NEW DELHI — When night falls in this gritty capital, gangs troll the darkened streets looking for easy prey among a portion of the city’s vast homeless population; thousands have been rounded up and carried off in trucks in recent years.

The police say they have increased patrols and set up roadblocks in an effort to stop the trafficking. In some cases, officers have infiltrated gangs in hopes of catching them in the act. But the brutal kidnappings continue, and the victims — scrawny cows, which are slowly losing their sacred status among some in India — are slaughtered and sold for meat and leather.

Cattle rustling, called “lifting” here, is a growing scourge in New Delhi, as increasingly affluent Indians develop a taste for meat, even the flesh of cows, which are considered sacred in Hinduism. Criminals round up some of the roughly 40,000 cattle that wander the streets of this megacity and sell them to illegal slaughterhouses located in villages not far away.

Many of the cattle in Delhi are part of dairy operations and their owners have neither the land nor the money to keep them penned. So the animals graze on grassy medians or ubiquitous piles of trash. Others too old to be milked are often abandoned and left to wander the streets until they die — or get picked up by the rustlers.