PSXII-41 Evaluation of grain sorghum hybrids reveals potential for improving ruminal fermentation

Abstract

Abstract In vitro incubations were used to compare fermentation characteristics of corn (uncharacterized hybrid) to 25 sorghum parental lines and hybrids (Clemson University; Richardson Seed Inc., Lubbock, TX; Scott Seed Company, Hereford, TX). Two experiments were conducted as randomized complete block designs using ruminal contents from two ruminally-fistulated steers (blocks). Grains were ground by a 1-mm screen and used as substrates (2 g, dry matter basis) in laboratory fermenters containing strained ruminal contents and bicarbonate buffer. Fermenters were equipped with pressure monitoring devices (ANKOM Technology, Macedon, NY) to quantify gas production as an indicator of microbial digestion. Cultures were incubated for 24 (experiment 1) to 30 hours (experiment 2), and gas production was recorded at 15-minute intervals. Dry matter disappearance was determined, and organic acid concentrations in the spent culture media were analyzed by gas chromatography. Experiment 1 compared corn to 24 sorghum cultivars, and experiment 2 compared corn to six sorghum cultivars, five of which were represented in experiment 1, plus one waxy hybrid. Data were analyzed using mixed models with cultivar as a fixed effect and block as a random effect. For gas production data, time and the interaction between time and cultivar also were used as fixed effects. For both experiments, there was an interaction between cultivar and time (P < 0.0001) for gas production, revealing large differences among cultivars with respect to their relative susceptibility to microbial fermentation. Similarly, dry matter disappearance; production of acetate, propionate, and butyrate; and acetate:propionate varied substantially among cultivars (P < 0.01), and in many cases exceeding measurements obtained with control corn. Sorghum cultivars used in these experiments varied widely in their susceptibility to digestion by ruminal microorganisms, revealing potential for development of hybrids that can compete with corn as energy sources while contributing to improved sustainability of feedlot production.