Nutritional Value of White Grape Pomace (Vitis Vinifera L.) and Effect of its Varying Levels on Growth Performance and Blood Charactristics of Broiler Chickens

 One of the most important challenges in poultry industry is supplying of feedstuff. The international prices of this feedstuff have increased the costs of poultry production, and therefore, reduced marketing margins. Additionally, due to the high amount of wastes from the agricultural sector and food industry, proper management of these resources and identifying the nutritional value, makes it possible to produce cheap and suitable ingredients for poultry which are not competitive with human food. Grapes (Vitis vinifera L.) are one of the largest fruit crop in Iran with annual production of 2.5 million metric tons. Grape pomace (GP) is a by-product of grape processing for ethanol, fruit juice and vinegar production and including stems, skins, seeds and peels and these residues are about 20-25% of the weight of the original grape. Considerable production of this by-product encourages animal nutritionists to study its nutritive value. It has shown that GP has about 8-13 % crude protein (CP), 6.2-8.4 % ether extract (EE) and 22.3-36.8 % crude fiber (CF) and 2642.19 kcal/kg apparent metabolizable energy (AME). Grape skins and seeds are rich sources of flavonoids. Studies have shown flavonoids have the capacity to act as powerful antioxidants by scavenging free radicals and terminating oxidative reactions. Also, phenolic component of grapes have shown inhibitory effect on bacteria. It was reported that inclusion of up to 10% GP in diets did not adversely affect broiler chickens’ performance and improved their antioxidant and immune responses.

Two independent experiments were conducted to determine the nutritional value and metabolizable energy of GP and study its effect on performance of broiler chicken. In the first experiment, AOAC method (3) was used for determination of proximate analysis of GP. Forced feeding method was used for determination of GP metabolizable energy. In the second experiment, a total of 450, one day old broiler chicks (Ross -308 strain) were used in a completely randomized design with six treatments, five replicates and 15 birds per replicate. Experimental treatments were the levels of 0 (control, basal diet, based on corn and soybean meal), 3, 6, 9, 12, and 15 % of GP included to basal diet. The diets were in mash form and formulated according to Ross -308 strain recommendations. Feed and water were provided ad libitum during the experiment. All broilers fed same diet in stater period (1-10 d of age) and turned to experimental diets from day 11. Feed intake (FI), body weight gain (BWG) and feed conversion ratio (FCR) of birds in each pen was recorded weekly and calculated for grower (11-24 d), finisher 1 (25–39 d), finisher 2 (40-49 d)  and total periods (11-49 d) for each bird. On day 49, one chick per replicate was slaughtered after 5 hours starvation and carcass characteristics were determined. At the end of experiment (49 d), blood samples were collected from one bird per replicate to determine blood biochemical characteristics.

 The results of this experiment showed that the GP contains about 7.13% CP, 4.92 % EE, 26.85 % CF and 5.86 % ash. Its gross energy and different terms of metabolizable energy such as AME, AMEn, TME and TMEn were 3371.75, 2223.58, 2221.04, 1527.63 and 1526.13 kcal/kg DM respectively. In biological part of experiment, and in total period, broiler BWG was decreased and FCR was increased when higher levels of GP (12 and 15%) were added to their diets in comparison with control. It was reported that GP contains high level of fiber and polymeric polyphenols as procyanidins could be bound and precipitated both dietary and endogenous proteins, and negatively affected poultry performance. Also, it was reported that GP tannins have adverse effects on nutrient utilization, and are toxic at high intake levels, due to their ability to bind proteins, minerals and carbohydrates. Relative weight of abdominal fat was decreased when high level of (15 %) GP used in broiler diet (P<0.05). The reduction in relative weight of thighs and abdominal fat, is probably due to reduced digestion and absorption of nutrients. It was indicated that polyphenols (specially condensed tannin) are able to inhibit a range of enzymes including α-amylase, α-glucosidase, lipase and trypsin activity, therefore the digestion of charbohydrate, lipid and protein were adversely affected. Blood serum concentration of triglyceride, cholesterol and HDL were decreased and LDL concentration was increased when GP levels were increased in broiler diets (P<0.05). The mechanism by which dietary GP supplements affect the concentrations of plasma lipids is not fully understood. However, it was showed that herbs and herbal products induce hypocholesterolemic effects by reducing the activity of 3-hydroxy-3-methylglutaryl-CoA reductase, the rate limiting enzyme in cholesterol synthesis.

In conclusion, the results of the present experiment shows that the crude fiber content of grape pomace is high and its crude protein content is low. Due to the high level of fiber content of grape pomace, its metabolizable energy is relatively low (1527.63 kcal/kg DM). Inclusion of up to 9% grape pomace in broiler diets had no negative effect on feed conversion ratio. Although, broiler performance, was depressed by dietary inclusion in higher levels.