Effects of a blend of essential oils and exogenous α-amylase in diets containing different roughage sources for finishing beef cattle

Abstract

Two experiments were carried out to evaluate the effects of feed additives and roughage sources on performance, carcass characteristics, meat quality, and total tract apparent digestibility of finishing bulls. In Exp. 1, 88 Nellore bulls were used in a randomized complete block design with a 2 × 2 factorial arrangement, to evaluate the effects of feeding sodium monensin (MON; 26 mg/kg DM) or the combination of a blend of essential oils + exogenous α-amylase (BEO+AM; 90 and 560 mg /kg DM, respectively of commercial product) associated with corn silage (CS) or sugarcane bagasse (SCB) on performance, carcass, and meat quality of finishing cattle. Bulls fed CS-based diet had a higher dry matter intake (DMI; P < 0.001), average daily gain (ADG; P = 0.015), final body weight (P = 0.049), carcass weight (P = 0.004), dressing percentage (P = 0.008), and ribeye area (P = 0.035), however, a higher gain:feed (G:F) was observed for SCB-fed animals (P = 0.016). No effect of roughage source was observed for fat thickness, fecal starch, or meat quality. Feeding BEO+AM increased ADG (P = 0.043), final body weight (P = 0.023), carcass weight (P = 0.023), and decreased fecal starch (P = 0.013) as compared to animals fed MON, with no differences in DMI and G:F. Feed additives did not affect carcass nor the majority of meat quality traits. In Exp. 2, eight rumen-cannulated Nellore bulls were used in a replicated 4 × 4 Latin square design to evaluate the total tract apparent digestibility of nutrients, ruminal fermentation characteristics, and rumen microbial protein synthesis of diets used in Exp. 1. Roughage source did not affect intake nor the total tract apparent digestibility of most nutrients, except for the digestibility of crude protein (P = 0.003), which was greater for CS than for SCB-fed animals. Higher acetate (P < 0.001) and acetate:propionate ratio (P = 0.001), and less propionate (P = 0.001) were observed in CS-fed animals. Roughage source did not affect purine derivatives concentration nor the synthesis of microbial nitrogen. Bulls fed BEO+AM had lower acetate (P = 0.036) and ammonia nitrogen (P = 0.017) concentrations but increased uric acid (P = 0.044) and synthesis of microbial nitrogen (P = 0.027) as compared to the MON-fed animals. Feeding corn silage improved animal performance and carcass characteristics regardless of feed additives. A combination of a blend of essential oils plus exogenous α-amylase improved animal performance and carcass characteristics compared to sodium monensin.