The deadly virus, which is carried by native fruit bats, killed a horse at J4S Equine Nursery at Cawarral, east of Rockhampton, on Saturday.
However, the death of the Anglo-Arab filly called Princess was the third at the property since July 28.
Authorities are checking to determine if the first two deaths were the result of Hendra.
Biosecurity Queensland veterinarians were yesterday at the Cawarral property, owned by John and Christine Brady, to take samples from the 25 horses.
Queensland Primary Industries acting chief veterinary officer Rick Symons said the samples would be sent to the Australian Animal Health Laboratory in Geelong.
"Initial results are expected later this week," he said.
Any horses that test positive for the virus will be euthanized as, even if horses recover, there is a chance of a relapse. Quarantine measures are expected to remain in place for at least a month.
"Biosecurity Queensland is also tracing the movements of horses that have left the Cawarral property in recent weeks.
The department understands that 11 horses have gone to eight locations - seven in Queensland (Darling Downs, Sunshine Coast hinterland, Cawarral area) and one in New South Wales, near Manilla.
"There is also one additional property that has had some minor contact with the Cawarral property. The 10 horses at this location have been restricted for movement.
"We are providing the owners with information about Hendra virus. Their horses are in isolation and we are arranging for them to be tested to exclude the possibility of any further infection.
"The Cawarral property and a neighbouring property are under quarantine. Horses at these locations will remain under observation until they can be cleared of any infection, which will be in about four week´s time."
Dr Symons said Biosecurity Queensland regularly tested horses to eliminate the possibility of Hendra virus infection.
"Although many possible cases are tested, Hendra virus is a rare disease in horses with only a dozen known incidents occurring since the virus was first discovered in 1994," he said.
Meanwhile, there is a worrying wait for staff at the horse property, who are being tested to see whether they have contracted the virus, which can be passed from horses to human.
Reports suggest stud manager Debbie Brown and horse manager Adrian Daniels had contact with blood and mucus from the dying horse.
About eight people on the property had close contact with the infected horse.
Early testing for exposure will not necessarily confirm exposure - the incubation period is five to 14 days - and staff are unlikely to know whether they have been infected for at least two or three weeks.
There have been six confirmed cases of Hendra virus in people, all in Queensland. All contracted the virus after contact with infected horses. Three of the cases proved fatal.
There have been no cases of human-to-human transmission.