Visitors shall not be admitted to the quarantine enclosure during any time that swine are in quarantine except that an importer (or his or her accredited agent or veterinarian) may be admitted to the yards and buildings containing his or her quarantined swine at such intervals as may be deemed necessary, and under such conditions and restrictions as may be imposed, by the inspector in charge of the quarantine station. On the last day of the quarantine period, owners, officers or registry societies, and others having official business or whose services may be necessary in the removal of the swine may be admitted upon written permission from the said inspector. No exhibition or sale shall be allowed within the quarantine grounds.