The Member for Northern Tablelands said at a conference in July: "I'm doing my best in my car to knock 'em down four at a time like I did the other night near Emmaville."

He told the gathering the pest animal was in "plague proportions" across NSW.

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"The fact is we need to take some pretty drastic measures to bring that population under control," he said.

The RSPCA said in a statement that they had "received a cruelty complaint in relation to comments made by Adam Marshall during a speech at a conference".

"RSPCA NSW inspectorate investigated and found no breaches under the Prevention of Cruelty to Animals Act 1979. The matter is now finalised."

A spokesperson for the MP told the media the investigation into an innocent joke was political correctness gone mad.

"Everyone knows this is part and parcel of driving in the county. Next thing you know we won't be able to eat venison or make a joke about Bambi without being reported."

It's believed the targeted complaint was made by activists headhunting the Agriculture Minister for political reasons.

Farm owner Lucy Faithfull, who lives on the Emmaville road, agreed the infestation by the introduced species is growing in strength, making driving at night a hairy prospect.

"We're driving a lot slower and a lot more cautiously than we ever have in the last ten years," she said.

"We saw three deer last night coming back from Bible study.

"We personally haven't hit any, but we're used to dodging things so perhaps we're bit more lucky than other.

"They're hammering all of our neighbors - it's not just us. They in mobs of 80, and I have never seen those sort of numbers."

A recent scientific survey commissioned by Glen Innes' Local Land Services found a study area supported some 5540 deer over a 135 square kilometre study area - over 41 deer per square kilometre.

That's the equivalent of around 8300 sheep, they noted.

Changes to the status of deer as a game animal introduced by Minister Adam Marshall mean it is easier for farmers to hunt the introduced pest.