Effect of Changes in Dietary Net Energy Concentration on Growth Performance, Fat Deposition, Skatole Production, and Intestinal Morphology in Immunocastrated Male Pigs

Abstract Background: Nutritional requirements of heavy immunocastrated pigs (IM) and thus the appropriate feeding strategies have not been determined. Methods: The effects of a reduced net energy (NE) diet, achieved by including up to 10% dietary fiber were studied in 41 IM pigs fed ad libitum with an extended period between immunization and slaughter (i.e. 8 weeks). Traits assessed included growth performance (before and after immunization at 112 days of age), fat deposition, intestinal skatole and indole production, intestinal morphology, and cell proliferation. Results: From 84 days of age, IM pigs were fed diets with low, medium, or high NE content (LNE, MNE, and HNE diets; with 8.5, 9.3, and 10.0 MJ NE/kg). There was no effect (P > 0.10) of feed NE concentration on average daily gain or the ratio of BW gain to NE intake in any of the periods studied. However, in the period from 143 to 170 days of age, there was a tendency for a higher NE intake (P = 0.08) in pigs fed the HNE diet along with higher (P < 0.01) backfat gain. Dietary treatment affected carcass composition as lower backfat thickness (P = 0.01) and lower area of fat over the longissimus muscle (P = 0.05) were observed in LNE and MNE pigs. In addition, higher lean meat content (P = 0.04) was observed in LNE pigs. Reducing the NE of the diet with fiber addition resulted in lower indole production in the ascending colon (P < 0.01), and higher skatole production (P < 0.01) in the cecum. Greater villi area, width, height and perimeter, crypt depth, and thickness of the intestinal mucosa in the jejunum, ileum, ascending colon, and descending colon were found for the LNE group (P < 0.01) than for the HNE group, while the MNE group was intermediate. Cell proliferation was not affected by dietary treatment (P > 0.05). Conclusion: The present results show that despite improved absorptive capacity (indicated by histomorphological changes in the intestinal mucosa), a reduction in dietary NE concentration reduces lipid deposition, without affecting performance or energy efficiency in IM pigs.