In vitro rumen fermentation and in vivo bloat dynamics of steers grazing winter wheat to corn oil supplementation

The influence of corn oil on in vitro ruminal gas production, bloat potential and weight gain of steers was investigated. Overall objectives were to: (1) quantify in vitro, the effect of sources of rumen fluid, levels of corn oil supplementation on rate of gas production, foam height and foam strength and (2) quantify the influence of corn oil on in vivo rumen fluid bio-film production, bloat potential and weight gain of steers grazing wheat pasture. In Experiment 1, in vitro gas production was measured from 0 to 6 h rumen incubation periods. In vitro rumen foam production and foam strength were measured. In Experiment 2, rumen cannulated steers (n = 18; 330 ± 22 kg) were randomly allocated to one of three treatments (0, 7.5 and 15.0 g corn oil of kg dry matter intake (DMI) steer−1 per day). Samples of rumen contents were taken at day −30, 0, 20 and 30 for analysis of rumen microbial protein fractions, rumen microbial DNA concentration and ethanol precipitable polysaccharide slime (referred to as bio-film). Bloat was visually scored (from 0 to 3) 5 days a week. In Experiment 1, mineral oil was used as a non-nutritive surfactant to serve as a non-nutritive negative control. In vitro rate of gas production was greater (P<0.01) for mineral oil than for corn oil addition to Bermuda grass rumen fluid in Experiment 1. Wheat forage rumen fluid exhibited no response to addition of either oil. Changing the sources of rumen fluid from Bermuda grass hay to wheat forage increased (P<0.01) the rate of gas and potential gas production. As microbial DNA mass in the source of rumen fluid increased, the rate of gas and potential gas production increased. Addition of either mineral oil or corn oil decreased (P<0.01) foam height and foam strength. In Experiment 2, daily feeding corn oil to steers grazing wheat forage had no effect on animal weight gain. Mean bloat scores and steer bloat day, however, were lower (P<0.01) for corn oil addition than for control. Bio-film complexes in clarified rumen fluid increased (P<0.01) at 15.0 g corn oil over control. It is concluded that addition of corn oil reduced bloat by reducing foam production and foam strength in the rumen. There was no nutritive benefit detected in terms of increased live weight gain with either dose level of corn oil.