to 100% of all feathers measured at 26 weeks.. Feathers Žintact or otherwise. were measured as they were collected, with no attempt made to estimate their original size. Long feathers, for example, originally measuring 14–16 cm, could be measured as 8–10 cm fragments, with only the thickest Žand stiffest. part of the quill Žcalamus. and rachis remaining. The rate at which feathers were cast by birds in Experiment 2 could not be measured, making it impossible to determine a rate of feather eating on the basis of floor feather counts. However, it seems reasonable to assume that moulting rate would have been roughly equal across pens containing the same number of birds. The moult resulting in the largest increase of loose feathers was age related Žoccurring between 9 and 11 weeks., but it is possible that slight differences in the rate of development of individuals could have caused variation in feather availability. Numbers of feathers counted could possibly have been affected by litter turnover and bird movement; only feathers on the litter surface were counted. In both experiments, levels of feather material detected in droppings were higher than levels reported previously for bantams ŽSavory and Mann, 1997b.. Feathers that had passed through the digestive system often had a yellow appearance making them distinguishable from uneaten feather material, and care was taken to ensure that only feather material contained within faecal fragments was counted. It is likely that the proportion of droppings containing feathers was an underestimate, since very small feathers were not detectable in droppings. In Experiment 2, levels of feather material in droppings increased with age ŽTable 4., presumably reflecting the cumulative nature of the measurement. Thus, the droppings examined could have been produced at any time
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prior to collection, and would not necessarily reflect the amount of feather eating then. Nevertheless, strong negative correlations between feather material in droppings and floor feather availability were observed at all ages ŽTable 4., suggesting that feather eating continued throughout the experiment and accounted for the observed depletion of feathers on the floor. The pecking damage seen in juveniles was not severe, and occurred mainly between 5 and 10 weeks of age, as reported previously ŽHughes, 1973.. Damaging pecking at this age tends to be directed at the tail and preen gland, and the back region in front of the preen gland is usually the first part of the body to be denuded of feathers ŽSavory and Mann, 1997b.. The feathers there are accessible, easily plucked, of a size preferred for eating Ž2–6 cm., and a liberal supply of preen oil due to their proximity to the preen gland may make them especially attractive. Comparisons between Experiments 1 and 2 can only be done to 14 weeks of age. In Experiment 2, no feather pecking or cannibalism took place, but high levels of aggressive pecking after the onset of lay led to some ‘bullied’ birds being culled Žas a result of pecking injuries to the head, neck or comb or weight loss.. True aggressive pecking is thought to be related more closely to social dominance than to feather eating and will not be discussed here. Feather eating took place in both experiments, but reached higher levels in Experiment 1. In Experiment 2, there were more loose feathers available at 12 weeks of age, less feathers in droppings and less partially eaten feathers than in Experiment 1. This suggests a possible threshold effect, where limited availability of loose feathers to eat at a particular age may redirect attention towards the feathers of pen mates. Recent work ŽJohnsen and Vestergaard, 1997. emphasised the importance of early rearing conditions Žlitter substrate. on the development of feather pecking behaviour, and it is possible that feather availability on litter in early life may affect subsequent pecking behaviour. The notion that feather eating may be a ‘precursor’ to subsequent damaging pecking is supported by the results of Experiment 1, where pens with the highest levels of feather eating and pecking damage as juveniles were also those where outbreaks of feather pecking and cannibalism occurred around the onset of lay. In conclusion, the data presented here show an association between feather eating and feather pecking, but are not sufficient to establish a causal link. In Experiment 1, damaging pecking was related to increased feather eating as indicated by both depletion of short feathers on pen floors and the presence of feather material in droppings. In Experiment 2, a moult at 9–11 weeks of age increased the number of feathers available, which were then depleted by feather eating. Short feathers were eaten preferentially, and long feathers were partially eaten when short feathers became scarce. It is proposed that once feather eating has become established, a low availability of suitably sized feathers may cause feather eating and pecking to be redirected towards other birds. In Experiment 1, high levels of feather eating as juveniles Žperhaps above a threshold level. were associated with outbreaks of feather pecking and cannibalism in adulthood. The relevance of feather eating in development of damaging pecking in commercial situations is unclear. However, since commercial layer pullets are usually reared on litter floors, with access to moulted feathers, the role of feather eating in development of feather pecking merits further study.
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Acknowledgements D.E.F. McKeegan is a British Egg Marketing Board Trust scholar and this work forms part of her thesis for a Ph.D. degree at the University of Edinburgh.
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