Inbreeding in the first generation does NOT usually cause defects nor temperament issues.
Any specific type of purebred dog? Inbred to a degree.
Specific breeds of horses? Inbred to a degree.
Purebred cats? Inbred.
Every single strain of mice? Inbred.Inbred and linebred for at least 40 generations!
Is continued inbreed good for the animals? No. After a couple generations, you're going to want to add new blood. The main issues that seem to pop up in corns is low fertility, small clutch size, small egg size, and non-feeder hatchlings.