PSVIII-2 Effects of post-ruminal yeast cell wall extract on dry matter intake, gastrointestinal fermentation and permeability, and concentrations of white blood cell types in beef heifers exposed to feed restriction

Abstract The objective of this study was to evaluate whether post-ruminal provision of a yeast cell wall extract (YCW) affected gastrointestinal fermentation characteristics and permeability, and white blood cell concentrations for heifers exposed to feed restriction (FR). 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 a 5-d baseline period followed by 5 d of FR where dry matter intake (DMI) was restricted to 30% of ad libitum intake. Data collection included daily DMI, and rumen, fecal and blood samples. Total gastrointestinal and post-ruminal permeability were measured using a ruminal dose of Cr-EDTA and an abomasal dose of Co-EDTA during the baseline and FR phases. Data were analyzed to determine the effects of YCW provision and phase, and the 2-way interaction. There were no TRT or TRT × phase interactions except for fecal propionate concentration. By design, DMI during FR was 30% (P < 0.01) of that observed during baseline (4.1 vs. 13.4 kg/d, respectively). The ruminal concentrations of acetate (45.4 vs. 69.2 mmol/L), propionate (14.5 vs. 26.7 mmol/L), and butyrate (9.9 vs. 16.5 mmol/L) were reduced (P < 0.01) by 34, 46, and 52%, respectively, with FR relative to baseline. Fecal propionate concentration (interaction, P = 0.04) numerically increased (P = 0.12) from baseline to FR for PLC (7.7 vs. 9.6 mmol/L, respectively), while YCW did not change among phases; however, no means differed. Exposure to FR reduced fecal butyrate concentration by 28% (P = 0.03). Gastrointestinal tract permeability (P < 0.01; 2.3 and 2.5% for total and post-ruminal, respectively) was greater during FR compared with baseline, with 2.0% of the Cr-EDTA and 1.6% of the Co-EDTA excreted in urine. The concentrations of neutrophils (P = 0.03) and eosinophils (P < 0.01) were greater during FR relative to baseline (2.28, 1.27 and 0.53, 0.30 ×106 cells/mL, respectively). Exposure to FR altered ruminal SCFA concentrations, increased blood concentrations of neutrophils and eosinophils, and increased gastrointestinal permeability suggesting an inflammatory response; however, post-ruminal provision of a YCW did not mitigate the response to a feed restriction challenge.