Thor Søndergaard, a gamekeeper from Berwickshire, was called to the scene of the three-vehicle crash on near Cockburnspath on Monday morning after a tractor and trailer, a lorry and a car collided at around 10:30am.
Dramatic images from the scene show the articulated lorry, which was carrying a cargo of pigs, lying on its side across both lanes of the carriageway.
Police, firefighters, paramedics and an air ambulance were all deployed to the crash, close to the East Coast Main Line, where officers later confirmed that three injured people were taken to the Edinburgh Royal Infirmary for treatment.
Mr Søndergaard said that, shortly after the crash, he was contacted by a police officer he knew and asked to assist.
When he and a local farmer arrived at around 11:25am, Mr Søndergaard managed to climb into the overturned lorry through a hole in the side.
“Either the firefighters had cut a hole, or it was made from the impact,” he explained.
The noise of the trapped pigs was deafening, he told The Scotsman. “We couldn’t hear anything else. When in the lorry we had to shout to hear each other.”
The pair put three seriously injured animals out of their misery.
The 46-year-old said he could see dozens of the pigs “suffocating” inside the truck and “lying on top of each other”, but officers at the scene told them not to remove any other animals.
“The fire chief didn’t want any more pigs on the road,” he said.
A Scottish Fire and Rescue Service spokesperson said: "We were alerted at 10.33am on Monday, November 16 to reports of a road traffic collision on the A1 near the village of Cockburnspath in the Scottish Borders.
"Operations Control mobilised five appliances to the scene of the incident involving four vehicles, one of which was well alight and contained a number of livestock.
"This was a challenging incident, therefore it was important to release the animals in a controlled way due to the location, which was in close proximity to the East Coast Main Line, and to ensure the safety of everyone at the incident ground as firefighters worked to extinguish the fire.
“Crews received professional advice from our partners at the Royal (Dick) School of Veterinary Studies via telephone prior to their attendance at the scene.
“When on scene, firefighters worked jointly with the vets to care for the livestock as they were safely released and transferred to an awaiting vehicle, but unfortunately, despite combined efforts, a number of them were lost.”
A Police Scotland spokesperson added: “The majority of the pigs were safely removed from the vehicle, however unfortunately approximately 70 died. Some of those had to be humanely destroyed.
“Officers worked together with other emergency services to assist the injured parties and livestock as well as ensuring the road was kept safe and secure.”
“An officer at the scene asked a local gamekeeper to attend to assist with a small number of animals that were suffering.”