Serum testosterone of neonatal male and female dogs

Serum testosterone (T) was determined for male and female dogs from Day 2 (48-72 hr after birth) through Day 49. For the first 20 days of life, the T levels of both sexes were relatively stable and very low by adult male standards. The level for males was ~0.15 ng/ml and was significantly higher than that for females which was ~0.10 ng/ml. The levels for both males and females, however, may be so low postnatally that they are not biologically significant. If there was a'masculinizing' perinatal surge in T secretion in males, it undoubtedly occurred prenatally.