Billions of laying hens are kept worldwide. Severe feather pecking (SFP) is a behaviour which occurs with a high prevalence on commercial farms. SFP, the pecking and plucking of feathers of another bird, induces pain and stress and can ultimately lead to cannibalism. Moreover, SFP can occur if a bird is unable to cope with fear and stress and is living in an inappropriate environment. SFP thus reduces the welfare of many laying hens worldwide. To prevent SFP it is essential to know the risk factors in its development. To that aim, first, two experimental studies were conducted to gain insight in the principles of SFP, and three on-farm studies were conducted to assess the risk factors of SFP under commercial conditions.
Factors which relate to SFP are high fearfulness as young and low levels of brain and peripheral serotonin (5-HT) and brain dopamine (DA). Furthermore, commercial laying hen lines can differ in SFP tendencies and associated traits indicating that SFP has a genetic component. In chapters 2 and 3, fear response as young and adult, and stress response, 5-HT and DA brain levels as adult were
compared in hens of two lines: the low mortality line (LML) selected on low levels of mortality due to cannibalism and individual performance vs. the control line (CL) which was selected on individual performance only. Hens were exposed to an Open Field (OF) test at 5 weeks of age and a Manual Restraint (MR) test at 33 weeks of age. At 33 weeks of age, levels of corticosterone (CORT) post MR and 5-HT and DA levels in four brain areas were determined. Hens of the LML were less fearful at both ages and had lower levels of DA in the arcopallium, a somatomotor area involved in fear and motor control, compared to hens of the CL. In chapter 2, it was also shown that fearful chicks had higher levels of CORT and higher activity levels as adult, compared to non-fearful chicks. Moreover,
presence of fearful animals in the group was related to average CORT levels of their pen members. Fearful hens may induce social instability in a group, and thereby affecting the stress-sensitivity of their group mates. These results indicate that groups differ in levels of fear and stress-sensitivity, and that fearfulness at a young age can lead to stress-sensitivity as adults, which create a risk for development of SFP.
In chapters 4, 5 and 6, the laying hen production chain consisting of parent stock, rearing flocks and laying flocks was studied. Risk factors for SFP could originate from previous parts in the chain. Therefore, in all on-farm studies, measurements of SFP, fearfulness, basal CORT and peripheral 5-HT system were obtained, and related to housing conditions and to previous parts in the chain. Fearfulness was assessed, on a flock level, by distance to a stationary person (SP) test and latency
of bird to approach a novel object (NO). Dekalb White (DW) and ISA brown (ISA) crosses whose pure lines differ in levels of fear, CORT, 5-HT and DA, were compared. First, parent stock (PS) flocks were studied and associations between production performance and measurements of fear, stress and 5-HT were conducted and related to group size conditions (chapter 4). Second, rearing flocks originating from PS flocks were studied throughout the rearing period (chapter 5). High levels of feather damage, CORT and 5-HT in the mothers were related to fearfulness and SFP in their offspring at flock level. Especially, a large flock size and limitation and/or disruption in litter supply affected SFP and levels of fearfulness and 5-HT (chapter 5). Finally, high levels of feather damage during the laying period were related to high SFP rearing, and high fearfulness during rearing and laying (chapter 6). These studies together aimed to determine the risk factors for the development of SFP and the resulting feather damage. The main outcomes of these studies are as follows.
Ø Parent stock flocks
DW flocks were more fearful of an SP and hens had higher levels of feather damage than in ISA flocks. ISA flocks, in turn, were more fearful of the NO and hens had higher 5-HT levels than in DW flocks. A small flock size led to higher feed conversion, mortality levels, and smothering events in ISA but not in DW flocks. These results indicate that DW and ISA PS flocks differ in levels of fear and
feather damage, and respond differently to their social environment. For both crosses, fear of an SP related to high mortality and fear of the NO related to low hen body weight, egg weight, and feed intake. High basal CORT related to low egg weight. High fear and stress levels in PS flocks may, thus, negatively affect (re)production, and thereby potentially negatively influence the developing
Ø Rearing flocks
In the DW cross, high CORT, feather damage, and 5-HT of mother hens related to high SFP and fearfulness of their rearing flocks at 1 week of age. At 5 weeks of age, a peak in both gentle feather pecking (GFP) and SFP was recorded, coinciding with a disruption in substrate availability (i.e. a temporal absence of substrate) and a limitation of substrate (i.e. limited amounts of substrate
provided) in some of the farms. Especially, ISA pullets showed higher SFP under substrate limitation and became more fearful under substrate disruption than DW pullets. ISA pullets had higher 5-HT levels than DW pullets. Only in the ISA cross, high 5-HT related to high fearfulness, specifically under substrate disruption. For both crosses, high fearfulness was related to high feather damage. Furthermore, in a level system (floor system where levels are gradually added) higher levels of SFP and feather damage were found compared to an aviary system (a tier-system with cages and litter area). These results highlight that; 1) parental effects exist in the development of fearfulness and SFP, 2) disruption and limitation in substrate availability can lead to high SFP at 5 weeks of age, 3) ISA pullets are more strongly influenced by environmental conditions than DW pullets and 4) a level housing, which coincided with a large group size, increase the risk of SFP and feather damage during rearing.
Ø Laying flocks
In our sample, 49% of the laying flocks had severe damage at 40 weeks of age, compared with 71%, 65% and 53% of the rearing flocks at 15, 10 and 5 weeks of age, respectively. High fear of a SP at rearing and high SFP at 5 weeks of age related to high levels of feather damage at lay. In a floor system and at a large flock size higher levels of feather damage were recorded than in an aviary system and at a small flock size. An adjusted management on the laying farm (i.e. aerated blocks, presence of roosters or a radio playing) reduced levels of feather damage compared to standard management. DW flocks were more fearful of the SP and NO than ISA flocks. This study showed that factors during rearing and laying contributed to feather damage at 40 weeks of age.
With the knowledge from the experimental and on-farm studies in this thesis, an assessment of the risk factors for SFP could be established. Risk factors for SFP are: high fear, stress and feather damage in DW parent stock, high fear of humans, especially for DW hens, litter disruption or limitation during rearing, large group sizes, and a floor or level system.
|Qualification||Doctor of Philosophy|
|Award date||29 Aug 2014|
|Place of Publication||Wageningen|
|Publication status||Published - 2014|
- feather pecking
- behaviour problems
- hormonal control
- stress response
- laying performance
- animal welfare
- animal behaviour
- animal physiology