**4. Effect of PE on bird growth performance and dietary available energy**

Dietary PE supplementation significantly improved (P < 0.05) gain to feed (G:F) ratio by 2 points and dietary NE by 0.34 MJ (**Table 2**). No changes (P > 0.05) were observed in dietary ME due to PE supplementation. The increase in feed efficiency is in agreement with the ability of spices and mixtures of spices to increase bile secretion, activity of the pancreatic, and brush border enzymes [43, 44]. Maize based diets produced higher (P < 0.05) daily FI and ME, although wheat based diets had higher NE (P < 0.001). The values of ME and NE were in similar to previous reports [9, 45]. In agreement with [24], there were dietary type x PE interactions (P < 0.05) observed in bird growth, as birds fed wheat diets did not respond (P > 0.05) to PE supplementation. Similar tendency (P = 0.074) was observed for daily feed intake. Compared to maize, wheat contains more water-soluble non-starch polysaccharide (NSP), a carbohydrate complex possessing antinutrient activity, which may reduce dietary nutrient availability [46], thus explaining the reduced performance of birds fed wheat based diets. The observed interaction may also be due to the relatively high fat content of the wheat compared to maize based diets, and not to the cereals alone. Widening the dietary ME to protein ratio is likely to affect body fat retention more than bird growth performance, suggesting an explanation for the inconsistency between weight gain and NE of birds fed wheat based diets. However, the impact of dietary formulation (cereals, protein sources, fat content etc.) on the effectiveness of supplementary PE in poultry nutrition warrants further investigation.

Although there is a lack of consistency between growth performance and dietary ME, this is in agreement with many studies [8, 10, 11] but is in disagreement with others [9]. The


evaluate the feeding quality of supplementary PE. This is in agreement with previous reports suggesting that NE is a more meaningful measure of energy utilisation with regard to predic-

Plant Extracts, Energy, and Immune Modulation in Broilers

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Dietary PE supplementation significantly improved hepatic vitamin E (P < 0.001) by 33.4% and coenzyme Q10 (P < 0.05) by 28.6% (**Table 2**). No changes (P > 0.05) were observed in hepatic antioxidants content due to dietary type (P > 0.05), although the response of wheat based diets tended (P = 0.062) to be higher compared to maize based diets. More importantly, the increase in G:F and NE is coupled with the increase in the hepatic concentrations of vita-

Infectious diseases have been demonstrated to reduce tissue antioxidants [52], suggesting that higher concentrations of vitamin E and coenzyme Q10 in liver may decrease the challenge provoked by infectious diseases. In addition, feeding a combination of PE in the current study resulted in not only improved feed efficiency, but also increased hepatic antioxidants retention compared with the non-supplemented diet. When birds are reared under commercial farm conditions, where the potential for challenge is greater, and fed diets supplemented with PE, then there may be improvements to their overall nutrition, antioxidant and health status, and resistance to diseases [48]. The improvements observed may indicate that vitamin E and coenzyme Q10 may be effective at reducing production and effects of free radicals [53]. Coenzyme Q10 is provided by the diet, however significant levels are also produced in the body. Increased concentration of coenzyme Q10 in the liver of the growing chickens is therefore likely the result of dietary PE supplementation and dietary sources should thus be considered beneficial at improving the antioxidant status. It has also been reported [13] that PE, increased the activity of the antioxidant enzymes of the mucosal cells of rats, thus reducing the intestinal cell dam-

age and cell turnover and sustaining the integrity of the intestinal mucosal layer.

As shown in **Figure 2** the expression of CD 40 LG, IFN-G, and IL-6 was reduced (P < 0.001 and P < 0.05, respectively) in birds fed PE compared to the control fed chickens in accordance with other reports [18, 19]. There was a cereal X PE interaction for IL12B, showing that dietary PE reduced IL-12B expression in a wheat but not in a maize based diet (P < 0.05). Both, IL-6 and IFN-G, are major pro-inflammatory cytokines, so if the levels of these cytokines are decreased this would indicate that there are lower levels of inflammation than in the other groups, presumably due to plant extracts. Birds fed with diets supplemented with the same PE mixture also reduced the expression of CD40LG and IL-12B genes. The IFN-G cytokine belongs to the T helper (Th) type 1 response and is driven by IL-12 production. Th1 type response drives the cell mediated inflammatory responses largely to intracellular pathogens [54] but chronically

**6. Effect of PE on the immune status of birds**

tion of the nutritive value of poultry diets [35].

min E and coenzyme Q10 [48].

**5. Effect of PE on hepatic antioxidant content**

Source: adapted from [47–51].

W, wheat-based diet; M, maize-based diet; PE, supplemental plant extracts (100 g PE/t).

1 There were 38 observations per treatment (three experiments involving male Ross 308 broilers).

2 There were 24 observations per treatment (two experiments involving male Ross 308 broilers).

**Table 2.** The effect of supplemental plant extracts in wheat and maize based diets on broilers daily feed intake (FI), daily weight gain (WG), gain to feed (G:F) ratio, dietary apparent metaboilisable energy (ME), dietary net energy (NE), concentration of hepatic vitamin E and coenzyme Q10.

results show an improvement in feed efficiency in association with improved NE but not with ME. The beneficial effects of supplementary PE to poultry diets may therefore be mediated via a decrease in the energy required for maintenance, thereby providing more energy for growth. The improvement in feed efficiency is likely explained by increases in dietary NE, suggesting that PE may be improving the metabolic efficiency of the conversion of energy into tissue. Usually NE is described as the ME of the diet corrected for the energy losses that result from the heat released during absorption of the dietary nutrients and accretion of body mass [35]. Changes in maintenance energy are more likely to be detected by determination of NE but not ME. Thus confirming that dietary ME may not be the most sensitive method to evaluate the feeding quality of supplementary PE. This is in agreement with previous reports suggesting that NE is a more meaningful measure of energy utilisation with regard to prediction of the nutritive value of poultry diets [35].
