29 C.F.R. § 780.325

(a) To determine whether an employee is “principally engaged” in the range production of livestock, one must consider the nature of his duties and responsibilities. To qualify for this exemption the primary duty and responsibility of a range employee must be to take care of the animals actively or to stand by in readiness for that purpose. A determination of whether an employee has range production of livestock as his primary duty must be based on all the facts in a particular case. The amount of time spent in the performance of the range production duties is a useful guide in determining whether this is the primary duty of the employee. In the ordinary case it will be considered that the primary duty means the major part, or over 50 percent, of the employee's time.

(b) Under this principle, an employee who spends more than 50 percent of his time during the year on the range in the duties designated as range production duties would be exempt. This is true even though the employee may perform some activities not directly related to the range production of livestock, such as putting up hay or constructing dams or digging irrigation ditches.