Thanks again to HRNSW Chairman of Stewards Graham Lock for emailing me the following explanation.
Serum is the key word. I have included a definition as well as the one in Graham's snip that I have attached (I hope it copies a bit larger this time)
The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. Also called blood serum.
I think many have read 'veterinary product' in the charges and thought serum could mean any liquid
It is great to have a Chairman prepared to clarify things for us