The Case Against Rye & Clover Pasture for HorsesRye and clover

By Jenny Paterson 01 April 2010

Clover is the cause of a wide array of health and behaviour problems, some of them so common we think they are normal, some way more severe causing frustration, accidents, loss of confidence in people, and unnecessary suffering and euthanasia of horses.

Without a doubt, these pastures directly impact your safety, enjoyment and pocket!!

I used to think that mycotoxins were the most serious problem with rye grass and clover.
Now I realise that serious mineral imbalances cause even more trouble.


Mineral Imbalances

From years of observations and ‘testing in White Cloverthe field’ I now believe that the # 1 cause of health and behaviour issues in grazing horses (including head-flicking, laminitis, musculo-skeletal and temperament) is grass in its vegetative (meaning short, green and growing) state.

How can this be?
Under the conditions of spring and autumn the grass has regular growth spurts for which it requires potassium and nitrogen. Therefore in any conditions right for growth it rapidly becomes high in potassium but not correspondingly high in sodium, flooding the horses system with potassium upsetting the delicate sodium:potassium ratio which the body tries so hard to maintain.

Rye-grass and clover are normally 3-4% potassium, more when fertilised (up to 7 or more%).

A horse grazing lush rye/clover pasture will easily consume up to 10kgs/day, translating to an intake of 300-400 gms of potassium (or much more if fertiliser has been applied) when their daily requirement is around 25gms. From that same volume of pasture the horse will be receiving a mere 2 gms of sodium.

All the literature says that excess potassium is easily excreted via the urine, but not in the absence of sufficient sodium.

When extra salt is added to feeds (at least 10gms per 100kg BW) the animal drinks more and this helps with excretion of potassium.

Grass in spring and autumn also becomes high in nitrates (protein) and the horse rids itself of excess nitrates by latching them on to calcium and magnesium and excreting them via the gut and the urine, rapidly depleting the horse of these other vital electrolytes. The electrolyte imbalance is therefore that of too much potassium and not nearly enough sodium, calcium and magnesium. This serious electrolyte imbalance leads to inflammation:

It is no coincidence that all of these scenarios are triggered seasonally under the same weather conditions or that the same feeding regime works on all of them and that sodium is anti-inflammatory.
(Reference: ‘Nitrate Toxicity and Sodium Deficiency Associated with Hypomagnesemia, Hypocalcemia and the Grass Tetany Syndrome in Herbivores’. T.W. Swerczek, DVM, PhD.)

The quickest recovery from behavioural and health issues such as laminitis is when all green is immediately and thoroughly removed from the diet.

This includes eliminating lucerne and the most microscopic green shoots coming thru the dirt. ‘Restricting’ the grass, mowing, putting other stock thru first; none of these cut the mustard.

The slightest green tinge can perpetuate their problem.

Ad lib hay (Make sure there is NO rye or clover in this hay!) is ideal until they are recovered and as an integral part of their future diet for prevention of relapses.

One or two feeds of beet and meadow or oaten chaff per day containing extra salt (for sodium, at least 10gms per 100gms body weight) and top quality vitamins and minerals for proper nutrition to ensure they don’t become deficient whilst on their strict diet.

It is excellent to soak the hay for obese insulin resistant horses.

Making changes to manage pasture so that ‘mature’ grass is available rather than grass in growth mode is part of long term prevention.

A lot of horses and ponies are locked up in yards and starved or kept on ‘Jenny Craig’ type paddocks which end up with very short grass, thinking that controlling the sugar intake and obesity is the answer. Not true! Horses and ponies on this very short grass are very prone to relapses of their problems especially after any rain!


Invisible and insidious, they are produced by endophytes inside the rye-grass.

Everyone knows about the Lolitrem B which causes the staggers in late summer and autumn. But more harmful is Ergovaline, prevalent at this time of the year. Ergovaline can have a vaso-constricting effect, (cuts off the blood supply to).

When the blood supply is constricted to the skin you get heat stress because it raises their core body temperature. When this happens to the uterus it may cause abortion, to the hind-gut it can be a cause of serious colic. rye and clover

Other symptoms in horses include agitation, sweating for no reason, sweating in the float, running around the paddock for no reason, grumpiness, girthiness, belligerence, bucking, aggressiveness, prolonged gestation, no top-line, hard to keep weight on. (All crossover signs of major mineral imbalances too).

What about low or zero-endophyte rye-grasses?
Where the endophyte content has been altered or removed? No form of rye-grass, even those with the endophytes removed, will ever be suitable for horses.


Photodynamic Pigments

These are the pigments present in all grasses but much more so in the dark green ones such as rye-grasses, clovers, lucerne, St John’s Wort, Buttercup and plantain. They make these plants the darker green colour. These pigments fluoresce, are activated by light, and are known to cause photophobia and photosensitisation.

This is the true cause of ‘mud-fever’ AND ‘sunburn’.

When you remove these plants from the horse’s diet these conditions go away and do not recur.
Click on Mud-Fever & Sun-Burn

So our best advice is to eliminate clover where possible. So many people report that this is one thing that makes the biggest difference to their horses. You need to do it when it is in growth mode ie as soon as spring growth kicks in.

Horses have completely different dietary requirements than cattle and clover is not a natural part of their diet. Talk to your contractor about which broadleaf spray to use. Sometimes it can take awhile for the clover to die off. Apparently double strength MCPA is good and works quite quickly. If you are growing hay this will mean your hay is clover free and it will also eliminate other undesirables such as cat’s ear and docks.

We horse owners are between a rock and a hard place when it comes to using sprays. But clover will interfere with the cycling of mares and therefore your breeding aspirations, it will cause many behavioural issues and laminitis, respiratory conditions. Red clover will turn mares into nymphomaniacs and geldings into stallions.

Worst of all it is one of the biggest culprits in causing the dreaded head-shaking.

So using a spray once a year is a comparatively minor concern. Our best advice is get rid of it!!


Whilst clovers and lucerne store their sugars as starch which is easily digestible, all varieties of rye-grass store their sugars as fructans which horses cannot digest.

When fructans reach the hind-gut the streptococcus bacteria have a feast and immediately proliferate and devastate the good flora, cause sloppy manures, metabolic chaos which can trigger laminitis.

Excess Carbohydrate

Rye/clover pastures are selected for rapid weight gain and milk production in livestock. The exact opposite of what we want for our horses!

Rye/clovers are very high in NSC’s (non-structural carbohydrate or sugars) and when kept at a young stage of growth by grazing they are also low in fibre. The modified modern varieties are even worse. You will hear them being referred to as ‘diploid’ or ‘tetraploid’ which means the cells of the plant are 2 or 3 times the size of unmodified plants. This translates to the plant being able to store 2 and 3 times the sugar!!


Some mares become ‘Nightmares’ in Spring... to the point where some people refuse to own mares as riding horses! In the past we have felt the same however our mares now are just as even tempered as the geldings – there are no hormonal issues at all despite mares and geldings all living together. One of the reasons for this is the following:

Red and sub-terranean clovers, and to a lesser extent, white clover, have a high phyto-estrogen content, and animals grazing pastures containing these clovers often tend to develop all sorts of fertility problems.

Phyto-estrogens are plant estrogens. When consumed by livestock they can exert potent ESTROGENIC activity thereby seriously hampering reproductive performance.

It is well known that sheep grazing subterranean and/or red clover do not exhibit normal seasonal breeding cycles and are prone to developing cystic ovaries. Fertility returns once the ewes are removed from clover pastures although long term reduction in fertility has been reported in flocks that are repeatedly affected.

We, and many other people over the last ten years, have observed similar effects in our mares. These issues no longer occur now there is no clover (or Lucerne) in their diet. We emphasize this point because many people notice that their mares are not cycling properly in the spring, right at the time when they want them to conceive.

Read Dee's story