Cattle and buffalo are different species. One inspector with a thorough knowledge of both species would be a rarity and rarity is expensive. Alternative, two inspectors would be needed for the one boat. This doubles up the costs and also takes up two extra berths on the boat.
https://www.abc.net.au/radio/programs/nt-country-hour/minister-ken-vowles-calls-for-exemption-to-live-export-observers/10455292