Abstract—The aim of this study was to estimate the digestibility of the fruit internal skin of different varieties of hazelnuts to propose hazelnut fruit skin as an alternative feed source as roughage in ruminant nutrition. In 2015, the fruit internal skins of three different varieties of round hazelnuts (RH), pointed hazelnuts (PH) and almond hazelnuts (AH) were obtained from hazelnut processing factory then their crude nutrients analysis were carried out. Organic matter digestibility (OMD) and metabolisable energy (ME) values of hazelnut fruit skins were estimated from gas measured by in vitro gas production method. Their antioxidant activities were determined by spectrophotometric method. Crude nutrient values of three different varieties were; organic matter (OM): 87.83, 87.81 and 87.78%), crude protein (CP): 5.97, 5.93 and 5.89%, neutral detergent fiber (NDF): 30.30, 30.29 and 30.29%, acid detergent fiber (ADF): 48.68, 48.67 and 48.66% and acid detergent lignin (ADL): 25.43, 25.43 and 25.39% respectively. OMD from 24 h incubation time of RH, PH and AH were 22.04, 22.46 and 22.74%; ME GP values were 3.69, 3.75 and 3.79 MJ/kg DM; and antioxidant activity values were 94.60, 94.54 and 94.52 IC 50 mg/mL respectively. The fruit internal skin of different varieties of hazelnuts may be considered as an alternative roughage for ruminant nutrition regarding to their crude and digestible nutritive values. Moreover, hazelnut fruit skin has a rich antioxidant content so it may be used as a feed additive for both ruminant and non-ruminant animals. Keywords—Antioxidant activity, hazelnut fruit skin, metabolizable energy, organic matter digestibility. I. INTRODUCTION HE world hazelnut production shows fluctuations depending on climatic conditions. Turkey is a leading country in hazelnut production; an average production is around 650.000 t/year which covers approximately 75-80% of total world production. The remaining 20% of hazelnut production is shared by Italy, USA, Azerbaijan, Georgia and Spain [1]. Turkey is producing 16 different hazelnut varieties in Giresun, Ordu, Trabzon, Rize, Artvin, Sinop, Samsun, Kastomonu, Bartın, Kocaeli, Duzce, Sakarya and Zonguldak provinces which are located in Black Sea Region of Turkey [1]. Hazelnut produced in Turkey is generally classified in three main groups according to fruits shape and features: RH, PH and AH. Hazelnut hull or hazelnut fruit internal skin is a by-product or waste obtained during hazelnut processing in factories [1]. Hazelnut fruit internal skin is obtained as waste in the amount N. Cetinkaya is with Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, Ondokuz Mayis University, 55139, Samsun, Turkey (phone: +905065816351; fax: + 903624576922; e-mail: nurcanc@omu.edu.tr). Y.S. Kuleyin is with Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, Ondokuz Mayis University, 55139, Samsun, Turkey (e-mail: serhatkuleyin@gmail.com). of 4-5% of the total processed hazelnuts according to data received from the hazelnut processing factory. The amount of this waste is around 26.000-32.500 t/year. Hazelnut has also been consumed by people without removing internal skin of hazelnut which indicates that internal skin of fruit is edible [2]. The crude nutritive value of a ruminant feedstuffs is determined by chemical analysis [3]. In vitro gas production technique is useful to evaluate the nutritive value of feedstuffs in which produced gas is regarded as an indicator of carbohydrates degradation [4]. Sallam suggested that gas volume is a good parameter from which to predict digestibility and microbial protein synthesis of the substrate by rumen microorganisms in the in vitro system [5]. OMD and ME values of feedstuffs have mostly been determined by using in vitro gas production method [4], [6], [7]. Nowadays, natural antioxidant sources as health promoting nutrients are gaining great importance in human nutrition [8]. There are several extraction procedures and determination methods for evaluation of the total antioxidant activity of plants [9], [10]. 2,2 diphenyl-1-picrylhydrazyl radical (DPPH) method has widely been used due to its simplicity and its simple reaction system which involves only direct reaction between radical and antioxidant [11]. Since synthetic antioxidants may be toxic and carcinogenic which they have also been well demonstrated with many studies, limitations or prohibitions on their use have been put in the application [12]-[14]. These consequences are directed animal nutrition scientists to search safe and natural resources. The objective of the present study was to estimate the digestibility and antioxidant activity of the fruit internal skin of different varieties of hazelnut to propose hazelnut fruit skin as an alternative feed source as roughage in ruminant nutrition. II. MATERIAL AND METHODS A. Animal Material The rumen fluid was collected from slaughtered cattle in Florya Meat Joint-Stock Company, Samsun, Turkey. Collected rumen fluids were immediately transferred from Florya slaughterhouse to the laboratory approximately in 5 minutes. B. Feed Material In 2015, the fruit internal skins of three different varieties of RH, PH and AH were obtained four times from hazelnut processing factories. C. Experimental Procedure Chemical analysis, in vitro gas production experiment and total antioxidant activity analysis were carried out with quartet Evaluation of Hazelnut Hulls as an Alternative Forage Resource for Ruminant Animals N. Cetinkaya, Y. S. Kuleyin T World Academy of Science, Engineering and Technology International Journal of Agricultural and Biosystems Engineering Vol:10, No:5, 2016 319 International Scholarly and Scientific Research & Innovation 10(5) 2016 scholar.waset.org/1307-6892/10004851 International Science Index, Agricultural and Biosystems Engineering Vol:10, No:5, 2016 waset.org/Publication/10004851