The effects of technology use in feedlot production systems on the health status of finishing steers

Abstract Text: Crossbred steers (n =336; initial BW = 379 ± 8 kg) were utilized in a RCBD (24 pens; 8 pens/treatment; 14 steers/pen) to determine the effects of technology use in feedlot production systems on animal health.  Treatments consisted of an all-natural treatment (receiving no growth promoting technologies; NAT), a conventional treatment (implanted with 40 mg of estradiol and 200 mg of trenbolone acetate on d 0, and fed 33 and 9 mg/kg of monensin and tylosin daily, respectively; CONV), and a CONV treatment plus the addition of a beta-adrenergic agonist (zilpaterol hydrochloride at 6.76 g/ton for the last 20 DOF with a 3-4 d withdrawal; CONV-Z).  Steers were observed daily for signs of respiratory disease and lameness.  Blood samples were collected from 7 steers/pen every 28 d until d 112 and then every 10 d during the beta-agonist feeding period to determine the hemogram.  At harvest, livers were observed for abscesses and lungs were palpated for abnormalities.  Three steers died during the study with necropsies indicating bloat (1-NAT; 1-CONV-Z prior to the zilpaterol feeding period; 1-CON-Z during the zilpaterol feeding period) as the cause of death and no steers required treatment for respiratory disease.  All blood analytes measured were within clinically normal concentrations throughout the experiment.  Treatment had no effect on red blood cells, hematocrits, reticulocytes, or platelets (P >0.34).  There was a Treatment × Time interaction for total white blood cells (WBC; P <0.01) with CONV and CONV-Z cattle having greater WBC counts than NAT cattle from d 28 (9.83 and 9.54 vs. 8.60 K/µL, respectively) through d 132 (10.83 and 11.25 vs. 9.83 K/µL, respectively; P <0.03).  There was a Treatment x Time interaction (P < 0.01) for neutrophils with CONV and CONV-Z cattle having greater neutrophil counts than NAT cattle from d 28 (2.57 and 2.47 vs. 1.99 K/µL, respectively) through d 132 (3.51 and 3.47 vs. 2.44 K/µL, respectively; P <0.03).  More monocytes were detected in the CONV and CONV-Z cattle compared to the NAT cattle (1.21 and 1.22 vs. 1.08 K/µL, respectively; P <0.01).  No differences in blood analytes were observed between CONV and CONV-Z during the zilpaterol feeding period (P >0.25).  There was no effect of treatment on liver abscesses (P =0.74) or lung abnormalities (P >0.09).  Collectively, this experiment demonstrates that growth promoting technologies did not affect overall health of finishing steers.

Keywords: beta-adrenergic agonist, blood analytes, health status