The Impact of Disease on Welfare

Welfare is usually defined in terms either of an animal’s ability to cope (Broom, 1986) or of health and behavioural needs. Indeed the very word “dis-ease” implies a state lacking “ease” or well-being. We feel it is important to consider disease holistically: that is to consider the animal’s ability to resist stress and the environmental challenges it faces. Whereas the outcome of poor welfare is expressed as disease, the relative contributions of various stressors will vary with each individual. The other chapters consider genetics, nutrition and environment in terms of the welfare of poultry. However, given the same housing, air, feed and water, some birds may become diseased and some remain healthy. Intrinsic biological variation results in a range of nutrient reserves and immune status at hatching, plus differences in genetic make up, social status and behaviour that interact with each other and further factors to provide different outcomes for the individual. In the pragmatic world of farming, flock health status may be frequently chosen as the index of welfare, but it is important not to lose sight of the health and well-being of each individual, even in flocks numbering tens of thousands of birds.