Rollo,
Actually corresponded with the Australian Stud Book. They said the Freeze Brands are done using special irons and Liquid Nitrogen in a process actually started in the US for cattle branding as a more humane method instead of hot-iron branding. It's really cold and freezes the skin and hide. It's a tricky process, but if done right, produces a lifetime signature.
The mark on the left side of the horse is a breeder's mark, that has to be registered like a trademark with the Book. On the right side, the 2 numbers listed are the number of the foal out of that crop (in numerical order from that breeder that year) and also the year of the foal crop. They must be registered with the Book.
Those brands last the lifetime of the horse. As you said, all registered Australia Bred TB's in Australia need the Freeze Brands.
Maybe find some more info.
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