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Simple Summary: Incorporating warm-season grasses into traditional cool-season grass equine rotational grazing systems can increase pasture availability during hot, dry months and bridge the "summer slump" forage gap. The objective of this study was to evaluate the impacts of this pasture management practice on the equine microbiome and to explore relationships between the fecal microbiota, forage nutrients, and metabolic responses of grazing horses. Results of this study indicate that distinct changes in microbial community structure and composition occur as horses adapt to different forages and that shifts in the microbial community were most influenced by forage non-structural carbohydrates and crude protein, rather than fiber. Interrelationships were found between these nutrients, glycemic responses, and Akkermansia and Clostridium butyricum. These bacteria were also found to be enriched in horses adapted to warm-season grasses. While the results of this study suggest that integrating warm-season grasses may not offer substantial metabolic benefits in healthy adult horses, this study did reveal new insights and targets for future research necessary to better understand the function of Akkermansia and Clostridium butyricum in the hindgut microbiome of grazing horses and possible roles in modulation of equine metabolic health. Integrating warm-season grasses into cool-season equine grazing systems can increase pasture availability during summer months. The objective of this study was to evaluate effects of this management strategy on the fecal microbiome and relationships between fecal microbiota, forage nutrients, and metabolic responses of grazing horses. Fecal samples were collected from 8 mares after grazing cool-season pasture in spring, warm-season pasture in summer, and cool-season pasture in fall as well as after adaptation to standardized hay diets prior to spring grazing and at the end of the grazing season. Random forest classification was able to predict forage type based on microbial composition (accuracy: 0.90 ± 0.09); regression predicted forage crude protein (CP) and non-structural carbohydrate (NSC) concentrations (p < 0.0001). Akkermansia and Clostridium butyricum were enriched in horses grazing warm-season pasture and were positively correlated with CP and negatively with NSC; Clostridum butyricum was negatively correlated with peak plasma glucose concentrations following oral sugar tests (p ≤ 0.05). These results indicate that distinct shifts in the equine fecal microbiota occur in response different forages. Based on relationships identified between the microbiota, forage nutrients, and metabolic responses, further research should focus on the roles of Akkermansia spp. and Clostridium butyricum within the equine hindgut. [ABSTRACT FROM AUTHOR]

Abstract Background Diet is a key driver of equine hindgut microbial community structure and composition. The aim of this study was to characterize shifts in the fecal microbiota of grazing horses during transitions between forage types within integrated warm- (WSG) and cool-season grass (CSG) rotational grazing systems (IRS). Eight mares were randomly assigned to two IRS containing mixed cool-season grass and one of two warm-season grasses: bermudagrass [Cynodon dactylon (L.) Pers.] or crabgrass [Digitaria sanguinalis (L.) Scop.]. Fecal samples were collected during transitions from CSG to WSG pasture sections (C–W) and WSG to CSG (W–C) on days 0, 2, 4, and 6 following pasture rotation and compared using 16S rRNA gene sequencing. Results Regardless of IRS or transition (C–W vs. W–C), species richness was greater on day 4 and 6 in comparison to day 0 (P

Equine microbiome research has rapidly moved from a fledgling field to a thriving and productive area of research. Impacts to the equine gastrointestinal microbiome have been examined related to travel, antibiotic administration, meal size, fiber type, breed, sex and nutrient level. Although advances in this field are exciting, data related to the dermal microbiota are sorely lacking. Conducting equine microbiome research presents unique challenges and opportunities. Coordination for data collection in conjunction with other studies will be reviewed. Diet is widely recognized as a significant modulating factor to the microbiome and will be reviewed as a potential consideration in equine dermal microbiome research. This presentation will highlight the limited data available on equine dermal microbiota and identify potential areas for further examination. Studies reporting the characteristics of equine dermal measures will be discussed and gaps in current understanding will be identified. Specific conditions including equine pastern dermatitis as well as wound dressing methods will be examined, and a discussion of future works will be included. Dermatological studies of the microbiome in humans and canines will be examined as a potential map for the future of equine dermal microbiome research. As microbiome research continues to evolve, its impact on equine health has become increasingly apparent. The skin functions as a protective organ and is the first line of defense against pathogenic invasion and immune function support. It is home to bacteria, fungi and viruses with many roles similar to those of the gastrointestinal microbiome. This presentation will highlight the critical need for increased understanding of the dermal microbiome in conjunction with current equine gastrointestinal microbiome studies. [ABSTRACT FROM AUTHOR]

Background: Diet is a key driver of equine hindgut microbial community structure and composition. The aim of this study was to characterize shifts in the fecal microbiota of grazing horses during transitions between forage types within integrated warm- (WSG) and cool-season grass (CSG) rotational grazing systems (IRS). Eight mares were randomly assigned to two IRS containing mixed cool-season grass and one of two warm-season grasses: bermudagrass [Cynodon dactylon (L.) Pers.] or crabgrass [Digitaria sanguinalis (L.) Scop.]. Fecal samples were collected during transitions from CSG to WSG pasture sections (C–W) and WSG to CSG (W–C) on days 0, 2, 4, and 6 following pasture rotation and compared using 16S rRNA gene sequencing. Results: Regardless of IRS or transition (C–W vs. W–C), species richness was greater on day 4 and 6 in comparison to day 0 (P < 0.05). Evenness, however, did not differ by day. Weighted UniFrac also did not differ by day, and the most influential factor impacting β-diversity was the individual horse (R2 ≥ 0.24; P = 0.0001). Random forest modeling was unable to accurately predict days within C–W and W–C, but could predict the individual horse based on microbial composition (accuracy: 0.92 ± 0.05). Only three differentially abundant bacterial co-abundance groups (BCG) were identified across days within all C–W and W–C for both IRS (W ≥ 126). The BCG differing by day for all transitions included amplicon sequence variants (ASV) assigned to bacterial groups with known fibrolytic and butyrate-producing functions including members of Lachnospiraceae, Clostridium sensu stricto 1, Anaerovorax the NK4A214 group of Oscillospiraceae, and Sarcina maxima. In comparison, 38 BCG were identified as differentially abundant by horse (W ≥ 704). The ASV in these groups were most commonly assigned to genera associated with degradation of structural carbohydrates included Rikenellaceae RC9 gut group, Treponema, Christensenellaceae R-7 group, and the NK4A214 group of Oscillospiraceae. Fecal pH also did not differ by day. Conclusions: Overall, these results demonstrated a strong influence of individual horse on the fecal microbial community, particularly on the specific composition of fiber-degraders. The equine fecal microbiota were largely stable across transitions between forages within IRS suggesting that the equine gut microbiota adjusted at the individual level to the subtle dietary changes imposed by these transitions. This adaptive capacity indicates that horses can be managed in IRS without inducing gastrointestinal dysfunction. [ABSTRACT FROM AUTHOR]

Integrating warm-season grasses into cool-season equine grazing systems can increase pasture availability during summer months. The objective of this study was to evaluate effects of this management strategy on the fecal microbiome and relationships between fecal microbiota, forage nutrients, and metabolic responses of grazing horses. Fecal samples were collected from 8 mares after grazing cool-season pasture in spring, warm-season pasture in summer, and cool-season pasture in fall as well as after adaptation to standardized hay diets prior to spring grazing and at the end of the grazing season. Random forest classification was able to predict forage type based on microbial composition (accuracy: 0.90 ± 0.09); regression predicted forage crude protein (CP) and non-structural carbohydrate (NSC) concentrations (p < 0.0001). Akkermansia and Clostridium butyricum were enriched in horses grazing warm-season pasture and were positively correlated with CP and negatively with NSC; Clostridum butyricum was negatively correlated with peak plasma glucose concentrations following oral sugar tests (p ≤ 0.05). These results indicate that distinct shifts in the equine fecal microbiota occur in response different forages. Based on relationships identified between the microbiota, forage nutrients, and metabolic responses, further research should focus on the roles of Akkermansia spp. and Clostridium butyricum within the equine hindgut.

Strongyles are nematode parasites that affect the large intestine and cecum of the horse, with symptoms ranging from loss of condition to colic. Thirty horses from the University of Connecticut campus were used to study the effect of gastrointestinal strongyles on the equine gut microbiome, immune response, body condition, and skin and hair coat conditions. This study included young (n = 16) and adult (n = 14) horses each fall and spring from Fall 2020 to Spring 2022, with young horses 1 to 5 years old and adult horses 6 to 19 years old. Fecal flotation analysis was performed at the beginning of each fall and spring season to classify horses as susceptible to parasites if they had 300 or more strongyle eggs per gram (EPG) or resistant to parasites if they had less than 300 strongyle EPG. Fecal and blood samples were collected each fall and spring to assess gut microbial composition, complete cell counts, and differential cell counts. Body condition scores and body weights were assessed twice per season. Dermatological conditions were recorded once monthly. A split plot design with age as the main effect and fecal egg count (FEC) as the split plot effect was used. Adult and young horses that were susceptible to parasites had significantly increased percentages oflymphocytes and neutrophils and decreased percentages of monocytes and eosinophils compared with horses that were resistant to parasites in Fall 2021 and Spring 2022 (P < 0.05). In adult horses, linear correlation analysis revealed that as parasite load increased, body weight decreased (r = −0.29) and complete cell count decreased (r = −0.29), although these trends were not observed in young horses. Ten percent of the variation seen in microbial community structure was due to phenotype. Linear correlation analysis revealed some changes in skin and hair condition, such as an increase in skin moistness (r = 0.32), tailhead moistness (r = 0.36), and hair thickness (r = 0.44) as parasite load increased and a decrease in hair luster (r = −0.32) as parasite load increased. The effects of strongyle infection on dermatology are still unclear as some of the effects seen contradict previous literature and warrant further investigation. Strongyle load may affect body weight in adult horses. Strongyle infection may affect immune response, but have a minimal effect on microbial composition. [ABSTRACT FROM AUTHOR]

Horses are hindgut fermenters with a highly complex microbiome populating the cecum and colon. This microbiome contributes an abundance of physiological functions to the host, including immune stimulation, defense against pathogens, neutralization of toxins, and regulation of gene expression in epithelial tissues. During bouts of infectious disease, antibiotic administration can disturb this microbiological environment, leading to adverse effects such as colitis and acute diarrhea. Horse owners often provide probiotics to horses receiving antibiotics in an attempt to protect against these adverse effects despite a lack of evidence for their efficacy. Thus, the purpose of the current study was to evaluate the effect of probiotics in horses receiving concurrent antibiotic treatment. Sixteen actively racing Standardbred horses were randomly allocated to one of 4 treatment groups [Antibiotics (A; Sulfadiazine/Trimethoprim), Probiotics (P; Herbs for Horses PROBIOPlusⓇ, Herbs for Horses, Guelph ON), A+P, or control (C)] in a 4-way crossover design. A and A+P horses received antibiotics from Day 0–10, P and A+P received probiotics from Day 0–28, and C horses received the same diet with no probiotic or antibiotic for 28 d. Fresh fecal samples were collected on days −1, 0, 1, 2, 9, 10, 11, 28, 29 and 30 from each horse. Analyses include fecal dry matter (DM; %), fecal pH, and fecal scores (FS; 0 – 9) were measured on all fecal samples. Data were analyzed using a 2-way RM-ANOVA (SigmaPlot Version 12) with fixed effects as horse, trial, day, and treatment and random effects as the intercept for the crossover design. Significance was accepted at P < 0.05. Fecal score in C horses (2.6 ± 0.3) was higher than in A+P horses (1.9 ± 0.2) on Day 10 (P = 0.04); FS of C horses (2.7 ± 0.3) was also higher than P horses (1.6 ± 0.3) on Day 9 (P = 0.02). Fecal DM was lower in C horses (26.9 ± 2.5%) than A+P horses (30.3 ± 2.5%; P = 0.03) overall, but there were no differences at any individual time point. Fecal pH was higher in C horses (6.6 ± 0.04) than P horses (6.5 ± 0.04; P = 0.008) and A+P (6.4 ± 0.04) overall; on Day 9 and 10, pH was lower in A+P (6.3 ± 0.1 and 6.2 ± 0.1, respectively) than C horses (6.7 ± 0.1 for both days). The antibiotic treatment had no differences on dry matter or pH between treatments. Interim results demonstrate that treatment with A+P is associated with an increase in fecal DM and concomitant reduction in FS. Fecal pH is reduced in horses receiving P and A+P. The practical implications of these data are as yet unclear but will be clarified upon completion of microbiome analysis which is currently ongoing. [ABSTRACT FROM AUTHOR]