Effect of vanillic acid supplementation on growth performance, carcass characteristics, blood metabolites, and meat quality of broilers fed oxidized restaurant oil

Introduction: Adding vegetable oils to broiler diets is common to supply energy and essential fatty acids and to increase diet palatability. Due to the high expense of vegetable oils, using restaurant oil in broiler diets has been increased. After the oxidation of these oils, certain compounds are formed, such as free radicals, peroxides, and secondary oxidation products such as malondialdehyde. These oxidation products have some negative effects on the growth performance and meat quality of broilers. One common method of inhibiting the oxidation process of oil is the use of antioxidants. The main active substance isolated from angelica and green tea, vanillin acid, is an oxidized vanillin compound consisting of phenols that inhibit lipid peroxidation in cells. In addition, vanillic acid has antioxidant, antimicrobial, anti-inflammatory, anticancer, and protective effects on the liver and may help improve broiler performance and meat quality. Therefore, this study was performed to investigate the effect of vanillic acid supplementation on growth performance, blood metabolites, and meat quality of broilers fed oxidized oil.
Materials and methods: This experiment was conducted as a completely randomized design on 144 one-day-old Ross 308 male broilers using a 2×2 factorial design with four treatments, four replicates, and nine chicks per replication. Experimental treatments included: 1. A basal diet with soybean oil, 2. A diet with oxidized oil, 3. A diet with soybean oil+100 mg vanillic acid, and 4. A diet with oxidized oil+100 mg vanillic acid. Diets were formulated as isocaloric and isonitrogenous, and then a vanillic acid supplement was added to experimental diets. Restaurant oil was replaced completely with soybean oil in treatments containing this oil. The performance traits, such as feed intake and body weight gain, were recorded for three periods including starter (1-10 days), grower (11-24 days), and finisher (25-42 days), and then, feed conversion ratio was determined. Broilers were treated for 42 days and one bird from each replicate was selected and blood samples were collected from the brachial vein. The collected samples were centrifuged at 3000 rpm for 10 minutes to separate the serum and the metabolites of the blood, including glucose, total cholesterol, and triglyceride, were analyzed. After slaughter, carcass and internal organs were weighted for measuring carcass traits. The breast and thigh were separated from the carcass and transferred to the refrigerator. Meat quality parameters, including water holding capacity, cooking loss, dripping loss, and meat pH, were measured one day after slaughter. The data obtained from this experiment were statistically analyzed using the GLM procedure SAS software. The comparison of means was conducted using the Tukey test at P<0.05.
Results and discussion: The results showed that in grower, finisher, and whole period, broilers fed by oxidized oil had the lowest feed intake (FI) and body weight gain (BWG), while the addition of vanillic acid improved FI, BWG, and feed conversion ratio (P<0.05). The interaction effect was significant for the growth performance and broilers fed with restaurant oil had the lowest BWG and FI, while vanillic acid-fed chicks had the highest BWG and FI (P<0.05). The relative weight of carcass, breast, and thigh was lower in broilers fed by oxidized oil, while vanillic acid supplementation caused a higher relative weight of these organs (P<0.05). The effect of treatments on the relative weight of internal organs was not significant. The effect of treatment on blood glucose was not significant. Vanillic acid decreased blood cholesterol, while oxidized oil treatment caused a decrease in blood triglyceride (P<0.05). The broilers fed by oxidized oil had lower meat pH and water holding capacity (WHC) and higher drip loss (DL) and cooking loss (CL), while vanillic supplementation decreased DL and CL, and increased pH and WHC (P<0.05). A negative impact of oxidized oil on growth performance has been reported due to the peroxidation products and their effect on the health of poultry and food. Vanillic acid is an effective compound with antioxidant and antimicrobial properties that can help in improving the negative effect of oxidized oil on performance and meat quality of broilers, by controlling the free radicals produced by oxidized oils.
Conclusions: Based on the results, the restaurant oil resulted in a decrease in feed intake, body weight, carcass, and breast relative to the broilers, as well as a decrease in the meat quality of the broiler, whereas the vanillic acid supplement increased BWG, FI, body weight and meat quality of the broiler fed with the oxidized oil. It can therefore be concluded that vanillic acid supplementation may be useful in improving the growth performance, carcass yield, and meat quality of broiler chickens when consumed in the form of restaurant oils.