Table 1. The advantages and disadvantages of the pig as a potential source of organs and cells for humans, in contrast with those of the baboon in this role.

	Pig	Baboon
Availability	Unlimited	Limited
Breeding potential	Good	Poor
Period to reproductive maturity	4-8 months	3-5 years
Length of pregnancy	114 ± 2 days	173-193 days
Number of offspring	5-12	1-2
Growth	Rapid (adult human size within 6 months)**	Slow (9 years to reach maximum size)
Size of adult organs	Adequate	Inadequate*
Cost of maintenance	Significantly lower	High
Anatomical similarity to humans	Moderately close	Close
Physiological similarity to humans	Moderately close	Close
Relationship of immune system to humans	Distant	Close
Knowledge of tissue typing	Considerable (in selected herds)	Limited
Necessity for blood type compatibility with humans	Probably unimportant	Important
Experience with genetic engineering	Considerable	None
Risk of transfer of infection (xenozoonosis)	Low	High
Availability of specific pathogen-free animals	Yes	No
Public opinion	More in favor	Mixed

^*The size of certain organs, e.g., the heart, would be inadequate for transplantation into adult humans.

^**Breeds of miniature swine are approximately 50% of the weight of domestic pigs at birth and sexual maturity, and reach a maximum weight of approximately 30% of standard breeds.