Erythrocyte counts and hematocrit values in both affected and non affected cows were
normal; hemoglobin concentration was lower in affected animals. One week later, the
hemoglobin value returned to its physiological level. However, the erythrocyte indices
MCH and MCHC were significantly decreased (p50.05) during the time of intoxication
and the appearance of clinical signs. These values were regained one week later (Table 1).
Other signs of acute nitrite poisoning or other illnesses were not found in the affected
animals prior to the incidence. All affected cows were in good health with high milk
production. Some of them were pregnant: in second and third trimesters. Blood obtained
from severely affected cows was tinted with a deep brown coloration, which was
pathognomonic of methemoglobinemia. The maximum value of MtHb at the peak of
incidence ranged from 27 to 53%. However, the severely affected cows were not sampled
because they were found dead. MtHb concentration in whole blood and nitrite in plasma
were higher (41.6 and 1.60 mmol L1), respectively, in all affected cows that showed severe
clinical signs of nitrite poisoning. It increased significantly (p50.05) over cows with no
clinical signs of nitrite poisoning (13.9 and 0.75 mmol L1) (Table 2). One week later, the