If birds can learn to associate different sensory properties of foods with different metabolic feelings caused by different protein contents, then they should be able to choose a balance of foods which makes them feel most comfortable. Broiler chickens given a choice between two foods, one containing a higher concentration of protein than required and the other a lower concentration, eat amounts of the two which will give a diet that is close to optimum for growth in terms of overall protein content. When both foods have excessive or insufficient protein the birds eat predominantly from that closer to their requirements. As broilers grow they choose a progressively lower protein diet in line with their reducing protein:energy requirements. Strains with higher potential rates of lean deposition voluntarily consume a higher ratio of high-protein to low-protein food compared with low-growth strains, while strains selected for high fat deposition eat less protein per unit of energy than lean birds. Males select higher protein diets than females. Although increases in environmental temperature would be predicted to reduce energy requirements and thus increase the protein:energy ratio in selected diets, heat-stressed birds do not increase the protein content of their diet, probably because of the high heat increment of protein metabolism. Short periods of access to one food alone are followed by a preference for the opposite food when access to both is restored. When given appropriate training, laying hens can balance their diet for protein but not as well as broilers. There is evidence that growing chicks can differentiate high-lysine from low-lysine foods but do not entirely balance their diet for lysine. Methionine-deficient broilers eat more of a methionine supplemented food than normal birds, while laying hens eat some methionine-fortified food when given a choice against a low-methionine food, but not enough to support normal egg production. It is concluded that poultry can show a great degree of ‘nutritional wisdom’ as far as protein is concerned but that they need to be allowed to differentiate between foods with different nutrient profiles by sensory means, and a lack of training might account for some of the poor results obtained.

Animals are exposed to various vibration and movement stimuli during transport. The vibrations are a potential source of stress in birds because the resonances they set up in the internal organs are likely to be major aversive stimuli. This paper considers the possible effects of vibration on broilers in transport by reference to the known effects of vibration on other species. The fundamental frequency of poultry transporters is between 1 and 2 Hz, with a secondary peak of 10 Hz and a chassis vibration in the lateral axis of 12–18 Hz. Suggested resonance frequencies for the viscera of broiler chickens exposed to vertical vibration are around 10 Hz, and so coincide with the secondary peak. Skeletal muscle responds to movement and vibration in order to maintain postural stability and reduce the effects of resonance. Standing birds maintain stability by wing extension and by flapping or squatting. Involuntary muscle and cardiac muscle are also affected by vibration with blood circulation, heart beat and possibly gut control changing as a result. Vibration-induced vasodilatation may occur, as may blood pooling in the organs, pulmonary damage and impaired thermoregulation. Biochemical changes resulting from vibration could have adverse effects on meat quality in birds unable to recover before slaughter.

The presence of harmful substances such as organochlorine pesticides, heavy metals, radionuclides and mycotoxins in poultry feed is sometimes unavoidable. The reduction of absorption of fat-soluble organochlorine pesticides (e.g. DDT or dieldrin) and enhancement of elimination from the body is not easy to accomplish. The level of more volatile compounds (e.g. lindane) can be reduced by freeze drying of the product. Removal of the fat from the product will also decrease the level of these lipophilic compounds. The absorption of (heavy) metals from the intestine shows many interactions which sometimes may be used in practical situations to reduce intestinal absorption, toxicity and residue formation of a particular heavy metal. Reduction of levels in contaminated products has not been described. Adsorbents such as bentonite or zeolite reduce, to some extent, the absorption of radionuclides in poultry. Mycotoxin formation in feedstuffs should and can, sometimes, be prevented. Ammoniation of feedstuffs is a good method of reducing aflatoxin levels. Adsorbents such as hydrated sodium calcium aluminosilicate may also help to alleviate mycotoxin problems arising from the feed.

Manual catching, handling and loading of poultry prior to transportation to slaughter have been identified as major sources of stress and trauma to the birds. Whilst extensive but generalized legislation and advice pertaining to the design and maintenance of containers exist in some countries, the complex logistics and demands of modern intensive poultry production exacerbate many of the fundamental difficulties associated with animal handling. Methods of removal of laying hens from cages of current design are often associated with overt injuries including fractures and dislocations - problems addressed in new UK guidelines. Modifications of cage structure and the mechanical conveying of birds may additionally prove beneficial in this context. Depopulation of broiler houses involving manual catching at rates of up to 1500 birds per man hour may also have a negative effect on bird welfare. Current practices require significant improvement, including operative education. Mechanized broiler harvesting offers an important and viable alternative procedure and its potential benefits are discussed.

The potentially harmful effects of adverse environmental conditions during the transport of poultry and their welfare consequences are of political and public concern as well as being important in terms of increasing bird mortality and reducing product quality. The principal stressors during transport are listed, together with the relevant methods of assessing physiological stress. Particular reference is made to the thermal environment because of the major effects of thermal stress. Three-dimensional mapping of temperature and relative humidity within bird containers on commercial transport vehicles has been carried out. This has demonstrated large thermal gradients and the existence of a ‘thermal core’ within moving vehicles in summer, and in winter when side curtains are closed. Laboratory based simulations have resulted in the development of a model relating the degree of physiological stress expressed by the birds to the thermal load. This model will help in formulating recommendations for improved vehicle and container design and transportation practices.

The procedures normally used for the removal of hens from cages at the end of their laying cycle and their subsequent transport to the slaughterhouse are described. Because 30% of live birds arriving at the slaughterhouse have been found to have one or more broken bones, discussion is focused on the principal factors involved in the aetiology of such lesions. These include the reduction in bone strength due to mineral depletion during lay, restricted physical movement and exercise within cages and the methods used to remove birds from their cages, in addition to the other sources of potential trauma associated with transportation from the farm to the processing plant.

It is known that the internal thermal microenvironments on poultry transport vehicles vary widely between journeys and according to position within the load on individual journeys. These variations are a consequence of the external climate, transport practices including stocking density, vehicle and container design and thus load ventilation. Studies have focused on the analysis of the aerodynamic properties of commercial poultry transport vehicles and relating the findings to ‘on–board’ thermal environments and their distribution and control. It has been possible to validate the use of 1/8th scale vehicle models in a wind tunnel to characterize the external air pressure and flow patterns driving ventilation of the bird containers. Supported by computational fluid dynamic analyses these techniques have facilitated the prediction of the effects of changes in vehicle structure and transport practices upon internal ventilation and thermal loads and therefore degree of physiological stress to which birds are exposed during transportation. The findings will form the basis of recommendations for improvements in vehicle and container design in order to optimize the poultry transport thermal environment.

Because of the possible short-term stress or injury in birds that may result from the effects of vibration during transport in road vehicles, studies have been initiated to characterize the various vibration frequencies in different axes found within bird containers on typical poultry transporters. Bird response is now being explored experimentally within the boundary conditions of vibration frequency and magnitude that have been established.

During the preslaughter period the welfare of birds can be compromised through temperature stress, emotional stress, dehydration, metabolic exhaustion and trauma to the skin, bones and soft tissues resulting in bruising and death. This paper focuses on the last three factors by reference to recent studies. An average of 0.19% broilers were found to be dead on arrival at the slaughterhouse with the principal cause of death being congestive heart failure (47%) followed by trauma (35%). Broken bones were found in 3% of broilers and in 29% of hens. Care is needed when interpreting the evidence of bruising because this may occur after death (during plucking) as well as before slaughter. Brief reference is made to gas stunning as a possible alternative to current methods.