Abstract
An experiment was conducted to evaluate the feed intake, nutrient digestibility and selected rumen parameters in feedlot bulls fed diets containing different feed additives. Six rumen-cannulated Nellore bulls (age = 8 ± 1.0 months; initial BW = 225 ± 13.2 kg) were distributed in a 6 × 6 Latin square design. Six experimental diets based on 30% corn silage and 70% concentrate on a dry matter (DM) basis were evaluated. Diets differed in feed additive on a DM basis, as follows: 1.4% bicarbonate and magnesium oxide in 3:1 ratio (BOX); 36 ppm lasalocid sodium (LAS); 30 ppm monensin sodium (MON); 25 ppm virginiamycin (VIR); 30 ppm monensin sodium plus 25 ppm virginiamycin (MV); and 3.15% commercial mineral supplement containing D-limonene and exogenous α-amylase (EOA). The experiment lasted 144 d, with six periods of 24 d. Each period consisted of 14 d for dietary adaptation, 3 d for feces and urine collection, and 7 d for omasal and ruminal digesta collection. Bulls fed the BOX diet showed greater (P < 0.05) intake of DM, organic matter (OM), neutral detergent fiber (apNDF), crude protein (CP), and starch compared to the other diets. Diets with LAS, MON, VIR, MV, or EOA did not influence (P > 0.05) the DM, OM, apNDF, CP, or starch intake of feedlot bulls. Bulls fed the EOA diet showed greater (trend; P = 0.09) ruminal digestibility of starch compared to the other diets. The feed additives did not affect (P > 0.05) the intestinal or total tract digestibility of starch, rumen pH, microbial efficiency, total rumen fluid, dilution rate, rate of intake, rate of degradation, or passage rate of the DM, OM, apNDF, and starch. In conclusion, LAS, MON, VIR, MV, and EOA diets reduced nutrient intake compared to BOX. Although all feed additives presented similar effects on rumen pH, temperature, and kinetics the presence of exogenous α-amylase in the EOA diet may increase ruminal starch digestibility and apparent total tract digestibility of DM and OM.
Highlights
Feed additives have been increasingly used worldwide to improve feed efficiency or to benefit the ruminal health, especially when greater animal growth performance is required, such as in feedlot systems [1,2,3]
Buffers and alkalizers have been replaced by ionophores [e.g., monensin sodium (MON) and lasalocid sodium (LAS)] and non-ionophore antibiotics [e.g., virginiamycin (VIR)] in feedlot diets
Studies [13, 14] have shown that animals fed diets containing essential oils plus exogenous α-amylase (EOA) may show increased feed intake, starch digestibility, and average daily gain compared to those fed diets with other feed additives, such as MON
Summary
Feed additives (e.g., buffers, ionophores, non-ionophore antibiotics, plant compounds with antibacterial properties, exogenous enzymes, etc.) have been increasingly used worldwide to improve feed efficiency or to benefit the ruminal health, especially when greater animal growth performance is required, such as in feedlot systems [1,2,3]. Recent surveys [2, 3] showed that more than 92% of the feedlots in Brazil and the United States use some type of feed additive in their receiving and finishing diets Buffers, such as sodium bicarbonate, were commonly used in feedlot diets in the past and are still an option to mitigate the occurrence of metabolic disorders and to increase intake and daily gain [4,5,6]. Plant compounds with antibacterial properties and exogenous enzymes have been increasingly used to replace antibiotics in feedlot diets [13, 14] In this context, studies [13, 14] have shown that animals fed diets containing essential oils plus exogenous α-amylase (EOA) may show increased feed intake, starch digestibility, and average daily gain compared to those fed diets with other feed additives, such as MON
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