The results of the experimental trial on broiler performance, carcass characteristics and blood metabolites are summarized in Tables 2, 3 and 4.
Growth performance
The 5, 10 and 15% DOP based diets enhanced body weight at day 49 of rearing compared to the control group. There were significant differences in broiler weight gain and feed conversion ratio among treatments due to dietary DOP (P<0.05). Significant improvements in FCR of (5 and 10% DOP), except in 15% DOP. In the final week of the trial, the groups fed with 5% and 10% DOP had a decline in FCR of 9% and 13%, respectively, compared to the control group. Additionally, during the period of 35-42 days, the 5% DOP group had better FCR values compared to the control group, with a statistically significant difference (P<0.05). The trial also found a significant enhancement in BWG of chicks after the incorporation of orange byproducts to their diets.
Our results are related to the findings of
(Vlaicu et al., 2020), who showed that adding orange pulp or essential oil (
Citrus sinensis L) to broiler diets had a significant impact on weight growth and feed conversion ratio. The improvement in FCR values observed in DOP-diets is consistent with the results reported by
(Abbasi et al., 2015), where hesperidin was found to enhance the activity of digestive enzymes
(Kamboh and Zhu, 2013). The composition of gut microbiota can also influence FCR since colonic bacteria enzymes can affect the structure of polyphenols, increasing their bioavailability
(Luca et al., 2019).
Our findings are similar to those reported by
(Oluremi et al., 2010), who demonstrated that orange pulp had a positive effect on body weight and feed intake throughout the experiment. However, our results partially agree with the experiments of
(Boumezrag et al., 2018 and
Alzawqari et al., 2016), where supplementation with orange peel or a combination of orange peel and lemon grass leaf had no effect on BWG, FI and FCR.
Carcass parameters
The inclusion of dietary dried orange pulp (DOP) in the diets resulted in a significant increase in liver and intestine yields (P<0.01). The liver efficiency in the 15% DOP group showed a 28% increase compared to the control broilers. Additionally, a significant decrease of over 26% in abdominal fat yield was observed in the 15% DOP broilers compared to the control group (P<0.05).
The increase in liver and intestine yields of broilers fed orange waste is attributed to the antioxidant property of flavonoids like naringin
(Goliomytis et al., 2015), also feeding soluble fiber-rich meals result in high-viscosity digesta and elevated cell proliferation
(Gonzalez-Alvarado et al., 2010). These findings were partially in line with
(Akbarian et al., 2013 and
Ebrahimi et al., 2014); where none of the dietary interventions had a significant influence on the mean weight of gizzard or liver. Our findings of abdominal fat yield are in agreement with those of
(Abbassi et al., 2015).
The improvement in abdominal fat yield for dietary orange pulp treatments may be due to presence of naringin in DOP and its role as a powerful antioxidant that be able to prevent oxidation and accumulation of fat by the inhibition of adipocyte proliferation and modulating fat metabolism
(Guo et al., 2016). The trial results were partially related to
(Pourhossein et al., 2015), proved that adding essential oil isolated from orange peel to broiler meals results in a higher live weight, showed no significant effect on the spleen weight and the broilers fed with sweet orange peel diet had a considerable rise in liver weight.
Blood parameters
The substitution of corn with orange byproducts in bird’s diets at 16 days of rearing had a significant (P<0.05) effect on serum glucose, total protein, cholesterol, triglycerides, Aspartate Amino Transferase (AST), Alanine Amino Transferase (ALT), Lactate dehydrogenase (LDH) and Creatine kinase (CK).
Serum glucose levels were significantly higher (P<0.05) in all dietary groups, except for the 5% DOP group, compared to the control group. Feeding the control diet resulted in a decrease in blood glucose levels by more than 68% compared to the 15% DOP-based diet. The elevated glucose concentration may be attributed to the main glycosylated flavanones, hesperidin and narirutin, found in citrus peel
(Chen et al., 2017).
Serum lipid fractions showed significant reduction (P<0.05) in total cholesterol and triglycerides, in broilers fed with DOP-based diets in comparison to control. An increase of more than 48% in TG blood concentration was noticed in the serum of control group compared to the 10% DOP group. The 10% DOP meal decreased the cholesterol in animal serum by more than 52% compared to the control diet.
Our findings are in agreement with
(Alefzadeh et al., 2016 and
Abbasi et al., 2015) concluded that dietary dried orange peel and orange pulp lowered blood cholesterol and triglycerides. This effect may be attributed to the hypocholesterolemic properties of citrus fruits. The flavonoids have been shown to inhibit the synthesis of cholesterol in the liver by inhibiting the activity of the hepatic enzyme 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase
(Gilani et al., 2018).
Feeding DOP-diets led to an increase in the serum total protein level (P<0.001) compared to the control diet; which can be ascribed to the transamination of phenolic and flavonoid compounds present in the orange wastes
(Akbarian et al., 2013).
Feeding DOP-based diets presented a significant decrease in AST levels compared to the control diet (P=0.014). Specifically, the serum activity of AST was reduced in 15% DOP group, which is more than 29% lower than the control group activity.
However, the results of ALT obtained in this trial were similar to
(Alagawany et al., 2021 and
Suliman et al., 2019), showed that orange byproducts have positively affected the liver enzymes in broiler chickens and quail. The decrease in AST serum levels observed in this study could be linked to naringin, a compound found in orange peel and byproducts which may reduce the liver cell enzyme leakage
(Jiang et al., 2020 and
Gibson et al., 2017).
The inclusion of DOP reduced the activity of LDH and CK (P<0.05). The lowest activities of (CK) were observed in DOP-based diets compared to the control group. A reduction of more than 46% was observed in the 15% DOP compared to the basal diet. The relative concentrations of LDH were significantly lower in DOP 10 and 15% than in the control group (P<0.01).
In the current investigation, the reduction of CK and LDH levels in the serum indicated that dietary flavonoids have beneficial effects against stress. This is in line with
(Akbarian et al., 2013), who found that dietary antioxidants such as hesperidin and dietary genistein are defenders against oxidative damage in poultry rearing and with
(Hao et al., 2019), who reported that naringenin has cardioprotective potential and reduces myocardial biomarkers such as AST, ALT, CK and LDH. Furthermore, DOP at different percentage in the diets from (21 to 49 days) age had a significant positive effect on chicken antioxidant status. These results are in agreement with those showed by
(Alzawqari et al., 2016), because citrus byproducts are a source of phenolic molecules and α-tocopherol with antioxidant properties
(Delgado-Pertinez et al., 2021).