U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version



Animal Feed Science and Technology 190, 2015


U.S. Government work


Sixteen ruminally cannulated crossbred steers (529 ± 45 kg initial body weight, BW) wereused to evaluate in situ dry matter (DM), neutral detergent fiber (aNDF), and N degrada-tion characteristics of low-quality prairie hay, blood urea-N (BUN) and rumen fermentationparameters in steers provided a protein supplement with or without Micro-Aid®(MA; plantderived saponin). Steers were allowed ad libitum access to chopped prairie hay (49 g crudeprotein (CP)/kg DM and 738 g aNDF/kg DM) and randomly assigned to one of four treat-ments: (1) no supplement (C), (2) cottonseed meal and wheat middlings: 920 g DM/d (PC;positive control), (3) MA added to PC to supply 1 g MA/d (MA1), and (4) MA added to PCto supply 2 g MA/d (MA2). Steers were individually supplemented 920 g DM once daily at08:00 along with a vitamin and mineral mix to ensure requirements were met. Orthogonalcontrasts were used to determine the effects of protein supplementation, addition of MAand level of MA inclusion. During in situ phase, forage samples were incubated for a 96 hperiod. Protein supplementation increased DM intake (DMI), particulate passage rate (Kp),and rumen digestibility of DM and NDF (P < 0.001), but there was no effect on rumen Ndegradability. The inclusion of MA did not impact DMI in either phase. Compared to PC,MA decreased Kp(27.8 and 22.7 g DM/kg/h, respectively; P = 0.02), resulting in an increasein rumen aNDF and DM digestibility (P < 0.001). However, there was no influence of MA onapparent total tract digestibility in the metabolism phase. Rumen protozoa concentrationswere suppressed (P = 0.01) with MA inclusion while lactate concentrations and microbialcrude protein (MCP) flow to the small intestine were increased (P = 0.05). There was noimpact on BUN, rumen ammonia, pH, volatile fatty acid (VFA) concentrations or N balancefor MA compared to PC diets. Supplementation improved N balance, MCP synthesis andincreased total concentrations of VFA and independent acetate and propionate concentra-tions. In conclusion, including MA in protein supplements increased rumen DM and a NDFdigestibility of forage, reduced protozoa concentrations and increased daily outflow of MCP.This is indicative of increased rumen fermentation rate and may ultimately impact animalperformance via increased energy and amino acid supply to the small intestine. However,more research is needed to validate this potential impact on animal performance.