Peer-reviewed publication · Horses · In the living system
Ponies kept on hay or haylage for years differed more clearly in urinary metabolites than in faecal bacteria.
- No humic or fulvic material tested
Ponies kept for years on hay or on haylage differed consistently in urinary metabolites but not in faecal bacterial diversity; with one group per forage, the forage cannot be separated from the group.
Leng et al., 2022 (first online 23 June 2021). Equine Veterinary Journal 54(3):614 to 625, May 2022 issue.
Scope, material and route
- Studied
- Welsh Mountain ponies, mares and geldings, aged 7 to 9 years at the start
- Design
- Longitudinal study of two groups formed in 2011, five years before sampling; the allocation method is not described
- What changed
- Haylage commercially produced from short-term ryegrass leys, all from one batch; hay grown on the study site in Wiltshire the previous year. Nutrient composition and amounts fed are not reported
- Route
- Feed (forage)
- Duration
- 13 months of monthly sampling, after five years on the assigned forage
Study design
Hay group
Hay grown on the study site.
10 ponies
- Urinary hippurateHigher in every month but one
Haylage group
Commercial ryegrass haylage, one batch.
10 ponies
- Urinary ethyl glucosideHigher in every month
Between the groups
- Urinary metabolite profileSeparated in 12 of 13 months
- Faecal bacterial diversityNo difference in any month
- SeasonMoved the community in both groups
Monthly sampling, July 2016 to July 2017, after five years on each forage
A sample in each month, July to July, marked above the bar.
- Grazing about 8 hours a day, July to September 2016
- Forage only October 2016 to March 2017
- Grazing April to July 2017
More study details
- Research question
- How does long-term hay or haylage feeding relate to the faecal microbiota and the urinary and faecal metabolome of ponies?
- Experimental unit and sample size
- 20 ponies in two sex-balanced groups of 10, each group housed and grazed as one unit; 260 faecal samples sequenced
- Comparator
- The other forage group, sampled in the same month
- Feeding and housing
- Group forage only from October to March; from April to September about eight hours' daily grazing in separate adjacent paddocks, with group forage overnight; loose housed in separate group pens in one barn
- Outcomes measured
- Faecal bacteria by 16S rRNA gene sequencing (V4 to V5); urinary and faecal metabolites by proton NMR spectroscopy; laminitis cases. Blood was collected but not used in this paper
Findings
Twenty Welsh Mountain ponies, kept for five years in two separate groups fed only hay or only haylage, were sampled monthly from July 2016 to July 2017. Both groups grazed separate paddocks for about eight hours a day from April to September. Faecal bacterial diversity did not differ between groups in any month and the dominant classes were broadly similar, although discriminant analysis flagged 102 bacterial groups that differed in relative abundance. Urinary metabolite profiles separated in 12 of the 13 months: hay-fed ponies excreted more hippurate, haylage-fed ponies more ethyl glucoside. Faecal metabolites differed little. With one group per forage, forage type cannot be separated from other group differences, and the authors describe the results as preliminary.
| Outcome | Comparison or result | Interpretation |
|---|---|---|
| Faecal bacterial diversity | No difference between hay and haylage in any of the 13 months (P > 0.05) | Null on diversity |
| Dominant bacterial classes | Little difference in Clostridia and Bacteroidia percentages; Clostridia read counts differed across all samples (P < 0.05) but not within any month (P > 0.05) | Small and inconsistent |
| Discriminant bacterial groups | 61 OTUs higher with hay and 41 higher with haylage; Fibrobacteria and Spirochaetes with hay, Epsilon- and Gammaproteobacteria with haylage | Driven by very high values in a small number of samples, as the authors note |
| Season | Diversity in all ponies higher in December 2016 (P < 0.05); communities oscillated through the year in both groups | Season moved the community as well as forage |
| Urinary metabolite profile | Groups separated in every month except June 2017 (overall model Q²Y = 0.60) | A consistent group difference in host and microbial co-metabolism |
| Hippurate and ethyl glucoside | Hippurate higher with hay in every month except June 2017; ethyl glucoside higher with haylage in all months | Hippurate is a host and microbial co-metabolite; ethyl glucoside derives from the diet itself |
| Urinary glucose | Higher with haylage in one month in the models; the integrated difference was not significant (P > 0.05) | The authors call for verification |
| Faecal metabolites | No separation across all samples; separation in one month by PCA and significant models in six months | Faeces carried little signal |
| Laminitis | Three ponies diagnosed during the study, all in the haylage group | Not tested statistically; three cases cannot show a forage effect |
Comparisons are between groups sampled in the same month. Most results are reported as model outputs and figures rather than group means. Values are extracted from the source as reported; no raw data were available.
Interpretation and limits
What this record supports
A consistent difference in urinary metabolite profiles, notably hippurate and ethyl glucoside, between these two groups of ponies fed hay or haylage over several years.
What remains uncertain
- Design. One group per forage: forage type is confounded with the group itself, its pen and paddocks, and the grass source (site-grown hay against commercial ryegrass haylage). Ponies were sampled individually, but the forage was applied to whole groups.
- Forage. Nutrient and sugar content and the amounts fed are not reported, so which property of the forage mattered cannot be said.
- Season. Both groups grazed pasture from April to September, and the authors link the oscillations to season and pasture.
- Bacteria. The abstract describes the bacterial profiles as different, while the discussion reports no significant difference at class level or in diversity.
- Health. No body weight, body condition or blood measure is reported. The three laminitis cases were not tested statistically and were diagnosed by an author who owns Equi Life Ltd, one of the funders.
- Reporting. June 2017 is called both month 11 and month 12, two month labels carry the wrong year, four excluded samples are listed as three, and Lachnospiraceae, a Clostridiales family, is grouped with Bacteroidales in the discussion.
Which part of the framework it informs
Environmental conditions
The physical, chemical and management context.
Microbial activity
What microbial communities do within that context.
This record informs this area.Observable function
What can be observed or measured in the host or wider system.
This record informs this area.
- a Large colon wall
- b Plant fibre
- c Bacteria
- d Mucus layer
Source, funding and review
- Source type
- Peer-reviewed publication
- Associated products
- No humic or fulvic material was tested. This record does not assess an associated product.
- Funding and relationships
- Funded by The Laminitis Trust (grant 35687) via a grant awarded by Equi Life Ltd (grant RN0279) to the University of Surrey, University of Reading and Imperial College. The conflict of interest statement says that Robert Eustace, joint senior and corresponding author, owns Equi Life Ltd and that Sue Emery is an employee.
- Review status
- Prepared as an editorial summary. External scientific review has not been completed.
- What was read
- Version of record read in full from the PDF on the University of Surrey project page; the accepted manuscript was also read from the University of Reading repository. The publisher's page blocked automated access. Supplementary tables and figures, including Table S1 on individual ponies, were not read.
- Original title
- Hay versus haylage: Forage type influences the equine urinary metabonome and faecal microbiota
- Authors
- Leng J, McNally S, Walton G, Swann J, Proudman C, Argo C, Emery S, La Ragione R, Eustace R
- Publication
- Equine Veterinary Journal 54(3):614 to 625, May 2022 issue, 2022 (first online 23 June 2021)
- DOI
- 10.1111/evj.13456
- Summary prepared by
- Carbon Biome Project
- Date added
- 19 October 2026
- Cite this summary
- Carbon Biome Project. Ponies kept on hay or haylage for years differed more clearly in urinary metabolites than in faecal bacteria. Evidence library record, added 19 October 2026. carbonbiomeproject.com/evidence/leng-2022-hay-versus-haylage-ponies/