Evaluating Ruminal and Small Intestinal Morphology and Microbiota Composition of Calves Fed a Macleaya cordata Extract Preparation

SIMPLE SUMMARY: Mucosal morphology and microbiota composition are key components of the gut development of calves. Adverse health events during pre-weaning and diet changes at weaning can create a lasting impact on those components. Phytogenic feed additives such as the Macleaya cordata plant extract preparations (MCE) improved the gut morphology and microbiota composition of pigs and poultry in previous studies. In this study, MCE was fed to dairy × beef crossbred calves before (6 to 45 d) and after weaning (45 to 90 d). The cumulative impact on the ruminal and small intestinal morphology and microbiota composition were evaluated at 95 d of age. Despite the minor changes in ruminal and intestinal microbial populations, MCE increased the rumen papillae length and villus height: crypt depth in the small intestine, suggesting the potential to enhance gut health and development. ABSTRACT: The objective was to determine the impact of feeding MCE on ruminal and intestinal morphology and microbiota composition of calves. A total of 10 male and 10 female crossbred (dairy × beef) calves (6 d of age) were assigned randomly to control (CTL; n = 10) or MCE-supplemented (TRT; n = 10) groups. The MCE was fed in the milk replacer and top-dressed on the calf starter during pre-weaning (6 to 49 d) and post-weaning (50 to 95 d) periods, respectively. Calves were slaughtered at 95 d to collect rumen and intestinal samples to determine volatile fatty acid (VFA) profile, mucosal morphology, and microbiota composition. The effects of MCE were analyzed by accounting for the sex and breed effects. Feeding MCE increased rumen papillae length (p = 0.010) and intestinal villus height: crypt depth (p < 0.030) compared to CTL but did not affect rumen VFA profile. The TRT had a negligible impact on microbial community composition in both the rumen and the jejunum. In conclusion, feeding MCE from birth through weaning can improve ruminal and small intestinal mucosa development of calves despite the negligible microbiota composition changes observed post-weaning.