Ammonia Toxicity in Cattle. II. Changes in Carotid and Jugular Blood Components Associated with Toxicity

Abstract

Two rumen fistulated cows, not adapted to urea, were given .5 g urea intraruminally per 1 kg body weight 16 hr after a previous feeding. Ammonia-N concentration 5 min after dosing rose from .13 to .71 mg per 100 ml for carotid blood and from .11 to .43 mg for jugular blood, then to 1.47 mg (carotid) and .95 mg (jugular) at time of toxicity. Toxicity, judged by appearance of definite muscle tetany, occurred between 17 and 30 min after dosing. The marked difference in ammonia concentrations in carotid and jugular blood suggests that the brain takes up ammonia rapidly. Other changes observed between dosing and toxicity were: rumen ammonia-N, 6.18 to 51.30 mg per 100 ml; rumen pH, 6.94 to 7.90; arterial blood pH, 7.44 to 7.50; arterial blood pO₂ , 87.1 to 96.1; blood lactic acid, 9.5 to 23.4 mg per 100 ml; blood glucose, 72 to 91.9 mg per 100 ml; and packed cell volume, 24.5 to 28.5%. Plasma protein did not change. Heart beat increased slightly to toxicity (63.8 to 71.8 beats per minute) and more markedly after toxicity. No significant changes in electrocardiographic patterns were observed. Emptying the rumens at toxicity resulted in complete recovery within 1 hour. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.