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    Re: [RC] The skinny on tall fescue and horses --was Pasture - Cora

    Lisa...the info is great....I live in southern Nevada...only have 2 geldings...am considering a pasture...are there any fescues I should not use...Cora
    ----- Original Message -----
    Sent: Tuesday, July 09, 2002 6:51 AM
    Subject: Re: [RC] The skinny on tall fescue and horses --was Pasture

    A little history on fescue, since there seems to be a lot of misinformation floating around (and my apologies if it gets more technical than usual--this is my area of specialty and I tend to get carried away)--
    Tall fescue was discovered growing on the Suiter farm in Kentucky in the late 20's, and produced such a nice stand of grass that handled grazing pressure, the climate, etc. that when the seed was released as Kentucky 31 in the 30's it sold like hotcakes.  This explains why it now covers approximately 35 million acres of pasture in the US alone.  However, in the 40's, they started to correlate fescue foot and summer syndrome in cattle with this grass, and in the early 50's found that it contained the endophyte.  It was not until the mid-80's that my major advisor in college proved definitively that the presence of the endophyte was connected to the problems in mares--until then it was accepted that it was a selenium deficiency, a fallacy that was promoted by a poorly designed study in Missouri where they compared mare response to Se/Vit. E injections in mares grazing fescue with mares grazing orchardgrass.  His graduate student, Julie Monroe, published the first paper showing this in 1988.  Tall fescue was never specifically bred for the purpose of maintaining the presence of the endophyte--the majority of fescue pastures were established long before anyone discovered the endophyte or started making connections between it's presence and the problems in cattle and horses.
    This endophyte produces about 9 different classes of alkaloids, several of which have been demonstrated to be the causative agents of fescue toxicosis.  The ones of most concern are the ergot alkaloids (related to the ones produced by ergot, which explains the similarities between fescue foot and ergot poisoning) and the lolines and perlolines.  The first group is the one which has the most impact on horses, as they act like a neurotransmitter called dopamine by preventing prolactin secretion from the pituitary gland.  This hormone is the main trigger in starting the development of the udder and stimulating milk secretion. 
    Besides the primary effect of depressing prolactin, the ergot alkaloids also have a secondary effect of depressing progesterone and increasing estrogen.  As I pointed out in an earlier post, the problems associated with the altered steroid profiles is compounded by the fact that the ratio between the two is altered--this creates problems with uterine contractions, placenta expulsion, etc.  We believe that the effects on estrogen also demonstrate that the alkaloids are crossing the placenta and affecting the foal, and this is supported by research that shows levels of ergocryptine in lamb fetuses in sheep injected with that alkaloid.  We also know that there are effects on thyroxine and cortisol levels.  The release of cortisol, thyroxine, estrogen, and progesterone are all under the control of the pituitary, so it's not surprising that the toxins affect those hormones. 
    Why do we keep grazing tall fescue if it's so bad?  Except for the toxins, the nutritive quality is great for a grass.  The presence of the endophyte also confers insect and disease resistance, drought tolerance, tolerance of high grazing pressure and high stocking rates (possibly becuase the endophyte seems to affect the growth pattern).  In the southeast, it's the best cool season forage going as far as stand life and persistence.  Endophyte-free varieties just don't stand up to the stresses of being a pasture grass in the fescue belt.  We are also finding ways to cope with or prevent the problems.  I was very fortunate to discover the effectiveness of the drug now called Equidone during my doctoral research, and am thrilled that it's soon to be released commercially.  Although I would prefer to find ways nutritionally to cope with the problem, in this case a drug is the best solution until an endophyte-free fescue is developed that performs as well or better than the infested varieties.
    Obviously, I can't reprint my dissertation for you here, and it would probably bore or confuse everyone but Susan and Heidi and Charlotte anyway.  However, if you want to see the article on the original study, or see a review that was created from my lit review and that of a colleague, Dr. Jim Strickland, go to www.equitox.com and go to the research link.  My article is the one about domperidone in horses, and the review is the one called Equine Fescue Toxicosis, Signs and Solutions.  Whatever happened to the dose titration study I did, I don't know....Dr. C. keeps promising to send me galley proofs....and has been for years!  LOL
    Lisa (Fescue Fungus Fighter Extraordinaire)

    [RC] Pasture, Linda B. Merims
    Re: [RC] The skinny on tall fescue and horses --was Pasture, Lisa Redmond