Assessing the experience of pain in animals is a difficult task, yet one that is important in animal welfare research. Some approaches to pain assessment in animals are reviewed here. General qualities of pain scales and specific parameters suitable for clinical and experimental pain assessments are discussed. It is argued that pain assessment will progress through an integration of objective and subjective observations of behaviour coupled with multiple measures in various other areas. Such multidimensional pain scales allow an adequate characterisation of the complexity of an individual animal's pain experience to be made. This knowledge improves the recognition and treatment of pain and will allow informed moral debate on the acceptability of practices such as castration and tail-docking of lambs.

The long-term effects of infra-red beak treatment (IRBT) in laying hens were investigated by examining beak-nerve function and anatomy over a range of ages. In IRBT and control (intact) birds that were ten, 30 or 50 weeks old, the responses of single sensory nerve fibres were recorded from the intramandibular nerve, which provides sensation to the lower beak. The beaks were also measured and subject to microscopic and radiographic examination. The responses of 386 nerve fibres were recorded including mechanoreceptors, thermoreceptors and nociceptors. Receptive field positions indicated that the entire lower beak was sensitive to thermal and mechanical stimuli, regardless of age or treatment. There was no evidence of a treatment effect on nociceptive thresholds at any age. Beak measurements demonstrated that application of IRBT at day-old affected, on average, 36% of beak area, and resulted in a 44% reduction in beak length by four weeks of age. Radiographs produced no evidence of adverse or pathological change in relation to IRBT. Microscopic evaluation of beak-tip anatomy revealed evidence of healing including re-epithelialisation, fibrovascular hyperplasia and bone remodelling. By four weeks of age there was limited nerve regeneration in IRBT beaks, including re-population of mechanoreceptors in some birds. In older birds, re-innervation and scarring was visible, but no neuromas or abnormal proliferations of nerve fibres were observed at any age. Collectively, the results suggest that IRBT does not result in chronic pain or other adverse consequences for sensory function.

Objective. Ornithonyssus sylviarum (northern fowl mite) and Menacanthus stramineus (chicken body louse) are key poultry pests currently controlled by exclusion or pesticide application. We studied how host beak condition affected their populations over time and how the lice and mites might interact on a host. Methods. Beak-trimmed or beak-intact white leghorn hens were infested initially with either mites or lice and subsequently challenged using the alternate ectoparasite species (reciprocal transfer), while other hens harboured only the initial ectoparasite species. Results. Beak-trimmed hens had far higher ectoparasite numbers relative to beak-intact hens, and the 2 ectoparasites showed evidence of grooming-mediated competitive asymmetry. On beak-trimmed hens, larger numbers of lice quickly nearly completely excluded mites in competition for enemy-free space (lower abdomen), while in the reciprocal transfer mites did not affect louse numbers on beak-trimmed hosts. The 2 ectoparasites co-existed on beak-intact hens, which were better able to defend the lower abdomen habitat by grooming. Conclusion. Lice are somewhat less damaging and much easier to control relative to mites, and might be used to eliminate mites in commercial, beak-trimmed flocks. Beak trimming impairs host grooming and contributes greatly to the high ectoparasite populations seen in commercial flocks. The study adds incentives for poultry breeders to develop more docile hen strains that can be held without beak trimming. This has advantages both to welfare advocates and producers who may no longer need to use insecticides for pest control or be concerned about worker exposure to pesticides.

Beak trimming is routinely practiced in the poultry industry to reduce the incidence of feather pecking, aggression, and cannibalism in egg layers. Feather pecking is painful to birds and potentially induces cannibalism. Cannibalism happens in all current housing environments, cage- and free-production systems, and is one of the major causes of bird death in commercial laying hens without beak trimming. However, beak trimming has solicited a great deal of debate concerning the relative advantage and disadvantage of the practice and its impact on welfare. Abird's beak is a complex functional organ with an extensive nerve supply and various sensory receptors. Beak trimming may cause pain (acute, chronic, orboth) in trimmed birds due to tissue damage and nerve injury. The complexity and plasticity of the nervous system and the animal's inability to communicate verbally make pain difficult to measure directly. However, pain in animals can be recognized and assessed using physiological and behavioural parameters in response to noxious events. When evaluating whether an animal is experiencing pain, a distinction should be made between what an animal may feel and what a human observing the animal may feel. It should be noted that beak trimming-induced pain in birds is genetic-, lesion-, and age-dependent. Based on the updated information, the authorwould like to indicate that 1 with some genetic flocks of laying hens, if beak trimming is needed to prevent featherpecking and cannibalism, it should be conducted at hatchery oryoungerthan 10 days of age; 2 however, the most desirable approach is to eliminate beak trimming through a genetic selection of birds with less cannibalistic and aggressive tendencies, and 3 another solution is to develop an alternative means of trimming that has fewer painful implications and safeguards welfare before non-cannibalistic stocks are commercially available.

A systematic review of investigations on productivity, mortality and cannibalism of laying hens housed in aviaries is presented. In Part One we reviewed the studies that compared these parameters between laying hens housed in aviaries and in conventional cages. In Part Two we investigated the relative impact of strain, beak trimming and rearing condition on productivity and mortality in aviaries. The comparative analysis revealed that aviary hens consumed 3.0 % more food than caged hens, and food conversion was 6.7 % higher in aviaries than in cages. On the other hand, the mortality rate and cannibalism rate did not differ significantly between the two housing systems. The analysis of causes of variation in productivity, mortality rate and cannibalism rate in aviaries revealed a strong effect of strain. Beak trimming was associated with a reduced prevalence of cannibalism rates but had no effect on overall mortality. It also reduced egg weight and food consumption. Early access to litter during the rearing period had a positive effect on egg weight; egg mass, food conversion and mortality rate. In conclusion, we found a slightly reduced productivity of aviaries in relation to cages although the mortality rates and the prevalence of cannibalism did not differ between these housing systems. To further improve productivity and reduce mortality of hens housed in aviaries we recommend the choice of suitable strains and the implementation of improved rearing conditions including early access to litter.

Bird behaviour, production, physiological measurements of stress, and pain as indicated by neural transmission in, and anatomy of the trimmed beak have been used as criteria to determine if beak trimming compromises bird well being. In addition, the welfare of those hens that are pecked by beak-intact hens has been evaluated. The welfare of a flock is assessed by mortality, incidence of cannibalism, feathering, and flock behaviour such as fearfulness or nervousness. Disadvantages of beak trimming include short-term and perhaps long-term pain, and short-term stress following beak trimming. Because feeding behaviour must adapt to a new beak form, a bird's ability to consume feed is impaired following beak trimming. Welfare advantages include reduced pecking, feather pulling, and cannibalism; better feather condition; less fearfulness and nervousness; less chronic stress; and decreased mortality. It appears that the welfare disadvantages are applicable to individual birds whose beaks are trimmed, while the welfare advantages are more applicable to the interactive flock. Behavioural evidence suggests that primary breeders of egg laying strains can select for more docile birds and minimize the need to beak trim. Therefore, using genetic stocks that require little or no beak trimming is the most desirable approach. However, under certain management systems (e.g., exposure to high intensity natural lighting) and with some genetic stocks, beak trimming is needed to prevent feather pecking and cannibalism. When employed, beak trimming should be conducted at 10 days of age or younger by trained personnel.

Beak trimming remains a controversial subject. It has undoubted economic advantages for the producer, in particular by reducing the incidence of cannibalism and feather pecking, but the procedure is traumatic for the bird and deprives it of important sensory feedback from its beak. It can have harmful neuroanatomical consequences: although the tissue damage is repaired the sensory receptors are not replaced, neuromas may form and become a source of chronic pain. The danger of neuroma formation is reduced and may be absent if the procedure is performed only in young birds. Beak trimming results in both immediate and more persistent effects on behaviour, food intake and body weight. Trimmed birds are generally less active, show less behaviour involving pecking, eat less and grow more slowly than controls. These changes are primarily a consequence of the sensory deprivation. In caged medium hybrid layers and growing broilers beak trimming is difficult to justify, whereas the incidence of pecking damage is so high in light hybrids in multi-bird cages at high stocking densities that beak trimming is universal. A case can also be made for its continuation, on welfare as well as on production grounds, in floor-housed flocks of laying fowl and breeding turkeys. In these contexts it reduces mortality by inhibiting feather pecking, cannibalism and, possibly, aggressive pecking. In the long term beak trimming should be phased out and undesirable behaviour controlled by environmental means and by increased effort being devoted to the genetic selection of commercial stocks which do not engage in damaging pecking, either in cages or when floor-housed in large flocks.