Low protein diets and synthetic glucocorticoids alter intestinal barrier function and performance of broiler chickens

The practice of reducing dietary protein along with supplemented amino acids has the potential to result in impaired performance and unbalanced supply of amino acids. There is little published information on the impact such diets have on intestinal health. An experiment was conducted to study the effect of low protein (LP) diets compared with a standard (SP) diet and a high protein (HP) diet on intestinal permeability and performance. This experiment had two parts. The first part was related to the growth performance study of the birds fed the three experimental diets in each phase of feeding (G/F: grower/finisher) in a completely randomised design. The three experimental diets were: LP (17/15% CP) fortified with essential amino acids, SP (20.2/19%) and HP (22/21%). Diets were formulated to meet the Ross 308 specifications. Low and SP diets contained the same level of essential amino acid concentration, while the HP diets contained 10% above the recommended Ross specifications. Each diet was replicated 6 times (10 male birds per replicate/pen). The second part investigated intestinal permeability and function on a subset of 72 male birds receiving the same three experimental diets. Glucocorticoids have been shown to induce gut leakage (Vicuña et al., 2015). On d 14, a total of 36 birds (12 birds per diet) were injected intramuscularly with dexamethasone (DEX), a synthetic glucocorticoid at 0.5mg/kg body weight. The injections were repeated on d 16 and 20. The remaining 36 birds received sham injections (saline solution). The fluorescein isothiocyanate dextran (FITC-d) method was utilized as the gut permeability test on d 21. All 72 birds were then euthanized for organ weights and tissue collection. Birds fed LP diets had lower body weight gain (BWG) and higher FCR compared to SP and HP diets in both grower and finisher phases of feeding (P< 0.001). For the challenge part, birds that received DEX showed higher FCR independent of dietary treatments. Diet and DEX interacted (P< 0.001) for BWG, whereby the effect of diet was only evident in sham injected birds. Birds fed LP had a higher (P< 0.05) FITC-d concentration indicating a more permeable intestine compared to HP but comparable to SP (Table 1). Independently, administration of DEX resulted in a significant increase in FITC-d concentration in all dietary treatments. The relative weights of lymphoid organs were also found to be lower in birds injected with DEX. Bursal atrophy was evident in LP diets and challenged group of birds (data not shown). The results of this experiment confirmed that intestinal barrier function can be impacted by both DEX and dietary protein level even when amino acids were supplemented at or above the industry recommendations. Further investigation is underway for the role of individual amino acids that have the potential to improve intestinal function and performance of birds fed low protein diets.

ACKNOWLEDGMENT: This research is part of a project supported by AgriFutures Australia.