Is there a link between mares coming into season and laminitis?

April 14, 2012

I’ve had a few interesting conversations by email and phone with a fellow owner of laminitic horses. This horse owner noticed that her mare’s laminitis bouts seem tied to the horse coming in season. The mare does better in winter when she goes out of season for an extended period of time. In fact, the mare often does better when environmental conditions are favorable for the mare to do worse, which is what made this owner look beyond the usual list of so-called “laminitis triggers” since that list wasn’t serving her well.

Estrogen rises in a mare during the preparation of the egg and drops if the egg is not fertilized and the uterine lining is shed.

A possible link between laminitis and rising estrogen makes sense since we know the most prevalent form of laminitis today is the insulin resistance form, and estrogen is a major player in insulin resistance.

I wasn’t looking for this link when my mares foundered. If I noticed a link between Angel’s cycles and her laminitis when she had her first bout in 2004, I didn’t write it down.

I did notice as a general rule that Angel came in season far more than most normal mares, and Goldie, her mother, also had that tendency. Goldie foundered before Angel. Those two mares had my worst cases.

Both mares stopped cycling after several bad bouts of laminitis. It was as if their body knew to shut down that process completely.

When I wrote my original article on laminitis and estrogen, the research on whether more mares developed laminitis was mixed. One study that reviewed a broad range of previous laminitis studies said the results were inconclusive.

If you look at this logically, here’s what we know in both the human and horse world on estrogen as it might relate to laminitis:

1) Young woman are reaching puberty earlier, and many researchers say that is due to things such as the estrogen mimics in plastics and other materials that are prevalent in a child’s world today. It only makes sense that some of these same plastics are in a young horse’s world, as well.

2) Dr. Mehmet Oz defined the link between fat, estrogen and insulin resistance in humans this way: Estrogen causes the body to make more insulin, and more insulin creates belly fat. Increased fat cells make estrogen.

Many horses that develop insulin resistance and laminitis get the cresty neck that scientists call “regional adiposity,” along with fat deposits over their tail and in their sheath area. Maybe for horses, their estrogen-related “belly fat” isn’t in their belly? Maybe it is in these three areas. We certainly know that horses are much fatter today than 100 years ago. Veterinarians refer to this as an epidemic. Are we feeding horses more? I am not feeding my horses more than my parents fed their Connemara herd 30 years ago; in fact, I’m feeding far less. I know this, because I often fed for my parents. I gave their horses several bales of hay at a meal rather than counting out flakes as I do now. And I fed grain — the kind of grain full of oats — by the coffee can rather than by the half cup, as I do now. My parents’ herd was made up of relatives of my herd. My parents had maybe 10 Connemaras at any one time on 14 acres. I had six on 8 acres — that seems fairly even. None of my parents’ Connemaras ever foundered. All of mine did. None of my parents’ horses were obese or had a cresty neck. All of mine are obese and have the neck.

There has to be something else going on in these horses now. Elevated estrogen caused by something environmental seems logical.

3) I continue to look at excess iron’s role in my horses’ cases. I threw out my horses’ trace mineral blocks over the winter because I discovered the blocks were 20 percent iron.

In looking for studies on iron and estrogen, I took a close look at a study published in 2001 by the Stehlin Foundation for Cancer Research in Texas that looked at iron’s role in estrogen-induced cancer. Remember, scientists now believe that laminitis makes the hoof wall proliferate in an out-of-control manner similar to cancer. The Texas study said that elevated dietary intake of iron raised the incidence of cancer in rats and hamsters and that adding estrogen increased iron accumulation in hamsters. The study suggested that, since other studies have shown that elevated body iron storage increases the risk of several cancers in humans, interfering with iron accumulation in tissues might offer an option for cancer prevention. I wonder if anyone has tried that in laminitic horses?


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