( ( ( ( ( ( ( The ( normal ( resting ( respiratory rate ) ) ) ) ( of ( an ( adult horse ) ) ) ) ( is ( ( ( about ( ( 12 to ) 20 ) ) breaths ) ( per minute ) ) ) ) , ) but ) ( that ( can ( ( increase ( to ( ( ( as ( much ( as 180 ) ) ) breaths ) ( per minute ) ) ) ) ( under ( heavy exercise ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (DT The) (JJ normal) (JJ resting) (NN respiratory) (NN rate)) (PP (IN of) (NP (DT an) (JJ adult) (NN horse)))) (VP (VBZ is) (NP (NP (QP (RB about) (CD 12) (TO to) (CD 20)) (NNS breaths)) (PP (IN per) (NP (NN minute)))))) (, ,) (CC but) (S (NP (DT that)) (VP (MD can) (VP (VB increase) (PP (TO to) (NP (NP (QP (RB as) (JJ much) (IN as) (CD 180)) (NNS breaths)) (PP (IN per) (NP (NN minute))))) (PP (IN under) (NP (JJ heavy) (NN exercise)))))) (. .)))
The normal resting respiratory rate of an adult horse is about 12 to 20 breaths per minute, but that can increase to as much as 180 breaths per minute under heavy exercise.
(ROOT (S (NP (NP (DT The) (JJ normal) (NN respiratory) (NN rate)) (PP (IN per) (NP (NP (NN minute)) (PP (IN in) (NP (JJ adult) (NNS humans)))))) (VP (VBZ is) (NP (CD 12-18) (NNS breaths))) (. .)))