## 2 Materials and Methods
#### 3.2.1 Serum Biochemical Parameters
The CBP or the VitE inclusion in HFA compared with basal diet decreased (by 19.4% on average) the TG levels in laying hens. Increasing CBP levels of the diet led to a linear decrease of TG content compared with the basal (by 39.6%) and the VitE (by 25.9%) treatments [50]. In LFA diets, the addition of CBP compared with basal and VitE diets decreased (by averages of 13.3% and of 28.8%, respectively) TG content [50]. Feeding GP to broilers led to a reduction of TG (by an average of 39.4%) in comparison with the control group, without significant differences between GP and VitE groups [34]. In contrast to these findings, broilers reared under thermoneutral conditions and fed with GSE in comparison with VitC did not show any significant effect on TG levels [40]. Nevertheless, in the same study, the highest GSE supplementation level led to a significant decrease of TG concentration (by 10.8%) compared with the basal diet. However, no significant differences between VitC and GSE groups or between VitC and control groups were found. In the same study, glucose was lower in GSE compared with the basal (by an average of 12.0%) and the VitC (by about 8.6%) fed animals after 28 days of trial, whereas no differences between VitC and control groups were observed. At day 42, lower values in GSE than control (on average 15.6%) and VitC groups (mean of 11.7%) were reported [40]. Conversely, TG and CHOL were not significantly influenced by feeding arise seed (AS; 1% and 2% of the diet) in Japanese quails in comparison with VitE (600 mg/kg) [32]. Only feeding AS (at 1% of the diet) tended to decrease (by about 23.4%) TG concentration compared with control and VitE [32]. Broilers reared under HS and fed a diet with olive leaves added (0.2% and 0.4% of the diet) or supplemented with VitE (250 mg/kg) had a lower CHOL than control, with the lowest value in OL with a lower dose than the control group (by 15.5%) [26]. The authors also reported lower and similar TG values in OL and VitE groups in comparison with control animals (on average reduced by 34%). Uric acid was also lower in OL with a higher dose than in OL with a lower dose and in VitE groups (by 28.9% on average) as well as in the control (by 0.48%). Significant changes of lipid metabolism parameters were observed when TO was supplemented in broilers [27]. More in detail, broilers supplemented with TO (0.01% and 0.02% of the diet) increased total CHOL (by 7.1% and 10.3%) in comparison with groups supplemented with VitE (100 and 200 mg/kg, respectively). Furthermore, HDL-C was higher (by 8.9%) in the case of TO inclusion at the lower level and lower (by an average of 4.2%) when TO was supplemented at the higher level in comparison with the VitE groups. Similarly, LDL-C was higher (15.7% by average) in TO treated animals than in VitE groups [27]. Finally, the TO supplementation increased all the mentioned lipid metabolism markers when compared to the control group. This study shows clearly the complete lack of the expected hypocholesterolem effect of thyme oil. Several PFAs (e.g., grape pomace, grapeseed extract, clove bud powder, green tea extract and powder, as well as marigold extract) had a general positive impact on lipid metabolism by decreasing cholesterol and increasing the HDL levels in a similar way or in greater extent in comparison with negative and positive controls. Among the tested PFAs, thyme oil was the only one that had negative effects on the serum biochemical parameters related to lipid metabolism.