Unidentified Toxin (possibly tannins)
Depression, inappetence, icterus (Jaundice), anemia, fatigue, tachypnea (rapid breathing), dyspnea (shortness of breath), abdominal discomfort, tachycardia (racing heart beat), cyanosis (bluish mucous membranes or skin from lack of oxygen), miscarriage/abortion in pregnant mares, discolored urine, hemoglobinuria, brown discoloration of mucous membranes and blood, death (Death can occur within 24 hours or as long as a week after ingestion)
The toxic principle of Swamp Maple is as of yet, unidentified. What is known is that the toxin is deadly to all members of the horse family (equidae) including ponies, donkeys, and zebras. The toxin works by causing oxidative damage to the hemoglobin of red blood cells reducing or eliminating their ability to carry oxygen from the lungs to the rest of the body. Additionally the toxin has also shown the ability damage the actual membranes of red blood cells. In vitro evidence suggests that tannins may be responsible for the dissolution or destruction of the red blood cells. The end result is widespread cellular death in all organs of the body due to oxygen starvation. The medical term for this process of demise is hemolytic anemia; the red blood cells will actually rupture releasing their hemoglobin into surrounding plasma. As more and more red blood cells rupture, the total number available to transport oxygen to the vital organs of the body decreases creating a condition known as 'anemia' or too few red blood cells and less than a sufficient quantity of hemoglobin. Due to this deficiency in hemoglobin and red blood cells, anemia leads to hypoxia (lack of oxygen) in organs. Since cells depend on oxygen for survival, anemia can have a wide range of clinical consequences as oxygen deprivation causes various organs to shut down.
The odds of Swamp Maple poisoning rise in the fall or after the occurrence of a storm when the leaves either fall or are stripped from their branches and become accessible to horses. There is some disagreement in the medical community as to whether the fresh leaves are toxic, with some authorities saying they are, and some saying they are not. Regardless of this disparity, it would be wise to err on the side of caution and assume fresh leaves to be toxic as well. All reliable sources agree that the wilted or dried leaves are deadly toxic to horses, and can remain that way for 30 days or more. Additionally the bark is also toxic and contains the "unidentified" toxin in levels comparable to those found in dried or wilted leaves. Most sources also agree the amount the average horse needs to ingest to suffer potentially fatal consequences is around 1.5kg (3.3 lbs) or 0.3% of total body weight, although any amount will begin damaging cells.
Even with aggressive treatment, the prognosis for horses that have ingested a large amount of Swamp Maple is guarded. Treatment for Carolina Maple poisoning, as it is for many types of poisonings is going to be symptomatic and supportive. If the ingestion was recent then activated charcoal may be of use. If the patient is suffering more advanced clinical signs then it is going to be important to monitor packed cell volume and kidney function. IV fluids are also recommended to provide support to the kidneys and prevent dehydration. In many cases a blood transfusion will be necessary in combination with drugs and supportive care. Due to the anemia reducing oxygen levels in the blood, treatment with 100% oxygen should also be considered.
There has been some success in treating horses that have ingested potentially fatal amounts of Swamp Maple as noted in the following excerpted paragraph from a Cornell University College of Veterinary Medicine case analysis:
"Two horses with red maple (Acer rubrum) toxicity responded to treatment with high doses of vitamin C (ascorbic acid), in addition to blood transfusions, and intravenous fluid therapy. The clinical course included Heinz body anemia, marked methemoglobinemia, depression, and evidence of severe tissue anoxia. Clinical recovery was dramatic with stabilization achieved 36 hours following the initiation of ascorbic acid therapy."--McConnico RS, Brownie CF. The use of ascorbic acid in the treatment of 2 cases of red maple (Acer rubrum)-poisoned horses. Cornell Vet, 82:293-300, Jul 1992
Although not specifically listed in the above excerpt, ascorbic acid (vitamin C) has shown to be effective at reducing methemoglobin (oxidized form of hemoglobin that has a decreased affinity for oxygen) back to hemoglobin as a dose rate of 30 to 50mg/kg twice daily as part of the IV fluids. It was noted that it takes two doses to reach adequate blood plasma levels.
Lastly and a bit less documented is the use of Oxyglobin (purified bovine hemoglobin) with blood transfusions. A treatment regimen that proved successful in two separate incidents, one involving a miniature horse and the second a pony at Tufts University. Although no details of the specific treatment regimen are available Oxyglobin is an oxygen-carrying fluid that can provide much needed oxygen to cells until recovery is complete, or it could be used to stabilize the animal until a full blood transfusion can be provided. As stated at the beginning of this section, even with aggressive treatment the prognosis for animals that have ingested potentially lethal levels of Swamp Maple is guarded. In the event you notice your horse ingesting this toxic plant, stop them immediately, remove any excess plant matter from the mouth, seek veterinary care.
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