Nine cattle have died on the NSW north coast in two separate outbreaks of botulism poisoning, reports ABC.

Livestock Health and Pest Authority vet, Matt Ball, warns farmers to keep cattle out of freshly fertilised paddocks for at least three weeks if poultry litter is used.

He says disposing of dead cattle by deep burial is better than burning the carcasses.

Mr Ball explained: "Cattle are attracted to ash and unfortunately in this case the fire hadn't been able to get right underneath the carcass, and so it left ash and some still-decaying carcase.

"And in the second outbreak associated with access to a poultry litter pile, and also because there is that feed within it, they will actually eat the matter, and not only is that against the law, sadly they can die from botulism."