Grand National 2017: The Last Samuri heads 40-horse line-up at Aintree

A sell-out crowd of 70,000 will cheer on the runners and riders at this year's Grand National

A field of 40 horses headed by The Last Samuri is set to contest the 170th running of the Grand National on Saturday.

Last year's runner-up will bid to become the first top weight to triumph since Red Rum in 1974.

A sell-out crowd of 70,000 is expected at Aintree Racecourse on Merseyside.

Vieux Lion Rouge and Definitly Red are among the favourites with bookmakers expecting up to £300m to be wagered on the race.

Travel for racegoers was expected to be disrupted as workers at three rail companies carried out a a 24-hour strike on the day of the Grand National.

The official going at the track is described as Good, Good to Soft in places and a dry, sunny day is forecast with temperatures reaching 16C.

Jockey Liam Treadwell will miss the big race after a fall at Aintree on Friday, although Katie Walsh has been passed fit to ride Wonderful Charm despite an arm injury.

Treadwell, who won the National in 2009 on 100-1 shot Mon Mome, will be replaced on 40-1 chance Tenor Nivernais by Aidan Coleman.

• Runners, riders, trainers, form - Grand National pinstickers' guide

• Quick guide to the big Aintree race

• Schedule and BBC coverage

• Listen: 5 live's 2017 Grand National Preview

Who are the favourites?

Vieux Lion Rouge, which translates from French to Old Red Lion, is a leading fancy after winning the Becher Chase over the National fences in December and February's Grand National Trial at Haydock.

Seventh in the National last year, he is one of four runners trained by David Pipe, and is about a 10-1 chance along with Definitly Red, an impressive winner at Doncaster last month for Brian Ellison.

The National is a handicap chase, with each runner allotted a different weight to carry by the official handicapper Phil Smith.

With 11st 10lb, The Last Samuri will be carrying more than a stone more than last year.

Vieux Lion Rouge (green cap) impressed during the Grand National Trial at Haydock in February

Other contenders near the top of the betting include the JP McManus-owned pair More Of That and Cause Of Causes, Haydock runner-up Blaklion, and the Scottish-trained One For Arthur.

However, the National has a habit of throwing up surprise results, as evidenced by recent years.

The past five winners have started at odds of 33-1, 25-1, 25-1, 66-1 and 33-1.

Irish trainer Mouse Morris scored an emotional victory last year with the now-retired Rule The World - 10 months after the death of his son Christopher.

Morris, who runs Irish National winners Rogue Angel and Thunder and Roses this time, said: "We're going there with no pressure as the likelihood of winning it two years in a row is probably non-existent."

What's the big deal?

Coverage of the National, over 30 fences and more than four and a quarter miles, is said to be followed by 600 million people worldwide.

The marathon test see runners negotiate iconic obstacles such as Becher's Brook and The Chair.

Terminally ill five-year-old boy Bradley Lowery is to be given honorary 41st place in the National racecard.

The race is again due to start at 17:15 BST, having been put back an hour by organisers last year in an effort to further increase the audience.

Armed police have been in attendance at the course during the three-day meeting which started on Thursday.

This year's race comes in the wake of the Westminster terror attack and marks the 20th anniversary of the National being delayed by an IRA bomb scare.

Walsh eyes historic victory

Katie Walsh will seek to become the first female jockey to win the National after overcoming a late injury scare.

Walsh was initially reported to be ruled out with a broken arm following a fall in the Foxhunters' Chase over the big fences on Thursday, but escaped with bruising.

"I feel fine, a bit sore but I'm 100%," said 32-year-old Walsh, who will ride 33-1 chance Wonderful Charm, with opponents including brother Ruby on Pleasant Company.

"There is only one Grand National and to get the opportunity to ride in the race again is brilliant."

Wonderful Charm is one of five runners for Paul Nicholls - along with Cheltenham Gold Cup fifth Saphir Du Rheu, Scottish National winner Vicente, Le Mercurey and Just A Par.

Are there safety concerns?

Known as a unique challenge for horse and rider, the race draws criticism from opponents, including animal welfare groups.

Officials believe amendments to the fences, and other alterations, introduced four years ago have helped improve safety.

The course spent £1.5m on changes after two horses were fatally injured in each of the Grand Nationals of 2011 and 2012.

Since then there have been no fatalities in the National itself, although in the same period there have been six in the four other races staged over the track during the year.

Analysis

BBC racing correspondent Cornelius Lysaght

Pleasant Company is my selection to win for trainer Willie Mullins and jockey Ruby Walsh. The team triumphed with Hedgehunter in 2005 and Walsh was also successful on Papillon, trained by his father Ted, five years earlier.

Pleasant Company put in a most encouraging performance to win at Fairyhouse. He'll keep out of trouble, before - hopefully - gradually picking off rivals and arriving late on the scene.

The Jonjo O'Neill-trained More Of That was a champion over hurdles, and a respectable sixth in this season's Cheltenham Gold Cup, giving the impression he's coming to the boil.

Scotland's One For Arthur is another gradually building his reputation, while Lord Windermere - who's not won since the 2014 Cheltenham Gold Cup - had top weight two years ago, but much less this time, and will have his favoured drier ground conditions. I can see him going well at big odds.

Cornelius' 1-2-3-4: 1 Pleasant Company 2 More Of That 3 One For Arthur 4 Lord Windermere

What's it like to ride in the National?

Jump jockey and BBC Radio 5 live pundit Andrew Thornton

"It's still a great test of skill. You need some luck and your horse to take to the fences.

"There's 40 runners, when most races wouldn't be near half that size, so you're hoping for a clear passage.

"It's wide open this year. Definitly Red is likely to be popular on Merseyside with supporters of Liverpool FC.

"I like Blaklion. The better ground will suit him, his jockey's in red-hot form and his trainer has won the race twice before."