There are many different characteristics of housing systems which affect the welfare of laying hens, particularly because welfare itself has many diverse aspects. When cause and effect relationships between systems and welfare are assessed, it is evident that no system currently under consideration is ideal. Of those priorities listed by UK authorities such as the Ministry for Agriculture, Fisheries and Food and the Farm Animal Welfare Council, all systems are likely to provide ‘freedom from hunger and thirst, adequate lighting and the company of conspecifics’. However, conventional cages are less likely than other systems to provide ‘freedom of movement, freedom from fear, comfort and shelter, suitable flooring and freedom to display most normal patterns of behaviour’. Alternative systems, though, often expose birds to the danger of disease, to aggression from dominant birds and to the risk of cannibalism or beak trimming to avoid it. Overall, welfare is compromised more in conventional cages than in well-run alternative systems, though welfare is more sensitive to poor management and to market forces in the latter. Problems in cages are also less likely to be alleviated by genetic selection than those in alternative systems. The ideal system for present-day stocks should combine the small group sizes found in cages with the freedom of movement and complex environment characteristic of alternative systems.

Live attenuated strains of Salmonella spp. make excellent vaccines against salmonellosis in experimental animals, eliciting a cell-mediated, mucosal and humoral immune response. In addition, new recombinant DNA technology permits the expression in Salmonella strains of protective antigens from unrelated bacterial, viral or parasitic pathogens. Exciting possibilities exist for a single live vaccine which could provide protection against two or more infectious agents. Recently, attenuated strains of the chicken pathogen Salmonella gallinarum have been considered as the basis of a live multivalent poultry vaccine and work is progressing on the expression of coccidial and herpes viral antigens in strains of Salmonella.

The use of lysozyme as a food preservative and the factors affecting lysozyme activity (temperature, chemicals, processing and complexes) is reviewed. Lysozyme inhibits the growth of deleterious organisms thus prolonging shelf life. Chemicals used to improve the preservative effect of lysozyme and those that inhibit the enzyme are discussed along with the stability of lysozyme in various chemical environments. Lysozyme has been used to preserve fresh fruits and vegetables, tofu bean curd, seafoods, meats and sausages, potato salad, cooked burdock with soy sauce, and varieties of semi-hard cheeses such as Edam, Gouda and some Italian cheeses. Lysozyme added to infant feeding formulae makes them more closely resemble human milk.