Egg production systems have become subject to heightened levels of scrutiny. Multiple factors such as disease, skeletal and foot health, pest and parasite load, behavior, stress, affective states, nutrition, and genetics influence the level of welfare hens experience. Although the need to evaluate the influence of these factors on welfare is recognized, research is still in the early stages. We compared conventional cages, furnished cages, noncage systems, and outdoor systems. Specific attributes of each system are shown to affect welfare, and systems that have similar attributes are affected similarly. For instance, environments in which hens are exposed to litter and soil, such as noncage and outdoor systems, provide a greater opportunity for disease and parasites. The more complex the environment, the more difficult it is to clean, and the larger the group size, the more easily disease and parasites are able to spread. Environments such as conventional cages, which limit movement, can lead to osteoporosis, but environments that have increased complexity, such as noncage systems, expose hens to an increased incidence of bone fractures. More space allows for hens to perform a greater repertoire of behaviors, although some deleterious behaviors such as cannibalism and piling, which results in smothering, can occur in large groups. Less is understood about the stress that each system imposes on the hen, but it appears that each system has its unique challenges. Selective breeding for desired traits such as improved bone strength and decreased feather pecking and cannibalism may help to improve welfare. It appears that no single housing system is ideal from a hen welfare perspective. Although environmental complexity increases behavioral opportunities, it also introduces difficulties in terms of disease and pest control. In addition, environmental complexity can create opportunities for the hens to express behaviors that may be detrimental to their welfare. As a result, any attempt to evaluate the sustainability of a switch to an alternative housing system requires careful consideration of the merits and shortcomings of each housing system.

Enteric bacterial infections in poultry pose a threat to intestinal health and can contribute to poor feed efficiency and livability of a flock. A variety of enteric bacterial diseases are recognized in poultry. Three of these bacterial diseases, necrotic enteritis, ulcerative enteritis, and spirochetosis, primarily infect the intestine, whereas other bacterial diseases, such as salmonellosis, colibacillosis, mycobacteriosis, erysipelas, and fowl cholera, affect a variety of organ systems in addition to the intestine. Diagnosis of bacterial enteritis requires monitoring of clinical signs in the flock and proper use of diagnostic methods such as necropsy, histopathology, bacteriology, and serology.

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Clostridial dermatitis of turkeys (CDT) has emerged as a major issue across most geographic regions of the United States. The prevalence and severity of dermatitis has increased over the last several years, since the time it was first reported in 1993. Cellulitis in poultry can be associated with Staphylococcus aureus or Escherichia coli, but the more recent field situation in turkeys is specifically associated with Clostridium spp. The prevalence of cellulitis is relatively low; however, the disease can be devastating in the individual flocks affected. Clostridium septicum, Clostridium perfringens, Clostridium sordelli, and S. aureus can cause cellulitis. Escherichia coli, Streptococcus spp., and other bacteria have occasionally been isolated from birds diagnosed with cellulitis. CDT appears as excessive mortality in older birds around 16-18 weeks of age. It has been reported from field experience as early as 7 wk of age. Clinical signs of CDT can range from sudden death to inappetence, depression, leg weakness, recumbency, and ataxia. The disease is characterized by reddish to dark or greenish discoloration of the skin around the thighs, abdomen, keel, tail region, back, and wings. The lesions can extend into the underlying muscles, and there can be gas bubbles under the skin which result in crepitation. Some cases present with dead birds having "bubbly tail," fluid-filled blisters associated with broken feather follicles around the base of the tail. Bubbly tail in breeder toms might not cause excessive mortality, but the lesions are so severe that the birds cannot be used for semen collection. Incidence of mortality from this condition can be severe and acute (i.e., rapid onset of high mortality). The dead birds decompose very quickly. Microscopically, there is necrosis, with or without inflammation of the skin, especially in the dermis and occasionally in the skeletal muscles, associated with large numbers of rod-shaped bacteria. Overcrowding, aggressive birds, poor-wet litter, decreased down time, a contaminated environment including feed and water, poor hygienic conditions, and contaminated vaccines and vaccine equipment, etc., can predispose birds for CDT. Preventative measures and treatment are discussed extensively in this review.

Two studies were conducted to determine the role of enteric viruses in Light Turkey Syndrome (LTS), which is characterized by lower weight in market age turkeys than their standard breed character. In the surveillance study, we selected four LTS and two non-LTS turkey flocks in Minnesota and collected faecal samples at 2, 3, 5 and 8-weeks of age. Astrovirus, rotavirus, and reovirus were detected alone or in various combinations in both LTS and non-LTS flocks. No coronavirus was detected in LTS flocks and no corona-or reovirus was detected in non-LTS flocks. In the second study, 2-week-old turkey poults were divided into two groups; Group A (challenged) was inoculated orally with 10% pooled faecal suspension from LTS flocks and group B (control) was inoculated with phosphate buffered saline (PBS). Clinical signs of depression, huddling, and lack of uniform size were observed in the challenged group but not in the control group. diarrhoea was observed in both groups but was more severe in the challenged group than in the control group. Birds in the challenged group shed astrovirus, rotavirus and reovirus, while the control group shed only astrovirus. Virus shedding in both groups was observed for up to nine weeks of age. Significantly lower body weights were seen in the challenged group starting at seven weeks of age and lasting until 20 weeks of age. These findings suggest that viral enteritis at an early age may set up conditions for the development of LTS in adult turkeys.