R3,
Below is the link from Canada making a notation on the theory of hypothyroidism in smaller horses possibly due to nitrate toxicity. Thyroid function, normal or abnormal, influences the growth of all animals, this notation in the Ontario website describes rather poorly and generally a PROPORTIONATE dwarfism. The dwarfisms I am researching are catagorized as DISPROPORTIONATE dwarfism.
Proportionate dwarfism refers to the "shrinking" of everything in proportion, including bone size. Disporportionate dwarfisms are NOT like that, They have certain bone growth that is abnormally "shortened". Malformed elastic or restricted joints due to underdeveloped bone from cartilage. Shorter long bones than should be for there size, BUT this is due to the disease affecting the LENGTH of the bone growth. That is the part of growth that is restricted.
In their description they describe generally, small PROPORTIONATE horses from small horses (possibly Miniatures or Shetland, dont know, they dont say). They go on to generally describe the foals as with musculoskeletal IMMATURITY, NOT shortened elastic or restricted joints. Meaning very refined, structure, ie. immature or premature looking. They also describe delayed cuboidal bone development, which is a bone in the lower legs of the horse, this description would in plain terms be immature cubiodal bone causing hyperextended joints, or weak legs and joints, like an underdeveloped foal. A large head is listed but not described in detail, and if it were severely domed I would think that would be mentioned.
Floppy ears are listed and I do not know of that as being a known common characteristic in dwarf foals in the Miniatures. I see the ears set back on the head due to the head's domed shape but not "floppy", they function fine.
Mandibular brachygnathia means the foals had a severe OVERBITE, that the lower jaw is underdeveloped. That is not what is seen in the Mniature dwarfs which is an underbite, that is a characterisitic quite common in the dwarfisms I am studying in the Miniatures.
Quote from a different section of the same website from Canada
"Brachygnathia refers to a malocclusion between the mandible and the maxilla. Mandibular brachygnathia is most common and refers to an abnormal shortening of the mandible which results in an overshot upper jaw or parrot mouth."
They did not give a reference paper or article, so I do not know where this informatin has come from.
They also strongly recommend testing thyroid levels and nitrate levels so as to not OVER diagnose this disease due to supposed low thyroid levels due to nitrate toxicity.
I am assuming this is the Canadian article you are refering to.
http://www.omafra.gov.on.ca/english/livest..._congenital.htm
Quote from the website--
"Dwarfism refers to the failure of appropriate growth resulting in a smaller horse. A dwarf horse can be proportionate or disproportionate. Proportionate dwarfs are a result of a deficiency in growth hormone while disproportionate dwarfs result from abnormal thyroid hormone levels. The latter results in a foal with musculoskeletal immaturity, characterized by delayed cuboidal bone development, a large head, silky hair coat, floppy ears and mandibular brachygnathia. Determination and interpretation of either growth hormone assays or thyroid hormone function is not entirely developed or understood in the equine, hence the importance of clinical diagnosis. Efforts towards characterizing thyroid function and growth hormone levels should be undertaken to prevent overdiagnosing this condition. A nitrate toxicity theory has been confirmed in certain foals born with "congenital hypothyroid syndrome". "
Below is a PDF file that you can open that lists in general terms and descriptions different types of dwarfisms in humans. It is very strait forward, so you should be able to read and distinguish the descriptions betwen the many types of dwarfisms.
BTW, Achondroplasia and other similar types of dwarfism are referred to as DISPROPORTIONATE dwarfism. These are the types I am researching and comparing to the Miniatures due to the physical similarities in which they manifest themselves.
http://www.tahperd.org/LINKS/links_pdfs/AP...ts/Dwarfism.pdf
I want to again try to explain my opinion, I strongly feel these types of dwarfisms I am working on are genetic in nature and NOT environmentally induced. The chances of a specific toxin in the environment, be at toxic levels ALL OVER THE WORLD, to produce this high number of dwarfisms is very scientifically unrealistic. If nitrates were that toxic all over the world you would see MASSIVE congenital malformations and deaths from numerous other animals including humans, not just our little Miniature horses.
BTW nitrate toxicity is relatively a low level toxin to horses when compared to sheep and cattle, due to the different digestive tracts, ruminants vs monogastrics, meaning it takes a higher level to affect horses than it does cattle or sheep. However, horses are more susceptible to nitrate poisoning than other monogastric animals due to the cecum. Below is a website about pollutants and ground water, where this info above came from.
http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-14/
I have done quite extensive searches for anything reported or documented, describing any type of birth defects from Nitrate poisoning that mimic DISPROPORTIONATE dwarfism. I have yet to find any. If you have any information describing any credible documentation with pictures or physical descriptions of horses being born with disporportionate dwarf characteristics from nitrate poisoning, I would really appreciate you sending it to me.
John
