It was announced in September that the centre of the fences, which have traditionally been made up of timber and protective rubber padding, would be trialled with a different make-up, more forgiving to horses, at the Becher Chase meeting in December.
On the day, jockeys gave an approval in what appeared to be a smooth change, with all the fences on the famous course looking outwardly the same.
Four obstacles were rebuilt with softer cores should the top spruce be knocked off during a race and came through their first tests with flying colours when used in the Becher Chase and the Grand Sefton Chase.
Sam Twiston-Davies, who won the two races on Hello Bud and Little Josh respectively, said at the time: “I would say if there were any changes it didn’t seem obvious.”
Conor O’Farrell, fourth on Swing Bill in the Becher Chase, said: “I felt that the course, including the new fences, rode very well and I had no issue whatsoever.”
Cores of open ditches such as The Chair have also been softened, although with real birch and not plastic.
McCain said: “It looks OK, but the proof will obviously be in the pudding.
“Obviously some people don’t think changes were really needed, but they want to move with the times and that’s fine. The fences look fine and safe. In principle it looks good, but we’ll just have to see what happens on the day.
“I think we have to be careful not to make the race too easy, as that leads to horses going faster and that creates its own problems, so we’ll see.”
Explaining the changes, clerk of the course Andrew Tulloch told The Observer: “There is a test about it (the National) but it needs to be a fair test. I think, like everything, things move on, new materials have become available.
“The essence of the race is the same.
“We’re always looking to improve it (the National) and not stand still. From my perspective, the welfare of horse and rider is the single most important thing.
“For the last five or six years, we at Aintree have been keen to look at an alternative.
“The problem was finding something that would work and give us longevity. The plastic will hopefully last a few years and, with the open ditches, we’ll see. If this works, we’ll stay this way.”
The RSPCA has reportedly welcomed the move, with equine consultant David Muir describing it as “very much” in the favour of horse welfare.
* Evan Williams is to target Barizan at the Paddy Power Imperial Cup at Sandown on Saturday after he bounced back to form at Taunton recently.
The Llancarfan handler fears the seven-year-old will not be rated high enough to run at the Cheltenham Festival where he has two entries.
However, he is hoping he might get into the valuable handicap hurdle at the Esher track .
Williams was delighted Barizan, a Grade One scorer as a novice, got back in the winning vein after having had a long time off through injury.
“He’s gone up 4lb. It probably won’t be enough to get him into the Festival,” said the trainer. “It might not be enough to get him into the Imperial Cup, but that is something we would look at.”