49 CFR § 392.60 - Unauthorized persons not to be transported.
(a) Unless specifically authorized in writing to do so by the motor carrier under whose authority the commercial motor vehicle is being operated, no driver shall transport any person or permit any person to be transported on any commercial motor vehicle other than a bus. When such authorization is issued, it shall state the name of the person to be transported, the points where the transportation is to begin and end, and the date upon which such authority expires. No written authorization, however, shall be necessary for the transportation of:
(3) An attendant delegated to care for livestock.
(b) This section shall not apply to the operation of commercial motor vehicles controlled and operated by any farmer and used in the transportation of agricultural commodities or products thereof from his/her farm or in the transportation of supplies to his/her farm.