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5 important points to avoid in horse feeding are being presented, which have triggered a lot of mixed reactions.

Are these statements regarding haylage too generalised?

Anyone who knows us, knows that we don’t believe in generalised answers. Especially from a therapeutic point of view, each horse must be considered and fed as an individual. We therefore answer most messages and questions with the following “…you can’t say that in general terms because we don’t know the horse and don’t have enough information” or “…you should take a detailed and holistic anamnesis”.

But: there are feedstuffs that can be generalised

and we do this deliberately. This is the case when a feed is not suitable for ANY horse, there are no exceptions. If we were to make a statement like “…for most horses…” instead of generalising, it would simply not be honest, but a lie. No exceptions to the points we have mentioned.

And yes, we know that there will probably be comments saying: “But I’ve been doing it this way for years and my horse looks good.” We understand there are plenty of horses that are fed this way and many of them look well.

But just because something works without problems does not mean that it is healthy or even beneficial to health. It is rather astonishing how long horses can compensate for incorrect and inappropriate feeding, because the survival instinct is ultimately stronger.

Let’s talk about this in a little more detail. In the following posts, we will go into the points mentioned and explain why these statements can be made across the board for all horses. In the next few articles, we will look at the topic of oil usage and the question of whether it is better to use organic or inorganic minerals to cover basic mineral requirements.

Haylage, brewer’s yeast and effective microorganisms in horse feeding

“Haylage, brewer’s yeast and Effective Microorganisms” are the topics of the next paragraph followed by explanation why they are not suitable to feeding your horses.

We will discuss these points together as they all relate to the problem faced by lactic acid bacteria. These are found in small quantities in the horse’s gastrointestinal tract, they find their way into the colon via the stomach. In a healthy well-functioning system, their numbers are balanced by Veillonellaceae bacteria, which immediately convert the lactic acid back into forms that can be utilised by the horse.

If additional lactic acid bacteria are reaching the large intestines, the balance is tipped, and acidosis occurs (hindgut acidosis). Scientists now consider this to be one of the main causes of metabolic disorders and diseases (for more information on this, see the nice review article by Rafat A.M. Al Jassim: The Bacterial Community of the Equine Gastrointestinal Tract and Its Relation to Fermentative Acidosis, Laminitis, Colic and Stomach Ulcers. Veterinary Clinics: Equine Practice: 25:2p199-215 from 2009).

haylage bales stacked on a field
If additional lactic acid bacteria are introduced into the intestine, the balance is tipped, and acidification of the colon occurs.
© Adobe Stock / Westwind

Muhonen et al haben schon 2009 (Effects on the equine colon ecosystem of grass silage and haylage diets after an abrupt change from hay1 | Journal of Animal Science | Oxford Academic ( showed that the amount of lactic acid bacteria increases rapidly when feeding haylage or silage, so that dysbiosis with an increase in lactobacilli and a drop in pH could be detected in horses within three weeks of starting to feed haylage or silage. The dramatic effects that an increase in lactic acid bacteria, especially Lactobacillus and Streptococcus, has on the health of the horse were already shown in 2008 by Milonovich et al (, who were able to prove the connection between a drop in the pH value in the large intestine and the development of laminitis.

There were two research projects running alongside each other, over the years: one project was about the proof of the harmfulness of lactic acid bacteria in the large intestine, which were always triggered by the feeding of starch or comparable molecules and, the other project was about, the investigations into the microbiome when feeding haylage.

The consequences of feeding haylage

It is only now that the research projects have been brought together to show that it is not only starch that leads to a pathological increase in lactate formers in the large intestine, but also haylage and that the resulting dysbiosis is associated with a significant decrease in cellulolytic microorganisms and an increased risk of hindgut acidosis, laminitis, and leaky gut syndrome.

Feeding lactic acid bacteria in the form of haylage or “Effective Microorganisms” (EM-A, Bokashi, which consist largely of lactic acid bacteria or promoting the colonisation of lactic acid bacteria, for example by feeding brewer’s yeast (J. C. Vázquez Chagoyán, ISBN: 978-1-62417-002-7, 2013) is therefore detrimental to intestinal homeostasis and, in addition to inadequate roughage utilisation, also leads to long-term health problems resulting from dysbiosis of the large intestine. The importance to maintain intestinal homeostasis for the horse’s health, is also demonstrated in these two articles: doi: and doi

A lot of information on the controversial topic of feeding haylage has been collated on our website. Feel free to take a look. Here, is the link to the haylage factsheet: .

Sources and studies on this topic

Opened books and notebooks
There are several studies and publications on the subject of haylage feeding. © Adobe Stock / C.Castilla

1.; Fact Sheet Series on Haylage for Horses; 27.3.2015

2. Peiretti & Bergero, Grass silages as feedstuff for horses; Journal of Food, Agriculture & Environment Vol.2 (3&4) : 182-185. 2004

3. Müller, Feeding silage and haylage to horses; XVI International Silage Conference; 2012

4. Müller, Wrapped Forages for Horses; Faculty of Veterinary Medicine and Animal Science, Department of Animal Nutrition and Management Uppsala; 2007

5. Jensen et al.; A comparative study of the apparent total tract digestibility of carbohydrates in Icelandic and Danish warmblood horses fed two different haylages and a concentrate consisting of sugar beet pulp and black oats; Arch Anim Nutr. 2010 Oct;64(5):343-56. 2010

6. Moore-Colyer et al., Mathematical modelling of digesta passage rate, mean retention time and in vivo apparent digestibility of two different lengths of hay and big-bale grass silage in ponies; Br J Nutr. 2003 Jul;90(1):109-18. 2003

7. Müller et al.; Effect of forage conservation method on microbial flora and fermentation pattern in forage and in equine colon and faeces; Livestock Science Volume 119, Issues 1–3, December 2008, Pages 116–128; 2008

8. Muhonen et al.; Effects on the equine colon ecosystem of grass silage and haylage diets after an abrupt change from hay; J ANIM SCI 2009, 87:2291-2298.; 2009

9. Hills et al.; Feeding behaviour of horse offered ensiled lucerne; Proceedings of the 13 th International Silage Conference, Auchincruive, Scotland, U.K., pp. 328-329.; 2002

10. Muhonen; Metabolism and hindgut ecosystem in forage fed sedentary and athletic horses.; Diss. Acta Universitatis agriculturae Sueciae, Uppsala1652-6880; 2008

11. Gere et al.; Post mortem survey of peripheral dental caries in 510 Swedish horses; Equine vet. J. (2010) 42 (4) 310-315; 2010

12. Hanche-Olsen et al.; Polyneuropathy Associated with Forage Sources in Norwegian Horses; J Vet Intern Med 2008;22:178–184; 2008

13. O’Brien et al.; Fungal contamination of big-bale grass silage on Irish farms: predominant mould and yeast species and features of bales and silage; Grass and Forage Science Volume 63, Issue 1, pages 121–137; 2008

A further selection of publications relating to the microbiome in the horse gut

If you would like to find out more about the current state of science in relation to the microbiome of the horse’s intestine, you will find a selection of publications here:

Adam K. M. G. 1951. The quantity and distribution of the ciliate protozoa in the large intestine of the horse. Parasitology, 41:301–311. doi:10.1017/S0031182000084158

Adam K. M. G. 1953. In vivo observations on the ciliate protozoa inhabiting the large intestine of the horse. Microbiology, 9:376–384.

Al Jassim R. A. et al., 2005. The genetic diversity of lactic acid producing bacteria in the equine gastrointestinal tract. FEMS Microbiol. Lett. 248:75–81. doi: 10.1016/j.femsle.2005.05.023

Alexander F., 1963. Production and fermentation of lactate by bacteria in the alimentary canal of the horse and pig. J. Comp. Pathol. 73:1–8. doi: 10.1016/S0368-1742(63)80001-6

Alexander F. et al., 1970. Bacteriophage-like particles in the large intestine of the horse. Res. Vet. Sci. 11:592–593.

Alexander F. et al., 1952. Fermentative activities of some members of the normal coccal flora of the horses large intestine. J. Comp. Pathol. Ther.62:252–259. doi: 10.1016/S0368-1742(52)80026-8

Argenzio R. A., 1975. Functions of the equine large intestine and their interrelationship in disease. Cornell Vet.65:301–331.

Baruc C. J. et al. 1983. The characterization and nitrogen metabolism of equine caecal bacteria. In: 8th Proc. 8th Equine Nutr. Physiol. Symp., Lexington, KY. p. 151–156.

Batista A. et al. 1961. Flora micoteca intestinal de equinos e asininos no recife. (In Portuguese.) Publ. Inst. Micol. Univ. Recife 326:116.

Bełżecki G. et al. 2016. Methods for the cultivation of ciliated protozoa from the large intestine of horses. FEMS Microbiol. Lett.363:fnv233. doi:10.1093/femsle/fnv233

Blackmore T. M. et al. 2013. Strong stability and host specific bacterial community in faeces of ponies. PLoS ONE 8:e75079. doi: 10.1371/journal.pone.0075079

Bonhomme A. 1986. Attachment of horse cecal bacteria to forage cell walls. J. Vet. Sci.48:313–322.

Bonhomme-Florentin A. 1969. Essais de culture in vitro des Cycloposthiidae, ciliés commensaux de l’intestin du cheval. Rôle de ces ciliés dans la dégradation de la cellulose. (In French.) Protistologica (Paris) 5:519–522.

Bonhomme-Florentin A. 1985. Attachement des Ciliés du caecum de cheval aux fragments végétaux – Dégradation des chloroplastes – Attachement des bactéries aux Ciliés du caecum. (In French.) Reprod. Nutr. Dev. 25:127–139. doi: 10.1051/rnd:19850112

Cann A. J. et al. 2005. Analysis of the virus population present in equine faeces indicates the presence of hundreds of uncharacterized virus genomes. Virus Genes 30:151–156. doi: 10.1007/s11262-004-5624-3

Choukevitch J. 1911. Etude de la flore bacterienne du gros intestin du cheval. (In French.) Ann. Inst. Pasteur (Paris) 25:247–276.

Costa M. C. et al. 2012. Comparison of the fecal microbiota of healthy horses and horses with colitis by high throughput sequencing of the V3-V5 region of the 16S rRNA gene. PLoS ONE 7:e41484. doi: 10.1371/journal.pone.0041484

Costa M. C. et al. 2015a. Characterization and comparison of the bacterial microbiota in different gastrointestinal tract compartments in horses. Vet. J.205:74–80. doi: 10.1016/j.tvjl.2015.03.018

Costa M. C. et al. 2015b. Changes in the equine fecal microbiota associated with the use of systemic antimicrobial drugs. BMC Vet. Res. 11:19. doi: 10.1186/s12917-015-0335-7

Da Veiga L. et al. 2005. Comparative study of colon and faeces microbial communities and activities in horses fed a high starch diet. Equine medicine 21:45–46.

Daly K. et al. 2012. Alterations in microbiota and fermentation products in equine large intestine in response to dietary variation and intestinal disease. Br. J. Nutr.107:989–995. doi: 10.1017/S0007114511003825

Daly K. et al. 2001. Bacterial diversity within the equine large intestine as revealed by molecular analysis of cloned 16S rRNA genes. FEMS Microbiol. Ecol. 38:141–151. doi: 10.1111/j.1574-6941.2001.tb00892.x

Davies E. 1964. Cellulolytic bacteria isolated from the large intestine of the horse. J. Appl. Bacteriol. 27:373–378. doi: 10.1111/j.1365-2672.1964.tb05044.x

De Fombelle A. et al. 2003. Characterisation of the microbial and biochemical profile of the different segments of the digestive tract in horses fed two distinct diets. Anim. Sci.77:293–304.

Dougal K. et al. 2014. Characterisation of the faecal bacterial community in adult and elderly horses fed a high fibre, high oil or high starch diet using 454 pyrosequencing. PLoS ONE 9:

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Dougal K. et al. 2013. Identification of a core bacterial community within the large intestine of the horse. PLoS ONE8:e77660. doi: 10.1371/journal.pone.0077660

Dougal K. et al. 2012. A comparison of the microbiome and the metabolome of different regions of the equine hindgut. FEMS Microbiol. Ecol.82:642–652. doi: 10.1111/j.1574-6941.2012.01441.x

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Fernandes K. A. et al. 2014. Faecal microbiota of forage-fed horses in New Zealand and the population dynamics of microbial communities following dietary change.

PLoS ONE 9:e112846. doi: 10.1371/journal.pone.0112846

Gaillard-Martinie al. 1995. Piromyces citronii sp. nov., a strictly anaerobic fungus from the equine caecum: A morphological, metabolic and ultrastructural study. FEMS Microbiol. Lett.130:321–326. doi: 10.1111/j.1574-6968.1995.tb07738.x

Garner H. E. et al. 1978. Changes in the caecal flora associated with the onset of laminitis. Equine Vet. J.10:249–252. doi: 10.1111/j.2042-3306.1978.tb02273.x

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Golomidova A. et al. 2007. The diversity of coliphages and coliforms in horse feces reveals a complex pattern of ecological interactions. Appl. Environ. Microbiol.73:5975–5981. doi: 10.1128/AEM.01145-07

Goodson J. et al. 1988. Effects of an abrupt diet change from hay to concentrate on microbial numbers and physical environment in the cecum of the pony. Appl. Environ. Microbiol.54:1946–1950.

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Hansen N. C. et al. 2015. High nutrient availability reduces the diversity and stability of the equine caecal microbiota. Microb. Ecol. Health Dis.26:27216.

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