Riverrose--when pregnant mares eat feed that is high in nitrates (or drink water that is high in nitrates) it can result in congenital hypothyroidism in their foals. Congenital hypothyroidism can cause severe dystocia. Mares may carry their foal longer term, yet when the foal is born it may look very dysmature, more like a preemie than an overdue foal. The foal may be born very weak, and may die without ever standing. The foal may live, but have legs too weak to allow it to stand--or it may be able to stand but be unable to walk. A major problem is the extensor tendons are very weak--so the foal can stand but when it tries to walk it cannot bring the front foot up and out properly, so it catches the toe and trips. It may be so severe that the foal simply cannot walk. The foal may have immature bones in knees and hocks--a condition called tarsal crushing syndrome....the foal might do okay for awhile, but as it matures and gains weight the small, malformed bones that makes up the hocks & perhaps the knees cannot support the added weight, and they are literally crushed. The knees on affected foals may get very large, symmetrical swellings on them--it looks like a tennis ball under the skin just above the knee. The foal may be born with a monkey mouth--an underbite.
We had a Morgan foal with this condition in 1991. She went some overdue, not too bad, and was born healthy, except for a slight underbite. After a couple of days she developed the tennis ball swellings over her knees, and she was catching her toes and tripping. She could trot and canter, but when walking would catch her toes and trip--not every step, but now & again. On downward transitions from trot or canter she would be likely to catch her toes and trip. We had the vet out when the swellings appeared (we feared joint ill) but our vet said no, it was just swelling on her extensor tendons--he was familiar with the condition but didn't name it for us. Shortly after this I received a mailing from the WCVM in Saskatoon, and its main article was on congenital hypothyroidism--symptoms matched our filly exactly. I contacted the researcher that wrote the article & talked with him. At that time he didn't know what caused the condition--it was something that appeared seemingly at random at some farms--it would be a problem one year and then never again at that farm.
In 2004 we again had problems; this time we lost 2 of our 4 foals born that year. They never got up, just faded away and died very soon after birth. Another breeder here had major problems that same spring, only she was having major dystocias and foals with weak legs--very weak legs in some cases. With testing she finally determined that her horses were deficient in iodine--and when she told me that I suddenly realized that congenital hypothyroidism had again raised its ugly head. She had told me that her foals had swollen legs but I hadn't seen them. I then described the swellings that our Morgan filly had years earlier and she said yes, that is the same as her foals. Had I seen the legs on her foals I would have realized, because the swellings are very distinctive.
At that point I again talked with the researcher (Dr. Andy Allen, who is the reference for the article I have linked at the end of this post) at WCVM and learned that he was now convinced that nitrates were responsible for this condition--he hadn't proved it yet, but he was convinced of it. He also told me that it seems that mares who had the problems with their foals were mares who were also deficient in minerals--iodine and perhaps copper and possibly others. Mares who were mineral deficient and on feed/water high in nitrates were affected. Mares with high nitrate levels in their diet were able to overcome the effect of the nitrates IF they were well balanced on their minerals. We discussed mineral supplements and I told him that I was now using Equest minerals--that, he said, is a good supplement and if I continue using it I will surely have no further problems. He said that because other farms in his studies had started using Equest & their problems had gone away. He was right--we have had no further problems. The other breeder who had such major problems started using a supplement that was high in iodine and the mares who got two weeks or more on the supplement prior to foaling had no issues--her problems were finally over for that year....and since.
Our Morgan filly, by the way, out grew her problems. Her underbite disappeared--by the time she was weaned her bite was perfect. The swellings on her knees went away and by the time she was a year old she was no longer catching her toes and tripping.
The year we lost the two mini foals we figured out that our problem was the hay we had been feeding. We had some poor grass hay that everyone else was eating; our bred mares, however, had been getting 2nd cut irrigated timothy--beautiful hay, but it no doubt had been stressed by a hot spell when the irrigation was turned off shortly before cutting, and stress would put nitrates in it. The hay was all gone by the time our foal losses occurred so we could not test it. Our mares would have been better off on the poor grass hay! A neighbor who used some of that same timothy that same spring had his QH mare go 30 days past her due date and she had a horrible dystocia--mare & foal both died. I would bet that the hay was responsible for that loss too.
So, if you're having issues with pregnant mares and nitrates--look carefully at your mineral supplement. If you aren't using one--get one.
Here is an excellend article on the subject:
WCVM Research
