PSXIII-16 - Selected feed additives to improve diet digestibility and carcass quality of feedlot-finished Angus crossbred steers

Abstract: Our objective was to evaluate the effects of supplementation using different feed additives on the apparent digestibility and carcass traits of feedlot-finished steers fed a diet consisting of 35% forage and 65% concentrate. This study was a randomized block experimental design with two treatments: Diet containing sodium monensin + virginiamycin (MO+VM, 20ppm and 15 ppm, respectively); and Diet with a blend of essential oils (Crina^® Ruminants, 90 ppm) + exogenous α-amylase (Ronozyme Rumistar^TM, 560 ppm) + 25-hydroxy-vitamin-D3 (Hy-D^®, 0.1 ppm), (EO+ENZ+HYD), with nine repetitions each (pens), where each experimental unit was represented by a pen (with two animals each). Thirty-six ½ Angus blood steers with an average initial weight of 400 kg were evaluated along an experimental period of 112 days, with 28 adaptation days and 84 evaluation days, divided into 3 periods of 28 days each. The digestibility evaluation was carried out at the end of the first and third experimental periods, both in a continuous time of 48 hours. For this, daily intake and leftovers were measured, total feces were collected, diets and leftovers from each pen were sampled for laboratory analysis. At the beginning and end of the experiment, using ultrasound, carcasses were analyzed for loin eye area, marbling ratio, subcutaneous fat thickness (SFT), and rump fat thickness (RFT). Means were compared by ANOVA using the GLM procedure (SAS, 1993), adopting a significance level of 5%. Fecal output (kg.day^-1), both in dry matter and natural matter, and fecal DM content were similar between treatments (P >0.05). Feeding EO+ENZ+HYD reduced (P< 0.05) fecal starch percentage by 20% and improved (P< 0.05) the apparent digestibility of DM and starch (5.16%, 67.40% and 95.50%) compared to the use of MO+VM (6.41%, 66.47% and 94.27%). These better results suggest a effect of a more favorable fermentation of the diet caused by modulation of the ruminal microbiota, optimization in the use of starch and increase in microbial protein synthesis caused by supplementation with EO+ENZ+HYD. Animals supplemented with EO+ENZ+HYD had greater (P< 0.05) RFT (12.22 mm) at slaughter compared to those supplemented with MO+VM (10.42 mm), and greater marbling and RFT gain over the finishing period (0.58 points and 7.50 mm) than those supplemented with MO+VM (0.32 points and 5.93 mm) after 112 days of feedlot. In conclusion, the blend of essential oils + exogenous α-amylase + 25-hydroxy-vitamin-D3 was effective in replacing the combination sodium monensin + virginiamycin, improving the apparent digestibility of DM and starch, as well as increasing marbling and carcass cover fat deposition of feedlot-finished steers.