Previous studies have reported conflicting data on gender differences in pl
asma IGF-I in postnatal pigs. There is also debate over the role of IGF-II
in regulation of postnatal growth. We have, therefore, determined the conce
ntrations of plasma IGF-I, IGF-II, and IGF-binding protein-3 (IGFBP-3) in b
oars, barrows, and gilts and related these to postnatal growth characterist
ics. Plasma concentrations of IGF-I were higher in boars than in gilts or b
arrows from 13 wk of age, and plasma IGF-II levels were generally higher in
barrows than in boars or gilts. Plasma IGFBP-3 levels were higher in boars
than in gilts or barrows at most ages. Between 15 and 23 wk of age, IGF-I
and IGFBP-3, but not IGF-II, were positively associated with growth rate, v
oluntary feed intake, and gain:feed ratio. Plasma IGF-II, but not IGF I or
IGFBP-3, was positively associated with backfat depth during this period. T
hese results support the hypothesis that circulating IGF-I and IGF-II are r
egulators of lean and adipose tissue growth, respectively.