Answer A is incorrect because "in part that" is an incorrect phrase. The correct version could be "in that", which would mean "for the reason that." However, inserting "part" between "in" and "that" makes it a very strange and incorrect hybrid. Also even if "in that" were used, it would convey the incorrect meaning. The clause which follows speaks about the goals that the cattle breeders want to achieve (the use of "should" points to the future) and not the past reasons that made them turn to crossbreeding.
Answer B is also incorrect. The structure is not parallel. A phrase and a clause are incorrectly joined with "and."
Answer C repeats the same mistake as answer B.
Answer D changes the meaning. It suggests that steers SHOULD acquire certain characteristics = it is advisable.
Answer E is correct.

Thanks,
Can u please elaborate why D is wrong and why e is correct ?
D is fine on parallelism ??