10/10/2023
Question
Is it safe to graze horses after a killing frost? What do I need to consider before turning them back out on pasture? Also, what defines a killing frost?
Response
A killing frost (or hard freeze) refers to a frost that is severe enough to end the growing season. The National Weather Service defines a hard freeze when temperatures fall below 28ºF for a few hours.
We recommend keeping horses off pastures for 7 days after a killing frost. Frost-damaged pastures are higher in nonstructural carbohydrates because plants can not use up their stored carbohydrates as efficiently. It can take plants 7 days to return to more normal nonstructural carbohydrate levels. Higher levels of nonstructural carbohydrates can lead to an increase risk for laminitis, especially in horses diagnosed with or prone to obesity, laminitis, Cushings, and Equine Metabolic Syndrome.
The decision to graze again after a killing frost depends on the condition of your pasture. After a killing frost, no additional regrowth of the pasture will occur, even though the pasture might appear green in color. If your cool-season grass pasture is
✅ taller than 3 to 4 inches, then grazing can resume 7 days after a killing frost and can continue until the pasture is grazed down to 3 to 4 inches.
❌ shorter than 3 to 4 inches, then no grazing should occur after a killing frost.
The 3- to 4-inch minimum height recommendation is necessary to help maximize winter survival and can help predict a vigorous and healthy pasture come spring. We do recognize horses rarely graze uniformly and pastures tend to have areas of both over and under grazing. Therefore, owners need to base decisions on the average appearance of the pasture.