- Clover’s energy, protein and fiber content make it a good feed source for horses.
- Mold-infected clover can cause slobbers, liver damage and bleeding in horses.
- Mold grows when the temperature is above 80 F and the humidity is above 60 percent.
- Bleeding only happens in horses eating moldy sweet clover hay.
- Red, white, alsike and sweet clovers commonly grow throughout the United States.
- Many horse owners use clover in pasture and hay mixes.
- Transportation departments also use clover for ditches and roadways.
Feeding clover to horses
Clover can be a good feed source for most horses because it provides useful energy and adequate protein and fiber. You can use clover in hay or pastures.
Clovers can sometimes mold, which causes slobbers, photosensitivity (reactive to light) and bleeding. These conditions can occur after horses eat affected clover either fresh or as hay.
Even with the chance of these problems, clover is still a useful forage for horses.
Mold tends to grow on clover when the temperature is above 80 F and the humidity is above 60 percent. To prevent problems with moldy clover:
- Fence your horses out of clover-rich pastures in very wet years or periods of high humidity.
- Mow, thin clover stands or improve water drainage to create air flow and lower the chances of mold.
- Allow clover more time to dry when using it for hay. Clover, especially red clover, takes longer to dry than other forage species.
- Use an herbicide if you want to remove clover from your pasture or hay field.
- When using an herbicide, be sure to carefully follow all grazing and harvesting restrictions and other information stated on the herbicide label.
Colic or founder
Grazing non-acclimated horses on any pasture can increase the chance of colic and founder in horses. Slowly acclimating your horse to pasture in the spring can prevent the risk of colic and founder. In addition, be cautious of grazing pastures after a frost when plants may be higher in sugar.
Problems caused by moldy clover
Slobbers is a well-known mold problem in red clover. Horses with slobbers can fill several five-gallon pails with saliva in one day. Slobbers can occur after eating affected clover in pasture or hay.
If your horse has slobbers, make sure they have free access to water to prevent dehydration.
Rhizoctonia leguminicola is the mold responsible for black spot disease in red clover. This mold produces the toxin slaframine, which causes slobbers. Slaframine can last for over 10 months in hay but declines over time.
The mold looks like black marker dotting on the underside of leaves. It normally lasts 2 to 4 weeks depending on the weather.
Photosensitivity and liver damage
Black Blotch disease is a lesser-known problem in red, white and alsike clover. The disease has appeared in Minnesota, Washington and areas of Canada.
Horses eating clover with Black Blotch disease can develop bad sunburn or photosensitivity. Photosensitivity is really a thickening and reddening of the white areas of skin due to liver damage. Black- or dark-haired horses can have liver damage even if you don’t see a sunburn.
The mold, Cymodothea trifolii, causes Black Blotch disease of clover and other legumes. The mold causes black blotches to occur on the underside of the clover leaves. These blotches are usually closer to the ground where the humidity is highest.
Research shows photosensitivity can also happen in horses grazing alfalfa with Cymodothea trifolii.
Bleeding appears in horses eating moldy white and yellow sweet clover. These clovers aren’t usually in pasture mixes, but commonly grow along roadways and in older hay fields.
Bleeding is only a problem in sweet clover that molds in hay. Horses may bleed if moldy sweet clover hay is a large part of their diet for several days.
An unknown mold changes naturally occurring cumarol in sweet clover to dicumerol, a blood thinning drug. Dicumerol clears quickly. Taking the horse off the hay is the best treatment.
In extreme cases, the horse may need Injections of vitamin K or blood transfers. But feeding a natural source of vitamin K, like fresh alfalfa hay, is usually all the horse needs.
Crimping sweet clover at cutting reduces, but may not completely get rid of the potential for molding. Crimping usually reduces drying times.
White clover (Trifolium repense)
- Three leaflets
- Serrated (toothed) leaf edges, up to the base of the leaf
- Most leaves have a white "V" mark
- Leaves are shiny underneath
- White flowers
Alsike clover (Trifolium gybridum)
- Three leaflets
- Finely toothed leaf edges, up to the base of the leaf
- Leaves don’t have a "V" mark
- Leaves are dull underneath
- White flowers
Red clover (Trifolium pretense)
- Usually hairy
- Reddish to purple colored flowers
Sweet clover (Melilotus species)
- Three leaflets
- Toothed leaf edges, up to the base of the leaf
- White or yellow flowers
- Red clover is from Asia and Europe.
- White clover is from the Mediterranean and western Asia.
- Sweet clover is from Russia.
- Alsike clover is from Europe and Asia.
- All clovers are perennials and reproduce by seed.
- White clover reproduces by seed and stolons.
- Stolons are reproductive stems found above ground.
Reviewed in 2021