Responses of Horses Grazing Warm- and Cool-Season Grass Pastures

The benefits of mixed warm and cool season forages on pastures are undeniable. Fresher nutrients than hay offers and savings from buying prepared forges are two benefits. In this study, they looked at the metabolic and bacterial effects of using mixed-season grasses and found some changes of uncertain significance. However, they conclude that these changes are unlikely to impact the horse substantially. I see no reason to change this practice; indeed, I encourage it in my pastures.
DrO

Animals (Basel). 2023 Mar; 13(5): 790.
Published online 2023 Feb 22. doi: 10.3390/ani13050790
PMCID: PMC10000167
PMID: 36899650
Fecal Microbiota, Forage Nutrients, and Metabolic Responses of Horses Grazing Warm- and Cool-Season Grass Pastures
Jennifer R. Weinert-Nelson, Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization, Project administration, Funding acquisition,1 Amy S. Biddle, Methodology, Formal analysis, Writing – review & editing,2 Harini Sampath, Methodology, Writing – original draft, Writing – review & editing,3,4 and Carey A. Williams, Conceptualization, Methodology, Investigation, Resources, Writing – review & editing, Supervision, Project administration, Funding acquisition1,*
Emanuela Valle, Academic Editor and Federica Raspa, Academic Editor
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Abstract
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.

Conclusions
In conclusion, distinct shifts in equine fecal microbial community structure and composition occur as horses adapt to different forages within an integrated warm- and cool-season grass rotational pasture system, but a substantial impact of this management practice on glucose metabolism in healthy adult grazing horses is unlikely. Forage NSC, WSC, and CP were the most influential nutrients driving these shifts in microbial composition. Results of this study underscore the potential for relatively small amounts of NSC to influence hindgut microbial composition and also that protein utilization may be an important ecological niche within the microbiome of forage-fed horses. Fecal BCFA and SCFA concentrations were higher in horses adapted to all pasture forages versus hay, but in comparison to forage nutrients, bacterial community composition did not have as strong an impact on fermentation metabolites, likely reflecting functional redundancy of the microbial community. The guild-based analytical approach utilized in this study also identified key relationships between specific bacterial groups associated with adaptation to warm-season grass pasture and forage nutrients, fecal metabolites, and equine glycemic responses to administration of oral sugar tests. Relationships identified in this study revealed new insights and targets for future research necessary to better understand the function of Akkermansia spp. and Clostridium butyricum in the hindgut microbiome of grazing horses, as these bacteria may play a role in modulation of equine metabolic health.

Keywords: equine microbiome, glycemic response, non-structural carbohydrates, rotational grazing