الكاتب: Multiple References

The problem of the indirect markers is the individual variation caused by such effects as inter-animal variation, lactation stage, lactation number and environmental factors. These tend to mask any effects due to provoked tissue irritation. This problem can be partly overcome by comparing the test quarter with other quarters ofthe same cow (Sheldrake et al., 1983; Mattila & Sandholm, 1985). However, local therapy may cause a response in the control quarters as well. This would decrease any difference between the treated and control quarters. Another evaluation method would be to use pretreatment values of the infused quarters as reference values, so that differences between the basal levels of two quarters in a cow would be eliminated (Rehm, 1983; Fox et al., 1986).