This study aimed to standardize the CASA system for sperm concentration of cat epididymal samples, using a Neubauer chamber as the gold standard. Epididymal spermatozoa were collected from 44 adult cats. The sperm concentration was evaluated in the Neubauer chamber and by the CASA system at a dilution of 1:200. After assays, the ejaculates were separated into four groups according to the sperm cell count in the CASA system; A (≤ 100), B (101 to 400), C (401 to 800), and D (˃ 800). The statistical analysis measured the agreement between techniques using the Bland-Altman test. A 95% confidence interval was adopted and the statistical program MedCalc 18.2.1 was used. Groups A, B, and D presented disagreement between the CASA system and the Neubauer chamber. Only group C (401 to 800 cells per field) demonstrated agreement between methods. It can be concluded that evaluation of spermatic concentration of domestic felines by the CASA system is reliable when the reading is performed within the range of 401 to 800 cells per field, and could represent a viable alternative to the Neubauer chamber.

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