It shall be unlawful for any common carrier to give any preference or advantage to, or entail any prejudice or disadvantage upon any particular person, company, firm, corporation, locality, or any class of business or traffic, by any rate, rule, regulation, or practice whatsoever. This provision shall not prevent any common carrier from giving preference as to time of shipping livestock, live poultry, uncured meats, fruits, vegetables, or other perishable property.