The objective of this analysis was to compare the greenhouse gas (GHG) emissions from contemporary grazing cattle production with bison grazing, both modern and historical. The data sets used in this analysis were derived from existing research and conservation properties located outside of Manhattan, KS (USA), which are home to stocker cattle, cow–calf production (CCS), and grazing bison. For stocker cattle, 10 years of animal production data (2007–2016) from season-long stocking (SLS, grazing 156 d) and intensive early stocking systems (IES; 76 grazing d and 2× stocking density) were used for GHG calculations. Enteric CH₄, manure CH₄, and direct nitrous oxide emissions were estimated using the IPCC tier 2 methodology. Historic bison (HGB) enteric CH₄ estimates were calculated using a stocking density of 0.15 ha/animal and assuming that only 13% of grassland was used by bison each year. Within contemporary systems, IES had the lowest emissions (463.3 kg CO₂-eq./ha/yr), while SLS, CCS, and MGB had the highest estimates (494.7, 493.9, and 595.9 kg CO₂-eq./ha/yr, respectively). HGB had the lowest estimated annual emissions at 295.7 kg CO₂-eq./ha/yr. These results imply that the historic grazing baseline of this grassland system is lower but similar to that of contemporary grazing cattle in the Great Plains region.

An experiment was conducted to evaluate the impact of feeding bio-fuel co-products on ruminal fermentation characteristics and composition of omasal digesta flow. Four ruminally cannulated Holstein steers (371 ± 5 kg) were used in a 4 × 4 Latin Square design. Omasal sample collection and triple marker technique was used to quantify fatty acid omasal flow. Treatments were applied as a 2 × 2 factorial where a steam flaked corn (SFC) basal diet (DGS-N CG-N) was replaced with 40% of diet DM as corn distillers grains (DGS; DGS-Y CG-N) or 10% of diet DM as crude glycerin (DGS-N CG-Y) or 40% of diet DM distillers grains and 10% of diet DM as crude glycerin (DGS-Y CG-Y). No effects were observed for the interaction of DGS and glycerin on measured rumen characteristics. Dietary inclusion of glycerin decreased (P = 0.05) ruminal content 4-h post feeding on a DM basis but did not influence DMI (P = 0.64). Feeding DGS had no effect (P = 0.34) on particulate passage to the omasum (kg/d) in spite of greater (P = 0.04) DMI. Feeding DGS reduced flow rate (% of rumen volume/h) (P = 0.05) but did not affect total VFA concentration (P = 0.46) or average ruminal pH (P = 0.72). No differences (P > 0.05) were observed in ruminal parameters when feeding glycerin, besides ruminal particulate content (kg) on DM basis (P = 0.05). An interaction of DGS and glycerin affected intake of stearic (P < 0.01), linoleic (P < 0.01), and linolenic acid (P < 0.01). An interaction of DGS and glycerin did not affect individual fatty acid flow with respect to intake for stearic (P = 0.17), linoleic (P = 0.18), or linolenic acid (P = 0.66). Dietary inclusion of glycerin had no impact on g of linolenic (P = 0.16) or linoleic (P = 0.32) acid transformed. A trend was identified for cattle fed diets with glycerin to have increased (P = 0.07) grams of conjugated linoleic acid (CLA; C18:2 cis-9, trans-11) per gram of linoleic acid intake, with no impact on the percent of saturated fat (P = 0.44) or unsaturated fat (P = 0.43) in omasal flow. For cattle fed diets with DGS, fewer grams of linoleic (P < 0.01) and linolenic (P < 0.01) were present in digesta flow per gram of intake. Inclusion of DGS in the treatment diets also increased (P < 0.01) stearic acid flow (g) and CLA flow (g) per gram of stearic and linoleic acid intake, respectively. Observed differences in CLA proportion post fermentation may indicate interrupted biohydrogenation when glycerin is fed. Inclusion of corn grain in cattle diets increases the dietary concentration of unsaturated fatty acids like linoleic acid. Ethanol co-products are most often made from corn grain in the United States and contain concentrated amounts of unsaturated fatty acids. Concerns with feeding ethanol co-products could arise for cattle producers because the increased unsaturated fat concentration of meat products can lead to shorter meat shelf life. Co-products from bio-diesel production, such as crude glycerin, can be used to replace grain and reduce total unsaturated fat without affecting dietary energy. This study evaluated the effect of ruminal microbes to transform unsaturated fatty acids to saturated fatty acids in diets where steam-flaked corn was replaced by co-products such as distillers grains and crude glycerin. When steam-flaked corn is replaced with distillers grains in beef cattle diets, the fat composition was shifted to a higher proportion of saturated fatty acids due to increased biohydrogenation by ruminal microbes. However, feeding crude glycerin in place of steam-flaked corn increased conjugated linoleic acid, an intermediate product of the fatty acid transformation pathway. Increased conjugated linoleic acid indicates glycerin may impact the ability of microbes to transform linoleic acid to a saturated form.