The effect of zilpaterol hydrochloride supplementation on energy metabolism and nitrogen and carbon retention of steers fed at maintenance and fasting intake levels

Authors: WALTERS, LEE-ANNE - West Texas A & M University; COLE, NOEL - Retired ARS Employee; JENNINGS, JENNY - Texas Agrilife Research; HUTCHESON, JOHN - Merk Animal Health; Meyer, Beverly; SCHMITZ, A - West Texas A & M University; REED, D - West Texas A & M University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2016
Publication Date: 10/24/2016
Citation: Walters, L., Cole, N.A., Jennings, J., Hutcheson, J., Meyer, B.E., Schmitz, A.N., Reed, D.D. 2016. The effect of zilpaterol hydrochloride supplementation on energy metabolism and nitrogen and carbon retention of steers fed at maintenance and fasting intake levels. Journal of Animal Science. 94:4401-4414. doi:10.2527/jas2016-0612.

Interpretive Summary: Beta-agonist compounds such as zilpaterol hydrochloride (ZH) have the ability to greatly increase weigh gain of finishing cattle late in the feeding period. It does this by repartitioning nutrients away from fat metabolism to lean muscle growth. However, some of the energetic effects of feeding SH are not known. Therefore we conducted an indirect respiration calorimetry trial to examine energy metabolism, apparent nutrient digestibility (appND), carbon retention (CR) and nitrogen retention (NR) of cattle supplemented with ZH). Beef steers (n=20; 463 ± 14 kg) were individually fed an a maintenance level of energy intake and were either fed ZH (90 mg/hd/d) or not fed ZH (CONT) for 20 days. Cattel were placed in respiration chambers (n=4) to quantify heat production. Steers were harvested after a 6 d ZH withdrawal and carcasses wer evaluated. No differences in dry matter intake, appND, O2 consumption or CH4 production (P = 0.12) were detected between treatments, however ZH cattle had greater CO2 production. Digestible and metabolizable energy did not differ (P = 0.19) between treatments, however urinary energy was greater in CONT cattle than ZH cattle. Steers treated with ZH tended to have greater heat production but the effect was reduced when corrected for body weight. Control cattle excreted more (P = 0.05) nitrogen in urine; thus nitrogen retention tended to be greater for ZH-fed steers. Feeding ZH increased dressing percent and loin eye area. Separable carcass lean and actual skeletal muscle protein (SMP) were increased with ZH. Results from this trial indicate that ZH treatment increases (P = 0.03) SMP and tends (P = 0.07) to increase nitrogen retention as well as modify HP during maintenance by increasing CO2 production.

Technical Abstract: An indirect calorimetry trial examined energy metabolism, apparent nutrient digestibility (appND), carbon retention (CR) and nitrogen retention (NR) of cattle supplemented with zilpaterol hydrochloride (Z). Beef steers (n=20; 463 ± 14 kg) blocked (n=5) by weight and source were individually fed and adapted to maintenance energy intake for 21 d prior to Z (90 mg/hd/d) or C treatment for 20 d (455 ± 14 kg at start of treatment). Respiration chambers (n=4) were used to quantify heat production (HP) during maintenance (M; d 12 to16 of Z period) and fasting heat production (FHP; d19 to 20 of Z period, total 4 d fast). Steers were harvested after a 6 d Z withdrawal and carcasses graded 24 h post-harvest. Control cattle lost more BW (P < 0.01; 9 vs. 2 kg, respectively) during M while BW loss of Z steers was greater (P < 0.01; 9 vs. 4 kg, respectively) during FHP although no differences (P = 0.76) were detected for gain:feed, ADG and end BW. No differences in DMI, appND, O2 consumption or CH4 production (P = 0.12) were detected between treatments, however Z cattle had greater CO2 production during M (P = 0.04; 2325 vs. 2185 L/steer; 23.6 vs. 22.4 L/kg BW0.75). Digestible energy and ME did not differ (P = 0.19) between treatments, however urinary energy was increased (P = 0.05; 0.091 vs. 0.074 Mcal) in C cattle. Steers treated with Z tended to have greater HP (P = 0.09; 12.44 vs. 11.69 Mcal, respectively) but the effect was reduced on a BW0.75 basis (P = 0.12; 0.126 vs. 0.120 Mcal/kg BW0.75, respectively). No treatment difference in FHP was observed (P = 0.32) although CO2 production (L/steer) increased with Z treatment (P = 0.04; 1423 vs. 1338 L/steer). Control cattle excreted more (P = 0.05) N in urine (39.8 vs. 32.4 g/d, respectively), thus NR (P = 0.07; 22.14 vs.14.12 g/d) tended to be greater for Z fed steers. Steers treated with Z lost more carbon via CO2 (P = 0.04; 1,036.9 vs. 974.3 g, respectively) although total CR did not differ between treatments (P = 0.23). Empty body weight (EBW), HCW and harvest yields (g/kg EBW) were not different between treatments (P = 0.13), whereas Z increased dressed yield (P = 0.02; 62.12 vs. 60.65%, respectively) and LM area (P = 0.02; 77.81 vs. 70.90 cm2). Separable carcass lean and actual skeletal muscle protein (SMP) were increased with Z (P = 0.04; 201.6 vs. 196.0; 41.2 vs. 38.4 kg, respectively). Results from this trial indicate that Z treatment increases (P = 0.03) SMP and tends (P = 0.07) to increase NR as well as modify HP during maintenance by increasing CO2 production