A recent study published in the Journal of Animal Science suggests immunologically castrated pigs are less susceptible to stress than physically castrated pigs.  This became evident as the immunologically castrated pigs were less vocal when workers entered their pens than pigs that were physically castrated.  Dr. Kimberly Guay, who co-authored the study, said high levels of vocalization in hogs are an accepted indicator of elevated stress.

Immunologically castrated pigs also showed more interest in their handlers. "They spent more time interacting with the humans - licking their boots, less shying away, and approaching handlers more quickly," said Guay. "They were certainly less shy."

The amount of time spent on pig-human contact did not differ between immunologically castrated pigs and physically castrated pigs, but the behavior of immunologically castrated pigs was more intense.  "That could indicate that they were less stressed about being handled," said Guay.

During transport to market, no immunologically castrated pigs were found "dead or down."  Among the pigs that were physically castrated, the dead and down rate was about 1 percent.