Effects of lubabegron removal on tissue concentration, calculated ammonia gas emissions, live performance, and carcass characteristics of beef steers

Objective

Our objective was to evaluate tissue residue levels, calculated NH₃ gas emissions and live and carcass growth in finishing beef steers fed lubabegron (LB).

Materials and Methods

In Exp 1, 50 steers were fed ad libitum a diet containing LB at 1.54 or 5.53 mg/kg of DM for 14 d, followed by a voluntary removal duration of 0, 1, 2, 4, 6, or 8 d before slaughter. Nongastrointestinal tract (GI) tissues collected and analyzed were muscle, liver, tongue, heart, bone, bone marrow, and tendon. In Exp 2, 700 steers were supplemented with either a diet containing LB at 3.5 mg/kg of DM or a negative control for 56 d. Supplementation was followed by removal durations of 0, 2, 4, 6, 8, and 16 d before slaughter. At slaughter, a subset of steers (35; 5 per treatment) were selected to sample GI and non-GI tissues for LB residues, and the remaining animals were used to evaluate the live and carcass growth.

Results and Discussion

In Exp 1, all non-GI tract tissues were below the 3 μg/kg limit of quantification (LOQ), except for the tongue. At the greater supplementation level (5.53 mg/kg) tongue had residues of 3.80 and 2.08 μg/kg for removal durations 0 and 1 d, respectively. Within GI tissues, steers supplemented with the lower dose (1.54 mg/kg) had detectable residues within the reticulum (0–2 d), rumen (0–1 d), omasum (0–4 d), and abomasum (0–2 d). Steers supplemented with the higher dose (5.53 mg/kg), had detectable residues within the reticulum (0–4 d), rumen (0–2 d), omasum (0–6 d), small intestine (0–1d), and large intestine (0 d). In Exp 2, the LOQ for LB residues was 1 μg/kg, and residues were detectable in liver (0 d), muscle (0–2 d), rumen (0–4 d), reticulum (0–4 d), and omasum (0–16 d). Steers supplemented with LB had greater final BW (P < 0.001), ADG (P < 0.001), G:F (P< 0.001), hot carcass weight (P < 0.001), DP (P < 0.001), and rib-eye area (P < 0.001) than the negative control. Furthermore, steers fed LB exhibited reduced marbling score (P < 0.001) and YG (P < 0.001) compared with control steers. Calculated NH₃ gas emissions were greater (P< 0.001) for control steers (6,204 g/head) compared with LB-supplemented steers (5,202 to 5,348 g/head).

Conclusions and Application

These results demonstrate that LB residue concentrations are affected by supplementation concentrations, tissue type, and duration of removal before slaughter. Furthermore, the LB supplementation results in greater red meat yield and decreased calculated NH₃ gas emissions.