## 4 Final and General Remarks  
The aim of the present work was to summarize the scientific evidences published in peer-reviewed journals concerning PFA use as alternative sources of antioxidants in poultry. The major part of the scientific papers is related to PFA and VitE as the most relevant synthetic antioxidant administered to the animals through the feedstuff, while only a few studies are available regarding VitC. Even if the effect of the PFA on the antioxidant status of the animals represents the main concern in this review, several other traits were investigated since null or positive effects on these relevant physiological functions of poultry are fundamental for their productivity. In general, both positive and negative effects were found in poultry by different researchers in relationship to the administration of PFAs on several animal functions and conditions, including growth, feed intake, feed utilization performances, blood biochemical parameters, antioxidant status, immunity, gene expression, and gut/ tissues development. Concerning growth performances, positive effects or similar results to the positive control (VitE or VitC administration) were obtained using oregano plant, rosemary volatile oil, _Forsythtia suspensa_ extract, and a generic polyphenol product as well as rosemary, oregano, and fennel volatile oil. A positive or neutral effect on feed use (F:G ratio) was found for oregano plant, green tea, and marigold extract or powder, which reduced feed intake, as well as for rosemary, oregano, and fennel volatile oil, which reduced FG ratio by increasing growth. Positive effects on energy, protein, and mineral digestibility were found also in relationship to the use of _Forsythtia suspensa_ extract. However, negative effects on digestibility were exerted by grape pomace and fermented and unfermented grape skin. The main biochemical traits investigated were those related to the lipid metabolism. A generalized positive effect was found in relationship to the capacity of several PFAs to increase HDL in a similar way or to a higher extent in comparison with negative and positive controls. This effect was shared by grape pomace, grapeseed extract, clove bud powder, green tea extract and powder, and marigold extract. In addition to this, grapeseed extract, clove bud powder, green tea extract and powder, marigold extract, anise seed, and thyme oil were demonstrated to decrease cholesterol in blood. Concerning the antioxidant status of poultry, among the parameters considered, a significant reduction of blood plasma MDA level was induced by grape pomace, clove bud powder, and olive leaf extract. Conversely, an increase of MDA content was induced by sweet chestnut in comparison with the control group. Some effect was observed also on antioxidant enzymes activity, such as GPx, which was increased by grape pomace, rosemary, and natural locopherol. On the other side, GPx activity was improved by olive leaf extract, whose effect was also positive on antioxidant capacity measured as FRAP assay. Poultry immunity was demonstrated to be affected by grape pomace and polyphenols in terms of increased antibody titers in comparison with negative and positive controls, respectively, while no effect was exerted by rosemary powder. A demonstration of the capacity of PFA to modify gene expression was given, for example, by grapeseed extract, whose use increased the expression of HSP in comparison with control groups. The PFA can affect gut and tissues structure and function, exerting some effects also on microbiota. An example was given again by grape pomace, which was shown to decrease villus height, crypt depth, and mucosal thickness, especially in comparison with negative control, increasing at the same time organs weight and intestine length. Clove bud powder improved tissue integrity and cell physiology, while, in another experiment, grape polyphenols had no effect on lymphoid organs. The form of PFA can affect the main physiological functions in different ways.