Most forage grasses (such as Tifton 85) produce prussic acid (HCN) in the young plants and new shoots.
The level of prussic acid reduces as the plants mature, but the reducion of prussic acid levels is much less during drought conditions.
When establishing a forage plot, it is comon practice to apply the selective broadleaf killing herbicide 2,4-D. A side effect of 2,4-D application is an increase in prussic acid levels 3 hours and 6 hours after application.
The combination of drought conditions and 2,4-D application, as well as early grazing on this plot are likely to be the culprit here.
In terms that the slashdot crowd can understand: Operator Error and Not Reading the Documentation are likely to be the cause.
And yes, I am an Agricultural Worker.
(Also, I know how to google for facts before I post.)