Objective  Effects of varied dietary energy compositions in feed on the growth, apparent nutrient digestibility (AND), serum metabolites, and hormone concentration in gilts were studied.

  Method  Ninety Landrace×Large white gilts with an initial body weight of 61.97±4.37 kg in a similar bodily appearance were randomly divided into 3 groups of 5 gilts each for the study. The gilts were fed with specially formulated forage that represented varied dietary iso-energetic and iso-nitrogenous energy structures. Diet 1 contained 49.70% starch, 2.81% lipids (EE) and 8.95% neutral dietary fiber (NDF); Diet 2, 43.52% starch, 5.68% EE and 12.53% NDF; and Diet 3, 37.13% starch, 8.73% EE and 16.02% NDF.

  Result  As the starch content decreased and EE and NDF increased in the diet, the average daily weight gain (ADG) decreased, and the feed/weight gain ratio (F/G) of the gilts increased. Compared to the groups fed with Diet 1 and Diet 2, which were similar, the gilts fed with Diet 3 showed significantly lower ANDs on dry matters, crude protein, crude fiber, NDF, EE, and ash from feed (P < 0.05). The concentrations of circulating triglyceride and total cholesterol increased, and insulin decreased with a decrease on starch and increases on EE and NDF in diet, while no significant differences found on serum glucose (P>0.05). The concentrations of serum IGF-I and leptin in the group fed with Diet 1 were higher than that in the group fed with Diet 3 (P < 0.05).

  Conclusion  Excessive reduction on starch and increase on EE and NDF in feed lowered the AND of the gilts reducing the forage utilization rate and altered the serum hormone secretion in gilts negatively affecting their growth performance.