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Growth and Reproductive Performance of Bulls and Heifers Fed Purified and Natural Diets II. Effect of Diet and Urea on Electrocardiograph and Respiratory Patterns¹

U. S. Department of Agriculture

Abstract

Two trials were conducted to study the effect of feeding a purified diet and infusing or feeding urea on the EKG and respiratory patterns of beef cattle. In trial 1, 21 bull and heifer calves were offered purified diets containing either urea or isolated soybean protein or a natural diet at 14 days of age, and were gradually weaned onto these diets at 84 days of age. EKG and respiratory patterns were obtained at approximately 18, 22 and 26 mo. of age. Long-term feeding of urea or the feeding of purified diets had no apparent effect on respiratory patterns, heart rate and the EKG patterns. In the second trial, two sets of fistulated twin steers, averaging 417 kg., were fasted for 18 hr. and then received a ruminal infusion of 100 gm. of urea per animal over a 30-min. interval. Ruminal pH and ammonia, EKG patterns and respiration rates were determined prior to and at 0.5-hr. intervals post-infusion for 4.5 hr. or until the steers lost their ability to stand. Average peak pH and ammonia-nitrogen concentrations (mg./100 ml.) for set I and II, respectively, were 8.3, 84.1; 8.1, 71.3. Approximately 1.5 hr. after these peaks were reached, set I steers were unable to stand and during this time their heart rate and R-wave amplitude (lead II) markedly increased, T-wave amplitude (lead I), P-R, Q-T and T intervals (lead I and II) markedly decreased, T wave (lead II) inverted and muscular tremors became intense. However, the steers returned to normal after being drenched with a 5% acetic acid solution. There were no apparent changes in respiration rate during this time and no physiological changes occurred in set II steers except for slight muscular tremors. Changes observed in the EKG patterns of steers during urea toxicity were not apparent when cattle were reared using urea as the dietary nitrogen source.

¹ The authors gratefully acknowledge the assistance of Harold Heatwole, Peter Reid and Garlen Smith in obtaining the physiological measurements.

² Animal Husbandry Research Division, ARS, Beltsville, Maryland.