47 Integrated warm- and cool-season grass rotational grazing management and the equine fecal microbiome

Abstract

Warm-season grasses can be integrated into traditional cool-season grass equine rotational grazing systems to increase summer pasture yield. The objective of this study was to evaluate impacts of this management strategy on the fecal microbiome of grazing horses. Eight mares were randomly assigned to 2 integrated rotational systems (IRS) containing mixed cool-season grass and 1 of 2 warm-season grasses: bermudagrass or crabgrass. Fecal samples were collected after a 3-wk adaptation to each of the following forages: initial cool-season hay (HAY-SP); cool-season pasture in spring (CSG-SP), warm-season pasture in summer (WSG), and cool-season pasture in fall (CSG-FA); and after transition back to hay in the fall (HAY-FA). Analysis of 16S rRNA gene sequences was conducted in QIIME 2, and taxonomy was assigned with SILVA. Alpha diversity metrics were analyzed using a mixed effects model, and β diversity by PERMANOVA. Amplicon sequence variants (ASV) were clustered into bacterial co-abundance groups (BCG) using Sparse Cooccurrence Network Investigation for Compositional data. A random forest classifier was applied to determine if forage could be predicted by BCG composition. BCG specific to each forage were identified by LEfSe, with significance set at LDA > 2.0. Differences were not found between IRS, and combined data are presented (n = 8). Alpha and β diversity metrics differed across forages ( P < 0.05). In addition, random forest modeling was able to predict forage type (accuracy: 0.78 ± 0.15), indicating that shifts in microbiome structure and species composition occur as horses adapt to different forages within IRS. BCG including ASV assigned to Oscillospiraceae and Lachnospiraceae families and within Christenellaceae R-7 group and Eubacterium coprostanoligenes group genera were identified by LEfSe as markers for all forages. BCG specific to HAY-SP included ASV within Roseburia, Blautia , and Saccharofermentans , while Bacteriodales BS11 gut group was enriched in CSG-SP. BCG including ASV from Alloprevotella and Denitrobacterium detoxificans were enriched in CSG-FA, and Streptococcus and Lactobacillus equigenerosa in HAY-FA. BCG members characteristic of WSG included ASV within Bacillus, Akkermansia, and Clostridium butyricum – taxa associated with healthy gut function and investigated for probiotic use in humans and other animal species. These results suggest incorporation of WSG in IRS may be of benefit to grazing horses. However, given the complexity of microbial community dynamics and limitations of taxon-based functional inference, future research is necessary to evaluate potential physiological implications.