Effects of zilpaterol hydrochloride on blood gas, electrolyte balance and pH in feedlot cattle

Abstract Text:

The objective of this study was to examine the effects of zilpaterol hydrochloride (ZH) on blood gas, electrolyte balance and pH in feedlot cattle.  Black-hided steers and heifers (n=96) were sourced from a commercial feedlot and transported to the Texas Tech University Beef Center in New Deal, TX.  Cattle were weighed and scanned using real-time ultrasound.  Resulting data were used to predict empty body fat percentage (pEBF %).  Steers (n=48; BW = 520 ± 30.4 kg; pEBF % = 26.2 ± 1.9) and heifers (n=48; BW = 466 ± 29.5 kg; pEBF % = 26.7 ± 1.7) were blocked within gender by pEBF % in a completely randomized block design and randomly assigned to pen (2 pens/block; 4 hd/pen) and treatment (6 pens/treatment): 1) control heifers (HC), 2) ZH heifers (HZ), 3) control steers (SC), 4) ZH steers (SZ).  Venous blood was collected in lithium heparinized tubes through the use of jugular venipuncture on day 5, 10, 15 and 20 of the ZH treatment period.  Blood samples were placed on ice and transported to an on-site station for prompt analysis.  Data were analyzed as repeated measures to assess effects due to treatment.  ZH treatment significantly increased potassium (K) concentration (P < 0.0001).  Calcium (Ca) concentration was reduced in both genders; but, a significant gender x treatment interaction (P = 0.0376) revealed that ZH decreased Ca with a greater magnitude in steers relative to heifers.  ZH treated cattle expressed a tendency for a lower partial pressure of oxygen (pO₂; P = 0.082) relative to control.  No significant gender x treatment interactions or main effects were detected (P ≥ 0.14) for blood pH, partial pressure of carbon dioxide (pCO₂), oxygen saturation (SO₂C), sodium (Na) concentration or percentage of hematocrit (Hct).  Collectively, these data suggest that only minor differences exist between ZH and control cattle with respect to blood gases and pH, such that a causative effect cannot be assumed.  The alterations in K and Ca indicate that biologically significant differences in the cation-anion difference (CAD) may exist when comparing treatment groups.  Furthermore, the significant reduction in blood Ca concentration in ZH treated cattle provides more insight to the well-known reduction in post-mortem tenderness associated with cattle fed a β-adrenergic agonist.

Keywords: cattle, zilpaterol hydrochloride, blood gas