Quantitative Feed Restriction Rather Than Caloric Restriction Modulates the Immune Response of Growing Rabbits1–3

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; Peyer’s patch surface area was determined by image analysis; plasma total immunoglobulin (Ig) G and anti-ovalbumin IgG; and fecal and plasma IgA concentrations were determined by ELISA; and ileal expressions of cytokines were measured by quantitative reverse transcriptase-polymerase chain reaction at ages 50 and 63 d. Results: The relative weight and size of the lymphoid organs were not affected by treatments. Concentrations of plasma total IgA (−41% at 63 d and −29% at 72 d), IgG (−22% at 72 d), and anti-ovalbumin IgG (−41% at 63 d) were lower with feed restriction. Fecal IgA concentrations were lower with quantitative restriction (−40%, −52%, and −65% at age 42, 50, and 63 d, respectively) and energy restriction (−56%, −46%, and −73% at ages 50, 63, and 72 d, respectively). Feed-restricted rabbits tended to have greater expressions of interleukin (IL) 1β and IL-2 and lower expressions of tumor necrosis factor α (P < 0.1). Conclusion: These results demonstrated that, in rabbits, restriction and, to a lesser extent, dietary energy concentration modulate gut immunity.