More Articles - Environmental Deformities

You said in your reply to my original question (Environmental Birth Defects That Mimic Dwarfism??? ) that you would be interested in seeing more articles. I was able to find a few more papers that gave some details about environmental deformities. I have not had a foal that I think had 'environmental deformities' vs 'dwarfism', so my interest is in knowing how to tell the differences should I have a foal with dwarf/dwarf-like feature. If it is environmental, then I would approach the problem from a completely different angle than if I was dealing with the dwarf gene.

Just a note, the article you quoted in answer to my initial question, is the ONLY one that I have found that talks about "mandibular brachygnathia" (parrot mouth/over-bite) being associated with the environmental syndromes. ALL of the other references talk about "mandibular prognathism" which is the undershot jaw/underbite which is a common trait in a dwarf foal.

The articles also talk about domed heads and hydrocephalus. Hydrocephalus can cause a domed head. Here are definitions of hydrocephalus in cattle, the first two sound very much like a description of a dwarf head...

hydrocephalus - …There are three forms that occur in cattle: in one there is gross distention of the cranium with normal facial bones; in the second there is a similar enlargement of the cranium with an accompanying achondroplastic dishing of the face and foreshortening of the maxilla and a shortening of the limb bones—these are the classical ‘bulldog’ calves; in the third the cranium is normal in size but there is internal hydrocephalus and the calves are blind and imbecile.

Nearly all the articles talk about deformed legs and joints and contracted tendons. Several of the dwarves that I have seen have had twisted limbs and contracted joints. The articles don’t really mention ‘disproportionality’ of the limbs as a symptom, just deformity. But, from your descriptions of the dwarf types, it is only in ‘type 2’ dwarvess that you would expect to see disproportionate legs manifested by shortened forelimbs. So, lack of disproportion, doesn’t rule out the environmental leg deformities mimicking dwarf characteristics, as not all types of dwarf have disproportionate legs at birth, some dwarves only have the deformed legs..

I guess from what I have been reading, I am still not seeing how a breeder can get a clear- cut idea of whether a foal with deformities that LOOK similar to those caused by genetic dwarfism is suffering from dwarfism or environmentally caused birth defects. What specifically will a person see that is different? Unfortunately, there were basically no photos to go with the articles, so it is hard to picture the differences that exist, or if the differences are indeed easy to tell apart. I am hoping that you can give a good description of how the two are different.

Anyway, here are the additional articles that I found. I will give the website address and then a short excerpt that mentions the specific deformities that seem to be in common between environmental deformities and true genetic dwarfism…

http://www.horseandhound.co.uk/horsecare/1370/71361.html

Signs of Hypothyroidism in foals

Weak at birth and often not full-term

Poor sucking and righting reflexes

Lack of coordination

hypothermia

Long coat

Respiratory problems

Stunted growth

Developmental bone and muscle problems, such as undershot jaw and bent legs

Early death

www.vet-med.wsu.edu/depts-vth/EquineNews

Hypothyroidism in Foals – “Tissues were received from a nine day-old non-viable Quarterhorse foal that died following a short illness. On microscopic examination, sever goiter (thyroid hyperplasia) was diagnosed on section of thyroid tissue and, within the heart muscle, there were areas of acute degeneration and mineralization consistent with a nutritional cardiomyopathy. No leg or joint abnormalities were observed, although madibular prognathism (lengthening of the bottom jaw or mandible relative to the upper jaw), was observed.”

http://www.pubmedcentral.nih.gov/articlere...gi?artid=548628

“Thyroid hyperplasia and musculoskeletal deformity (TH-MSD), a syndrome of neonatal foals well recognized in western Canada (1–4), where it is considered an important cause of foal mortality and reproductive loss (5), has not been commonly reported in eastern Canada. The musculoskeletal deformities observed include flexural deformities of the limbs, muscular weakness, mandibular prognathism, and doming of the head.”… ”There was pronounced mandibular prognathism*…” (*note - this is an underbite)

http://www.westernhorsereview.com/reader/a.../nutrition.html

“…It is characterized by foals being born weak or dead with contracted tendons and a deformed jaw (elongated lower or shortened upper)”…

http://animalag.wsu.edu/newsletters/CWAATQ...Nwsltrfeb07.pdf…” and the birth of foals that commonly have mandibular prognathism, the fine skin and soft silky haircoat of premature foals even though they are over term, incomplete ossification of the cuboidal bones of the limbs, flexural deformities of the forelimbs, and commonly ruptured digital extensors. Some have hydrocephalus and some patent urachus.”…

I get the feeling you really feel that the dwarfism we have inthe Miniatures is caused solely on hypothyroidism due to environmental causes, like nitrate levels or iodine. I really dont think whatever I say will change that, so all I will do is comment on my opinion of the article you presented anything else I say will not be of any consequence to your opinion

As for hydrocephalus it is caused by water on the brain. Of course it will make a head domed, but again what does that have to do with an inherited disease that has a consistent type all over the world. Some dwarfisms in humans have hydrocephalic characteristics, so what, I think you are getting confused as to what I was commenting about from the original thread. Oh and bulldog calves from dexter cattle have a test for that dwarfism, and it is inherited as an autosomal recessive with carriers that are smaller than normal non-carriers, with carriers showing disproportionate legs to body but do not show the disease which is lethal in homozygous form.

A quote from your first article listed

"In the past, the thyroid gland has been blamed for more than its fair share of problems. But the latest technology and improved blood tests indicate that true thyroid disease in horses is quite rare, and ensuring the right levels of iodine in your horse's diet can prevent most problems."

The second would not open

But from what I could read, I guess you are getting confused with hypothyroidism and dwarfism, since there was no dwarf disproportionate leg or body characteristics. There are many diseases that have one or two syptomatic characterisitcs or more with dwarfism, again one horse, not a dozen or so or hundreds all over the world in various environments

About the third article

This article was on 1 (0NE) foal not a even a dozen or even 100, but one foal. I cant tell you how many things or various degrees of exposure can cause congenital malformations in only one animal in only one species, there are probably millions of examples.. In other words there are billions of things randomly that can happen all over the world, and there are things that can happen that look like an inherited disease that occurs by chance and not due to a dwarf gene, this foal looks like one of those examples.

A quote from your third article listed

"The etiology of this disease is highly debated. Poor nutritional management of the mare appears to be the most likely cause in most cases. Pregnant mares fed diets that contain high levels of nitrate or that are iodine deficient have been associated with an increased risk of producing an affected foal (4). Also, the presence of fungal toxins in the diet of pregnant mares has been associated with congenital thyroid hypoplasia (9).

In this case, the mare was fed a diet of moderate quality hay and oats throughout gestation, with no mineral supplementation or access to pasture. The mare may have been iodine deficient due to the lack of mineral supplementation, the hay may have contained nitrate, or both. Nitrate is more likely to be present in greenfeed (immature cereal crops). Forage grown under stressed conditions, such as dry weather, has an increased probability of containing nitrate (10). The summer of 2001 was very dry in southwestern Ontario, which may have resulted in an increased nitrate level in some Ontario forages. The forage grown during the summer of 2001 would have been fed during the latter two-thirds of gestation to mares that were bred late in the season (May and June 2001). The equine fetal thyroid gland becomes active by the 4th or 5th mo of gestation (2) and may be most susceptible to insult from poor nutritional conditions in the early to middle part of gestation.

The dry summer of 2001, combined with lack of mineral supplementation, may have predisposed some late-bred mares in Ontario to produce hypothyroid offspring in the spring and summer of 2002. However, it is important to note that there are other potential sources of nitrate, including contaminated drinking water and irrigated pastures. Further investigations should be conducted regarding the prevalence and etiology of TH-MSD in foals in Ontario to increase awareness of this disease."

I dont see how this can explain all of the dwarf Miniatures all over the World in different environments.

As to aswer your fourth article, if he was one of the researchers that published with Dr Allen then they should talk because DR. Allen's work is getting used as reference with one of the syptoms as "mandibular brachygnathia" that is seen. So there are either typos which is likely and or more likely variable characteristics of both parrot and monkey mouthed seen which would not suprise me in the least, since they explain how the hypothyroidism is affecting the growth of the head.

A quote below from the fourth says how regional it was.

"I happened to be one of the researchers involved in looking into this Syndrome in 1994-95. The Syndrome, which is specific to western Canada, has been recognized since the late '70s."

In your fifth article all I found was this, it was not what you qouted but I think you are refering to the same thing. Again what does this have to do with dwarfs seen in Australia, New Zealand, Europe or US that have not been exposed to the mustard plant, or for that matter, since these foals have to be put down right away or die early, how does that explain adult dwarfs that are five or ten years old.

Congenital Hypothyroid Dysmaturity

Syndrome

This syndrome with a whopper of a name

applies only to foals. An affected mare may

have an abnormally long pregnancy, abort or

give birth to an abnormal foal. Affected foals

often have an abnormal jaw, immature hair

coat, fine skin, poorly-calcified hock and knee

bones, abnormal curvatures of the front legs,

congenitally-ruptured tendons and other

abnormalities. Most effected foals die or need

to be euthanized.

The cause of this disease is believed to be the

ingestion of late winter/early spring weeds by

mares during late pregnancy. Mustards and

other members of the Brassica family are

believed to be the main culprits. Chemical

compounds in these plants seem to have

goitrogenic (thyroid-stimulating) effects, even

though the foals are not born with goiters.

The risk factor is present in both fresh and

dried plants, so weedy hay is also a concern.

Nitrates may also be involved in this

syndrome, but that is under investigation.

Horse owners should feed weed-free hay to

pregnant horses and keep these animals out

of weedy areas until after foaling. Mares that

have foaled one affected foal are at higher

risk to do so again, perhaps because of a

behavioral component that involves

preferential eating of the toxic weeds.

I really think I have beat a dead horse for the last time.

John