Biochemical changes in avian tissues during infection

Major sources of error in studies of diet--infectious disease interactions relate to failure 1) to define the stage of a disease cycle; and 2) to determine the extent of disease involvement at time of sampling. The former can be determined from clinical and biochemical observations from time of inoculation to recovery or mortality; the latter can be calculated from indexes obtained from histological preparations, changes in body temperatures, and other clinical symptoms, including weight loss and efficiencies of feed utilization. Other significant errors are derived from the normal 24-hour dynamics of particular tissue constituents, which include oscillations and circadian rhythms. Experimental designs and accuracy of data are always helped by prior knowledge of 24-hour patterns of these normal fluctuations. For example, such patterns will reveal that enzyme and hormonal changes are far more dynamic than body water changes. Studies of nutrition--disease interactions are extremely complex and the researcher must be aware of and eliminate as many sources of experimental error as possible to avoid confounding the data.