Effects of dietary supplement sources on the rate and extent of in vitro ruminal degradation of alfalfa-based diets for cattle

Two ruminally cannulated steers [928 ± 25.5 kg body weight (BW)] were fed alfalfa hay at 2.0% of BW and served as donors of rumen fluid. Treatments were early-bud alfalfa (CON) or a combination [dry matter (DM) basis] of 80% early-bud alfalfa with 20% of corn silage (CS), brome grass hay (BGH), soybean hulls (SBH), beet pulp (BP), corn grain (CORN), dried corn distillers’ grains with solubles (DDGS), or wheat middlings (MIDD). Tubes were incubated at multiple time points over a 72 h period and assessed for rate and extent of digestion. Samples were run in duplicate and replicated over 3 d. The potential extent of DM and organic matter (OM) degradation increased (P < 0.001) with CS, SBH, BP, CORN, and DDGS supplementation compared with CON. All supplements except MIDD decreased (P < 0.001) the fractional rates of DM and OM degradation compared with CON, with BGH, SBH, and DDGS having the lowest rates. Supplementation of SBH had the lowest (P < 0.001) initial rate of DM and OM degradation. These data indicate that SBH increases the extent of digestion while reducing the initial rate of degradation, suggesting that SBH has potential to reduce the incidence of frothy legume bloat.