( That ( ( is ( because ( mares ( ( ( ( ( cycle normally ) ( in ( the ( northern hemisphere ) ) ) ) ( during ( the ( ( spring and ) early ) ) ) ) summer ) ( as ( ( ( the ( day length ) ) ( -LRB- ( and ( light -RRB- ) ) ) ) increases ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ is) (SBAR (IN because) (S (NP (NNS mares)) (VP (VBD cycle) (ADVP (RB normally)) (PP (IN in) (NP (DT the) (JJ northern) (NN hemisphere))) (PP (IN during) (NP (DT the) (NN spring) (CC and) (RB early))) (NP (NN summer)) (SBAR (IN as) (S (NP (NP (DT the) (NN day) (NN length)) (PRN (-LRB- -LRB-) (CC and) (ADJP (JJ light)) (-RRB- -RRB-))) (VP (VBZ increases)))))))) (. .)))
That is because mares cycle normally in the northern hemisphere during the spring and early summer as the day length (and light) increases.
(ROOT (S (NP (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN increase)) (PP (IN in) (NP (NN length)))) (VP (VBZ happens) (PP (TO to) (NP (NN metal) (NN railroad) (NNS tracks))) (PP (IN during) (NP (NP (DT the) (NN heat)) (PP (IN of) (NP (DT a) (NN summer) (NN day)))))) (. .)))