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
Authors: Armes Wyatt D , Villot Clothilde , Chevaux Eric , Griebel Philip , Mutsvangwa Timothy , Hogan Natacha , Penner Gregory 
Published: September 2024

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 &lt; 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 &lt; 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 &lt; 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 &lt; 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 &lt; 0.01) was greatest on REC1 d2 (4.84 ×106 μmol/mL) and eosinophil concentration (P &lt; 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 &lt; 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.