The charity found animals being transported in terrible conditions
The RSPCA is calling for a tightening of European Union rules on the transport of live animals to prevent "unacceptable suffering".
It says new evidence shows that farm animals are being transported over long distances in appalling conditions.
Undercover RSPCA inspectors have tracked and filmed a number of livestock journeys across continental Europe.
In one case, they followed a consignment of 360 sheep on a 10-day trip from Spain to Greece.
At one point the lorry was parked in the sun in temperatures of 40C and by the end of the journey 50 of the animals were dead.
The animals and the consumer both
lose out - it's senseless
The society says this clearly broke existing rules but animals can legally be transported for more than 30 hours.
It wants new laws banning journeys of more than eight hours with tougher enforcement and more frequent health checks.
A new RSPCA report detailing the cruelty and called Standing Room Only, was
being presented today to farm animal welfare minister Elliot Morley MP.
The charity claimed that not only do animals currently suffer on a vast scale, but that
consumers finish up with a poorer food product.
Dr Julia Wrathall, deputy head of the RSPCA's farm animals section, said:
"Our undercover officers have witnessed blatant disregard for transport laws
and the welfare of the animals.
"A huge body of scientific evidence shows that even healthy animals can
suffer serious stress, dehydration and fatigue in transit.
"Others can be injured due to poor handling, overcrowding and on-board
conditions. The resulting meat can be left bruised or dry.
"What is the point of moving livestock, often across several countries, just
to slaughter them at the end of the journey? The animals and the consumer both
lose out - it's senseless."
The charity also criticised the delayed implementation by the European Commission of tighter rules, including a maximum eight hour transfer.
The UK government says it supports stronger laws.
The national farmers union says the EU should clamp down on rogue operators on the continent rather than introduce complex new rules which could disadvantage British farmers.