The controversial badger cull is underway, farmers have confirmed.
The pilot scheme started on Tuesday in west Gloucestershire and west Somerset, which will see around 5,000 badgers killed over six weeks.
Defending the cull, Environment Secretary Owen Paterson said he used to have pet badgers as a child.
But opponents vowed to scupper the cull with their protests.
"Well, dear folks, something awful is happening," tweeted former Queen guitarist and animal rights activist Brian May.
In a letter to its members, National Farmers' Union president Peter Kendall said the cull was "an important step not just for cattle farmers but for the whole farming industry".
He wrote: "We cannot go on culling tens of thousands of cattle every year because of TB while knowing the disease exists in wildlife uncontrolled.
"It is why the NFU will be working with the pilot companies to ensure the successful delivery of these pilot culls over the coming weeks."
But there is widespread opposition to the cull. Campaigners last night turned out in large numbers at the two pilot sites to protest against what they have called an "inhumane" measure.
But Kendall said that he hoped people would come to understand that the culls are "absolutely necessary".
He said: "It is also useful to remember our own survey this summer, which showed that two thirds of the public either support or have no opinion on these badger culls.
"I hope that when time shows that these culls have reduced TB in cattle - just as has happened in Ireland - that even more people will understand that while sad, these culls are absolutely necessary.
"I hope that you will continue to show support for those farmers who are facing the nightmare of TB on farm and especially for those who are in the culling areas.
"You can rest assured that the NFU is working hard to support its members and the companies concerned with the culls."
Last night Somerset Badger Patrol held a vigil event in Minehead against the cull.
A statement on its Facebook page after the event said: "Over 200 people tonight at the procession, thank you all so much for coming... We fight on, knowing that we are right helps."
Stop The Cull claimed on its Facebook page that more than 500 people turned out to protest at both sites last night.
An anti-cull activist was yesterday arrested at a site belonging to the Department for Environment, Food and Rural Affairs (Defra).
The man, named in reports as Jay Tiernan, who runs the Stop The Cull campaign, was chased on foot by police and arrested after climbing over a barbed wire fence into Aston Down in Stroud. He was arrested by Gloucestershire Police on suspicion of aggravated trespass at the site.
He told ITV News that he was trying to gather photographic evidence after hearing reports that 200 "rusty cages" and "industrial sized fridges" were being prepared to hold dead badgers.
On Thursday a High Court judge made an order to stop farmers involved in badger culls being harassed and abused.
Mr Justice Turner granted an injunction at a High Court hearing in London after lawyers representing the National Farmers' Union (NFU) said farmers had been targeted.