On the pathogenesis of abortion in acute nitrite toxicosis of pregnant dairy cows.
Six cows, 220 to 260 d pregnant, were used to study possible abortifacient effects of absorbed nitrite. Maternal and fetal bloodvessels were catheterized. Nitrite was infused intravenously (i.v.) for 30 minutes on Days 1, 3 and 5, commencing at least 5 d postcatheteration. The dose used was 7, 9.5 and 12 mg NO(2)(-)/kg bodyweight, respectively. Nitrite caused a dose-related (P < 0.05) conversion of maternal hemoglobin (Hb) into methemoglobin (MHb); a 30 to 50% decrease of mean arterial bloodpressure; an increase in heart rate, with dose-related recovery periods; and a decrease in partial oxygen tension (PO(2)) of maternal blood. Maternal partial carbon dioxide tension (PCO(2)), pH and electromyographic activity of the uterus were unchanged. Fetal changes included a small increase in MHb content, variable changes in heart rate (tachycardia and bradycardia), and decreases in fetal PO(2), with considerable differences between animals. All calves were born alive. Three cows calved early, 2 to 3 d after the highest nitrite dose. The hematological and cardiovascular data suggest that these three fetuses experienced a more serious hypoxemic stress than the other fetuses.
van 't Klooster
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AT
Department of Large Animal Medicine and Nutrition Faculty of Veterinary Sciences State University of Utrecht Yalelaan 16, 3584 CM Utrecht The Netherlands.
Taverne
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MA
Malestein
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Akkersdijk
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EM