We too had a run about with this, but unfortunately lost out mare.
We had turned out our two girls and their 3-4 month old colts in the morning, all were fine when we turned them out, gave them their grain which they were munching on, as well as their hay and they were on pasture. Ran into town for a couple hours and when we got back we found our pintaloosa girl Lexi down by the gate (away from her foal, and the other pair) with her head hanging low, wringing wet with sweat and breathing extremely hard. My initial reaction of course was colic, so ran and got a lead rope and tried to get her to walk while my mom ran to call the vet. That's when I started to suspect something other than colic, she wasn't kicking her belly, trying to roll, bite her sides etc. Vets told us to load them in and get them to the clinic ASAP. Looked her over and pulled blood, ran a blood test and found she was VERY, deathly low on calcium (vet made the comment had a COW been that low, she'd been dead) So they IV'd her calcium and made the decision to leave her there overnight so they could keep a constant flow to her and try to pull her out, also decided to pull the colt and wean him as he would only pull her down again nursing. Was heartbreaking to load the little guy into the trailer without momma and put him back in the stall without her, but looking back, I truly think he "knew" something was going on, wasn't a whinny or cry out of him the entire ride home nor in the stall, no running around frantic looking for her.
Vets told us that they would call us if there were any problems or if we needed to rush her to the main campus clinic. Through the night no call, about 5:30-6 am the phone rang and my heart sunk, was them telling us she'd taken a turn for the worse and if we wanted any slim chance of saving her we needed to move her now. When we got down there she was laying down on her chest, how she had the strength to hold her head up I don't know. She had started head pressing as well so had skinned her forehead
I was ready to put her down right then, but my dad looked at me and said "We got to try", so we loaded her onto the trailer and made a mad dash for the hospital. Unfortunately, we lost her by the time we got there.
It was one of the toughest things I have been through and still to this day, 3 years later, it haunts me and I still cry.
Needless to say I keep a VERY close eye on mares during lactation to try to prevent this again. I'm sure I feed my girls "too well" and if I notice a foal is pulling a mare down and upping her feed doesn't help, then I'll wean.
With the frequent mention of foals and nursing - does one assume that nursing foals dimish the calcium supply in the mare? Is there a prevention by giving the mare something extra while nursing? And I saw mention of foal age ....... that too is associated with the risks?
Yes, a foal nursing will pull the mare's calcium level down, during lactation so much of that calcium goes into milk production, that at times the mare's body doesn't keep enough for herself. The mare we lost was a HEAVY milker, she didn't have a huge udder prior to foaling, but once she foaled and that foal started nursing she milked like a cow. Our vet recommended good feed, good hay (told us a good mix of alfalfa/grass) would help. If we noticed a mare starting to get pulled down by her foal, increase her feed and if that didn't help, to wean, especially if the foal was eating grain/hay well. Our little guy was 3 1/2 months old, MUCH earlier than I normally wean, but he did fine, he was drinking water, creep feeding and eating hay well and continued to do so after losing her, we did not supplement him with any milk replacer or milk based products, and he grew normal and held his weight etc.