Laboratory Mice and Rats segmentation by type distinguishes four primary sub‑categories—inbred, outbred, transgenic and knock‑out strains—across the two species. Inbred mice, characterized by genetic uniformity, dominate pre‑clinical efficacy studies, accounting for roughly 35 % of total unit sales, while outbred mice, valued for phenotypic variability, contribute about 20 % of the market, especially in toxicology screens. Transgenic mice, engineered to express or suppress specific genes, represent the fastest‑growing segment, now comprising 25 % of revenue, driven by CRISPR‑based target validation. Knock‑out rats, though newer, hold an emerging 10 % share, reflecting expanding use in cardiovascular and neuro‑behavioral models. The residual 10 % encompasses hybrid and specialty strains that support niche research. Collectively, these type categories shape procurement patterns, pricing structures, and supply‑chain dynamics, thereby defining the overall market size for laboratory rodents. Regulatory guidelines such as the OECD Test Guidelines mandate specific strain usage, influencing demand elasticity. Moreover, breeding cycles differ; mice reproduce every 6‑8 weeks, enabling rapid stock turnover, whereas rats require 10‑12 weeks, affecting inventory levels and cost structures.