Body weight and implant effects on animal performance, sera metabolites, and blood pressure in feedlot cattle

The study objective was to evaluate growth performance, sera metabolites, carcass characteristics and pulmonary arterial pressure as effected by body weight and implant status. Crossbred steers (n = 20) were used in a 2 × 2 factorial design: [body weight: light (L), or heavy (H); implant: Non-implanted (NoIMP), or Implanted (IMP)] with steer as the experimental unit. Initial weights for L and H steers were 398 ± 27.6 and 547 ± 25.2 kg, respectively. Implanted steers received a Revalor-200 (200 mg TBA + 20 mg E2, Merck Animal Health, Madison, NJ) on d 0. Cattle within treatments were group housed in common pens (n = 5 steers/pen). Bodyweight, blood samples, and pulmonary arterial pressure were collected on d 0, 14, 35, 70 and 104. Cattle were fed once daily to provide ad libitum access to feed. The finishing diet contained (DM basis) 13.3% CP, 2.13 Mcal/kg NEm, and 1.45 Mcal/kg NEg. Growth performance and carcass traits were analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC). Sera metabolites were analyzed as repeated measures over time, with day as the repeated measure. For all analyses, an α level < 0.05 determined significance. Heavy cattle consumed 2.2 kg more per head of DM daily than L cattle (10.14 vs 7.90 kg/d) and IMP steers consumed 1.0 kg more DM daily than NoIMP steers (9.52 vs 8.57 kg/d). Cumulative ADG did not differ between the L and H steers (1.41 vs 1.52 ± 0.06 kg; P = 0.20). Implanting increased (P < 0.01) ADG by 39 % (1.22 vs 1.70 ± 0.06 kg). No differences (P > 0.05) in ADG were observed in NoIMP vs IMP cattle beyond d 70 (1.21 vs 1.01 ± 0.16 kg; P = 0.38). Serum urea - N concentrations were lower (P < 0.01) in L cattle subjected to IMP during the study and tended to increase over time for the other treatments. Ribfat, HCW, LM, marbling score, calculated YG, and EBF were greater (P ≤ 0.05) in H vs L. IMP cattle had heavier HCW (P < 0.01) but decreased marbling scores (P = 0.05) compared to the NoIMP group. Mean pulmonary arterial pressure was greater (P < 0.01) for H vs L cattle which may predispose heavier cattle to right - sided heart failure. The steroid implant had no effect on pulmonary arterial pressure (P > 0.49). The study reaffirms the effects of implanting on growth performance and carcass characteristics in cattle. In addition, elevated BW leads to increased pulmonary arterial pressures which increases the risk of right sided heart failure.