Complex sentence: Other breeds were cross bred in an attempt to increase the size and stature of the Suffolk Punch, as well as to improve the shoulders, but they had little lasting influence, and the breed remains much as it was before the attempts took place.
Split into simpler sentences: Other breeds were cross bred in an attempt to increase the size and stature of the Suffolk Punch, as well as to improve the shoulders. However, they had little lasting influence, and the breed remains much as it was before the crossbreeding attempts took place.