https://www.zmescience.com/ecology/animals-ecology/antivenom-made-precious/

Plenty of blood mass, easy to handle and house, widely available.

It is possible for a human to immunize themselves against venom by injected low, dilute doses over time. But you risk (1) venom related toxicity, or (2) venom allergic sensitization. It's also just deeply impractical, dangerous in ways medicine does not accept for a reasonable risk to volunteers, and takes a long time to do safely (multiple small doses > one dose)