A person who has chartered a car for the purpose of transporting livestock shall have the right to ship in the same car, at his own risk, different kinds of livestock. The shipper shall have the right to load said car by separating his stock with gates or bars, or by putting upper-decks at his own expense and without injury to the car; the shipper shall be responsible for all damage that may occur by reason of its being so loaded. Any railroad company refusing, without sufficient reason, to move or transport a car so loaded, shall be liable to the party injured thereby to double damages, to be recovered before any court having jurisdiction.