483 DMI, gastrointestinal tract fermentation and permeability, and white blood cell responses in beef heifers provided post-ruminal yeast cell wall extract following feed restriction

Abstract The objectives of this study were to 1) evaluate gastrointestinal fermentation characteristics and permeability, and white blood cell concentrations as beef heifers recovered from a feed restriction (FR) challenge, and 2) determine whether post-ruminal provision of a yeast cell wall extract (YCW) modulated responses. Ruminally cannulated beef heifers (n = 8) were used in a 2 × 2 crossover design. Treatments (TRT) included an abomasal infusion of a placebo (PLC; maltodextrin) or YCW derived from Saccharomyces cerevisiae (2 g/dose) infused at 0600 and 1800 h. Heifers were subject to 5-d of FR (offering 30% of ad libitum DMI) followed by five 5-d recovery phases (REC1, REC2, REC3, REC4, and REC5). Daily DMI, and rumen, fecal, and blood samples were collected on d 5 of FR, REC1, REC3, and REC5 with an additional collection on d 2 of REC1. Total gastrointestinal and post-ruminal permeability were measured using a ruminal dose of Cr-EDTA and an abomasal dose of Co-EDTA, respectively, during FR, REC1, REC3, and REC5 with concurrent urine collection. Data were analyzed to determine the effects of YCW provision, day, and the 2-way interaction. There were no TRT or TRT×day effects for any variables except DMI (interaction, P = 0.04), where DMI did not differ during the FR challenge; however, heifers provided YCW had a greater increase by REC1 compared with PLC heifers without any means differing. DMI progressively increased from FR, to REC1, REC2, and REC5. Ruminal acetate concentration increased (P 0.01) from FR (45.4 mmol/L) to REC1 d5 (60.1 mmol/L) and increased further to REC3 (67.3 mmol/L) with no change thereafter (68.3 mmol/L in REC5). Ruminal propionate concentration increased (P 0.01) from FR (14.5 mmol/L) to REC1 d2 (27.7 mmol/L) and was not different thereafter. Similarly, butyrate concentration increased (P 0.01) from FR (7.9 mmol/L) to REC1 (d 5; 15.0 mmol/L) and was not different thereafter. Fecal acetate, propionate, and butyrate concentrations were not affected by day (P ≥ 0.12). Total gastrointestinal and post-ruminal permeability were greatest during FR (P 0.01; 2.6% and 2.2% of the infused marker was excreted in urine, respectively) and decreased to 1.6% and 1.1%, respectively, in REC3 followed by an increase in REC5 for total (2.0% of infused) but not post-ruminal (1.0% of infused) permeability. The concentration of neutrophils (P 0.01) was greatest on REC1 d2 (4.84 ×106 μmol/mL) and eosinophil concentration (P 0.01) was greatest during FR (0.53 ×106 μmol/mL), least on d 2 of REC1 and increased on d 5 of REC1 but was not different thereafter. WBC (P 0.01) gradually decreased (P = 0.02) from FR and REC1 d2 to REC3 and REC5. Post-ruminal provision of YCW may accelerate increases in DMI early in the recovery from FR, yet treatment did not modulate ruminal or fecal SCFA, blood concentrations, or gastrointestinal permeability.