Three of the Aintree Grand National fences, including the famous Becher's Brook, are to be made safer, the British Horseracing Authority (BHA) said.
The changes are among interim measures arising from a review group set up after this year's race when two horses died.
The fatalities followed four at the three-day meeting in 2010 and five the year before. Since 2000, 33 horses have died at the spring festival, bringing regular protests from animal welfare groups.
The drop on the landing side at Becher's will be reduced by four or five inches (10-12.5 cm), though the height remains the same at 4ft 10 ins (1.47 metres).
Levelling work will be carried out on the landing side to reduce the drop at the first fence which horses often approach too quickly after the start.
At the fourth fence, viewed as one of the most difficult along with Becher's, the height will be cut by two inches to 4ft 10 ins (1.47 metres).
"The findings relate specifically to the Grand National course and its fences which will be subject to a balanced package of modifications with the aim of enhancing safety for competitors," A BHA statement said.
The changes follow expert analysis of all races run on the National course since 1990 when it was significantly remodelled.
They also follow consultation with animal rights groups, trainers and jockeys and will have been made in good time for Aintree's next race on the National course in December.
"It is not possible to completely eliminate risk in horse racing," managing director Julian Thick said. "However, I am confident the course changes we are announcing today will, over time, have a positive impact."
The results of a full review will be published in October but it is known that among items being considered is a new post-race wash-down and cooling area for all horses.
Ballabriggs, this year's winner on a warm day, was too exhausted to be ridden into the winner's enclosure and had to be continuously hosed down before recovering fully.
