Olivia Dunne Rides Horse At ACMs

Forget Tigers -- at least, for one evening -- LSU gymnastics star Olivia Dunne was all about a horse on Thursday night ... hoppin' on a famous one to celebrate her appearance at the ACMs!!!

Livvy had no issues whatsoever climbing on Sheriff the Bar Horse while out in Dallas for one of the biggest nights in country music ... not even changing out of her ballroom gown to enjoy the moment.

Dunne appeared to have an absolute blast on the horse ... grinning from ear to ear as photogs snapped pics of the Tigers gymnast.

As for why the animal was out at the big country music awards show -- which went down at Jerry Jones' Ford Center -- Sheriff is famous in Dallas ... constantly being seen at local hot spots and Cowboys games.

Dunne, meanwhile, seemed to enjoy the rest of the night at the show outside of the ride on Sheriff ... even snagging a pic on the red carpet with former Team USA gymnast Nastia Liukin.