|Abstract or Summary
- In the presence of internal or external stressors, the body requires sources of energy that aide cells to combat inflammation. Fatty acids are an important source of energy and are vital components of cell membranes. Dietary fatty acids (n-6 and n-3) are of importance in immune function because they are precursors to metabolites that are potent mediators of inflammation. Poultry diets are high in n-6 fatty acids, which exert pro-inflammatory effects, and low in n-3 fatty acids, which tend to be less inflammatory. Delayed access to feed after hatching has been reported to impact the development of organs associated with immunity. Based on this information, two experiments were conducted in broiler chickens to determine the effect of dietary polyunsaturated fatty acid (PUFA) and the influence of time of feeding on bird performance, tissue lipid status, immune responses and expression of cyclooxygenase 2 (COX-2) upon challenge.
In experiment 1, birds were fed diets that contained 3.5% oxidized yellow grease (low n-3) or 3.5% canola oil (high n-3). Birds were fed early (<5 hrs post-hatch) or late (>24 hrs post-hatch). Intramuscular injection of lipopolysaccharide (LPS) or phosphate buffered saline (control) was used as the immune challenge. Feeding high n-3 diets resulted in an increase in n-3 fatty acids in the liver in all treatment groups upon LPS challenge (P<0.05). LPS injection led to a decrease in total n-6 fatty acids in the liver when compared with control birds (P<0.05) fed early high n-3 and late low n-3. However, in spleen tissue, upon LPS challenge, increase in total n-3 fatty acids was observed only in birds fed early high n-3 and birds fed late high n-3. Plasma non-esterified fatty acids were lowest in high n-3 birds fed early (P<0.05). The spleen tissue total fat content was lowest in early high and late high n-3 birds (P<0.05). Breast muscle thiobarbituric acid reactive substances (TBARS) were higher in birds fed high n-3 compared to birds fed diets low in n-3 (P< 0.05). The delayed type hypersensitivity response was higher in birds fed high n-3 diet when compared to all other treatments (P<0.05). Thigh muscle of LPS challenged birds from early low n-3 and late high n-3 was significantly higher in TBARS when compared to control birds (P<0.05). There was no difference in final body weight, cut-up yield and organ weight of birds (P>0.05) except liver and thigh muscle weight percents were lowest in birds fed low n-3 (P<0.05).
In the second experiment, birds were fed diets containing 3.5% sunflower oil (low n-3) or 3.5% fish oil (high n-3). The birds were either fed early (<5 hrs post hatch) or late (>48 hrs post-hatch). No effect due to time of feeding was observed (P>0.05). Birds fed high n-3 diets had higher C20:5n-3, C22:5n-3, C22:6n-3 and total n-3 fatty acids and birds that were fed a low n-3 diet had higher levels of total n-6 PUFAs (P<0.05). LPS challenged led to a decrease in spleen C22:5n-3 of birds fed late high n-3 when compared to control birds within the same treatment group (P<0.05). LPS challenged birds showed an increase in C20:4n-6, total polyunsaturated fats and total n-6 fatty acids in birds that were late fed low n-3 compared to control birds within the same treatment group (P<0.05). LPS challenged birds from early and late high n-3 had higher liver total saturated fats when compared to control birds of the same diet (P<0.05). LPS challenge led to an increase in liver total n-6 fatty acids in birds fed late low n-3 when compared to control birds within the same treatment (P<0.05). LPS birds from early and late high n-3 diets were higher in total liver n-3 fatty acid content when compared to birds fed low n-3 diets (P<0.05).
Plasma isoprostanes showed no difference among treatment groups (P>0.05). Liver vitamin E was higher in control birds from early high n-3 groups when compared to the other treatments (P<0.05). Plasma vitamin E was highest in early low n-3 upon challenge when compared to the other treatments (P<0.05). LPS challenge resulted in an increase in vitamin E in the lung, small intestine and plasma of low n-3 birds. COX-2 expression in the spleen tissue increased due to LPS challenge. Time of feeding and diet had a significant effect on COX-2 protein expression (P<0.05).
These results indicate that type of dietary fat and time of feeding may alter the inflammatory response upon challenge in broiler birds. During inflammation, lipid substrates for the activated immune system are provided by fatty acids. Therefore, dietary management strategies directed at attenuating immune tissue lipid content may prove to be beneficial in enhancing bird health and in increasing production performance in broiler chickens.