Physiological Changes and Blood Lactic Acid Values in Beef Steers Fed DES Under Ad Libitum, Restricted and Compensatory Conditions

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Abstract
The purpose of this study was to determine the influence of diethylstilbestrol (DES) and differing nutritional regimens on respiratory and heart rates, electrocardiogram (EKG) patterns, rectal temperature and blood lactic acid values of steers. Sixteen Angus steers were fed a 75% concentrate diet ad libitum for a 28-day standardization period. Eight steers were then fed 20 mg DES per steer per day and eight steers served as controls (no DES) during a 28-day ad libitum feeding period followed by a 35-day period of feed restriction during which the animals lost approximately 0.9 kg daily. After this period the animals were fed ad libitum for 60 additional days. The same diet was fed during the entire trial. Data were obtained six times during the trial. Body temperature and blood lactic acid were not affected by the imposed treatments. During ad libitum compared to restricted feeding, respiratory and heart rates were greater (49 vs. 37 respirations/min. and 110 vs. 67 beats/min., respectively), the P amplitude was larger (.19 vs. .12 mv) and the Q-T, T and T-P intervals were shorter (.30 vs. .40, .12 vs. .14 and .11 vs. .37 sec, respectively). As heart rate increased, 60% of the compression of the EKG pattern occurred in the T-R interval and 25% occurred in the Q-T interval. DES had little effect on respiratory rate. During ad libitum and restricted feeding, the DES steers generally had a greater heart rate, (99 vs. 92 beats/min.) shorter Q-T and T intervals (.33 vs. .35 and .12 vs. .13 sec, respectively), and lower more erratic T amplitudes (−.06 vs. −.24 mv) than the control steers. These results suggested a DES effect separate from energy intake, and changes in the T amplitude indicated DES may cause small changes in the refractory time of the ventricular muscles. Under the conditions of this study, however, myocardial changes attributed to DES did not appear great enough to affect the efficiency of the heart muscle. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science