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Urea Toxicity Studies in the Bovine

Oklahoma Agricultural Experiment Station, Stillwater^,4,5,

Abstract

In a preliminary trial, three pregnant cows were fasted for 24 hr. and dosed by drench with urea at a level of 0.44 gm./kg. body weight. Symptoms of urea toxicity appeared within 10 min. Acetic acid in 5% v/v solution, administered 29 min. later, appeared to lessen toxicity symptoms for about 35 minutes. Afterwards, the symptoms became severe and the animals died. Rumen-fistulated steers were given urea at levels of 0.11, 0.22 and 0.33 gm./kg. body weight. Rumen fluid and peripheral blood NH₃-N levels rose quickly and were near peak levels within 15 to 20 min. after urea administration. Several experiments were then conducted to determine a method of handling pregnant cows to obtain high blood NH₃-N levels for a short period of time but to keep the cow alive: Cows were fed a poor-quality grass hay up to the time of urea administration. Four hours prior to urea administration they were fed grain sorghum at a level of 5 gm./kg. body weight for a standard weight of 352 kg. with adjustments for greater weights being made on the basis of W⁷⁶_kg. When urea was administered as a drench at a level of 0.44 gm./kg. body weight, with acetic acid being given at a level of 2 moles/mole of urea 15 min. later, the cows died. However, if they received in addition acetic acid at a level of one mole/mole of urea 180 min. after the urea they survived. Blood NH₃-N levels were quite high at both 15 and 180 min. after urea administration. Using this procedure, 29 pregnant cows were treated and only one death occurred. Treated cows and their paired controls were kept under regular management conditions for another 12 months and treatment had no effect on number of calves born, birth weight, weaning weight of the calves, or weight changes and rebreeding performance of the cows.

¹ Department of Animal Sciences and Industry.

² Department of Veterinary Medicine and Surgery.

³ Department of Veterinary Pathology.

⁴ Approved by the Director.

⁵ Partial financial support provided by: American Cyanamid Company, Princeton, New Jersey; Ralston Purina Company, St. Louis, Missouri; Phillips Petroleum Company, Bartlesville, Oklahoma; E. I. duPont de Nemours and Company, Wilmington, Delaware; Moorman Manufacturing Company, Quincy, Illinois; Nipak, Inc., Dallas, Texas; and Monsanto Company, St. Louis, Missouri.