Ah, October. As the days start to shorten, the weather becomes cooler, the leaves start to fall, and Congress approaches, there are a few concerns that horse owners should have when it comes to their horse’s health.

Grass Laminitis

Often thought of as a “spring grass” problem, owners of horses who are currently diagnosed with laminitis, or may be prone to laminitis, should be on the alert for clinical signs of founder in the fall as well. As the fall weather becomes cooler, it becomes more favorable for grass to grow well. Grass produces fructans, or simple carbohydrate sugars, by photosynthesis when it is growing, and the levels of fructans are higher in the grass during the spring and fall months. One of the major known causes of laminitis is ingesting an overload of grass fructans. If you have a horse who has laminitis, or has a disease like PPID or Cushing’s, be wary of all-day turnout on quickly growing pastures, even though the weather is much more suited to it this time of year.

Red Maple Leaf Toxicity

As the weather cools and the leaves begin to turn colors and fall to the ground, be on the lookout for red maple leaf toxicity. Red maple leaves, from the tree Acer rubrum, contain a toxic substance known as gallic acid. Gallic acid causes a condition called hemolytic anemia. Hemolytic anemia is a condition where the red blood cells (RBCs) burst within the horse, either inside the vessels (called intravascular) or outside of the vessels (called extravascular). Horses will have severe depression, anorexia, muddy mucous membranes, and hemoglobinuria (dark red urine). Horses usually die quickly – within 24 hours – from the lack of RBC’s to carry oxygen through the bloodstream, and remove the toxins. What is interesting is that fresh leaves don’t seem to cause the problem as commonly as wilted or fallen leaves in the fall. It is strongly recommended to remove any red maple leaves from in or around your pastures. If this is not possible, then frequent raking and removal of the leaves is recommended, as well as keeping horses away from pastures that contain fallen red maple leaves. Most horses will not eat the red maple leaves unless there is nothing else to eat in the pasture because they taste bitter, so also making sure that there is sufficient hay provided when grazing is inadequate can also help keep horses from eating red maple leaves if they do happen to fall or blow into your pasture.

Black Walnut Toxicity

Black walnut toxicity is the onset of acute laminitis secondary to exposure to black walnut wood, bark or nuts. What is interesting is that horses don’t actually have to ingest the black walnut wood to cause the laminitis, but just touching the wood with their feet causes it. Most horse owners are familiar with being wary of buying shavings from a furniture maker or other source that may contain black walnut shavings, but many owners are not aware that the actual walnuts can cause the same problem – I once diagnosed black walnut toxicity in a horse who was turned out underneath of several black walnut trees that had dropped their nuts, and the walnuts were stuck in the sulci of his soles! For obvious reasons, turning a horse out or near black walnut trees is not recommended. It does not take much wood or walnut exposure to cause a problem, even just a couple nuts stuck in the feet can cause a serious case of laminitis.

West Nile Virus

Also thought of as a summer disease when the mosquitoes are heavy, we do tend to see an upsurge of clinical cases of West Nile Virus in late September and October when the weather goes through periods of warming-up prior to the first good freeze of the winter. The West Nile Virus came to the US in the early 2000’s, and is a viral disease, carried by mosquitoes. It causes severe and debilitating neurologic disease in horses, and can be fatal. There are several effective vaccines available for West Nile Virus, and boostering them in late summer/ early fall is recommended if you are in an endemic area for WNV. In conjunction with vaccination, owners should use techniques for managing mosquitoes and avoiding peak mosquito time. This includes destroying mosquito breeding habitats by removing all potential sources of stagnant water, dumping and refilling water containers weekly, using insect repellents, fly sheets and hoods, and bringing horses inside during daylight hours when mosquitoes are at their peak.

Tanis MacDonald Walker, DVM graduated from the Atlantic Veterinary College on Prince Edward Island and currently practices both small animal emergency and equine medicine in Delaware. You can email her at tanis_macdonald@hotmail.com or visit her at www.drtanis.com. You can also write to her in care of InStride Edition.