Core bacteria in the gut of horses showed some stability over time in study

This percentage of core bacteria identified in the equine gut is considerably smaller than the core identified in some other species.
This percentage of core bacteria identified in the equine gut is considerably smaller than the core identified in some other species.

Researchers have shown that a core bacterial community in the hindgut of horses shows some degree of stability over time when the animals are on a uniform diet.

The study team said that understanding how the bacterial hindgut community of the horse changed − or did not change − over time was essential to provide a baseline for interpreting the impact of dietary management or disease.

“Indeed, it is essential to characterize the core community that is stable over time, in healthy animals on a fiber-based diet, to enable comparisons to be made with different diets and disease states,” they said.

In their study, carried out in Britain, the researchers showed that there was a degree of stability, with 65% of bacteria retained within the bacterial community of the hindgut of horses over a six-week period whilst on a uniform diet.

The core community persisted over time in horses fed on two different fiber-based diets, with only relatively minor changes in the relative abundance of different species.

The effect of time (p: period 1 v period 2,6 weeks apart) and diet (d: diet 1 = hay plus chaff diet, diet 2 = hay plus balancer) on the relative abundance (%) of bacterial phyla in equine feces. Image: Dougal et al. doi: 10.3389/fmicb.2017.01502
The effect of time (p: period 1 v period 2,6 weeks apart) and diet (d: diet 1 = hay plus chaff diet, diet 2 = hay plus balancer) on the relative abundance (%) of bacterial phyla in equine feces. Image: Dougal et al. doi: 10.3389/fmicb.2017.01502

“This degree of stability is not markedly lower than values reported for the human gut,” Charles Newbold and his colleagues reported in the journal Frontiers in Micobiology.

Work by researchers in 2013 showed that humans retained more than 70% of bacteria after a one year period and still retained around 60% after five years.

The researchers used 12 horses and ponies of mixed breed, aged 5 to 16, who were clinically obese. Their owners had sought help with weight correction for the animals.

The horses went on a weight reduction program through reduced calorie intake.

They were randomly assigned to one of two fiber-based diet formulated to be equal in calories, each of which provided 1.25% of body mass in dry matter.

Diet 1 comprised of 0.8% of body mass in a chaff-based complete feed, plus 0.45% of their bodyweight in low energy grass hay. Diet 2 comprised 0.1% of body mass of a nutrient balancer plus 1.15% of the same low-energy hay used in the other diet.

Fecal samples were collected at week 10 and week 16 for DNA-based analysis.

The sampling time points were chosen so that the horses had been on the same diet for 10 weeks to acclimatize, but also at a time point when weight loss was predicted to cease.

Indeed, at week 10 animals had lost on average 4% of body weight, and by the second sample collection at week 16 had only lost a further 1%, showing body weight was reasonably stable during this sampling period.

The effect of time (p: period 1 vs. period 2, 6 weeks apart) and diet (d: diet 1 = hay plus chaff diet, diet 2 = hay plus balancer) on the relative abundance (%) of bacterial phyla making up the core microbiome (defined by being present in all samples (each animal/diet combination) included in the study and being present at 0.1% relative abundance or greater,) in equine feces. Image: Dougal et al. doi: 10.3389/fmicb.2017.01502
The effect of time (p: period 1 vs. period 2, 6 weeks apart) and diet (d: diet 1 = hay plus chaff diet, diet 2 = hay plus balancer) on the relative abundance (%) of bacterial phyla making up the core microbiome (defined by being present in all samples [each animal/diet combination] included in the study and being present at 0.1% relative abundance or greater,) in equine feces. Image: Dougal et al. doi: 10.3389/fmicb.2017.01502
For each diet and period combination, the most abundant phyla were the Bacteroidetes followed by the Firmicutes.

There was a clear reduction in Bacteroidetes with an increase in Firmicutes over time, they said.

The DNA work indicated that up to 21–28% of the total sequences recovered fell within the core bacteria, which was defined as being present at 0.1% relative abundance or greater in all samples. This percentage was somewhat larger than earlier work has shown, but was still considerably smaller than the core identified in other species.

There was, they reported, a high degree of variability between individual horses in the study, which was consistent with the findings of work by other researchers.

“While this work explored stability of the bacterial community at the end of a weight loss trial, when body weight was stable, further work is needed to look at changes in the microbiota during the weight loss phase,” they noted.

Dougal K, Harris PA, Girdwood SE, Creevey CJ, Curtis GC, Barfoot CF, Argo CM and Newbold CJ (2017) Changes in the Total Fecal Bacterial Population in Individual Horses Maintained on a Restricted Diet Over 6 Weeks. Front. Microbiol. 8:1502. doi: 10.3389/fmicb.2017.01502

The study, published under a Creative Commons License, can be read here

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