The ammonia tolerance test in horses.

Clinically normal horses (n = 8) with ages ranging from 5 to 8 years, were starved for 12 h and their plasma ammonia concentrations were measured. The mean fasting plasma ammonia concentration was 17.8 +/- 3.8 mumol l-1. After dosing ammonium chloride at a dose rate of 0.02 g kg-1, there was a significant increase in plasma ammonia concentration, with a maximum rise after 20 min (P less than 0.05). To investigate the influence of temperature on plasma ammonia concentrations of stored samples, 8 plasma samples were stored at -20 degrees C and 4 degrees C respectively. The plasma ammonia concentrations were measured after 6, 12 and 24 h in each of the stored samples. Plasma ammonia concentrations increased significantly after 12 and 24 h when stored at 4 degrees C (P less than 0.05). When plasma was stored at -20 degrees C there was no significant increase from baseline concentrations during 24h (P greater than 0.05).