种 here is zhǒng ('seed/breed/strain'), not zhòng ('to plant'). In this animal-husbandry sense it is firmly pèizhǒng. Compare 物种 (species), 品种 (variety/breed), all third tone.
register
Technical/farming term - not used for humans. For human reproduction use 怀孕 (pregnant), 生育 (procreate), etc.
