hurdle: Becher's Brook is arguably Aintree's most famous -- and dangerous -- fence. Picture: PA
Alterations to the start of the course, which had been criticised for making the horses too tense, will help to create a more controlled environment, the British Horseracing Authority (BHA) said.
The start will be moved forward 100 yards to a position further from the crowd and grandstands, with measures taken to stop horses getting caught up in the starting tape.
But the authority has resisted calls to remove Becher's Brook, arguably Aintree's most famous fence, where two horses fell to their deaths in April this year.
Instead, its design will be reviewed, and the fence's landing zone will be levelled out. The race will continue to have 40 horses and riders but the size of the field will be monitored.
The RSPCA said: "We remain concerned that two significant issues have not been addressed sufficiently by these changes. These are the impact of Becher's Brook and the field size, which remains the same.
"While the proposed improvement at Becher's by the additional levelling of the adverse slope on the landing zone can only be beneficial, we believe the remaining many complexities of this fence mean it continues to pose a serious and unacceptable threat to horse welfare."
John Baker, who runs Aintree Racecourse as part of his role as north-west regional director for Jockey Club Racecourses, said there was a "delicate but important" balance to be struck between the race's enduring appeal and reducing risk.
He said: "With regard to the modifications and improvements made to the course, all the measures have been carefully considered and are evidence-based, in line with Aintree's ongoing commitment to safety and welfare. We will continue to repeat this process on an annual basis and monitor the many variables involved.
"However, we are fully aware in racing that you cannot remove risk altogether."
A spokesman for Ayr Racecourse, which hosts the Scottish Grand National and made a number of changes to the course following the deaths at Aintree, said it was unlikely the review would have any impact on its operation.
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