Transient increases in glutamate dehydrogenase (GLDH) activity occur in neonatal foals.

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Liver analyte measurement is important in the evaluation of sick animals. Liver injury in horses is recognized by increased glutamate dehydrogenase (GLDH), sorbitol dehydrogenase (SDH), and aspartate aminotransferase (AST) activities, whereas biliary pathology is identified by increased alkaline phosphatase and γ-glutamyl transferase (GGT) activities or bilirubin concentrations. We have observed high GLDH, but not SDH, activities in neonatal foals admitted for conditions other than liver disease. Only one previous study have evaluated GLDH activity over time in healthy neonatal foals; however, SDH activity was not measured. We aimed to evaluate changes in liver analytes in neonatal foals over time. We measured serum liver analytes (GLDH, SDH, GGT, AST, total, direct, and indirect bilirubin) and creatine kinase activity of 11 clinically healthy foals before and at various times after suckling until 46 days of age. Analytes were also measured in colostrum and mare serum. Median GLDH activities increased after birth to peak at 3-4 days of age (106 U/L, reference interval, 0-8U/L). Median SDH activities had a lower peak at 3-4 days (15 U/L, reference interval, 0-11 U/L) and were frequently discordant with GLDH. There was no association between foal and mare serum or colostral enzyme activities. AST activity plateaued at 5-6 days, whereas GGT activity and total and indirect bilirubin concentrations peaked at 14 and 3-4 days of age, respectively. Transient increases in GLDH, SDH, and GGT activities and total and indirect bilirubin concentrations occur in clinically healthy neonatal foals and do not necessarily indicate relevant liver disease.