Figure 1. Mean growth hormone concentrations (ng/ml serum) for barrows (n 5 15), barrows receiving testosterone
propionate (TP; n 5 16) and boars (n 5 16). Blood samples were collected every 15 min for 2 h before and 2
h after i.v. injection of n-methyl-d, l-aspartate (NMA; 2.5 mg/kg BW). The dark bars represent the 2-h period
prior to NMA administration and the open bars represent the 2-h period following NMA injection. Values are
means 6 SE and within treatments, bars with different superscripts differ (P , .05).