While pasture can continue to supply a significant part of your horse’s nutrition into the fall months, there are a few things you need to watch for to help you avoid problems.
Milder temperatures and fall rains can combine to produce a second ”flush” of pasture grasses in the fall. This new growth can pose a laminitis hazard to horses prone to problems on spring pastures. Sugar levels in more mature growths of grass may also creep up as the nighttime temperatures cool off and the plants do not utilize as much sugar overnight as they did when nights were warm.
The shifts in carbohydrate profiles in the grasses can also produce some gastro-intestinal upset and diarrhea in any horse. Grazing on plants that have been subjected to a frost is particularly likely to do this. The exact cause isn’t clearly understood, but a carbohydrate shift is again a strong possibility. The grasses respond to cold stress by greatly increasing their levels of simple sugars and storage carbohydrates, like fructans and starch. This helps protect the plant cells from freezing but can cause havoc with the micro-organisms in the horse’s large bowel.
On another front, as pasture grasses become mature their level of poorly fermentable fiber rises. This may make the level of digestible nutrients that are exposed to enzymes in the small intestine less, and lowers the caloric value overall. Since your horse is becoming fuzzier at the same time, as his winter coat starts to come in, it’s very easy to miss a loss of condition.
Failing pasture quality also often results in horses sampling plants that they normally wouldn’t touch, making fall a high-risk time for plant poisonings. Some plants are even at their most toxic this time of year, including horsenettle, white snakeroot and the toxic fungus that can infest perennial ryegrass. Acorns consumed in large quantities can also cause problems.