Relationships of plasma insulin-like growth factor (IGF)-I and IGF-II concentrations to growth in purebred Landrace and Yorkshire female pigs

The present study was undertaken to investigate the relationships of plasma insulin-like growth factor (IGF)-I and IGF-II concentrations during the growing period to multiple growth measures and estimates at 90-kg body weight (BW) and thereby to evaluate plasma IGF concentrations as potential indicators for the growth measure in the pig. Jugular blood samples were obtained from 151 Landrace and 241 Yorkshire female pigs, which had been born of approximately equal numbers of a low (<μ−0.5S.D.)- and a high (>μ+0.5S.D.)-ADG line dams in each breed, at 25-, 60- and 90-kg BW. Backfat thickness (BFT), loin muscle area (LMA) and lean percentage were measured or estimated by ultrasonography at 90-kg BW, after which breeding values for ADG (ADG-BV) and BFT (BFT-BV) were predicted. Plasma IGF-I concentration at 25-kg BW was correlated with BFT in Landrace (r=0.26; P<0.01); in Yorkshire, these two variables tended to be correlated (r=0.12; P=0.09). Plasma IGF-I concentration at this BW was also correlated (P<0.01) with BFT-BV (r=0.29 and 0.30 in Landrace and Yorkshire, respectively; P<0.01) and also with the lean percentage (r=−0.25, P<0.05 in Landrace; r=−0.25, P<0.01 in Yorkshire). Plasma IGF-I concentration at 60 kg was positively correlated (P<0.01) with ADG (r=0.36) as well as ADG-BV (r=0.40) in Landrace, whereas in Yorkshire, IGF-I concentration at this BW was correlated with ADG only (r=0.21; P<0.01). Plasma IGF-II concentration at 60-kg BW was correlated with ADG and ADG-BV in Landrace, but in Yorkshire, the ADG-BV was correlated with IGF-II concentration at 25-kg BW. In conclusion, plasma IGF-I concentration during the growing period is indicative of the growth potential to some extent in purebred Landrace and Yorkshire female pigs.