Natural additive (aqueous extract) in rabbit diet: effects on performance and oxidative and innate immunological status

Abstract - Natural antioxidants are receiving increased attention in human and animal nutrition because of their association with food quality characteristics and immune responses 1, 2. Aromatic plants and their essential oils are good sources of natural antioxidants, such as phenolic compounds, e.g., eugenol, thymol, carvacrol 3. Plant such as Oregano (Origanum vulgare) has attracted great interest as its essential oil is rich in the monoterpenes, thymol and carvacrol, which exhibit good antioxidant and antimicrobial activities in vitro and in vivo, together with stimulating animal digestion 4. The present study aimed to evaluate the effect of dietary supplementation with an Oregano aqueous extract on performance and oxidative and innate immunological status of growing rabbits. The experimental protocol was planned according to University of Perugia Animal Committee guidelines and the trial was carried out at the experimental farm of the Department of Agricultural, Food and Environmental Science (University of Perugia, Italy). At weaning (30 days of age) 240 weaned New Zealand White rabbits of both sexes were randomly allocated to three dietary groups, homogeneous for live weight and gender (40 rabbits/group), and housed in single wire net cages (600 x 250 x 330 mm) until 80 days of age, when they were weighted and slaughtered. The study was replicated with identical experimental designs during two consecutive cycles, for a total of 80 animals/group. Dietary groups were: Standard diet - with no supplementation (S); Standard diet + 150 ppm Vit E - positive control (E); Standard diet + 0.2% oregano (Origanum vulgare) aqueous extract (O). All diets, provided by Mignini&Petrini (Petrignano di Assisi, Perugia, Italy) were isoproteic and isoenergetic and the main ingredients were alfalfa meal, sunflower seed meal, wheat bran, barley and sugar beet pulp. The oregano extract was provided by Phenbiox (Calderara di Reno, Bologna, Italy) after an enzyme-aided extraction from leaves using water as solvent. The extracts were added to the diets by spraying during the mixing of ingredients. Feed and water were available ad libitum. The temperature and lighting schedule in the rabbitry were 15–18 °C and 16L:8D, respectively. In order to calculate the feed conversion ratio (FCR) and average daily gain (ADG), feed consumption were recorded daily and rabbits weight weekly. At the slaughter, blood samples (2 mL for each rabbit) were collected from the marginal ear vein of 30 rabbits/group at 80 day of age and the natural immune responses were evaluated by analyzing lysozyme (Lys), Serum Bactericidal Activity (SBA) and Haemolytic Complement Assay (HCA) in serum 5. The oxidative status was evaluated using commercially available kits (Diacron International Srl, Grosseto, Italy) that evaluates the serum’s ability to oppose the massive oxidative action of a hypochlorous acid (HClO) solution (AOP values) or the reactive oxygen metabolite concentrations (ROMs). The extent of muscle lipid peroxidation of raw Longissimus dorsi muscles (LD) was evaluated by spectrophotometer as reported by some authors 6. Oxidation products were quantified as malondialdehyde equivalents (mg/kg of muscle). Muscles were obtained from eight rabbits/group at 80 days. The data were analyzed by SPSS Dietary treatments significantly affected the live weight (LW) and ADG at the end of the trial; particularly, O fed animals had higher LW (2344 g vs 2296 and 2277 g, respectively; P<0.05) and ADG (30.7 g/d vs 29.7 and 29.2 g/d, respectively; P<0.05) compared to E and S groups; whereas, FCR was not influenced by the experimental diet. The blood oxidative status (AOP and ROMs) did not significantly varied among the different animal groups, however, the oxidative stability (TBARs) of the LD meat for all supplemented diets led to a lower TBARs content compared to the control (S) group. Indeed, the inclusion of extra vitamin E reduced TBARs of LD meat, as did supplementation with oregano extract (0.17 and 0.18 vs 0.24 mg MDA/kg meat, respectively. P<0.05). A better natural immune response was observed in O and E vs S groups which showed significantly higher HCA (74.9 and 69.6 vs 45.4, respectively; P<0.05) and SBA (26.4 and 28.5 vs 15.8, respectively; P< 0.05) values. The HCA assay is very useful for assessing the onset risk of infections or the gravity of ongoing diseases [7]. SBA, in particular, expresses the serum capacity to counteract the GRAM- bacterial growth [8]. This study showed that an adequate phytogenic additive dietary supplementation in growing rabbits can exert a positive effect on productive performance, natural immune responses and give protection against meat lipid oxidation.