Animal welfare is being neglected on long journeys across Europe amid a booming livestock trade, the BBC's Victoria Derbyshire programme found.
Livestock hauliers were found to routinely break EU laws for the protection of animals in transit.
It follows monitoring by welfare charities in Bulgaria, an EU entry point to Turkey and the Middle East.
The UK government said it would "take steps to control the export of live animals for slaughter" post-Brexit.
UK exports of live cattle, sheep and pigs have tripled in value over the past five years, to more than £21m in 2016, according to HM Revenue and Customs.
The market is fuelled by a desire among some religious communities for live animals and, in some cases, difficulties in rearing livestock and refrigerating meat.
Across the EU, total exports of live cattle and sheep were worth more than €4bn (£3.5bn) last year, according to Eurostat, the EU's statistical office.
Exports of cattle and sheep from Europe to non-EU countries such as Turkey, with lower animal welfare standards, have increased in value by about 50% since 2012