Answer:
It made him feel degraded and disgusted with slavery.
Step-by-step explanation:
In Narrative of the Life of Frederick Douglass after the death of Frederick's master, the master's property was to be divided between his two children. Therefore all the property were gathered to be valued, and Frederick together with his fellow slaves being considered "property", they were gathered to undergo the valuation too.
Being ranked among pigs and horses, and being subjected to the same thorough examination during the valuation made Frederick feel degraded, he saw how dispensable and utterly without free will the slaves are. That made him feel increasingly disgusted with his slave status.