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Effect of ractopamine hydrochloride and zilpaterol hydrochloride on the electrocardiogram and blood lactate in finishing steers
Thirty Angus steers (506 kg +/-5.5kg) were used to examine the effect of ractopamine hydrochloride and zilpaterol hydrochloride on the cardiac physiology and blood lactate concentration of finishing beef steers. Cattle were randomly assigned to 1 of 3 treatment groups: control (CON), ractopamine hydrochloride (300 mg∙animal-1∙d-1; RAC), and zilpaterol hydrochloride (8.3 mg/kg DM basis; ZIL). Cattle were allowed to acclimate to pens and Calan Gate feeders for 43 d prior to trial initiation. Steers were housed in outdoor dirt-floor pens with ad libitum access to feed and water. Holter electrocardiograph (ECG) monitors were placed on cattle on days -2, 6, 13, and 24 of the trial and recorded continuously for 72 h, 24 h, 24 h, and 96 h, respectively; d 0 was the first day of beta agonist feeding. Blood samples were obtained via jugular venipuncture for complete blood count, serum chemistry and blood lactate (BL) analysis at the time of ECG monitor application. Electrocardiogram recordings were evaluated for mean heart rate (MHR) in beats per minute (bpm), ventricular (VPB), and supraventricular arrhythmia events per day (SVPB). Cattle fed ZIL (77.6 bpm +/- 1.19) and RAC (78.4 bpm +/- 1.18) had greater MHR than CON (74.2 bpm +/- 1.27). No differences were observed in VPB, or SVPB in the CON, RAC or ZIL treated cattle. No differences were found among treatments in arrythmia rate when classified as single beat, paired beat, or greater than 2 beats per event. Single beat events represented 84% of VPB and 90% of SVPB events. No differences were observed in BL among CON (3.1 mmol/L), RAC (2.9 mmol/L) and ZIL (2.8 mmol/L). Creatinine Kinase (CK) increased (P<.03) in ZIL cattle (220.3 U/L), compared to CON (111.9 U/L) and RAC cattle (120.2 U/L) at d 13. On d 24 CK was increased in ZIL (226.9 U/L), than CON (132.5 U/L) and RAC (135.4 U/L).
In conclusion, RAC and ZIL increased MHR in feedlot cattle, but had no effect on arrythmia rate, arrythmia classification or blood lactate. Also, ZIL increased CK compared to CON and RAC on days 13 and 24.
Keywords: Beta Agonist, Electrocardiogram, Blood Lactate, Cattle