Metabolic adaptation and hormonal regulation in young rabbit does during long-term caloric restriction and subsequent compensatory growth

An experiment was performed to assess the metabolic adaptation An experiment was performed to assess the metabolic adaptation and hormonal regulation in young female rabbits during long-term food restriction and subsequent compensatory growth during rearing. Feeding level was either ad libitum (AL, no. = 52) or restricted (R, no. = 52). From 6 to 12 weeks of age, food intake of R was kept at a constant level. This resulted in an increase in relative restriction as compared with AL to 0.54of AL intake at 12 weeks of age (restriction period). Thereafter food intake gradually increased to 0.95 of AL at 17 weeks of age (recovery period). During the last 5 days before insemination at 17.5 weeks of age, all animals were fed to appetite. Blood samples were taken weekly from 6 to 17 weeks of age from 11 animals in each group. Growth rate of R was reduced during the restricted period (29 (s.d. 2) v. 44 (s.d. 5) g/day for R and AL, respectively; P < 0.05), but was higher in the recovery period (30 (s.d. 3) v. 27 (s.d. 4) g/day, respectively; P < 0.05). At first insemination, AL rabbits were heavier than R (4202 (s.d. 388) v. 3798 (s.d. 220) g, respectively; P < 0.001). During the restricted period, plasma glucose was constantly lower (P < 0.05) in R. Insulin levels paralleled those of glucose, being lower (P < 0.05) in R than in AL. Restriction reduced (P < 0.05) circulating corticosterone and tri-iodothyronine (T3) levels in R. Leptin, non-esterified fatty acids, and plasma urea nitrogen levels were similar for AL and R during food restriction, whereas triglycerides were similar until 10 weeks of age, after which the levels were lower in R. During the recovery period, the food intake of the R but not AL rabbits increased. Insulin was the only hormone in R rabbits that had returned to levels found in AL rabbits by the 2nd week of the recovery period. Glucose, T3, and corticosterone levels returned to levels found in AL rabbits between 3 to 4 weeks after refeeding. Non-esterified fatty acids, triglycerides, and leptin were higher (P < 0.05) in AL rabbits from 13 weeks of age onwards. The pattern of changes in the endocrine status during food restriction and compensatory growth in rabbits do conform with those from other species, although some specific changes may vary depending on the severity of food restriction and its duration.