Influence of low-level tannin supplementation on comparative growth-performance of Holstein and Angus x Holstein cross calf-fed concentrate-based finishing diets for 328 days.

The objective of the current study was to evaluate the effects of tannin and monensin supplementation in feedlot diets and breed (Holstein vs. Angus × Holstein) on growth performance, energetic efficiency, and carcass characteristics. Eighty purebred Holstein calves (HOL; initial body weight (BW) = 130 ± 5 kg) and eighty Angus × Holstein calves (AXH; initial BW = 129 ± 6 kg) were blocked by initial BW and randomly assigned to 40 pens. Dietary treatments consisted of a steam-flaked corn-based diet supplemented with 1) no feed additive (CON); 2) 30 mg of monensin/ kg of dry matter (DM) (MON; Rumensin 90, Elanco, Greenfield, IN); 3) 1.5 g tannin)/ kg of DM (TAN; ByPro, 70% condensed tannin, SilvaFeed, Indunor, S.A., Buenos Aires, Argentina); 4) M+T, the combination of MON plus TAN dietary treatments. Data were analyzed as a randomized complete block in a 2 x 4 factorial arrangement of treatments, using pens as experimental units. There were no interactions (P > 0.05) between feed additives and breed. Supplemental MON increased (P ≤ 0.04) initial 112-day BW and gain efficiency. However, there were no dietary treatment effects (P > 0.10) on overall growth performance. Monensin supplementation decreased (P = 0.04) minimum daily ruminal temperature compared with other dietary treatments during July, but TAN did not affect ruminal temperature. Holstein steers had greater (P = 0.04) overall DM intake compared with AXH, with no difference (P = 0.19) in overall ADG, leading to increased (P < 0.01) gain efficiency for AXH compared with HOL. Dietary net energy for maintenance and gain, based on growth performance, were greater (P ≤ 0.01) for AXH vs HOL. Compared with HOL, AXH steers had greater (P ≤ 0.01) carcass weight, dressing percentage, kidney, pelvic, and heart fat, 12th rib fat thickness, longissimus area, and preliminary yield grade. Holstein steers had lower (P ≤ 0.04) minimum average ruminal temperature during June compared with AXH, with no differences (P ≥ 0.14) between breeds during July or August. Results indicate that feed additives did not appreciably affect steer growth performance and carcass characteristics, but crossbred AXH steers had greater growth performance, efficiency of dietary energy utilization, and carcass quality measures compared with HOL. This study observed a reduction (4.7%) in maintenance energy expenditure in AXH compared with HOL, implying in maintenance energy coefficient of 0.086 vs 0.082 for HOL and AXH, respectively.