METABOLIC CHANGES DURING THE TRANSITION FROM THE FED TO THE ACUTE FEED-DEPRIVED STATE IN PREPUBERAL AND MATURE GILTS

The present study compared the metabolic response to acute feed depriv ation in ovariectomized prepubersal (P; n = 6), 62 +/- 2 kg BW, and ma ture (M; n = 6) gilts, 124 +/- 4 kg BW. Blood was collected at 1, 2, 3 , 4, 6, 8, 12, 16, 20, 24, 28, 32, 40, and 48 h after initiation of fe eding. Samples were quantified for glucose, insulin, free fatty acids (FFA), beta-hydroxybutyrate (HBA), IGF-I, IGF binding proteins (BP)-1 to -4, cortisol, and amino acids (AA). At 24 h, blood samples were col lected every 15 min for 8 h and an additional 1 h after i.v. injection of GnRH (.2 mu g/kg BW) and growth hormone-releasing factor (GRF; 1 m u g/kg BW). Samples were assayed for growth hormone (GH) and LH. Serum insulin concentrations Were lower (P < .05) in P gilts. Plasma glucos e concentrations were similar. Serum FFA concentrations were greater ( P < .05) in P gilts. Serum concentrations of HBA were greater (P < .00 1) in P gilts at 4 h. Serum IGF-I concentrations Were lower (P < .05) in P gilts by 16 h. Serum IGFBP-1-4 levels were similar. Serum cortiso l concentrations were similar. Serum concentrations of the essential i soleucine, lysine, threonine, valine, and phenylalanine were greater ( P < .05) in P gilts at 40 h. Serum LH concentrations and response td G nRH were similar. Basal serum GH concentrations and peak response td G RF were greater (P < .05) in P than in M gilts. The transition from fe d to unfed state occurs more rapidly in P than in M gilts.