Effects of two levels of quantitative feed restriction for a 7- or 14- days period on broilers blood parameters

ABSTRACT

Background: Compensatory growth after a feed restriction (FR) period, associated with increased feed intake and digestive adaptation allows the broilers chickens to demonstrate better food conversion efficiency and meat yield when submitted to an early-age food restriction. Differences in levels of feed restriction or on the period of feed restriction need to be adapted to each broilers strain, and should balance an adequate physiological response towards compensatory growth for production of the most suitable carcass, the smallest stress and an adequate immune-competence levels. So far, investigations showed considerable variations concerning broilers response to early life restrictions, physiological associate changes, compensatory growth and fat deposition. This experiment had been done to compare the effects of quantitative feed restriction imposed in different intensities and durations on the blood concentrations of energy, protein and lipid metabolites. Materials, Methods & Results: Five experimental treatments included T1 corresponded to controls (ad libitum); T2 and T4 groups were submitted to 25 and 50% feed restriction for one week; and T3 and T5 were feed deprived in 25 and 50% for two weeks, in three replicates of 10 pieces per treatment. Periods previous and subsequent (up to 42 days) to FR periods were fed ad libitum. All chickens were fed with ad libitum before and after the completion of the restriction period. Feeds were based on corn and soybean meal, and were formulated to contain the same protein and energy levels in all treatments; feed was adapted to the three main phases of the rearing period the starter period (1-21 days of old), grower period (22-35 days old) and the finisher period (36-42 days old). At the end of the study, at 42 days of age, one bird per group, totalling 3 birds per treatment, was randomly selected for blood collection. Blood samples (1 mL/bird) were collected into EDTA tubes from the wing veins by the end of the experiment, at day 42. Samples were transferred to the laboratory for analysis within 2 h of collection. After centrifugation (3000 g, for 10 min at room temperature) plasma was harvested and stored in eppendorf tubes at -20ºC, until assayed. Severe restriction for a 2 week period showed the highest concentrations for Uric Acid (UAc), Triglycerides, VLDL, as well as the lowest for cholesterol and LDL; also, the highest ratios HDL/LDL were observed in this group, suggesting that birds in this treatment are more susceptible to protein catabolism during fasting and more prone to fat deposition in the carcass. In opposition, mild feed deprived birds showed the highest cholesterol and LDL concentrations in blood along with the lowest UAc, triglycerides and VLDL plasma values; they also showed lower HDL/LDL ratios than controls or severely feed deprived birds. No differences were observed between groups in glucose plasma concentrations. Discussion: The results suggest that feed restriction for longer periods may predispose the bird metabolism for an increased susceptibility for fat deposition, in comparison to the controls or the mild feed restriction treatments. Data gathered in the present study showed that quantitative feed restriction starting by day 8, followed by ad libitum was associated with changes in plasma metabolite concentrations. These changes varied between the two different intensities of FR and the two periods of FR evaluated. The results suggest that, for the same intensity of feed restriction, the length of deprivation may not be a determinant factor in mild FR. However, when severe FR is imposed, the length of FR may be a risk factor for excessive protein catabolism and increased VLDL availability, with the latter favouring precocious fattening of the carcasses. New studies are warranted to strength these results in particular on respect to the establishment of the influences of such changes in plasma metabolites with fatness and fat distribution on broilers.