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Working for better management options and cohabitation through compromise and communication for the American Wild Mustang

You Be the Judge, 8th Edition, February 05, 2010 – Calico Miscarriages & Malnutrition…

Posted by Texas Mustang Project on February 5, 2010

You Be the Judge 
8th Edition 
February 05, 2010 
By: Tracie Lynn Thompson  

With the death toll rising in the Calico Complex HMA Gather, several individuals have been emotionally affected by the reports of miscarriages. Veterinarian Richard Sanford released a document on February 02, 2010 reporting that the cause of these miscarriages was nutritional deficiencies in the mares, citing that “the miscarriage reduces the energy demand on the metabolism of the mare”. 

The daily gather updates on estimate the total number of mares who have had miscarriages as 20-30 on January 29, 2010, with 3 more miscarriages since then as of today. This number is the estimated count of approximately 900 mares at the Fallon facility. With these numbers, the percentage of mares miscarrying calculates to approximately 3.5%. 

From the beginning of this gather, reports from the onsite observers and those in the general public have disputed the very notion that the Calico horses were malnourished or starving. They claim that the BLM is using this as an excuse to remove the horses from the HMA to either (a) make way for the Ruby Pipeline, or (b) make room for more cattle grazing permits. The basic for this dispute is a multitude of photographs taken of the gathered horses in Calico showing strong, muscled, “fat and healthy” horses. 

Further claims state that the miscarriages are not a result of nutritional deficiencies, but are in fact a direct result of the gather operations themselves. Reports are widespread of added physical and psychological stress on already heavily pregnant mares by the helicopters, journey to the corrals, further “chaos” in the chutes and corrals, and subsequent transport to the Fallon facility. This stress is purported to be the actual reason for the miscarriages. 

To date, gather officials from the BLM have not directly denied that the added stresses could have contributed to the miscarriages. However, they maintain their position that some of the horses of the Calico Complex HMA are in fact malnourished and starving, and that without immediate action more of the population will suffer the same fate. As well, they maintain that the majority of mares who have miscarried have been in poor body conditions to begin with, and had they not been so, the miscarriages would likely not have occurred. 

So two questions are evident: 

1.)    Are the horses of the Calico Complex HMA malnourished and starving? 

2.)   If so, is this the reason for the miscarriages, or is it due to stress from the gather? 

Let’s start with #1: 

It has been clearly evident in photographs by both the BLM and by the public observers that there are horses in good body conditions just as there are horses in poor body conditions being gathered. The overall ratio is hard to quote at this point in time simply due to lack of information available. However, reports from both the BLM and the public observers state that there are a small number of the poor horses when compared to the number of healthy horses. 

So what’s the issue? Misinterpretation. 

The BLM has maintained their position on this issue from the start. The officials state that they are implementing preemptive measures to prevent further horses from suffering the effects of dehydration and malnutrition. These projections are based upon data collected from the range itself, the body conditions of the horses from the range, and the meteorological projections of drought for the upcoming summer months. 

Wild horse advocates have also maintained their positions on this issue. Advocates claim that the range’s condition is sufficient to provide viable nutrition sources to the current populations of the HMA. Their claims are based upon –oddly enough – much of the same data that the BLM uses as support for their claims. Advocates further their claims by the number of grazing permits renewed in this fiscal year, as well as the prior fiscal year and the fiscal year to come. 

From this perspective, it is hard to say who is right and who is wrong. So let’s look at this from a different perspective. 

There are malnourished and starving horses on the Calico Complex HMA currently. We know this to be true because we have seen the photographs of the poor and emaciated horses who have consequently either died or been euthanized as a result of this condition. We cannot be 100% what the future will hold for the horses of this HMA in regards to this coming summer’s conditions. 

What we can do is try to do the best that we can with what information we have right now. If that information tells us that the horses will not suffer the detrimental effects of malnutrition, starvation and dehydration were they to be left on the range, then we must decide for ourselves whether or not to support that decision. If our currently available information tells us that the horses will suffer the detrimental effects of malnutrition, starvation and dehydration were they to be left on the range, our hearts and our consciences demand that we do what we can to prevent this from happening. 

To answer #2: 

The answer of #1 shows that there are malnourished and starving horses on the HMA. So is this a reason for a mare to experience a miscarriage? Several Wild Horse Advocacy blog sites have quoted a study done in Canada by Dr. Bob Wright, Veterinarian, Disease Prevention, Equine and Alternate Species, OMAFRA and Dr. Dan Kenney, Diplomat, A.C.V.I.M., Ontario Veterinary College, University of Guelph. In this publication, the Drs state the following: 

“Nutritional deficiencies have not been associated with abortion in mares. In general, if mares are in good condition (body condition of greater than 2 on a scale of 0 to 5, where 5 is very fat), they will carry a foal. Mares that are too thin, however, will not cycle or conceive.” 

This quote is taken from under the heading “Noninfectious Abortions”, and the sub-heading “Nutritional Deficiencies”. 

This quote has been the principal basis for the claim that the mares did not suffer miscarriages as a result of malnutrition as reported by Dr. Richard Sanford, but were in fact caused to have these miscarriages by the added physical and psychological stresses of the gather operations.   

On the same website from which the above quote was copied, a mere two paragraphs below this quote under the heading “General Comments”, is the following statement: 

“In spite of common beliefs, injury seldom causes abortion. Experimental rough manual manipulation of the pregnant uterus has not caused abortion or embryonic death.” 

We’ll come back to this in just a moment. 

First, I would like to say a few words about equine husbandry. In every piece of literature you find about equine reproduction and care of the broodmare, one of the very first instructions given is under a heading with similar subject material of “Nutritional Needs of the Pregnant Mare”. These sections will often go on to explain how for the first two trimesters, the pregnant mare’s nutritional requirements are the same as before pregnancy. Mares in early- and mid-gestation can easily maintain their weight on good quality legume (clover or alfalfa) pasture or hay and a trace mineral salt block. (But according to range data collections the range does not have “good quality legume pasture or hay”.) 

The section will continue on with information such as how the period of greatest development is during the last trimester, when 60% to 65% of fetal growth occurs. The mare’s nutritional needs increase during this time to meet her own requirements, as well as those of the rapidly growing fetus. 

In the last three months of pregnancy, the mare’s protein and energy requirements increase 32% and 20%, respectively. Unless you are feeding your mare a high-quality forage, she may need up to 4 pounds of a high quality grain mix per 100 pounds of body weight daily to meet her increased requirements. She’ll also need more calcium and phosphorus in order to mineralize the developing fetal skeleton. 

Calcium requirements increase by 85% in the last trimester – an amount that can’t be met simply by increasing your mare’s feed. At this stage, you’ll want to supplement a grass hay diet with a 50:50 mixture of trace mineralized salt and dicalcium phosphate, fed free-choice. To avoid possible bone disease in foals, it’s important that pregnant broodmares be fed nutrients to meet but not exceed recommended requirements. 

The next heading in this literature might read something along the lines of what not to feed your pregnant mare. Certain herbs, roots, and grasses can be toxic to both the dam and foal. These can include but are not limited to Wooly Loco Weed, Devil’s Claw, and one the most particularly threatening is the Tall Fescue Plants and Grasses. All of these species are known to grow in arid climates and in the Western US. All of these species are also detrimental to fetal health with toxicity ultimately causing spontaneous abortion, or miscarriage. 

Now, as for the claims that nutritional deficiencies cannot cause spontaneous abortions – or miscarriages – in late term pregnancies, there are several equine veterinary medical journals and publications who report the opposite finding. In fact, basic internet searches for broodmare nutrition yielded more results opposing the aforementioned finding than several variations in search criteria for supporting documentation. (However, the aforementioned finding was the first search result on the page out of some 194,000 results.) 

An article on reports the effects of certain vitamin deficiencies on the fetal mortality rate. For instance, a deficiency in Vitamin A can cause such symptoms as a depressed appetite, weight loss, a dull haircoat, night blindness, and long-term deficiencies can cause abortion in broodmares. Sources of Vitamin A include green forage and yellow vegetables. Vitamin A, or retinol, is an important factor in bone and muscle growth of young horses, in reproduction, and in healthy skin. New research has revealed that vitamin A has a key role in the immune response to infection as well and its main precursor is beta-carotene. 

Studies by Kathleen Crandell of Kentucky Equine Research Inc. showed that if mares are maintained on hay alone with no green pasture and no vitamin A supplementation, the subsequent growth rates of their foals is reduced significantly. As hay is stored over a period of weeks and months, its vitamin A content is drastically reduced. If pasture is scarce, and the mare relies on hay as her major forage source, supplementation of vitamin A may be necessary to avoid this scenario. Research by Dr. Crandell has also shown that mares without access to green grass and a vitamin A supplement can have smaller foals and these foals do not have the compensatory growth to catch up after birth. 

Tom Riddle, DVM, of Rood and Riddle Equine Hospital in Lexington, Ky. said the broodmare’s diet should consist of concentrates, hay, and pasture. “Each component of the diet should be analyzed when formulating the nutritional program of the pregnant mare,” he recommended. Riddle further recommended that the mare receive between 2.25-2.5% of her total body weight in feed (hay and concentrate) with 12-14% crude protein. The calcium:phosphorus ratio should not exceed 3:1, with 1.2-1.5:1 being ideal. He warned against diets high in calcium, since they could possibly cause osteochondritis in the foal. In instances where alfalfa hay is fed, a phosphorus supplement might be necessary to balance out the high calcium content of the hay. 

From various other equine health sources: 

“It is essential that adequate amounts of calcium, phosphorous, zinc, manganese and copper be supplied to the mare in order to ensure proper development of the unborn foal. Phosphorous deficiencies can also lead to reduced fertility in the mare after foaling and reduced milk production.” 

“Other causes of abortion include chromosomal factors, poor nutrition, poisonous plants, toxins, medications and other physical or environmental factors.” 

“Noninfectious causes of abortion can include older mares with a fibrotic uterus and systemic illness of the mare, for example colic or endotoxaemia.”  

For there to not be a link between spontaneous abortions or miscarriage in the equine female, there sure are an awful lot of publications and recommendations placed on the subject of proper nutrition for the pregnant mare. Common horsesense tells us that the pregnant mare needs optimal nutrition to provide for the “extra mouth” her body is feeding. It also tells us that the older a mare is the less likely she is to have a healthy foal –much less carry that foal to term – especially if she is in the least bit malnourished. 

Could these spontaneous abortions have been induced by the stress of the gather operations? Of course they could have, and they most likely were. Could they have been prevented were the gather operations not a factor? Quite possibly yes, they could have. 

If this were the case, would the foals have been born healthy on the range? More than likely, no, these foals would not have been born with a healthy start in life.  More likely than not, these foals would have been afflicted with a variety of birth defects, stunted growth, and possibly genetic / chromosomal abnormalities. If they had lived into adulthood with these effects and were allowed to breed, these traits could be passed on to further generations, thus weakening the gene pool. 

The information presented in this edition is based upon equine medicine, but is also part speculation. The reasoning for this speculation is merely due to the lack of evidentiary documentation specific to these cases. As usual, I have tried to shed light on a dark subject with factually based information. I hope that I have accomplished this for you all, the readers. If not, I hope that at least you were able to walk away with some new knowledge of the very intricate designs of the pregnant equine’s physiology.          

 As always, stay safe… And never give up! 

 Thank you, 

Tracie Lynn Thompson
Owner & Lead Instructor
Lessons Learned Equine Instruction
(409)658-4491 cell 


© 2010 Tracie Lynn Thompson. All rights reserved. 

 For more information on this subject, follow the links below: 


14 Responses to “You Be the Judge, 8th Edition, February 05, 2010 – Calico Miscarriages & Malnutrition…”

  1. R.Thompson said

    My first question would be how much suitable feed grasses and legumes are available on the normal range of these horses on a suitable feed per acre percentage basis? Next I’d ask how many acres of same is available per horse on the range? Until I could know these things, I couldn’t make a judgement on potential horse conditions. I have a lot more to read I’m sure.

    I am by no means expert on the needs of wild horses, but I am familiar on an empirical basis for those of working quarter horses as well as hunter-jumpers, kept primarily in pasture, not stalled. That empirical experience is a minimum of 3 acres per horseper year with a minimum of 75% coverage (over sandy soils) of suitable feed grasses, here consisting of field grasses interspersed with alfalfa and clover at about 20% or more. In these instances a grain supplemental feeding was/is also utilized consisting of either sweet feed of 10% protien content or crimped oats once daily (twice daily if competing)…plus 2nd cutting alfalfa flakes equivalent to 2 or 3 per horse in winter months, depending upon the activity and size of the horses invovled. This level of feed availability, with normal exercise, kept the horses in a healthy fit condition, with ribs palpable but not apparent to the eye, normal hair coats (shaggy in winter months) and with no muscle atrophy.

    I need to read more to see how the above compares to what is available for the Mustangs in their normal range habitat, and how or if their metabolism is similar. I suspect the range for Mustangs no where near approaches what I’ve experienced as a minimum. There may be good reasons for this being still acceptable, but I don’t know them yet. Obviously there are no supplemental grain feedings available for free ranging Mustangs. That would imply their territorial needs are greater than our own domestic horses. It does appear to me, from the various controversies over range land use that the Mustangs are being confined/constrained more and more and not able to occupy their former alloted ranges.

    As for feed requiremtns for 3rd tri-mester mares in foal, it is the same as specified in the aritcle. This again raises the question in my mind of a potential metabolic difference between our horses and the Mustangs. I realize I am not addressing the specifi issue of miscarriage by Mustangs. I can’t until I know more about the feed situation. As for “stress” on pregnant mares, I’d need to know about how the the actual gathers are performed. My experience, when dealing with a band of 20 or more horses, was that they were rounded up and driven to the barns in the evening by working herding dogs, sometimes assisted by a single drover afoot. Some stress but I suspect not similar to helicopters and ATV’s.

    As I said, I have a lot more to read about the Mustang before anything I say is germane to the real issues at hand. As a prior “Fed” myself I am suspicious of easy answers, not becasue the working stiff level personnel don’t care (they do) but because the senior executive management levels demand it….they like everything in one sentence “bullets” with pretty green, amber or red bars on Powerpointless charts. When you distill details enough, you get manure.

    • Again, “quoting” previous statements made by officials of the BLM & WH&B Program…
      A wild horse requires up to something like 200 acres per horse due to the nutritional needs of the horse being entirely supplied by the range, not an outside source such as humans giving prepared feed or hay, extra supplements, etc.
      For me personally, this has actually been an area of in depth research without results that meet my own – albeit hihg – expectations. However, I am continuing this research as it seems to be one the key points in this situation, (Poor Range = No Food = No Wild Horses). I need much more time and data to fully digest this one! (plz pardon the pun LOL)

  2. reveil39 said

    This brings up the question again: Is there a reason why the horses are gathered in the middle of winter, forcing them to run for miles on slippery and icy terrain?

    • R.Thompson said

      Good point. It occurred to me. I forgot to add it to my questions. Just what is the “magic” of January and February for these gathers?

    • The “quoted” reason is that the horses are further down the mountain during the winter months and therefore would not have to travel as far to reach the trap sites.

      • true15 said

        If distance is one of the factors in making a decision, it can’t be the only one.
        I can run a mile in Spring when I can see where I am going, but I would not even last a few feet, let alone even a quarter mile trying to run on ice covered rocks, downhill, and pursued by helicopters.
        That’s probably the reason why the hoofs came off some of the foals, and why they were so many “spontaneous” abortions.

        • No, it’s not the only factor for the decision, just one of them.
          As humans, we are not very well equipped for this type of terrain. However, as horses who have evolved, were bred-born-raised on this terrain, the Wild American Mustang has a much more well equipped body for such undertakings. Their hoof walls are thicker than those of a domesticated horse as a result, and they are surefooted as a matter of instinct. Without this instinct, they would not be as capable of escaping predators.
          As for the hoof sloughings, there have been suggestions made that this is a clinical presentation of the hoof disease Laminitis. Laminitis is most easily described as an inflammation of the hoof wall, much like when you slam your finger in a car door or hit your thumb with a hammer, but physical trauma is not a prerequisite. The result is a coagulation of blood under the laminae, or hoof wall, causing pressure to build. Eventually, as with your slammed fingernail, the hoof wall will separate. Unlike your slammed fingernail, regrowth is easier said than done.
          One possible cause is nutritional abnormalities.
          Check out for more info &

        • jan eaker said

          I concede that wild horses are built for the terrain they are in, however, running to get away from a predator, and running for their lived from a helicopter are entirely different things, I don’t think they have to run 14-15 miles to get away from whatever predators are left in the wild.
          ANd if they are built for their range, then they are also built to survive and thrive on the forage available to them, some of the older horses were in poor shape, but I would expect that in older wild horses, the fact that they are still alive is testament to the amount of forage available. Most of the pictures I have seen are of healthy, beautiful horses.
          It still amazes me that the land can’t sustain the horses, but there’s more than enough forage for cows and sheep.

        • I was going to make the same point as Jan. These horses live here all the time with the same average forage. And, evidently they DO have healthy foals all the time as witness all those wonderful looking horses.

          So, what was different here? The gather of course. I just cannot convince myself that the stress inflicted on these mares at a critical time in their pregnancies wasn’t the most important cause of these miscarriages.

  3. Suzanne & Jan,

    I did not mean to sound as though I thought the stress was not a factor, or the exact cause of the abortions. In the last paragraphs of the edition I state this in my “answers to my own questions” portion. I also do not agree with the allowance of forage to the livestock permitees vs. allowance to the horses. But this is another topic in its entirety. And yes, running from a predator and running from a helicopter are two totally different things on the outside, but to a horse’s psychological state, they are two in the same. He sees that flying, loud machine as something that is threatening his life. Biologically and psychologically, Fight or Flight systems kick into overdrive.
    I agree: they do have healthy foals, they are built to survive and thrive on the forage available to them, I would also expect older wild horses to be poor, and the fact that they are still alive is testament to the amount of forage available, but look at what condition some of them are in… That in itself is a testament all of its own as to what the forage available is like for them, both quantitative and qualitative.
    Thankfully, most of the horses we’ve seen pictures and video of are in good shape. But again, remember that they are in heavy winter coats and we cannot judge as to their actual body conditions by visual inspection only. (Kind of like the shaggy dog who looks like he weighs over a hundred pounds, but get him wet or shave off the hair and he’s only about fifty pounds.)
    The message of this edition was not to say that the gather and its resulting stress was not the cause of the abortions. It was more to clarify some of the confusion about whether or not the nutritional health of the mare could cause abortions due to other reports that stated the contrary.


  4. Lisa LeBlanc said

    I’m probably gonna get a spankin’ for this but…
    Domestic equines, as a result of living in relative luxury with their human partners, have evolved in a few short generations to depend on the necessities of nutritional supplementation. Their diets, while varied, are therapeutically administered for a wide variety of physical ailments or enhancements, i.e., to toughen hooves, improve coat health and shine, strengthen bone, increase muscle.
    In the wild, no such supplementation exists. Wild equines depend instead on the variety and diversity of the available plants and grasses and natural mineral licks, and a physical constitution acquired by generations of selective breeding of Wild Equines before them. While I’ve no doubt they are subject to the rigors of a wild existence it may be that lifestyle that allows, for instance, a stallion with a broken tibia to heal and survive or a 25 year old mare to give birth to a healthy foal on soil that would probably kill, in a few days, a domestic foal through an infection of the umbilical.
    They have adapted, if not after centuries then many decades, to the stresses of a roaming band of grazers. And Nature is a hard taxmistress; those who cannot adapt to diet, weather, water restrictions – perish. Whatever nomenclature is preferred – Wild or Feral, they are by any definition, wild animals. And any wild animal is going to suffer physical and mental trauma when induced by terror into a situation completely alien to them.
    It’s foolish for the Bureau to attach the same physical requisites for Wild Equines as they do for domestics. Domestic equines are tough, strong and hardy animals that are nonetheless dependent on their human partners to help them meet their needs. While there are physiological similarities – because they are the same species – wild equines are under no such limitations.
    I admire and respect the Wild Ones, their physical toughness, their fierce independence, and find any loss of them to natural causes repugnant. Left to their own destinies, who can say for certain how Nature would cull them? But since they are NEVER left to a natural, unattended lifestyle – since no agency will admit that they fill a genuine ecologically beneficial niche – we may never have that answer.

  5. sandra longley said

    I have been breeding mares for 40 years-abortions-late term are not that common..on a farm-you would expect a rhino outbreak…generally a late term abortion will be twins, or a uterine infection or the foal gets the umbilical cord tangeled around itself-cuts off blood supply, dies and starts the abortion process..Never having run my mares for miles in terror, I can only image.(and could not find any articles that dealt with THAT possibility) My first thought was the fight or flight syndrome might trigger oxytocin release/or prostaglandin ect..that is my first thought..I started to research that and got sidetracked-mares that are nursing one foal while carrying another are under greater stress…we would be weaning about 4-5 months..Mares typically would have to be very close to dying of starvation in order to abort…and we have not had pictures to document all those mares..only i video-1 mare seen…but I have heard different accounts from different blm officials-would all those mares have aborted at the same time out in the wild…i doubt it…The next question-were those late term abortions or mid term-i haven’t heard anyone give that figure on the fetuses..Why on earth are mares foaling that time of year…I have to have mares under lights to get some of the early foals they are having in the holding pen now..even mares who cycle year round don’t tend to be fertile during that time..we fool mother nature with lights-wild horses run according to mother nature..Is it fertility drugs?

    • No, they really aren’t all that common… in the domesticated mares. Personally, I have *thankfully* never had a mare miscarry. But in the wild mares, the environmental variables are completely different where reproduction is concerned. And as you also found, publications detailing this subject seem to be nonexistent. The oxytocin/prostaglandin route was also one of my first thoughts, and still is in the back of my mind. Parasympathetic actions on adrenal & dopaminergic receptors – in any mammal – cause way too many hormone releases for those two NOT to be released in great quantity. But again, case relevant studies documenting this phenomena are either not available or simply don’t exist.
      The “double duty” mares also came up. Body conditions and nutritional health of these mares must be of *at least* moderately adequate capabilities to sustain both offspring AND herself. Physiologically the body’s point of view states that safety and preservation of the self prevails over the safety and preservation of the offspring, born or unborn; hence, abandoned foals and spontaneous abortions.
      The weaning ages are also an interesting point. Without the presence of double duty, the process of weaning in the wild is typically dependent upon two factors: the dynamics of the mare/foal relationship and the physical ability of the mare to continue nursing. The relationship dynamics aspect is based on more factors than there is time to discuss here, but suffice it to say – when the mare “decides” it’s time, then it’s time. The physical ability of the mare is relevant in this situation because of the outcomes we’ve noted thus far, such as the undersized/underdeveloped colts and the body conditions and overall poor health of mares. The correlation of mare health to foal/colt growth and development is astonishingly overlooked by many. Basic principles of biology state that without proper nutrition cells do not grow normally. (Round peg + Square hole = Not gonna happen)
      I have not asked the question of mid vs. late term as of yet. From the conversations so far, it appears that these were late term and not mid-term. However, I will add it to the list of questions and post the answer.
      The foaling season of wild horses *usually* begins in March/April and continues through May/June; by this standard these mares are 1-2 months early. I don’t think that it is fertility drugs. I am more inclined to go with the nutritional line of thought. Nutritional health plays a big role in the reproduction processes, and can cause any number of complications in the female reproductive organs – including the timing of estrus.
      I have not studied the reproductive patterns of the Calico horses as of yet, so the following is based on typical timing and is hypothetical. If the mare’s nutritional health at the *normal* time of estrus prevented her from cycling, but soon thereafter (say, late March/Spring) she was presented with more adequate nutritional sources, it is possible from a physiological standpoint that estrus could begin and reproduction could occur in almost a “rebound” type of situation. Continued adequate sources of nutrition (like through Summer) would sustain the pregnancy, even if the nutrition were *only adequate* and not optimal. However, resulting fetal development may also be *only adequate* and not optimal.

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