Pseudo Lactation not Pregnant

For going on three weeks my mare has been experiencing uncomfortably full teats. When gently expressed there is a full force thin stream of fluid. This fluid is milky but almost totally transparent.

Urine culture came back negative
Cushings test run earlier this month before this started came back very WNL

The vet spoke with their internist who said they’ve been getting about a call a week this summer and it is a weed creating elevated levels of phytoestrogen?

She hasn’t changed fields and there are no discernible new weeds and the property was sprayed back in the spring. The other mare on property is totally fine.

Only change of note was that she got a new pasture mate (gelding) the day of onset. Guessing correlational not causal but just as a FYI. They had a shared fence line for 9 months so it doesn’t seem logical that crossing a fence barrier would create this issue.

With support from the vet I bumped her Regumate to the maximum level to see if hormonal support helped her regulate but no change.

She is happy to have them handled (thank you summer allergies) and there’s no heat or evidence of mastitis. I haven’t expressed them beyond checking once a week or so to make sure that the fluid isn’t looking or smelling weird thinking that expressing could trigger the body to produce more fluid?

Is there anything else I should be doing or can ask the vet? I’ve been putting a thin layer of desitin on the sides to make sure she doesn’t chafe but I feel at a loss about next steps.

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I’ve never experienced this before but I would be asking the vet about checking hormone levels via bloodwork. Also, could an ovarian tumor cause this?

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On this front, it might simply be that this mare likes that weed that there is a small amount of, whatever it is, and the other mare does not like that weed.

Horses like to do weird things to keep us guessing.

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I’m experiencing this for the second time with another young horse.

About ~17 years ago I had a young mare do this. Said mare is now 19 and still occasionally expresses fluid, despite never being pregnant. But when she was 2 she actually bagged up. We couldn’t find anything wrong, vet decided it was phytoestrogens from the pasture + high soy diet.

This summer my current 2 year old started doing the exact same thing. She eats much less soy than my other horse did at this age. Different farm, different state, nearly identical presentation. I didn’t call the vet this time around because BTDT with no real answer. The only notable difference is that this mare developed some severe photosensitivity later on in the summer that may or may not be related. :woman_shrugging:

So, no answers for you but you’re not alone!

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We had one mare out of a group that would bag right up with any alfalfa growth in her pasture. It was the weirdest thing, and never bothered any of the other mares she was turned out with.

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