AFST: Influence of quebracho tannin extract fed at differing rates within a high-roughage diet on the apparent digestibility of dry matter and fiber, nitrogen balance, and fecal gas flux

Abstract

Sustainable ruminant production is an important element in meeting the high-quality protein requirements of an increasing global population. Gaseous byproducts from ruminant production such as methane (CH4) and nitrous oxide (N2O) can reduce energy efficiency and be detrimental to the environment. Condensed tannins (CT) are interesting alternatives for improving animal and system-level efficiency due to their potential for improving nitrogen use efficiency and reducing enteric CH4. In this study, a Latin rectangle design using four periods and 8 English crossbred steers (435 ± 17 kg BW) were used to determine the effects of quebracho tannin (QT) extract. We evaluated how QT inclusion at 0, 15, 30, and 45 g/kg of dietary dry matter (DM) within a roughage-based diet affected metabolic parameters and fecal gas emissions. Using metabolism crates, total collection of excreta occurred over 4 d followed by an enumeration of fecal gas fluxes via static chambers. The 45 g/kg inclusion rate affected intake and increased fecal DM production (P ≤ 0.01). Addition of QT affected all digestion coefficients (P < 0.001) with a linear reduction as QT level increased. Reduced digestibility led to greater daily energy excretion with increasing QT inclusion (P < 0.001), resulting in a linear reduction in daily digestible energy (DE), DE/kg DM intake, and DE-to-gross energy ratio. Greater daily fecal energy and N outputs were observed with increased QT (P < 0.001), but no difference in concentrations. The feeding of QT resulted in a linear shift in the route of N excretion from urine to feces (P = 0.005). For fecal gas flux, cumulative CO2 and N2O decreased linearly with increased QT supplementation; by contrast, CH4 displayed a cubic relationship with the 30 g/kg treatment having the least emissions. Total CO2 equivalents (CO2e; CH4 + N2O) displayed a cubic relationship with emissions being largely driven by CH4 production (r = 0.99, P < 0.01). In contrast, gross CO2e (Total CO2e + CO2) displayed a linear reduction in emissions as QT inclusion increased, with CO2 having the largest influence (r = 0.99, P < 0.01). Emission factors displayed a linear decrease in fecal N emitted as N2O-N with increased QT inclusion (P < 0.05). We concluded that feeding QT above 15 g/kg DM could reduce fecal CO2 and N2O emissions but also apparent digestibility and N balance. Determination of energy fractionation and urinary gas emissions are required to fully define the influence of CT upon system efficiency.