In Vitro Rumen Gas Production and Degradability of Different Feeds in Cattle and Bison

The in vitro gas production technique was used to evaluate differences in rumen fermentation of different feedstuffs using bison and beef animals fed similar rations. Rumen fluid was collected via esophageal tube from animals fed the same grass hay (100%) for the evaluation of forages (alfalfa hay, alfalfa meal, grass hay), fibrous byproducts (soyhulls, corn gluten feed, wheat middlings), and protein meals (canola, cottonseed, distillers grains with solubles, linseed, soybean), whereas rumen fluid collected from animals fed the same diet (35% grass hay and 65% concentrate) was used for the evaluation of grains (dry corn, dry barley). All feeds samples were ground to pass a 2 mm screen. Gas production was fitted to a logistic model separating gas production into fast and slow pools. Data were analyzed separately for each run (forage; protein meals+ byproducts; grains) as a factorial design with feed and rumen fluid as the main effects and their interactions. Mean comparisons were performed by using the Tukey test with P < 0.05 as the significant level.
Rumen inoculum source resulted in differences in the gas production kinetics and the partitioning of end products of fermentation (digestibility, gas, microbial biomass, VFA) such that beef inoculum resulted in faster fermentation rates of forages and fibrous byproducts. For protein meals and grains, beef inoculum resulted in faster fermentation rates, less gas produced, higher DM digestibility, less biomass, and more VFA.
Significant interactions were observed for several parameters within each category of feeds. Of interest, bison inoculum was more effective at digesting grass hay (67.2 vs. 63.3%) whereas beef inoculum resulted in higher DM digestibility for alfalfa hay and meal (74.4 ±9.5 vs. 71.9±11.4%). Beef inoculum resulted in higher digestibility of soyhulls (88.8 vs. 76.9%) with no differences between the two sources of inoculum for corn gluten feed and wheat midds digestibility (75.7 vs. 77.7%). Beef inoculum resulted in higher DM digestibility for barley (90.3 vs. 75.0%), whereas corn DM digestibility was not different between the two inoculum sources (92.2±1.00). Differences in rumen fermentation between bison and cattle may be attributed to differences in microbial populations.