Ask the expert: Fall grazing

Krishona Martinson
University of Minnesota Extension
Ag News

Question: A friend told me it is not safe to graze my horse in the fall. Is this true?  

Response: I believe what your friend is referring to are the recommendations surrounding grazing after the first killing frost.

Frost damaged pastures can have higher concentrations of nonstructural carbohydrates, leading to an increase in the potential for founder and colic, especially in horses diagnosed with or prone to obesity, laminitis, Cushings and Equine Metabolic Syndrome.

To help prevent these health issues, wait up to a week before turning horses back onto a pasture after a killing frost. Subsequent frosts are not a concern as the pasture plants were killed during the first frost.

Why do nonstructural carbohydrates increase during the fall? During the day, plants carry out the process of photosynthesis. In this process, they make carbohydrates as an energy source for the plant.

A second process, respiration, is carried out when the plants use up the carbohydrates they produce during the night for energy. Plant respiration slows down when temperatures are near freezing.

As a result, the plants hold their carbohydrates overnight. Freezing can stop respiration and lock the carbohydrates in the plant for over a week. Thus, plants tend to contain more carbohydrates in colder temperatures or after a frost. Often, horses will prefer forages after a frost due to the higher carbohydrates levels.