External supporting research Starch, fiber & microbiome Peer reviewed EXT-S06

High-Fiber vs High-Starch Microbiota Across the Horse Digestive Tract

In 19 healthy horses, high-fiber and high-starch diets produced significantly different microbial communities across most regions of the digestive tract. High-starch feeding was associated with lower microbial diversity in several hindgut compartments, more amylolytic bacteria and smaller populations of several core fiber-associated bacterial groups.

Original study title

Microbiota characterization throughout the digestive tract of horses fed a high-fiber vs. a high-starch diet

Starch Fiber Hindgut fermentation Microbiome Microbial diversity Microbial diversity Digestive tract Gut barrier

Study at a glance

Year 2024

Study type Randomized comparative dietary intervention study

Sample 19 horses: 10 high-fiber and 9 high-starch

Duration 129 days, including a 72-day final feeding period at the target ration

Population Healthy young Bardigiano horses, approximately 14 months old

Publication Peer-reviewed journal article

EquiNectar tested? No

Peer reviewed Yes

Open access Yes

Relationship External supporting research

Healthy horses studied

152

Samples collected from eight digestive tract regions

1.2 vs 7.0 g/kg

Starch per kg bodyweight per meal, high-fiber vs high-starch diet

7 of 8

Digestive tract regions with significant microbiota differences between diets

Research question

What did the researchers want to understand?

How does feeding a high-starch diet compared with a high-fiber diet alter microbial diversity and bacterial community composition in different regions of the equine digestive tract?

Researchers

Study authors

Federica Raspa

University of Turin

Stefania Chessa

University of Turin

Domenico Bergero

University of Turin

Paola Sacchi

University of Turin

Ilario Ferrocino

University of Turin

Luca Cocolin

University of Turin

Maria Rita Corvaglia

University of Turin

Riccardo Moretti

University of Turin

Damiano Cavallini

University of Bologna

Emanuela Valle

University of Turin

Research organizations

Research institutions

University of Turin

University
Italy

University of Bologna

University
Italy

Methodology

How the study was conducted

Study design

Nineteen healthy Bardigiano horses with a mean age of approximately 14 months were studied in Piedmont, Northwest Italy.

After a two-week acclimatization period, the horses were assigned to either a high-fiber group of ten horses or a high-starch group of nine horses.

Both groups received the same meadow hay but different complementary pelleted feeds.

Feed quantities were gradually increased during the study. During the final 72 days, the high-fiber diet supplied approximately 1.2 g starch per kg bodyweight per meal, while the high-starch diet supplied approximately 7.0 g starch per kg bodyweight per meal.

The high-fiber horses consumed approximately 815 g starch per day compared with approximately 4,900 g per day in the high-starch group.

The feeding period continued for 129 days after arrival at the farm.

At the end of the experiment, samples were collected directly from eight digestive tract compartments and subjected to 16S rRNA amplicon sequencing.

The study was approved by the Ethics Committee of the Department of Veterinary Sciences at the University of Turin.

What was measured

Microbial communities were sampled directly from eight regions of the equine digestive tract: the duodenum, jejunum, ileum, caecum, sternal flexure, pelvic flexure, right dorsal colon and rectum.

A total of 152 intestinal samples were analyzed.

DNA was extracted and the V3-V4 region of the bacterial 16S rRNA gene was amplified and sequenced using the Illumina MiSeq platform.

Microbial alpha diversity was assessed using Chao1, Shannon and observed species richness indices.

Beta diversity was assessed using PERMANOVA analysis based on Bray-Curtis distances to determine whether overall microbial composition differed according to diet.

Differences in individual bacterial taxa were assessed with correction for multiple comparisons using the false discovery rate method.

The researchers also used PICRUSt2 analysis to predict potential functional differences between the microbial communities associated with the two diets.

Study findings

Key results

• Nineteen healthy Bardigiano horses were assigned to a high-fiber diet or a high-starch diet.

• A total of 152 samples were collected from eight regions of the digestive tract: duodenum, jejunum, ileum, caecum, sternal flexure, pelvic flexure, right dorsal colon and rectum.

• Overall microbiota composition differed significantly between dietary groups in seven of the eight sampled regions.

• Microbial diversity was greater on the high-fiber diet in several hindgut compartments, including the caecum, pelvic flexure and right dorsal colon.

• High-starch horses had substantially greater Enterobacteriaceae abundance in the jejunum, 7.5% compared with 0.7% in high-fiber horses.

• Fibrobacter abundance in the caecum was 3.8% in high-fiber horses compared with 0.3% in high-starch horses.

• Fibrobacter abundance in the sternal flexure was 4.3% in high-fiber horses compared with 0.5% in high-starch horses.

• Streptococcus was more abundant in the caecum of high-starch horses.

• Amylolytic Succinivibrionaceae were more abundant in the pelvic flexure and rectum of high-starch horses.

• Rectal samples from high-fiber horses contained greater relative abundances of Lachnospiraceae and Ruminococcaceae, both members of the equine core microbiota.

• Horses receiving the high-starch diet produced less formed feces during the study.

• The authors concluded that diet significantly influences microbiota composition throughout the equine intestinal tract and recommended fiber-rich feeding to reduce high-starch-associated dysbiosis.

Interpretation

What do the findings mean?

This study provides unusually detailed evidence that diet influences microbial ecology throughout the equine gastrointestinal tract, not simply in fecal samples.

The high-fiber diet was associated with greater microbial diversity in several major hindgut regions, including the caecum, pelvic flexure and right dorsal colon.

The high-starch diet produced a distinct microbial profile characterized by greater abundance of several bacteria associated with starch utilization and fermentation, while reducing the abundance of several bacterial groups associated with fiber degradation and the core hindgut microbiota.

In the caecum, Fibrobacter represented 3.8% of the microbial community in high-fiber horses compared with 0.3% in high-starch horses. In the sternal flexure the corresponding figures were 4.3% and 0.5%.

Streptococcus was more abundant in the caecum of high-starch horses, while Succinivibrionaceae were more abundant in both the pelvic flexure and rectum.

The findings support a model in which excessive starch delivery alters the substrates available to intestinal microorganisms, which in turn changes microbial community structure and fermentation potential.

The results do not imply that starch should be eliminated from horse diets. They demonstrate that the amount of starch reaching the gastrointestinal microbial ecosystem matters.

In practice

Why this research matters

Horses have a limited capacity to digest large starch meals before feed reaches the hindgut. When more starch escapes digestion in the small intestine, it becomes available to microbial populations in the large intestine.

This study demonstrates how substantially that dietary difference can influence the microbial ecosystem.

Horses receiving the high-fiber diet showed greater microbial diversity in several hindgut regions and greater abundance of bacterial groups including Fibrobacter, Prevotella and other members of the normal core microbial community.

The high-starch diet was associated with increased abundance of several starch-utilizing or potentially less desirable bacterial groups, including Succinivibrionaceae and Streptococcus, together with reduced abundance of some fiber-associated bacteria.

Importantly, these changes were not confined to feces. Diet-related differences were detected throughout the digestive tract.

The research reinforces the importance of forage provision, sensible starch intake and meal size, and strategies designed to limit excessive delivery of rapidly fermentable carbohydrate to the hindgut.

Research transparency

Study limitations

The study involved only 19 horses, with ten receiving the high-fiber diet and nine receiving the high-starch diet.

The horses were young Bardigiano horses of a similar age and were managed within one production system. This reduced variation within the study but limits direct extrapolation to adult leisure, breeding or performance horses.

The two dietary treatments differed considerably in total feed intake, starch, fiber, protein and energy supply. The study therefore examines two distinct feeding systems rather than isolating starch as the only dietary variable.

The high-starch diet was deliberately substantial. During the final feeding period it supplied approximately 7.0 g starch per kg bodyweight per meal, considerably above commonly recommended starch feeding levels. The results should therefore not be interpreted as showing that any use of concentrate feed produces the same microbiome changes.

The horses were not used as their own controls and fecal microbiota were not sampled before and after the feeding intervention. The authors identify this as an important limitation because pre-existing individual microbial differences could have contributed to some findings.

Microbial function was partly inferred from 16S sequencing data rather than directly measured through metagenomic or metabolomic analysis.

The study population was slaughtered at the end of the experiment, allowing direct sampling throughout the digestive tract but preventing longitudinal follow-up.

The findings demonstrate associations between dietary treatment and microbiota composition but do not establish that every bacterial change observed was harmful or resulted in clinical gastrointestinal disease.

EquiNectar context

How this research relates to EquiNectar

This research did not test EquiNectar and was conducted independently of Tharos Ltd.

Its relevance to EquiNectar is strongly mechanistic. The study demonstrates that diets differing substantially in starch and fiber content can produce measurable changes in microbial diversity and bacterial composition throughout the equine digestive tract.

The high-starch diet was associated with increased abundance of several starch-utilizing and fermentation-associated bacterial groups, together with reduced abundance of several bacterial groups associated with fiber degradation and the normal core hindgut microbiota.

Of particular relevance, the researchers found greater abundance of amylolytic Succinivibrionaceae in horses receiving the high-starch diet and linked this finding to the presence of undigested starch reaching the hindgut.

Published EquiNectar research separately examines whether supporting carbohydrate digestion earlier in the digestive tract is associated with changes in fecal pH, microbial populations and fermentation metabolites.

This study therefore provides independent evidence for the biological pathway that makes reducing excessive starch delivery to the hindgut relevant. It does not demonstrate that EquiNectar reproduces the microbiome of a high-fiber diet or prevents high-starch-associated dysbiosis.

Tharos / EquiNectar involvement

None. This study was conducted independently of Tharos Ltd and EquiNectar. EquiNectar was not evaluated in the research.

EquiNectar evaluated No

Transparency

Funding & competing interests

Funding statement

The authors declared that no financial support was received for the research, authorship or publication of the article.

Competing interests

The authors declared that the research was conducted without commercial or financial relationships that could be construed as a potential conflict of interest.

Source record

Publication details

Journal

Frontiers in Veterinary Science

Publisher

Frontiers

Year

2024

Volume

Pages / article

1386135

DOI

10.3389/fvets.2024.1386135

PMID

38807937

Species

Horse

Population

Healthy young Bardigiano horses, approximately 14 months old

Sample

19 horses: 10 high-fiber and 9 high-starch

Duration

129 days, including a 72-day final feeding period at the target ration

Setting

Piedmont, Northwest Italy

View original source ↗ Read full text ↗

Recommended citation

Raspa F, Chessa S, Bergero D, Sacchi P, Ferrocino I, Cocolin L, Corvaglia MR, Moretti R, Cavallini D, Valle E. Microbiota characterization throughout the digestive tract of horses fed a high-fiber vs. a high-starch diet. Frontiers in Veterinary Science. 2024;11:1386135. doi:10.3389/fvets.2024.1386135.

High-Fiber vs High-Starch Microbiota Across the Horse Digestive Tract

What did the researchers want to understand?

Study authors

Federica Raspa

Stefania Chessa

Domenico Bergero

Paola Sacchi

Ilario Ferrocino

Luca Cocolin

Maria Rita Corvaglia

Riccardo Moretti

Damiano Cavallini

Emanuela Valle

Research institutions

University of Turin

University of Bologna

How the study was conducted

Key results

What do the findings mean?

Why this research matters

Study limitations

How this research relates to EquiNectar

Funding & competing interests

Funding statement

Competing interests

Publication details

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