The state's Department of Primary Industries has reported "a much more hopeful turn overnight and today", and lifted the ban on horse movements.
"Departmental veterinary staff and local vets have attended the horses of concern to us," a spokesman said. "They have advised that while we do have multiple cases of mild respiratory disease on the north-west coast which we need to investigate further, none of the horses show strong evidence of equine influenza infection.
"Samples taken from the initial suspect horse on Friday were all negative for equine influenza.
"The negative test results, mild symptoms and absence of further cases gives us sufficient confidence to relax the standstill order immediately.
"Horse owners can now move their horses but gatherings of more than 10 horses off their home property will continue to be prohibited.
Properties currently under investigation will also continue to be subjected to quarantine restrictions.
"Formal racing events can go ahead under strict biosecurity conditions."