There are assorted accomplishments titled a "Grand Slam" in equestrian competition:
Contents
Grand Slam of Show Jumping
The Grand Slam of Show Jumping, named Rolex Grand Slam of Show Jumping, was created in 2013. It brings together the three Majors, and refers to the achievement of winning all three:
Grand Slam of Eventing
The Grand Slam of Eventing, created in 1998 is named Rolex Grand Slam of Eventing. It brings together the three Majors, and refers to the achievement of winning all three:
References
Equestrian Grand Slam Wikipedia(Text) CC BY-SA