Alfalfa Toxic for Animals?
Answered by: Conrad Richter
Question from: Lucy Wilkinson
Posted on: May 7, 2002

I have been doing some research about using herbs to treat animals, and have come across a question I can’t seem to find the answer to. Many herbal preparations for pets seem to use alfalfa (Medicago sativa), yet I have just found alfalfa on a list of herbs that are considered toxic to animals (from a database at the University of Illinois Veterinary Medicine Library). The database has no explanation of why it is toxic, it just presents pictures. I also noticed that it has not been updated since 1996! I can’t seem to contact anybody there to find out what’s going on. Do you have any knowledge of this?

That alfalfa could be considered toxic for animals is news to us. Alfalfa is one of the most benign herbs we know. Of course, individuals may develop allergies, even life threatening ones, to just about anything, including alfalfa. But as far as we know alfalfa is safe for both humans and animals.

There are reports suggesting that some of the constituents of alfalfa could be dangerous. The trouble is that these assertions, as far as we can make out from the literature, are more theory than reality. For example, alfalfa sprouts are known to contain the toxic amino acid canavanine. But by the time alfalfa sprouts are ready to eat the concentration is so low that it does not present a problem to human health. Canavanine in high concentrations can indeed be toxic, so its presence in alfalfa seeds probably rang some alarm bells.

If you look hard enough you will find toxic substances in just about anything including safe foods that you and I eat every day. The question is not be the presence or absence of these substances, but their levels. Years of practical experience growing and eating alfalfa seem to confirm that levels of canavanine are too low to present risks. In an article on the myths of natural toxins in sprouts (, Warren Peary and William Peavy, Ph.D, wrote:

"While some writers may make canavanine sound like a dangerous carcinogen – it isn’t. Canavanine is a non-protein amino acid that’s toxic in high amounts. In the dry seed it serves as a storage protein, a growth inhibitor, and a defense against natural predators. As you might guess, as the sprout grows, canavanine falls rapidly to insignificant levels. The text, ‘Seed Physiology’, clearly states that ‘Canavanine... is non-toxic to mammals at low concentration.’

"Canavanine is so irrelevant that the 1980 text, Toxic Constituents of Plant Foodstuffs, doesn’t even mention it. A 150-pound human would have to consume 14,000 milligrams of canavanine all at once for it to be toxic at the same level it is toxic in mice. This is an incredible amount! It is doubtful that with a generous helping of alfalfa sprouts, you would get more than a few milligrams."

There are credible reports that alfalfa hay can present a danger to animals if it is contaminated. Alfalfa hay contaminated with poisonous weeds has been known to injure animals. There is also a beetle called the "blister beetle" that contains a natural toxin called cantharidin that has been known to kill livestock. Reportedly just 50 beetles can kill a horse. Blister beetles are common in southern U.S. states, but they have reached as far north as Michigan. Blister beetles feed on alfalfa blossoms so late cuts can end up being contaminated with enough blister beetles to endanger animals. For more information see

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