(plaintiff cattle producers claimed that federal government employee acted negligently in causing their cattle to become ill and die when the employee suggested the use of particular seeds to plant on pasture land that was enrolled in a government conservation program; trial court determined that employee's conduct was discretionary under the Federal Tort Claims Act; plaintiffs claimed that seed mixture similar to Alsike Clover which is toxic to cattle; employee's role was to investigate pasture conditions and make seed mixture recommendation without regard to cost or policy interests that Congress sought to protect; trial court decision reversed because policy considerations not in issue and, as such, employee's actions not within exception discretionary exception function to Federal Tort Claims Act).