JIM MIDDLETON, PRESENTER: Cows are held in high regard in India but that doesn't stop millions of them being illegally herded across the border to slaughter houses in Muslim dominated Bangladesh.
The smuggling network is vast and many people profit from the trade. Human rights groups say as a result, hundreds of people are also beaten, tortured and sometimes killed by border security forces.
Legalising the trade might help stop the violence, but for many of India's Hindus that is too much to stomach.
India correspondent Stephanie March reports and a warning some of the images in this story may be distressing.
STEPHANIE MARCH, REPORTER: Cows are revered and protected in Hinduism and in much of India they are treated like gods.
SANTOSH KUMAR SARKAR, HINJU NATIONALIST (TRANSLATED): Cows are very important animals, not only do cows giver us milk or we can use them in the fields but the cow is like a God to us.
STEPHANIE MARCH: Killing a cow is a crime in most Indian states; in some parts it attracts a five year prison sentence. It is also illegal to export them for slaughter.
But legislation and religion are not enough to save this sacred animal from being put to death.
Across the border in neighbouring Bangladesh, Muhammad Zakir has been selling beef from this market in the capital Dhaka for 30 years. Most of the meat he sells comes from Indian cows.
MUHAMMAD ZAKIR, BUTCHER (TRANSLATED): In India they ever a big space for the cows because it is a big country. Our country is small it is difficult for us to keep the cows.
STEPHANIE MARCH: Home to 150 million people, Bangladesh is one of the most densely populated places on earth. Its Muslim majority population has a big appetite for beef but its domestic supply falls far short of demand.
Thousands of cows come through this cattle market in India's West Bengal state every day. Many of them are bound for Bangladesh; it is thought two million cows are smuggled across the border each year, creating an illegal industry worth almost US$1 billion.
At 19, Utpal Mondan is the sole wage earner in his family of five. He lives in a village in Murshidabad in West Bengal, two kilometres from the Bangladesh border. He earns his living smuggling cows.
UTPAL MONDAN, COW SMUGGLER (TRANSLATED): If it is a small cow I get paid less. If it is medium size, a little more. If it is big I get more money, like two, three or four thousand Rupees per pair.
STEPHANIE MARCH: That is at least 20 times more than what he will make in a day working legitimately as a farm hand. Many of the people living on the Indian side of the border are Muslim but Utpal is one of a smaller number of Hindus involved in the trade.
UTPAL MONDAN (TRANSLATED): We know that the cow is God but we have to hand it over to those people. What we do, we do it for money.
STEPHANIE MARCH: He is the end of the line for a vast smuggling network that includes people from all levels of society, from poor farmers to corrupt politicians and police.
SREERDHA DATTA, MAULANA ABUL KALAM AZAD INST OF ASIAN STUDIES: It is unthinkable that something on this substantial amount, it takes place on a continued basis for years without the tacit understanding of either the politicians or the State Governments.
STEPHANIE MARCH: It is a good income for those involved but for some it comes at great risk.
Most of the border is fenced, and patrolled by members of India's Border Security Force, a heavily armed wing of the police.
Most of the time, Utpal has enough money to bribe the Border Security Force, who then turn a blind eye to the smuggling. But when he doesn't, he has to try to sneak across.
UTPAL MONDAN (TRANSLATED): Because the Border Security Force are aggressive, sometimes they use firearms and sometimes boys are killed. Lots of incidents like that have happened in my area.
STEPHANIE MARCH: This video emerged on YouTube last year. It purportedly shows border security forces torturing and humiliating a suspected cow smuggler. Human rights advocates say over the past 10 years, at least 1,000 people have been killed along the India-Banglo border by security forces. Many, are simple villages who have been mistaken for cow smugglers.
Legalising the trade could be one way to reduce the number of deaths on the border. It could also create much needed revenue extremes for India's central and State Governments and ensure a reliable supply chain for Bangladesh.
But any moves to legalise the system would be met with strong opposition. The day after the ABC met cow smuggler Utpal Mondan, members of the Hindu nationalist group the RSS staged a rally in his village.
(Sound of rally group chanting)
Rallies like these are regular features in border communities. Chanting "Victory for mother India" the activists urge locals and Government to do their bit to stop the illegal cow smuggling trade.
SANTOSH KUMAR SARKAR (TRANSLATED): If the Government made the cow business legal in India, we will not accept it, we will protest it throughout the states.
STEPHANIE MARCH: Agreement on what is worth more to the people of India, the life of a cow or the life of a person is a long way off.
JIM MIDDLETON: India correspondent Stephanie March reporting.