The significance of the impact of ovine Johne's disease as a cause of economic and production loss continues to generate debate. Recent Australian work suggests that on infected properties in a high prevalence area of Australia, annual mortality rates may reach 20%, with a reduction in gross margin on average of 6.4%. OJD mortalities often occur within the first four years of life, when the animal is most productive and the cost of OJD may have been underestimated due to discounting effects on wool production, growth and reproductive performance through the sub-clinical and clinical stages of the disease. As part of an extensive epidemiology trial, serum biochemical parameters, body weight and wool growth and quality parameters were measured over 2 years in 83 sheep naturally exposed to OJD at pasture. Lambs were selected for inclusion in the trial retrospectively based on histopathology lesions and tissue culture results consistent with OJD infection. Control animals were selected randomly from a cohort of unaffected animals. In preliminary univariate analysis of variance or covariance, serum albumin differed significantly between histopathological categories of sheep in two or more periods. Levels were significantly lower in sheep with severe lesions leading to clinical disease. This was apparent before the onset of clinical disease. Mean albumin level in sheep with severe lesions that survived to the end of the trial was significantly lower than that in controls at the last time point (P<0.01). There were differences in wool parameters and bodyweight measurements in sheep with severe disease compared to uninfected cohorts at the same time points. The biological significance of these findings will be investigated for correlation between wool and bodyweight changes, serum albumin and severity of disease over time.