A large number of feed and supplement companies have apple cider vinegar (ACV) products, including Omega equine, Hilton herbs, Gold label, Equimins, NAF, Global Herbs, Simple Systems and Wendals herbs to name a few.
Apple cider vinegar is vinegar made from apple juice. Yeasts use the sugar to produce alcohol (ethanol) and when the alcohol is exposed to oxygen bacteria called Acetobacter ferment the alcohol to acetic acid, which makes vinegar. Vinegar contains very little in the way of nutrients. 100ml (100g) contains only around 20 calories with traces of sugar, sodium, calcium, and around 1g carbohydrates.
Some of the claims made for ACV in horses include:
- acidifies the stomach
- acidifies the urinary tract
- acts as a probiotic
- aids absorption of minerals
- aids circulation
- aids muscle stiffness
- alkalizing agent
- balances pH levels
- cleanses the digestive tract
- helps relieve itching
- improves coat condition
- improves digestion
- improves immune function
- improves joint flexibility
- increases appetite
- acts as a blood cleanser
- maintains stamina
- natural antibiotic
- natural insect repellent
- prevents arthritis
- relieves the soreness and stiffness of equine arthritis
- removes toxins
- supports and maintains healthy bone integrity
- supports clear skin
- supports hard, healthy, fresh hooves
- supports the respiratory tract
Almost all of these purported benefits have no scientific basis or evidence and are false, and most make no sense whatsoever. These are “old wives’ tales” that are used for marketing. Let’s look at a few.
- “Acidifies the stomach” – the stomach is already very acidic. Adding more acid may not be a good idea for horses with or prone to gastric ulcers.
- “Alkalizing agent” – vinegar is acidic. Not sure how it alkalizes!
- “Acts as a probiotic” – it’s true that if there is sediment present, this may contain bacteria but it’s not considered a probiotic. Plus, most ACV products have been filtered to remove sediment.
- “Increases appetite – not proven, and in people ACV is used as an appetite suppressant!
I was only able to find two scientific papers on ACV in horses. The first is from 1989 (Hintz et al. 1989) and concerns horse prone to developing enteroliths (mineral accumulations of magnesium-ammonium-phosphate around a foreign object such as a piece of metal, pebble, bailer twine, hair, rubber, etc, that form round, triangular, or flat stones inside the bowel usually over a number of years. Small enteroliths are generally passed in the droppings, but large enteroliths can get trapped in the intestine and impair the passage of the contents of the gut and may ultimately get trapped in the digestive system causing damage to the lining of the gut. Affected horses may show signs of colic, abnormal droppings and weight loss. The recommendation was to feed 200ml ACV per day to lower caecal pH, which in turn may reduce the development or rate of development of enteroliths.
The only other reference is from 2022 (Fletcher et al. 2022), where ACV was part of the treatment of an oro-antral fistula (an abnormal opening between the oral cavity and the maxillary sinus). Many different treatments were used, and its unclear to what extent the ACV was effective.
Even for regular vinegar or acetic acid, there are very few studies in horses! One study by Nadeau et al. (2003) demonstrated that gastric tissue exposed to acetic acid (“vinegar”) leads to decreases in mucosal barrier function of the non-glandular portion of the equine stomach. Other potentially negative considerations when feeding ACV or ordinary vinegar are that the acidity may lead to tooth damage and irritation of the oesophagus.
There are a greater number of studies of ACV in people where a typical dose would be 30ml per day. This would equate to ~200ml per day for a 500kg (1100lb) horse. Of the equine ACV supplements I reviewed, none recommended feeding at this rate, with some suggesting as little as 30ml per day.
In studies in human subjects, ACV has been found to cause a small decrease in appetite (1 study), weight (1 study), tryglycerides (2 studies) blood glucose (2 studies), body fat (1 study) but to have no effect on insulin (2 studies), cholesterol (2 studies), HDL (2 studies) or LDL (2 studies). These studies typically fed 20-30ml ACV per 70kg daily for 12 weeks.
ACV fed at a rate of 0.43ml/kg for 6-12 weeks has small effects on appetite (reducing), weight, blood lipids, blood glucose and body fat in people. This would be the equivalent to feeding 200ml ACV per day to a 500kg (1100lb) horse. However, there is no indication that the same effects would be found in horses. In addition, ACV may lead to adverse effects, including tooth damage, oesophageal irritation and increased risk of gastric ulcers.
Fletcher JR, Yuen KY, Stewart AJ, Young AC, Gibson JS, James OA, Medina-Torres CE, Forde BM, Sole-Guitart A. Successful treatment of a chronic oroantral fistula infected with extensively drug-resistant bacteria using long-term oesophageal tube feeding and several non-conventional treatments in a horse. Aust Vet J. 2022 Mar;100(3):107-113.
Hintz HF, Hernandez T, Soderhold V, et al.: Effect of vinegar supplementation on pH of colonic fluid. Proc 11th Equine Nutr Physiol Symp, Stillwater, Oklahoma, May 18-20,1989, pp 116-118
Nadeau JA, Andrews FM, Patton CS, Argenzio RA, Mathew AG, Saxton AM. Effects of hydrochloric, acetic, butyric, and propionic acids on pathogenesis of ulcers in the nonglandular portion of the stomach of horses. Am J Vet Res. 2003 Apr;64(4):404-12. doi: 10.2460/ajvr.2003.64.404. PMID: 12693528.