Is Alfalfa Bad for Horses? Eleven Objections, and the Two That Hold Up

Walk into any yard and mention alfalfa. Someone will tell you it makes horses hot. Someone else will bring up the kidneys, or the calcium, or a friend whose gelding got ulcers on chaff. The advice arrives with total confidence and almost never with a source.

Alfalfa (lucerne, if you grew up calling it that) has collected more folklore than any other forage. So it is worth putting the common objections next to the research. Of the eleven that circulate, two survive. The rest either have no evidence behind them or, in two striking cases, have evidence pointing the opposite way.

Does alfalfa make horses hot?

This is the big one, and it is the objection with the weakest foundation.

Nobody has ever run a study that changed the protein in a horse's diet and then measured its behaviour. Not one. What has been tested is starch, the kind you get in grain and hard feed. Bulmer et al. (2019) took ten Welsh ponies and fed each of them two diets in turn, so every pony acted as its own comparison. One diet was hay plus dried alfalfa. The other was hay plus a starchy compound feed. Both delivered the same amount of energy per day, so the only real difference was fibre against starch.

On the starchy diet, the ponies changed pace more often, spent less time investigating their surroundings, startled more readily at anything new, and were scored by observers as tense and nervy. Their gut bacteria shifted in step: fewer of the bugs that break down fibre, more of the ones that produce lactic acid.

The ponies eating alfalfa were the calm ones. On the same energy intake. That is the closest thing to a direct test of "alfalfa makes them hot" that exists, and it runs against the claim.

Two things do hold up, and neither is the fault of the plant. Alfalfa carries roughly a fifth more energy per kilo than average hay. Swap one for the other kilo for kilo in the bucket of a horse in light work and you have quietly raised its energy intake by 15 to 25%. That energy goes somewhere.

Molasses, and the number that actually matters

The second is molasses. The percentage printed on the bag tells you less than you would think, because what reaches your horse is that percentage multiplied by how much you feed.

Take a manufacturer's own figures. A standard alfalfa chaff runs around 12% sugar. The molasses-free version of the same product runs around 4.5%. Feed two kilos of the sweetened one and roughly 240 g of sugar goes into your horse. Two kilos of the plain one delivers 90 g. Since sugar and starch are the things with a proven effect on behaviour, the molasses is a far better suspect than the alfalfa it is stuck to.

To be straight about our own: the ESTE Balancer contains 3% beet molasses and about 4% sugar overall. A full daily dose for a 500 kg horse is 250 g, so the sugar in it comes to roughly 10 g. Hand your horse a single medium apple and you have just given nearly twice that. Set it against two kilos of molassed chaff and it is about a twenty-third as much, or against an average day's hay, somewhere around 1%.

The objections that do not survive

Protein damages the kidneys. No feeding trial, no tissue study, and no test of kidney function has ever shown that a high-protein diet harms healthy kidneys in horses. Miller and Lawrence (1988) fed mares 12.9% against 18.5% protein and found no sign of damage. Oliveira et al. (2015) fed 24 sport horses four different protein levels. The horses passed more nitrogen out in their urine, exactly as you would expect, and it changed nothing about their water balance. The worry drifted in from human dieting, where the idea has itself largely been dropped. Where caution is warranted is in a horse that already has kidney or liver disease, and there the concern is real.

The calcium to phosphorus ratio is dangerous. Alfalfa gives a wide ratio, not a back-to-front one, and that distinction is where the claim falls apart. Adult horses cope with ratios well above the textbook 1.5:1 to 2:1, as long as they are getting enough phosphorus in absolute terms. That condition is the whole story. A wide ratio only becomes a problem if you got there by feeding too little phosphorus. And "big head", the disease people have in mind when they raise this, is caused by the exact opposite: too little calcium alongside too much phosphorus, or certain tropical grasses that lock calcium away where the horse cannot absorb it. Alfalfa is the treatment for big head, not the cause.

Alfalfa causes free faecal water. The only study comparing affected horses against healthy ones found the reverse. Lindroth et al. (2021) matched 50 affected horses against 50 controls across 50 farms. The affected horses were eating less alfalfa, less straw, less usable protein and less structural fibre, and roughly twice as much hard feed for their bodyweight. Every relevant finding pointed the same way. If your horse's droppings have changed, our guide to faecal water syndrome is a better place to start than cutting the alfalfa.

Protein causes joint problems in growing horses. The condition meant here is osteochondrosis, usually shortened to OCD, where cartilage fails to form properly in a young horse's joints. Savage and colleagues (1993) fed foals far more protein than the recommended level and found no cartilage damage at all. What did cause the damage in those same experiments was too much energy. Protein was not the culprit.

Alfalfa and ulcers: the answer depends on the form

Here is the first objection that holds up, though not in the shape most people repeat it.

A horse's stomach comes in two halves, and alfalfa treats them differently.

• The top half has a thin lining with no real defence against acid, and it is where most of what owners call ulcers shows up.
• The bottom half is where the acid is made, and its lining is thicker and built to cope.

For the top half, the evidence on alfalfa is good. Nadeau et al. (2000) fitted six horses so the contents of the stomach could be sampled directly, then fed them alfalfa plus a little grain, or grass hay on its own, in turn. On alfalfa the acid was measurably weaker for the first five hours after a feed, and those horses had fewer and milder ulcers up there. Bäuerlein et al. (2020) ran the tidiest version of this test, feeding alfalfa hay against meadow hay in equal amounts and at a similar chop length, with the assessors kept in the dark about which horse had eaten what. The top half improved on alfalfa again.

The bottom half is where it turns. Four separate lines of research link coarse chopped alfalfa, fed in large amounts, to damage low down in the stomach. The most useful is Vondran et al. (2016). Seventy foals were fed the same amount of protein, delivered either as coarse alfalfa chaff, as alfalfa pellets, or as grass hay. The chaff group came out clearly worse. The pellet group came out clean.

Be careful how much weight you put on all of this. The five-hour window is about as long as an antacid lasts, not a whole day, and in that study the alfalfa came with a little grain alongside it, so the two are hard to separate. Nobody has yet measured alfalfa's acid-soaking power against grass hay in a horse directly. On the other side, the suggested explanation for the damage low down, that coarse fragments scratch and irritate the lining, has never been shown to happen. It is a theory the researchers offered to make sense of their own results. The follow-up study in adult horses, the one quoted most confidently of all, did not produce a solid result at the site everyone cites. And the study that would settle the question has never been run: hay against chaff against pellets, in the same horses, in one trial.

Insulin: a real finding that is not an alfalfa problem

On sugar alone, alfalfa is a safer bet than most grass hay, at roughly 8.8% sugar and 1.3% starch. But Loos et al. (2022) found something the sugar figures miss. They fed sixteen mares, eight of them with an insulin problem, either alfalfa pellets or a shop-bought protein supplement, matched so that both meals delivered the same protein. The mares with the insulin problem produced a far bigger insulin spike than the healthy ones. Their blood sugar did not rise at all. That combination points to the protein driving the insulin, not sugar.

The clinicians who spent twenty years saying some of their insulin-resistant horses reacted to alfalfa were right. The reason was not the one they gave.

The conclusion is not "avoid alfalfa", though. The study found the protein source made no difference. The shop-bought supplement did exactly the same thing at the same protein dose. What matters is how many grams of protein land in one bucket, not which plant they came from. A soya-based balancer behaves the same way. For a horse with an insulin problem, smaller feeds spread through the day do more good than swapping one protein source for another. For a sense of the dose involved: the study fed 125 g of protein in a single meal to a 500 kg horse. If you are managing a sugar-sensitive mare, our guide to feeding through laminitis risk covers the practical side.

What to ask before you cut it out

If someone tells you their horse cannot tolerate alfalfa, the useful first question is which form, and how much. Two kilos of coarse chaff and a spoonful in a balancer are completely different things, and nearly all of the worrying evidence is about the first.

The second question is whether the product contains molasses, and if so, how many grams of sugar that adds up to at the amount you actually feed.

Our own ESTE Balancer contains a modest amount of alfalfa, around 50 g in a daily dose for a 500 kg horse. The whole dose carries about 29 g of protein, roughly a quarter of the 125 g in a single meal that produced the insulin response in that study, and the proportion stays the same at every bodyweight because the dose scales with the horse. It is also not coarse chaff. We are not going to tell you that small amount does something remarkable for your horse's stomach, because the studies showing a benefit all fed 5 to 10 kg a day and nobody has tested a few hundred grams. What the evidence supports is narrower and more useful: there is no reason to think a small amount of alfalfa does any harm, and most of what you have heard about the plant describes a different product at a completely different scale.