Farms.com (April 9) – Dr. Rebecca Bishop, an equine surgeon at the University of Illinois Veterinary Teaching Hospital, explains the seasonal differences. “The biggest risk in winter is impaction,” said Dr. Bishop. “Horses eating hay tend to have drier ingesta. Add in dehydration if horses have reduced water intake due to freezing weather. This combination can lead to slower movement of food through the gut and, in turn, large colon impactions.”
https://www.farms.com/ag-industry-news/preventing-spring-colic-in-horses-522.aspx