A shipment of live lambs was expected to leave Dover on Wednesday, after a protest by animal rights activists stopped a similar export in Northumberland.
Millions of animals are transported every year
About 2,000 sheep were being loaded on to the cargo ship MV Caroline at the Kent port.
Protesters say it is the same shipment that was due to leave Berwick-upon-Tweed in Northumberland on Tuesday, but which was abandoned due to a week-long protest.
Port authorities in Berwick admitted they were stopping sailings of lambs from the Scottish borders following a "great number" of calls from campaigners.
Northumbria Police are investigating some of the calls to the Northumberland port.
Some of the calls had been threatening, port authorities say.
The port's harbour master said animal rights protesters swamped his office with calls, some threatening "reactions" if shipments of live animals continued.
He said: "Police are investigating the nature of some of the calls.
"Due to these threats and possible delays caused by protesters, plans for a second consignment to Rotterdam that would have sailed out on Tuesday have now been abandoned."
On Wednesday about 30 members of protest group Kent Action Against Live Exports, said they would stage a demonstration at the eastern arm of Dover harbour.
A Kent Police spokesman said the situation would be monitored.
The MV Caroline was positioned off the port waiting for directions from the export operator.
A spokesman for the Dover Harbour Board said: "We are
expecting a cargo to leave Dover today, but we are only concerned with shipping issues, not the cargo.
"The situation will be monitored by the police, and any protests will not be allowed into the port."
Angie Petro, of Kent Action Against Live Exports, said campaigners had to build on the success of the protest at Berwick.
She added: "Our main concern is that live exports have now resumed following the lull we see every year.
"I believe we can now build on the success at Berwick, and try and urge Dover Harbour Board to stop these exports. The campaign at Berwick shows it can be done."
In August, the European Commission announced new, stricter rules on the transportation of live animals to help ease their suffering during long journeys.