The aim of this study was to determine the effect of vitamin E and
polyphenols on the antioxidant potential and meat quality of broiler chickens
fed diets supplemented with low-quality oil. The experimental materials
comprised 120 male Ross 308 broilers (six treatments, 10 replications, two
birds per replication). Dietary supplementation with vitamin E and/or
polyphenols was applied in the following experimental design: group I
(negative control) – without supplementation without low-quality oil; group
II (positive control) – without supplementation
The quality of oil as a source of energy in poultry diets influences growth performance and the health status of flocks. Low-quality oil added to broiler chicken diets decreases productivity (Anjum et al., 2002; McGill et al., 2011), increases mortality (Anjum et al., 2004) and decreases the quality of animal products (Zhang et al., 2011). Diets rich in polyunsaturated fatty acids (PUFAs) increase susceptibility to lipid peroxidation and decrease the antioxidant capacity of animals. Rancid lipids that undergo auto-oxidation processes contain free-radical-generating substances that exert adverse effects on the health status of birds. Oxidation reactions produce harmful peroxides that are converted into hydrocarbons, ketones, alcohols, organic acids and aldehydes (Baião and Lara, 2005) including malondialdehyde (MDA) with mutagenic and carcinogenic properties. Oxidation reactions also decrease the content of vitamins A and E and carotenoids (Bayraktar et al., 2011; Koch and Hill, 2016). Increased production of reactive oxygen species (ROS) disrupts redox balance and contributes to oxidative stress with harmful implications for health (Koch and Hill, 2016).
Supplementation with antioxidants is an effective method of minimising the adverse consequences of low-quality oils in animal diets. Recent years have witnessed growing levels of awareness among consumers and food producers regarding the origin of feed additives in livestock nutrition. The demand for products of natural origin continues to increase.
Polyphenols are substances of plant origin which possess antioxidant
properties and may reduce the negative effects of oxidative stress (Brenes
et al., 2016; Lipiński et al., 2017). Their antioxidant potential is
comparable with that of the major biological antioxidants:
The results of in vitro and in vivo studies demonstrated that polyphenols deliver positive effects in animal nutrition (Alonso et al., 2002,; Torres et al., 2002; Viveros et al., 2011; Gessner et al., 2013; Kamboh and Zhu, 2014; Chen et al., 2018), including in animals whose diets contain oxidised oils or oils rich in PUFAs (Sobotka et al., 2012; Lu et al., 2014; Kishavy et al., 2016).
The research hypothesis postulated that polyphenols from onions and grape seeds can partially replace vitamin E in terms of antioxidant activity in broiler chickens fed oxidised oil. The aim of this study was to determine the effect of polyphenols and increased inclusion levels of vitamin E on the antioxidant potential and meat quality of broilers fed diets supplemented with low-quality oil.
The experiment was approved by the Local Ethics Committee for Animal Experimentation in Olsztyn, Poland. The experimental materials comprised 120 male Ross 308 broiler chickens (six treatments, 10 replications, two birds per replication). The chickens were kept in cages without litter (two birds per cage). The experiment lasted 35 d. The body weights of birds were determined at weekly intervals. Feed intake and mortality rates were also monitored, and the data were used to calculate the feed conversion ratio (FCR).
The birds were fed ad libitum starter (1–14 d of age) and grower (15–35 d of age) diets in mash form, which fully met the nutrient requirements of broiler chickens (Nutrient Requirements of Poultry, 2005), and they had free access to water.
The Proviox Nucleus preparation (Provimi, France) used in the study contains
polyphenols obtained from onions (quercetin and flavonols) and grape seeds
(catechins, flavonols, procyanidins and anthocyanidins). Broiler chicken
diets were supplemented with 50 % vitamin E in the form of dl-
Experimental design.
Feed and breast meat samples were assayed for dry matter (DM), crude ash, crude protein (CP), ether extract (EE) and crude fibre (CF) by standard methods (AOAC, 2005). Vitamin E concentrations were measured by chromatography (HPLC – high-performance liquid chromatography) (Shimadzu, Japan), according to the method described by Polish Standard PN-EN ISO 6867 (2002). The amount of metabolisable energy and the content of amino acids and minerals in broiler chicken diets were calculated according to the Nutrient Requirements of Poultry (2005). The composition and energy value of diets without supplemental vitamin E are presented in Table 2.
Composition (%), content of vitamin E (mg kg
Blood samples were collected from broiler chickens on day 35. The activity of
superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) was determined
in heparinised whole blood. Total antioxidant status (TAS) and the
concentrations of vitamins A and E were determined in the blood serum. Blood
samples were stored at a temperature of
Total antioxidant status, SOD and GSH-Px activity were determined with the
use of the Randox kit according to the manufacturer's recommendations. The
activity of SOD was measured as the percent inhibition of the rate of
formazan dye formation (505 nm wavelength). The activity of GSH-Px in
heparinised whole blood was determined with the use of cumene hydroperoxide.
In the presence of glutathione reductase and NADPH (nicotinamide adenine dinucleotide phosphate), oxidised glutathione is
converted to a reduced form, and NADPH is oxidised to NADP
Serum samples (1 mL) were deproteinised with anhydrous ethanol (1 mL),
extracted with 5 mL of n-hexane (Vortex 5') and centrifuged (3000 rpm,
10 min, 4
Vitamin E equivalent (vitamin EEq) was calculated based on the activity of
tocopherols relative to
At 35 d of age, 10 birds per group were slaughtered and carcass quality was evaluated. Samples of fresh breast muscles and liver were assayed for the concentrations of lipophilic vitamins (retinol, total tocopherols) as described by Rettenmaier and Schüep (1992), hydrophilic vitamins (vitamin C) as described by Omaye et al. (1979), and thiobarbituric acid-reactive substance (TBARS) values according to Sørensen and Jørgensen (1996).
The percentage content of breast muscles in the carcass and abdominal fat,
heart and liver in live body weight was determined. Samples of fresh breast
muscles were assayed for proximate chemical composition (AOAC, 2005) and meat
quality parameters including acidity (pH15 and pH24, with the WTW 3310 pH
meter and a Hamilton Double Pore probe), colour in the CIE
Breast muscle samples were assayed for the concentrations of fatty acids
after methylation of extracted lipids (Peisker, 1964) by chromatography,
including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs),
n-3 and n-6 polyunsaturated fatty acids (PUFAs), hypercholesterolemic fatty
acids (OFAs) and hypocholesterolemic fatty acids (DFAs), in accordance with
the criteria proposed by Barowicz et al. (2000) and Leskanich and
Noble (1997). The fatty acid percentages were calculated with the Microsoft
Excel (Microsoft Excel 2013) software and the mean value of each fatty acid
was used to calculate the following indexes:
peroxidisability index (PI) – (% monoenoic atherogenicity index (AI) – (C12 thrombogenic index (TI) – (C
Segments of the gastrointestinal tract were emptied to determine their
weights and pH of their contents. Dressing percentage was calculated as the
ratio of carcass weight to live weight.
Growth performance of broiler chickens fed low-quality oil.
The AV and POV of rapeseed oil were determined according to Polish Standards PN-88/C-04288/06 and PN-88/C-04288/10, and MDA concentration was determined as described by Esterbauer et al. (1991).
The results were processed statistically by one-way analysis of variance and
Duncan's test. The arithmetic mean (
The applied antioxidants did not improve the growth performance of broiler
chickens fed diets containing oxidised rapeseed oil (Table 3). Broiler
mortality was not recorded in groups receiving diets supplemented with 100 mg kg
At 35 d of age, no differences in TAS or SOD activity were found between
groups (Table 4). The addition of polyphenols to diets (groups V and VI)
increased GSH-Px activity in the blood of broiler chickens (
Antioxidant status of broiler chickens fed low-quality oil.
a, b –
The addition of polyphenols to diets (group VI) led to an increase (by
46 % on average,
Broiler chickens fed diets supplemented with antioxidants were characterised
by higher (
The vitamin C content of breast muscles was similar in all chickens (Table 4).
The lowest retinol content (24 % on average,
Low-quality dietary oil had no significant effect on carcass dressing percentage or the percentage content of breast muscles in the carcass (Table 5). However, dressing percentage tended to increase in broilers fed diets without rancid oil (group I) and diets containing rancid oil and supplemented with polyphenols (group VI).
The effect of antioxidants on carcass quality, structure of the gastrointestinal tract and digesta pH in broiler chickens fed low-quality oil. BW stands for body weight.
a, b –
No differences in the percentage content of the heart, liver and abdominal
fat were found between groups (Table 5). The analysed antioxidants had no
significant effect on the weight and pH of the crop and proventriculus in
all groups. Higher gizzard weight (by 24 % on average,
The meat of broilers fed diets without oxidised oil (group I) and diets
supplemented with 100 mg kg
Physicochemical properties of breast muscles in broiler chickens fed low-quality oil. WHC stands for water-holding capacity.
a, b –
The breast muscles of broilers fed diets supplemented with polyphenols were
lighter (
No significant differences in natural drip loss or the water-holding
capacity of meat were found between groups (Table 6). The analysed meat
samples did not differ in the content of dry matter or protein (Table 6).
Crude fat content was nearly two-fold lower in the breast muscles of
broilers fed diets without oxidised oil (group I), compared with birds fed
diets with oxidised oil and without antioxidants (group II) and diets with
the highest inclusion level of polyphenols (group VI) (
The analysed breast muscles of broiler chickens did not differ in the content of SFAs (Table 7). Broilers whose diets did not contain oxidised oil (group I) were characterised by lower concentrations of total MUFAs and higher content of PUFAs, relative to the remaining groups.
Percentage content of fatty acids in the breast muscles of broiler chickens.
a, b –
The content of n-3 PUFAs tended to decrease in broilers whose diets were
supplemented with polyphenols only relative to the negative control group
(group I). The breast muscles of birds given polyphenols only (group VI) and
broilers fed low-quality oil without antioxidants were characterised by a
lower content of n-6 PUFAs, DFAs, a lower
Vegetable oils are added to poultry diets to increase the energy value of
feed rations. Oils rich in PUFAs are more susceptible to peroxidation.
Oxidised products are characterised by high ROS levels and a reduced content
of fat-soluble vitamins (Panda and Cherian, 2014). Research shows that
dietary supplementation with oxidised oil compromises production results
(Cabel et al., 1988; Lin et al.,1989; Engberg et al., 1996; Wang et al.,
1997; Anjum et al., 2004; McGill et al., 2011; Tavarez et al., 2011; Kishavy
et al., 2016). In the present study, oxidised rapeseed oil as dietary
stressor did not affect the growth performance of broilers, but birds whose
diets were supplemented with antioxidants had higher final body weights,
although the differences noted were not statistically significant. The
evaluated antioxidants did not improve performance parameters. Similar
results were reported by Açıkgöz et al. (2011), in whose study
moderately oxidised oil did significantly affect the body weights of male
broilers, feed intake and feed conversion, and a vitamin E dose of
200 mg kg
Dietary stressors like oxidised feeds are a source of free radicals, which
induce oxidative stress in birds (Lu et al., 2014). The results of numerous
studies have confirmed that oxidised dietary oils decrease the
concentrations of antioxidants (retinol,
In the present study, polyphenols contributed to an increase in the carcass dressing percentage of broilers fed oxidised rapeseed oil, which could suggest that polyphenols exert protective effects against the harmful consequences of peroxidation products. Rancid oil, with or without antioxidants, had no effect on carcass quality. Birds fed diets with the addition of vitamin E were characterised by higher gizzard weight and higher pH of gizzard digesta. Açıkgöz et al. (2011) and Tavarez et al. (2011) did not observe differences in carcass dressing percentage, carcass weight or breast muscle weight of broilers whose diets contained rancid oil and were supplemented with vitamin E or antioxidants (propyl gallate and ethoxyquin). Zduńczyk et al. (2002) did not report differences in the carcass dressing percentage or abdominal fat content of turkeys fed oxidised oil. In the work of Anjum et al. (2004) and Racanicci et al. (2008), chickens fed oxidised or fresh oil did not differ in carcass dressing percentage or gizzard weight. Liver weight increased in birds given low-quality oil (Anjum et al., 2004). In the literature, there is a general scarcity of studies investigating the effect of polyphenols on carcass dressing percentage and the structure of the gastrointestinal tract in broilers fed low-quality dietary oils.
Peroxidation induces changes in the fatty acid profile of oils and fats.
Low-quality oils with high AV and POV are sources of free radicals that exert
adverse effects on unsaturated fatty acids and meat quality. Oxidative damage
compromises the quality of poultry meat, including its colour, structure and
water-holding capacity, and increases drip loss (Holownia et al., 2003; Sihvo
et al., 2013; Zhang et al., 2011). In the current study, low-quality rapeseed
oil increased pH
In the present study, the content of PUFAs was higher and the AI was lower
in chickens that did not receive oxidised oil and in broilers whose diets
were supplemented with vitamin E alone or vitamin E and polyphenols relative
to birds that were fed oxidised oil without antioxidants. Similar
observations were made by Sheehy et al. (1994) in whose study, PUFA
concentrations were higher in the lung tissue of chicks receiving fresh oil
and in birds given oxidised oil with vitamin E, and they were lowest in
the group of birds fed oxidised oil without antioxidants. Racanicci et al. (2008)
also reported a decrease in the concentration of C
It can be concluded that the applied antioxidants had no effect on the
growth performance of chickens fed oxidised oil. Increased dietary inclusion
levels of vitamin E and/or polyphenols improved the antioxidant status in
the blood and increased the content of non-enzymatic antioxidants in the
liver and breast muscles of broilers fed low-quality oil. The tested
antioxidants had no influence on carcass quality parameters in chickens fed
oxidised oil. However, birds fed diets with the addition of vitamin E were
characterised by higher gizzard weight and higher pH of gizzard digesta.
Dietary supplementation with vitamin E and polyphenols or polyphenols alone
contributed to a lighter colour and lower pH of breast muscles and an
increase in the content of fat and ash in the breast muscles of broilers fed
oxidised oil. The breast muscles of birds receiving supplemental vitamin E
were characterised by higher concentrations of n-6 PUFAs and DFAs, a more
desirable
The data sets are available upon request from the corresponding author.
The authors declare that they have no conflict of interest.
This paper was edited by Manfred Mielenz and reviewed by two anonymous referees.