Normal Blood Values of the American Miniature Horse
By Roger B. Harvey, DVM Texas A&M University originally published in the Feb/March 1987 issue of Miniature Horse World magazine
Although sub-sized ponies have been used as draft animals in European mines for several hundred years, U.S. pony fanciers have traditionally ignored this style of equine. However, in the last two decades, U.S. breeders began selection for a smaller animal and developed a registered breed, The American Miniature Horse (AMH). While breed standards call for animals no taller than 34 inches at the bottom of the withers, many animals are smaller (approximately the size of a large dog) and are often purchased as a novel backyard pet.
The Veterinarian is faced with a different type of equine patient and the valid question arises: does this breed require different laboratory reference values or are AMH laboratory data comparable to that reported for other horses?
An experiment was desinged to establish normal blood values for the clinically healthy AMH and compare them to the reported values for full-sized horses (FSH).
A herd of 49 clinically healthy AMH (35 mares and 14 stallions) ranging from 1-17 years of age, located on a private ranch in Fort Worth Texas, were subjects of this investigation. They were in good body condition, had received regular worm prevention treatments, had low worm egg counts in the feces and were negative for Equine Infections Anemia (Coggins Test). The AMH were allowed free grazing on an imporved winter rye grass and oat pasture.
The majority of the AMH biochemical test results are within the range of the values considered normal for FSH. However, there are some differences which should be pointed out:
Potassium leverls in AMH are statistically higher than FSH, where phosphorus is numerically higher.
Magnesium levels, although not statistically lower than the levels for FSH, are certanly very low normal.
T3 and T4 (thyroid) values for the AMH appear to be in the low normal range of that for FSH. It is unknown what significance these levels hold, however, thyroid function plays an important overall role in metabolism and fertility.
The red and white bloodcell data indicate that AMH, like donkeys and ponies, have fewer red blood cells than FSH, but each cell is larger so it can carry more oxygen.
The white blood cells are the ones that fight infection and disease. The two major ones, neutrophils and lymphocytes, in AMH have a ratio to each other that seems to be in reverse of that for FSH. No one is willing to speculate on what this may mean. One fact is clear, AMH have more white cells than FSH.
The AMH , a popular and novel breed of equine, has become a new clinical patient for the veterinarian. Research and laboratory data on this breed have been almost non-exixtent. Hopefully, the informaiton contained in this paper will allow us to understand better some of the normal and abnormal clinical features of these horses, and how to care for them better.
NOTE:Miniature owners should provide their veterinarians with a copy of this article – especially the tables included with this article.