V. Sandilands

Providing laying hens with perches: fulfilling behavioural needs but causing injury?

1. The EU laying hen directive, which bans standard battery cages from 2012, has implications for animal welfare, particularly since housing laying hens in extensive systems, while increasing natural behaviour and improving bone strength, is associated with a greater level of bone fractures, predominantly of the keel bone, compared to birds housed in cages. 2. The aetiology and welfare consequences of keel and other bone fractures are not well understood and could have important implications for housing system designs. While proposed alterations to layer housing are based on the desire to fulfil behavioural needs and increase bone strength, there appears to have been little consideration of the effect of system on potential injury. 3. In addition, there are variations in how the directive is interpreted. For example, egg producers housing hens in extensive systems in Scotland and Northern Ireland must provide hens with aerial perches, whereas in England and Wales they do not. Aerial perches may be implicated in bone fracture injuries. 4. This paper reviews the prevalence of bone fractures in the egg-laying sector of the poultry industry and the literature on perches. It also explores how bone fractures may be occurring. 5. We propose some means of reducing bone fracture, namely through improved housing designs and genetic selection.

Behaviour of food restricted broilers during rearing and lay : effects of an alternative feeding method

Broiler breeders are subjected to quantitative food restriction in order to control their growth, and this restriction is particularly severe during rearing. While such restriction improves some welfare problems associated with ad libitum feeding, it causes others: birds routinely show abnormal oral behaviours and have elevated plasma corticosterone concentration (PCC) and changes in white blood cell counts (WBCs). The aim of this study was to examine if feeding birds qualitatively restricted diets ad libitum during rearing could reduce signs of impaired welfare, as judged by behaviour and blood indices of stress, while also meeting commercially desired growth rates and uniformity. Furthermore, we examined what carry-over effects such a feeding method had on birds in the laying phase when all birds were fed on a conventional quantitative restriction regime. During rearing (1-20 weeks of age), pens of birds were either fed limited amounts of standard basal diets (Control, i.e. quantitative restriction), or ad libitum diets consisting of standard basal diets with gradually increasing levels of calcium propionate (CaP) and a constant level of oat hulls (OH), designated CaP+OH (i.e. qualitative restriction). Results showed that, during rearing, weights and weight uniformity were similar for the two groups. During feeding motivation tests, Control birds always consumed more food than CaP+OH birds. This suggests that Control birds were more highly motivated to feed than CaP+OH birds, although care has to be taken in interpreting these results. Treatment did not affect PCCs or WBCs, but there was a general decline in PCCs with bird age. All reported behaviours differed significantly between treatment groups during rearing, but disappeared during lay when all birds were fed a similar amount of food. Control birds spent up to 50% of time in object pecking during rearing periods, but this behaviour was virtually non-existent in birds in the qualitative feeding regime. Overall, the results indicate that broiler breeders can be successfully limited in growth rates by qualitative food restriction and this results in significant changes of behaviour that suggest improvements to bird welfare.

Causes of keel bone damage and their solutions in laying hens

Keel bone damage (KBD) is a critical issue facing the contemporary laying hen industry due to the likely pain leading to compromised welfare and reduced productivity. Recent reports suggest that KBD, while highly variable and likely dependent on a host of factors, extends to all housing systems (including traditional battery cages, furnished cages and non-cage systems), genetic lines, and management styles. Despite the extent of the problem, the research community remains uncertain as to the causes and influencing factors of KBD. To combat these issues, the current review was produced following discussions from the 1st International Keel Bone Damage Workshop held in Switzerland in April 2014. This exercise sought to assess current knowledge, foster novel collaborations, propose unique methodologies and highlight the key areas where innovative research is needed. The following paper is based on the content of those discussions and presents nine recommendations for future research efforts.

Physiological responses of laying hens during whole-house killing with carbon dioxide

1. Poultry on farms are sometimes required to be killed in an emergency, such as during a disease epidemic, yet none of the available methods are ideal. Whole-house carbon dioxide (CO2) administration has practical advantages, but gives rise to welfare concerns. 2. The study measured the body temperature, respiration, cardiac and brain activity (EEG) responses of 10 adult hens placed in tiered cages in a deep pit house while the entire flock (28,000 end-of-lay hens) was killed with CO2. Video and thermographic images were also recorded. Liquid CO2 was injected into the building producing a gaseous concentration of 45% within 19 min. 3. Those hens nearest the gas delivery site showed delayed respiratory, cardiac and EEG responses compared with those at more distant locations. Although sub-zero temperatures were recorded in the immediate vicinity of some birds, body temperatures indicated that they did not die of hypothermia. 4. EEG characteristics strongly associated with unconsciousness were used to determine an unequivocal time to loss of consciousness; this ranged from 6·0 to 10·5 (average 7·8) min after onset of gas injection. Distinctive cardiac and respiratory responses were seen following gas exposure; in particular, birds responded to inhalation of CO2 by deep breathing. 5. The primary welfare concern is the duration of unpleasant respiratory effects, such as deep breathing, while the birds were substantively conscious. However, the concentration of CO2 to which the birds were exposed while conscious would not have stimulated nasal and oral nociceptors. Time to death varied between 12·0 and 22·1 min after gas delivery.

Review of gaseous methods of killing poultry on-farm for disease control purposes.

Poultry may need to be culled in the event of an outbreak of disease. Gassing has advantages over mechanical and electrical methods or overdoses of anaesthetics because large numbers can be killed simultaneously and little or no handling of the birds is required. However, gaseous killing methods may have welfare implications for the birds, which may find various gases more or less aversive, may undergo respiratory distress and/or experience convulsions, and may remain conscious for a considerable time before they die. In addition, the gases used may present health and safety risks to human operators, and be difficult to supply and deliver.

Assessing leg health in chickens using a force plate and gait scoring: how many birds is enough?

Meat chickens from experimental flocks were tested repeatedly from three to six weeks of age using gait score (GS) and force plate (FP) techniques, and the findings were related to postmortem results for leg health. This initial study indicated that five weeks was the optimal age to test birds using the FP to indicate abnormalities and pathologies. Birds (n=492) with a range of walking styles were then selected at five weeks of age from three commercial flocks, gait scored and tested using a FP. A subsample of these birds (n=191) was examined postmortem, and relationships between leg abnormalities and pathologies, GS and FP results were investigated. Models of leg abnormalities and pathologies with GS or FP measurements as covariates left much variation unexplained; hence, the number of birds that would need to be tested using these methods to assess the flock prevalence of leg abnormalities or pathologies is high.

Hypothalamic agouti-related protein expression is affected by both acute and chronic experience of food restriction and re-feeding in chickens.

The central melanocortin system is conserved across vertebrates. However, in birds, little is known about how energy balance influences orexigenic agouti‐related protein (AGRP) and anorexigenic pro‐opiomelanocortin (POMC) expression, despite the fact that commercial food restriction is critical to the efficient production of poultry meat. To enable contrasts to be made, in broiler‐breeder chickens, between levels of food restriction, between birds with the same body weight but different feeding experience, and between birds moved from restricted feeding to ad lib. feeding for different periods, five groups of hens were established between 6 and 12 weeks of age with different combinations of food restriction and release from restriction. AGRP and neuropeptide Y expression in the basal hypothalamus was significantly increased by chronic restriction but only AGRP mRNA levels reflected recent feeding experience: hens at the same body weight that had recently been on ad lib. feeding showed lower expression than restricted birds. AGRP expression also distinguished between hens released from restriction to ad lib. feeding for different periods. By contrast, POMC and cocaine‐ and amphetamine‐regulated transcript mRNA levels were not different. These results showed that AGRP mRNA not only reflected differences between a birds weight and its potential weight or set point, but also discriminated between differing feeding histories of birds at the same body weight. Therefore, AGRP expression potentially provides an integrated measure of food intake experience and an objective tool to assess a birds perception of satiety in feeding regimes for improved poultry welfare.

Avian reflex and electroencephalogram responses in different states of consciousness.

Defining states of clinical consciousness in animals is important in veterinary anaesthesia and in studies of euthanasia and welfare assessment at slaughter. The aim of this study was to validate readily observable reflex responses in relation to different conscious states, as confirmed by EEG analysis, in two species of birds under laboratory conditions (35-week-old layer hens (n=12) and 11-week-old turkeys (n=10)). We evaluated clinical reflexes and characterised electroencephalograph (EEG) activity (as a measure of brain function) using spectral analyses in four different clinical states of consciousness: conscious (fully awake), semi-conscious (sedated), unconscious-optimal (general anaesthesia), unconscious-sub optimal (deep hypnotic state), as well as assessment immediately following euthanasia. Jaw or neck muscle tone was the most reliable reflex measure distinguishing between conscious and unconscious states. Pupillary reflex was consistently observed until respiratory arrest. Nictitating membrane reflex persisted for a short time (<1 min) after respiratory arrest and brain death (isoelectric EEG). The results confirm that the nictitating membrane reflex is a conservative measure of death in poultry. Using spectral analyses of the EEG waveforms it was possible to readily distinguish between the different states of clinical consciousness. In all cases, when birds progressed from a conscious to unconscious state; total spectral power (PTOT) significantly increased, whereas median (F50) and spectral edge (F95) frequencies significantly decreased. This study demonstrates that EEG analysis can differentiate between clinical states (and loss of brain function at death) in birds and provides a unique integration of reflex responses and EEG activity.

Thermal nociception as a measure of non-steroidal anti-inflammatory drug effectiveness in broiler chickens with articular pain

Pain associated with poultry lameness is poorly understood. The anti-nociceptive properties of two non-steroidal anti-inflammatory drugs (NSAIDs) were evaluated using threshold testing in combination with an acute inflammatory arthropathy model. Broilers were tested in six groups (n = 8 per group). Each group underwent a treatment (saline, meloxicam (3 or 5 mg/kg) or carprofen (15 or 25 mg/kg)) and a procedure (Induced (arthropathy-induction) or sham (sham-handling)) prior to testing. Induced groups had Freund’s complete adjuvant injected intra-articularly into the left intertarsal joint (hock). A ramped thermal stimulus (1 °C/s) was applied to the skin of the left metatarsal. Data were analysed using random-intercept multi-level models. Saline-induced birds had a significantly higher skin temperature (± SD) than saline-sham birds (37.6 ± 0.8 °C vs. 36.5 ± 0.5 °C; Z = −3.47, P < 0.001), consistent with an inflammatory response. Saline was associated with significantly lower thermal thresholds (TT) than analgesic treatment (meloxicam: Z = 2.72, P = 0.007; carprofen: Z = 2.58, P = 0.010) in induced birds. Saline-induced birds also had significantly lower TT than saline-sham birds (Z = −2.17, P = 0.030). This study found direct evidence of an association between inflammatory arthropathies and thermal hyperalgesia, and showed that NSAID treatment maintained baseline thermal sensitivity (via anti-nociception). Quantification of nociceptive responsiveness in a predictable broiler pain model identified thermal anti-hyperalgesic properties of two NSAIDs, which suggested that therapeutically effective treatment was provided at the doses administered. Such validation of analgesic strategies will increase the understanding of pain associated with specific natural broiler lameness types.

Current and novel methods for killing poultry individually on-farm

This review examines methods for culling small numbers of poultry on farm, considering both common techniques and methods that are yet to be tested on poultry. The aim of this review is to inform the design of experiments that will assess the pros and cons of culling techniques. The methods reviewed include manual and mechanical cervical dislocation, crushing methods (such as burdizzos or pliers), percussive devices, blunt force trauma and a brain-stem piercing device. Previous work on these approaches, of which there is a limited dataset, has relied on behavioural and brain activity as proxy measures of unconsciousness (insensibility) and death, however there remains some uncertainty as to when birds can be considered unequivocally insensible. These factors will be considered when deciding which of the methods will be recommended to be taken forward for further assessment.