The ABC reported that the likely cause of the high mortality incident on the Brahman Express  was a parasitic disease known as coccidiosis....not botulism as so widely touted. In a statement to ABC Rural a DAFF spokesperson said "coccidiosis has been identified as a potential cause of the deaths, however a definitive diagnosis has not yet been reached." They couldnt say much else really as its a pretty embarrassing mistake in diagnostics if it were confirmed - botulism is a neuromuscular disease with quite obvious clinical signs (tongue paralysis especially evident in cattle) due to a toxin whilst coccidiosis causes gastrointestinal disease and is due to a parasite...not hugely similar in presentation to botulism...unless someone is about to write up a very novel presentation of coccidiosis.
But in the end who would know...cocci seems a very unusual cause of mass sudden death also so both seem implausible. Bottom line is that there should have been a vet onboard to assess these cattle clinically and there wasnt...just a stockperson with a 4 day accreditation course.

More than 150 cattle died on the Brahman Express after it left Darwin on March 14, prompting the Indonesian government to suspend imports from the export yard until the cause was confirmed. Australian authorities were quick to claim that it was most likely botulism, a non-contagious disease.
Zach Hope from the Sydney Morning Herald delved deeper and has stated "But who knew what, and how the Indonesians were informed, remained mysterious."
The Australian government has refused to answer even the most basic questions. Disgracefully, "most of what we know comes from authorities in Indonesia. Late on Thursday, the government there made it known it had demanded Australia investigate why Indonesian officials were allegedly told by the crew that only eight cattle had died aboard the Brahman Express when in fact it was 151." SMH interviewed former live ex vet, Dr Lynn Simpson and her full responses are well worth reading..."The reason for misrepresenting the numbers – which neither the Australian government nor shipping company Vroon would confirm – could have been related to fears about Indonesia potentially turning the boat and its roughly 2300 live animals away, she said. Such a move would have created a debacle at sea good for no one, especially the cattle. “[The empty ship] has probably scurried away,” Simpson said. “Then maybe Australia phoned the Indonesians later to say, ‘Oh gee, really sorry about that’.”
Logs showed the ship left the Indonesian port of Medan about 24 hours after its arrival, and before news emerged of the deaths. Botulism has still not been officially confirmed as the cause of death but no other diagnoses have been provided by the as-ever non-transparent Dept of Ag.