Effects of feed restriction and diet nutrient density during re-alimentation on growth performance, carcass traits, organ weight, blood parameters and the immune response of broilers

Two hundred and ten one-day-old male chickens of the Ross 308 strain were randomly allocated to one of seven treatments (five replicates of six birds per treatment). The control birds were fed ad libitum throughout the whole experimental period. In the remaining treatments (T15-5, T15-10 and T15-15, and T30-5, T30-10 and T30-15), the feed restriction was 15 and 30% ad libitum intake between 8 and 14 days of age (starting period), whereas during growing (15-28 days) and finishing periods (20-42 days), the feeds contained 5, 10 and 15% higher energy and protein contents than the respective control feeds. Compared with the controls, T15 and T30 chickens suffered 12% and 20% body weight reduction at the end of the starting period, but both groups were heavier (P<0.05) than the controls at the end of the experimental period, mainly due to a higher (P<0.05) body weight gain during the finishing period, irrespective of the diet nutrient density. When the whole experimental period was considered, the feed restricted broilers showed a lower (P<0.05) feed conversion ratio than the controls and no negative effects were observed on carcass traits. The abdominal fat relative to carcass weight was higher (P<0.05) in the T15 broilers than in the controls and the T30 broilers. A positive correlation (P<0.05) was observed between the total, HDL and LDL cholesterol contents in the blood and abdominal fat percentage. The dietary treatments had no or a low impact on the relative weight of the organs and immune response of the broilers.