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Roger Weller, geology instructor
by Cynthia Chestnutt
Mineral Excess, Deficiency, and Complication in
Living in the Southwest United States
Many people have gone to great lengths to address their own health issues,
ensuring that they are taking vitamins, or eating foods that contain the right
kinds of vitamins and minerals that their body needs. It is not surprising to
know that our equine friends also have a variety of mineral needs when it comes
to ensuring their optimum health. What we feed our horses has a profound effect
on their growth, ability to resist disease, and in some cases to survive.
Perhaps considered by some the most troublesome mineral complication in the
horse is the development of enteroliths in the intestine of the horse.
Enteroliths are hard stones, that can be from small pea size stones all the way
up to stones weighing several pounds. They are extremely painful to the horse as
they cause an obstruction in the intestine of the horse. During the development
phase they may only partially block the intestinal path way. Many can move along
the digestive tract and be expelled by the horse during normal excretion.
However, if they continue to grow, they eventually block the entire intestinal
pathway causing extreme and urgent colic which can only be resolved with
Enteroliths otherwise known as struvite are made up of magnesium, ammonium, and phosphate. Enteroliths also contain calcium, titanium, iron; aluminum and nickel however these minerals tend to compose less that 10% of the enterolith content.
Beautiful but sometimes deadly enteroliths:
There are several hypothesis of why enteroliths are more common in the
Southwestern parts of the United States. One of those is the belief that the
increased popularity of feeding alfalfa to the horses in the Southwest. Alfalfa
hay contains increased amounts of ammonium and magnesium. It is thought that
there is an excessive amount of free ammonium released in to the large colon of
the horse, and this combined with the magnesium and phosphate ions forms
struvite crystals. Studies show that in fact 98% of horses with enteroliths had
a diet composed of at least 50% alfalfa hay which is interestingly also high in
calcium, magnesium, ammonium, and phosphate. While enteroliths do exist in other
parts of the country the mineral composition of the enterolith seems to mimic
that of the composition of the soil and feed in those regions.
One important note worth asking is why is alfalfa grown in the Southwest high in
magnesium? It is believed to be higher due to the majority of it being grown in
serpentine soil. “A serpentine soil is derived from ultramafic rock,
in particular serpentinite a rock formed by the hydration and metamorphic
transformation of ultramafic rock from the Earth's mantle.” As you may already
know ultramafic rocks are low in silica content and high in magnesium and iron.
The results of growth in this type of soil? You guessed it: alfalfa with high
levels of magnesium.
Yet another hypothesis is that the magnesium and or calcium content of the water in conjunction with high magnesium in the alfalfa may be the culprit. In personal experience having lost a horse with an enterolith, alfalfa was removed from his diet completely and yet stones reformed. The water he drank was high in calcium. Still others believe the formation of the stone is caused by a bacterial infection that hydrolyzes urea to ammonium and raises urine pH to neutral or alkaline values. In horses urine pH is also noted to be increased and this is also how struvite is formed in dogs and humans.
While it may seem like a good idea to avoid high magnesium, and high ammonium
feeds, magnesium deficiency comes with its own host of problems. Magnesium
deficiency is associated with horses that are excitable and nervous, can
attribute to Insulin Resistance (where cells become resistant to the glucose
uptake action of insulin) and contribute to obesity in the horse.
Insulin resistance is of particular concern as the consequences of uncontrolled
insulin resistance leads to a chronic debilitation in the horse known as
laminitis. Most non-horse people know that laminitis was the debilitating
last straw for Barbaro, however laminitis can also be caused by insulin
resistance due to mineral deficiency. (Some mineral excesses have also
caused laminitis.) Laminitis occurs when the coffin bone of the hoof separates
from the hoof wall. The result is a failure of the structure of the hoof
to support weight. This of course results in intense pain for the horse.
Often laminitis only occurs in the front feet. The photo below shows a
horse with a typical laminitis stance as he attempts to shift weight from his
sore front feet to his rear.
Should the laminitis become chronic and uncontrolled distortion of the hoof
capsule may result.
According to Katy Watts
of safergrass.org, who had dedicated her research to investigating hay
composition and horses all over the country, says the horses of the Southwest
are nearly all deficient in magnesium despite the high levels of alfalfa being
fed. It is thought however, the competition of other minerals compete for
absorption with magnesium and is therefore still deficient. Here is the
southwest excess calcium leads to magnesium deficiency despite excess magnesium
In addition, other commonly deficient minerals in the Southwest are: Copper,
zinc, and selenium. According to Jim Sprinkle from the University of Arizona
Agricultural and Life Sciences Extension, when Arizona rangeland soils carry low
levels of trace minerals, the forage plants are also deficient in these minerals
While selenium may be deficient in Arizona, supplementation can be tricky as a little of bit of selenium is good however over supplementation can equate to the loss of mane and tail and even the sloughing of the hoof. Selenium is toxic in high doses and may result in death of the horse.
While copper deficiencies are considered rare, the symptoms can include more
subtle problems in horses such as thin bones, swelling of joints, and if severe
deformity in the limbs.
An interesting symptom of zinc deficiency is brittle weak hooves. Many believe this is simply an attribute of the dry desert arid regions, however can also be caused by a deficiency of zinc, biotin, or any of the other building blocks needed for keratin formation in the hoof.
There are a variety of minerals needed by horses in Southwestern United States. Since the majority of horses in this region do not have access to fertile pasture land horse owners find that they must meet their horse’s requirements with dried hays. The downfall means horses often lack much needed minerals they could normally source foraging on their own through a variety of terrains. Even so soil levels of the ground lack many minerals horses need to support healthy functioning in which the pasture or hay is grown. The recommendation is to test all your hay that you feed, and then purchase a supplement that contains the balancing minerals your hay is deficient in.
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