Physiological Responses to Des in Heifers

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 ffbitum 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 lo~t 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/rain., respectively), the P amplitude was larger (.19 vs. .12 my) 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-P interval and 25% occurred in the Q-T interval. DES had little effect on respiratory rate. During ad libitum and restric-