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

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Twelve Charolais steers (initial shrunk BW = 223 ± 21.5 kg) were used in a 73-d feeding experiment to evaluate the use of CH 4 and CO 2 emissions, and O 2 consumption as biomarkers in the estimation of energy intake by growing beef cattle fed a high-concentrate diet when integrated with backward dietary energy partitioning calculations. Steers were housed in a pen equipped with Calan gates with access to an automated head-chamber system ( AHCS ). Steers were randomly assigned to 1 of 3 treatments according to DM intake as a multiple of maintenance, which are 1.1 ( 1.1M , n = 4), 1.4 ( 1.4M , n = 4), and 1.8 ( 1.8M , n = 4) of a 13.0 MJ/kg diet. The diet fed was 350 g of chopped sorghum hay (CP = 64 g/kg of DM; in vitro digestibility = 578 g/kg of organic matter ( OM )) and 650 g of concentrate (CP = 191 g/kg of DM; in vitro digestibility = 918 g/kg of OM)/kg of DM. The concentrate consisted of 418 g of flaked corn, 85 g of cottonseed meal, 130 g of distillers’ grain, and 175 g of limestone/kg of DM. Steers were supplemented daily with 1.0 kg of alfalfa pellets ( Medicago sativa; CP = 166 g/kg of DM; in vitro digestibility = 870 g/kg of OM) that were fed through the AHCS as bait. Methane tended ( P = 0.07), and CO 2 emissions and O 2 consumption ( P < 0.01) increased with the increasing feeding rates. Calculated intake for gross energy ( GE ; 71.4, 86.9, and 106.7 MJ/d, respectively), digestible energy ( DE ; 61.1, 72.1, 86.7 MJ/d, respectively), and metabolisable energy ( ME ; 50.35, 60.19, 73.30 MJ/d, respectively) increased concurrently with the increases in energy retention and heat production. The predicted intake rates for GE (63.1, 78.3, and 93.9 MJ/d, respectively), DE (52.8, 63.9, and 73.6 MJ/d, respectively), and ME (42.0, 52.0, and 60.2 MJ/d, respectively) increased concurrently with the increase from 1.1M to 1.8M. Pearson correlations of calculated and predicted GE, DE, and ME intake rates agreed closely (r = 0.95, 0.88, and 0.85, respectively). This experiment shows that with multiple short-term breath measurements from an AHCS, BW, and an estimate of average daily gain that GE, DE, and ME intakes by cattle consuming a high-concentrate diet can be predicted.