149 Using respiratory gas flux and backward dietary energy partitioning to estimate energy intake by beef cattle fed a high concentrate diet

Abstract Twelve Charolais steers (BW = 498 ± 47.4 kg) were used in a 73-d feeding experiment. Our objective was to determine if CH4 and CO2 emissions, and O2 consumption could be used as biomarkers to estimate energy intake in growing beef cattle when integrated with backward dietary energy partitioning calculations when fed a high concentrate diet. Steers were housed in a pen equipped with individual feed bunks with access to an automated head chamber system (AHCS; GreenFeed, C-Lock, Inc., Rapid City, SD). Steers were randomly assigned to 1 of 3 treatments according to DMI as multiple of maintenance, which are 1.1 (1.1 M, n = 4), 1.4 (1.4 M, n = 4), and 1.8 (1.8 M, n = 4). The diet fed was 35% chopped sorghum hay (CP = 6.39% of DM; in vitro OM digestibility = 57.77%) and 65% concentrate (CP = 19.10% of DM; in vitro OM digestibility = 91.84%). The concentrate consisted of 41.75% flaked corn, 8.5% cottonseed meal, 13% distillers’ grain and 1.75% limestone. Steers were supplemented daily with 0.85 kg of alfalfa pellets (Medicago sativa; CP= 16.55%; in vitro OM digestibility = 87.01%) that were fed through the AHCS as bait. Methane tended (P = 0.09) and CO2 emissions and O2 consumption (P 0.01) increased with the increasing feeding rates. Measured gross energy (GE; 21.9, 24.8, 29.5 Mcal/d, respectively), digestible energy (DE; 19.7, 22.0, 25.8 Mcal/d, respectively), and metabolizable energy (ME; 17.2, 19.2, 22.7 Mcal/d, respectively) intake levels increased with the increases in energy retention and heat production. The predicted values for GE (17.4, 23.6, 28.2 Mcal/d), DE (15.1, 20.8, 24.4 Mcal/d), and ME (12.6, 17.9, 21.3 Mcal/d) intake rates increased with the increase from 1.1 M to 1.8 M. Comparison of measured and predicted GE, DE, and ME intake rates agreed closely (r = 0.95, 0.93, 0.92 Pearson correlation, respectively). This experiment shows that together with multiple short-term breath measurements from an AHCS, BW, and an estimate of average daily gain, GE, DE, and ME intakes by cattle consuming a high concentrate diet can be predicted.