Background info:

Invasive pests and diseases cost Australia millions of dollars every year, from management and eradication to lost agricultural output and environmental impact. A major pathway for biosecurity risk material to enter the country is via mail.

The government is reviewing its K9 surveillance system at Melbourne's mail centre. They have asked You to design an experiment comparing the effectiveness of different dog breeds at sniffing out a new type of snack, which is mainly found in mail from Thailand (though it has also been detected in mail from other countries). The snack contains pork, which you cannot bring into Australia without the proper certification, due to the risk of African Swine Fever.

Three breeds of dog are being compared: beagles, Labradors and German shepherds. Between them, the dogs have 720 parcels to check: 360 from Asia, 180 from Europe and 180 from North America. Parcels may be of different sizes. After a dog has checked a parcel, a biosecurity officer will also inspect the parcel (the same biosecurity officer will check all parcels). A record is made if any pork snacks are found; however, due to software limitations, it will not be clear from the record whether it was the dog or officer who made the discovery.

make the experimental design.

Question: What is the experimental unit in this case, and what is the treatment?

I am very confused with what is the experimental unit and what is the treatment in this case.