Officials are inspecting some 300 animals after a joint north-south raid on a border farm suspected of being involved in livestock rustling.
PSNI and Gardai conducted searches across Armagh and Monaghan, finding 35 cows and 15 sheep at a South Armagh farm, while 250 sheep were discovered on a nearby farm across the border.
More than 20 PSNI officers in up to eight vehicles were involved in the searches.
A recently dead calf was found at the south Armagh farm.
The PSNI forced the door of a barn with tools. A man approached them with a key to open it.
PSNI Insp Leslie Badger told the BBC: “You have to consider your security when you are doing these operations. It’s not only the terrorism element to Northern Ireland, but also the criminality element - we have some criminals out there who would try to frustrate police actions and disrupt us.”
He added: “We rely heavily on our partners in the Republic of Ireland, An Garda Síochána, and it’s with their help we can go in here - a property that straddles both sides of the border.”
No evidence of rustling was discovered but police did discover breaches in animal welfare and cattle documentation, including ear tags which did not belong to the herd they found.
The operation had successfully helped to disrupt crime, Mr Badger said.
Newry & Armagh DUP Assembly candidate William Irwin welcomed the operation.
“I very much welcome the PSNI’s efforts in tackling and targeting organised rural crime and in particular their focus on recent livestock thefts,” he said.
“There has been a growing concern amongst the farming community that livestock is being routinely stolen by organised crime gangs who are then flouting every traceability rule in the book to put these animals into the food chain. In this operation police were acting under specific intelligence and that type of interaction from the community is vital in these types of operations.”
“The impact of this livestock and machinery theft has a detrimental effect on our farming industry and I know from speaking with farmers who have been affected by this type of crime, it costs farmers money and also great inconvenience. The PSNI has been successful in recent weeks targeting specific areas where animal thefts have been regularly occurring and after their actions, levels of crime reduced noticeably.
“The issue of livestock theft brings up all sorts of serious issues in terms of animal records and traceability and of course the question of where these animals are ending up and what is happening with these records. I welcome this intelligence led operation on rural crime on both sides of the border and I would urge police to continue in their efforts to stamp it out.”