LV 400 2, 4-D weed killer is a brand name for the chemical 2, 4-D, 2-ethylhexyl ester. It's used to kill broadleaf weeds and woody brush in pasture, crops and range land. The chemical is approved for use on pastures at a rate of 1 to 4 pints per acre without removing cattle or horses after use.
Recommended Pre-Grazing Interval
According to the manufacturer's label, there is no pre-grazing interval necessary when LV 400 2, 4-D is applied to established pastures at a rate up to 4 pints per acre, a maximum of two times per year. A pre-grazing interval is the amount of time after herbicide is applied when it is safe to reintroduce grazing animals to the area. LV 400 2, 4-D has a pre-grazing interval of seven days when applied to post-emergent or pre-harvest corn fields, however.
Recommended Pre-Harvest Interval
Wait seven days after applying LV 400 2, 4-D to hay pastures before harvesting hay. Though there is no specific research on LV 400 2, 4-D's effect on horses, they should never be fed hay harvested fewer than seven days after LV 400 2, 4-D application. LV 400 2, 4-D levels can build up in an animal's body over time if they are repeatedly exposed to the chemical, and may eventually cause toxic effects.
Toxicity Research in Sheep and Cattle
A 1970 research study by L. M. Hunt, B. N. Gilbert and J. S. Palmer determined that repeated exposure to 2, 4-D, 2-ethylhexyl ester caused lower plasma calcium and higher plasma magnesium levels in yearling sheep and yearling cattle, occasionally resulting in fatal kidney and thyroid damage. The dead animals also showed increased blood urea nitrogen levels. Tested levels in the study were higher than the levels that could be expected when grazing horses or other animals on correctly treated pastures.
Common Sense Precautions for Horses
Because LV 400 2, 4-D has been shown to be toxic to grazing animals at high levels, always follow label directions for use, and store unused containers of the herbicide securely, where horses cannot access them. Consider keeping very young, very old and immune-compromised horses off of freshly treated pastures for a few days as an added safety precaution. Don't apply LD 400 2, 4-D right before rain or allow it to flow into waterways.