Fasting in horses induces an increase of totabl bilirubin within 1 day, which persists for the duration of the fast. Bilirubin concentrations decrease rapidly after cessation of the fast. We have seen total bilirubin concentrations as high as 12 mg/dL as a consequence of fasting in horses. The increase in total bilirubin is due to increased unconjugated bilirubin. Hypotheses for fasting-induced hyperbilirubenemia are decreased glucose (decreased conjugation) and competition for uptake by free fatty acids. A mild increasing in total (and unconjugated) bilirubin also occurs in anorexic ruminants (up to 2-3 mg/dL).
Figure reproduced with permission from: Hepatic function by Tennant B in “Clinical Biochemistry of Domestic Animals”, 5th edition, Kaneko et al, eds, pg 344, 1997; Copyright Elsevier.