Relationships between performance traits and the expressions of growth hormone, insulin-Like growth facto -I, and insulin in pigs selected for growth or leanness

Selection for growth rate or backfat thickness (BFT) in pigs is related with changes in the blood plasma concentrations of growth hormone (GH) and insulin-like growth factor-I (IGF-I). Two experimental pig selection lines based upon a common commercial Large White (LW) selection line were selected for increased growth rate (F-line), or decreased BFT (L-line), respectively. We report here on the statistical evaluation of the phenotypic relationships between growth rate and BFT on the one hand, and (1) mRNA expression levels of GH and its transcription factor pituitary-specific transcription factor-1 (Pit-1), (2) GH protein plasma pulse pattern components and (3) IGF-I and insulin plasma concentrations on the other hand. Residual regression coefficients (RRC) and residual correlation coefficients (RCC) were used to evaluate the phenotypic residual relations between the traits and the hormone levels. Growth hormone mRNA levels, and to a lesser extent Pit-1 mRNA levels, were inversely related with BFT and growth rate when these traits were fitted separately in the model suggesting that GH is more closely related to the traits than Pit-1. Within line evaluation showed that GH mRNA levels had significant RRC with the performance traits in both lines, while Pit-1 mRNA levels were only significantly related to BFT in the L-line in both analyses. When growth rate and BFT were fitted together in the model GH mRNA levels had also significantly RRC with growth rate and BFT. Growth hormone mRNA levels seem to be more closely related with BFT than with growth rate. Growth rate was inversely related with the GH plasma baseline value in both lines. Growth hormone baseline concentration, and to a lesser extent GH area under the curve, were inversely related to BFT. However, GH level-line-specific effects were only found for the baseline concentration in the F-line. A positive relationship between growth rate and plasma IGF-I concentrations was found in the L-line. These results suggest a relationship between GH mRNA expression and performance traits in pig lines selected for growth rate or against BFT. No such relationship could be found for its pituitary-specific transcription factor. Furthermore, specific components of the GH blood plasma pulse pattern were related to specific performance traits in these selection lines. The IGF-I blood plasma concentrations were related to growth rate in these selection lines.