NZ Rugby have concluded their investigation into the treatment of the Ranfurly Shield after images surfaced on social media in September.

The organisation has confirmed that the Shield was accidentally dropped on the floor- but drug testing still hasn't identified the white substance from the photos.

Hawke's Bay Rugby CEO Jay Campbell says NZ Rugby tested the Shield thoroughly, and the report only identified plaster.

"The release was quite clear- they said it was inconclusive. The report says the only substance they were able to pick up was the plaster from the back of the shield."

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