Quantitative Feed Restriction Rather Than Caloric Restriction Modulates the Immune Response of Growing Rabbits

Background: Short-term feed restriction strategies are used in rabbits to reduce postweaning digestive disorders, but little is known about the involvement of the immune system in these beneficial effects. Objective: In the present study, the consequences of feed and energy restriction on immune response were investigated. Methods: At weaning, 320 male and female rabbits were assigned to 4 groups differing in dietary digestible energy (DE) concentrations and intake levels: a low-energy ad libitum feed (LE100) group, a low-energy restricted feed (LE75) group, a high-energy ad libitum feed (HE100) group, and a high-energy restricted feed (HE75) group. The high-energy groups consumed 10.13 MJ DE/kg of feed, whereas the low-energy groups consumed 9.08 MJ DE/kg (formulated values). Intake amounts for the restricted groups were 75% those of the ad libitum groups. Rabbits consumed these diets until age 63 d, after which they consumed feed ad libitum for 9 d. Ten rabbits per group and per age were killed at ages 42, 50, 63, and 72 d. Spleens and appendixes were weighed, Peyers patch surface area was determined by image analysis, plasma total immunoglobulin (Ig) G, anti-ovalbumin IgG, and fecal and plasma IgA concentrations were determined by ELISA, and ileal expressionsof cytokines weremeasured by quantitative reverse transcriptase-polymerase chainreaction at ages50and 63d. Results: The relative weight and size of the lymphoid organs were not affected by treatments. Concentrations of plasma total IgA (241% at 63 d and 229% at 72 d), IgG (222% at 72 d), and anti-ovalbumin IgG (241% at 63 d) were lower with feed restriction. Fecal IgA concentrations were lower with quantitative restriction (240%, 252%, and 265% at age 42, 50, and 63 d, respectively) and energy restriction (256%, 246%, and 273% at ages 50, 63, and 72 d, respectively). Feed-restricted rabbits tended to have greater expressions of interleukin (IL) 1b and IL-2 and lower expressions of tumor necrosis factor a (P < 0.1). Conclusion: These results demonstrated that feed restriction and, to a lesser extent, dietary energy concentration modulate gut immunity. J Nutr doi: 10.3945/jn.114.197871.