Feed Materials in Focus – Linseed and Hormones in Mares



You may have seen claims that linseed/flaxseed should not be to fed to mares because it’s “oestrogenic”. 

Oestrogenic (estrogenic) means stimulating oestrogen (estrogen) producing (-genic = causing or producing). Increased oestrogen is linked to estrus behaviour (“heat”) and can include tail raising, frequent urination and erratic/unpredictable behaviour towards both horses and people. 

Clearly if linseed could induce such behaviour it would be unwise to feed it to mares. 

So what evidence is there that linseed is likely to affect mares’ behaviour adversely? 

Below is a quote from Dr Eleanor Kellon from a post in 2009: 

“All phytoestrogens are not created equal! A common feature is that they can bind to estrogen receptors. However, what the effect of that binding is depends on the type of phytoestrogen. In flax/linseed, it is lignans, which are very different from things like genistein or dicoumarol. 

“The lignans in flax/linseed are transformed by bacteria in the bowel into compounds that can bind to estrogen receptors. Unlike other phytoestrogens, they DO NOT STIMULATE THE ESTROGEN RECEPTOR SO THEIR EFFECT IS ACTUALLY ANTI-ESTROGEN!. For example, soy stimulates estrogen receptors and flax/linseed can at least partially block that soy effect.” 

So apart from from its high omega 6 (inflammation causing) and low omega 3 (inflammation reducing), this is another reason not to feed to soy to mares. 

In addition, a study published in 2011 by Swanson and Hammer found no evidence of linseed/flax stimulating hormones in mares.


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