Can My Ponies Be Under a Black Walnut Tree for Shade?
I have 2 ponies who need shade sometimes on hot days, so I put them in my round pen which is underneath a big Black Walnut Tree. It always drops nuts in the fall, big brown walnuts. In the past, I always picked them up, in the fall, as I know they can be toxic to horses (correct?) So far, so good. Ponies have been fine for the past 4 years I've had them here.
However, this year, the tree is dropping yellow fruit that are nubby and, I assume, baby walnuts that have not developed fully (correct?) Are these also toxic to ponies and horses? I've been picking them all up but I can't always see the "crumbs" or little pieces that break off in the grass that the ponies eat. What should I do? It's the only shade they have and only put them in there on VERY HOT days. Please advise.
I'm very worried as their pasture has no trees/no shade at all, plus, the owner sprays Tru Green on it in Spring and Fall, besides. So, my choices are a shade-less pasture that's been sprayed or a shady round pen under a mature Black Walnut Tree. If anyone has room on their farm, or in their heart, to help us out and provide a place temporarily (we can't afford board) please get in touch! Thank you.
Washtenaw County Michigan
Black walnut toxicity in horses is primarily associated with horses who have come into contact with black walnut shavings. The toxic substance juglone is found in the roots and wood of the tree. Horses will show signs of toxicity manifested as laminitis (founder) when they are exposed to as little as 5 - 20% of black walnut shavings in their bedding. The toxin is absorbed through the soles of their feet. Its extremely important to trust your shavings resource.
In a pasture setting, it would be harder for horses to come into contact with the toxic substance. There is an older case study of broodmares that were affected from exposed roots of a black walnut tree, as they spent most of their time standing underneath it for shade. Often, you will find fences around black walnut trees that are located in the pasture, to keep horses off of exposed roots.
A more likely risk of exposure in the pasture would occur when a walnut tree has been removed and the stump ground down. If the shavings are left, horses could potential be exposed to the toxin if they stand in the area. Therefore, it's important to remove all shavings associated with the tree's removal. The fallen fruits can become moldy and are also toxic to dogs and livestock. While I have never heard of horses eating the walnuts, I wouldn't put anything past a hungry pony!
Best practice are to remove fallen branches and nuts from the pony's access. You may want to consider using temporary fencing to block off your pony's access to the tree when the fruit is falling in large amounts (see attached image of MSU horse paddock trees). Horses will usually avoid eating toxic plants if they have access to good grazing or hay. Below is an online article from Ontario MAFRA that can give you more details to help you base your management decisions.