To convert grass into haylage, the cut grass needs lactic-acid (LA) bacteria to ferment it., and we've already gone into why this isn't great news for the horse's fragile microbiome. This same LA bacteria is then consumed by the horse when the horse eats haylage. And by their very nature, LA bacteria create lactic-acid as their waste, so overall the whole lactic=acid subject is all about acid in the gut system, creating an overly acidic pH value where acid doesn't belong - from the stomach/foregut onwards, the environment should be completely pH neutral, around 7.
Here's where haylage may be detrimental. Being a sugar-loving pro-inflammatory bacteria, the LA bacteria start feeding from the sugar (and protein) in the diet but unlike the friendly biome microbes, LA bacteria don't make any beneficial nutrients, only lactic acid itself as a waste product. This is bad news - due to the now enhanced acidic pH value in the intestines (both small intestine and large intestine in the hindgut region, aka hindgut acidosis), the intestinal mucous membrane wall becomes inflamed and breaks open like a zipper being pulled apart. Cue Leaky Gut syndrome, which now leads to major health issues in the body, and one of the many causes of faecal water syndrome in horses.
These days, hindgut acidosis is prevalent everywhere, and certainly a factor in many of our client enquiries. It's vital that we do everything we can to prevent LA bacteria getting in the hindgut/cecum as it lowers the pH to aggressively sour levels, creating a toxic state of dysbiosis in the gut microbes, which as we know, leads to a downward health spiral. For the record, my connie, Murphy, can't touch haylage - his gut literally goes into almost immediate projectile faecal-water mode.
The hindgut is also where the B-vitamins are produced, including the essential B6 and B12; lactic-acid stops this, so this then has significant effects on the entire metabolic process and, among other things, promotes the occurrence of a detoxification disorder known as cryptopyrroluria (KPU). This is still new science, with KPU a relatively new label to reach the mainstream, so much is still to be learned about it; what is known is that it significantly affects liver, kidney and lymphatic function.
There's also a myth relating to haylage supposedly being a high energy source - wrong Its alleged high protein value is due to bacterial protein from the LA bacteria, not a beneficial protein for the gut to break down into amino acids to be utilised. Worse still, due to the disruption in the cecum's biome, the vital energy source - the main reason for living for the hindgut's biome - from the digesting plant fibre cellulose can't be used effectively to provide the horse with the energy it needs.
Lactic-acid presence creates an immensely negative burden on the horse's body. If present it can be coverted into glucose by Veillonellaceae bacteria, but the body isn't able to adequately convert the ever-increasing large amounts, so its then stored in the connective tissue - yes, we're talking tendons/ligaments/muscles etc. This results in what looks like weight gain; however, it's not about increase in muscle mass or fat, but the storage of lymph in the tissue, which is trying to dilute the acidic pH value. This hyperacidity can't be seen in the blood count because the kidneys are doing their darned-ness to keep the blood pH constant. Next to the intestines, the kidneys are the next most damaged organ from feeding haylage.
This storage of acid in the connective tissue also has a knock-on effect on how the horse performs - yet another haylage effect, this time on the musculoskeletal system. If you're feeding haylage and if your horse is hard to ride, if they're a bit stiff, if it's hard to get them going, if they have tendonitis or swollen legs, and if this is all accompanied by a general reluctance, it could all be due to the LA making the muscles too acidic.
Finally, any forage wrapped in plastic will change the pH so there's always the risk of bacteria, yeast and mould surviving. Dry haylage has a pH of around 6 which means bacteria, yeast and mould can survive. There's also the grim risk of fermented dead animals, i.e. field mice, in the haylage which create Chlostridium botulinum bacteria, and this will spread throughout the whole bale, unlike in a hay bale where the dead mouse doesn't ferment because there's no humid fermenting environment, so in hay the decay remains static.
Botulism poisoning has been known to cause fatal poisoning from dead mice found in haylage - 98% of horses will not surviving chlostridium poisoning; stats from Germany show up to 100 horses/year die from it and what is known is that these horses were all fed on haylage. This is serious yet the horse-community isn't talking about it - this itself should be enough reason to not feed haylage - it's just not worth the risk.
- Haylage contains LA bacteria, which creates lactic acid in the intestines. There's always the risk of LA bacteria getting into the horse from eating grass/hay anyway, so LA bacteria is often found in the front section of the foregut, where some will then survive the stomach acid and pass through into the intestines.
- The hindgut environment is hot! Which makes it a perfect breeding ground for LA bacteria; dysbiosis can appear in just 3-weeks - https://academic.oup.com/jas/article/87/7/2291/4731169?login=true
- Zinc is needed to neutralise the acid, so if we're not feeding a mineral balancer the horse is going to be deficient.
- Haylage also puts extra work on the liver, as the liver needs active vit. B6 (produced in the hindgut) to transform the lactic acid so it can be excreted. However, the LA bacteria evolve quicker than they can be excreted, which means the liver has to work extra hard.
- There's less equine-appropriate 'energy' created in haylage.
- There's also a 'wrong type of grass' issue. If grass is cut late for haylage, i.e. when the grass has seeded and become coarse and stemmy (the best grass for the best hay!), this is difficult to convert to haylage as the LA bacteria won’t find enough of its preferred nutrient energy source, i.e. starch/sugars, to produce enough lactic acid to get a pH lower than 5 to ferment the grass into haylage.
- It's thought that one winter on haylage may lead to a complete wipeout of the hindgut biome.
Of course there'll be many people shouting out that their horses are fine on haylage. However, the systemic haylage-effect takes time to accrue before we see symptoms - don’t be misled into thinking a horse is fine on haylage.
Overall, haylage leads to reduced performance of the horse and long-term damage to health, where the consequences are often only noticeable years later and therefore rarely put into direct context - https://www.nature.com/articles/ismej200867