Effect of Dietary Olive Leaves (Olea europaea L.) Extracts and/or α-tocopheryl Acetate Supplementation on Performance and Intestinal Morphology of Chickens From 7 to 28 Days of Age

Antibiotic feed additives have long been used as growth promoters (10). However, consumers and health authorities increasingly dictate that the use of synthetic food additives should be phased out and, where possible, only natural products should be used. Hence, alternatives from natural sources with potential antioxidant activity are investigated (16). Olive leaves are a good source of several antioxidants including oleuropeoside compounds such as oleuropein and verbascoside, and flavonoid compounds such as luteolin, luteolin-7-glucoside, apigenin-7-glucoside, diosmetin, diosmetin-7-glucoside, rutin and catechin, and simple phenolic compounds such as tyrosol, hydroxytyrosol, vanillin, vanillic acid and caffeic acid. Oleuropein, the most prominent compound, may reach concentrations of 60 - 90 mg/g dried leaves (8). Most of these phenolic compounds have been shown to possess substantial antimicrobial and antioxidant activities in vitro. However, in vivo investigations on the antioxidant and antimicrobial activities of olive leaves as a dietary supplement to food producing animals have not been conducted (33). The present study was designed to evaluate the effects of dietary α-tocopheryl acetate, olive leaf powder (OLP) and olive leaf extract (OLE) as feed additives on the growth performance and small intestinal morphology of male broilers. The experimental protocol was approved by the Animal Care Committee of the Ferdowsi University of Mashhad, Iran. The chickens (120 Ross 308 male birds) were placed at one day old in a single colony in a floor pen containing fresh wood shavings to a depth of 10 cm, and all were fed on a starter ration. At 7 d old, 6 replicate cages containing four chicks selected at random were assigned to each of 5 dietary treatments using a completely randomized design, giving a total of 30 experimental cages. The study was completed at 28 d of age. Dietary treatments included a negative control group (NC) fed a corn soybean meal based diet without feed additive supplementation, a positive control (PC) group fed a diet with 250 mg of α-tocopheryl acetate/kg, a test group OLP fed with 10 g of olive leaf powder/kg, and two test groups remaining OLE fed with 120 or 240 mg of olive leaf extract/kg. The birds were provided with one hour of darkness following a period of 23 h light, from the start to the finish of the study. Each cage was provided with a single feed trough and nipple line, with three nipples per cage, to provide ad libitum access to feed and water. On day 7, 14, 21 and 28, body weight and feed intake were measured after a 6-h fast to determine average daily gain, average daily feed intake, and feed conversion. On d 28, one bird per cage randomly selected and killed to determine small intestinal morphology and lymphoid organ weights. Sample sections (2. 5 cm in length) were taken from the middle region of the jejunum. The tissues were stained for measurement of villus length, villus width, crypt depth and thickness of muscle layer. The General Linear Models of SAS (17) were used to analyze all the data. Chicks fed with diet containing 240 mg of OLE/kg had the highest average daily gain. ِِDressing percentage and the percentage of breast muscle in the carcass were significantly higher for chicks fed diets supplemented with OLP and OLE compared with those fed NC diet. Similar to our results, Chinese herbal medicine supplementation enhanced BW gain of female broiler chicks at 7 to 21 day of age, when compared with the non-supplemented group. There were no significant differences in daily feed intake between the different treatments from 7 to 21 day of age (17). Also Christaki et al. (12) found that laying Japanese quails diet supplementation with olive leaves (10 g/kg or 20 g/kg) resulted in a tendency (p = 0. 054) for higher egg production percentage. The benefits of dietary olive leaves are possibly due to the presence of polyphenols and particularly oleuropein, the main active component in this material (12). The inclusion of OLP and/or OLE in diet significantly decreased the relative lengths of duodenum. Villus height, crypt depth, epithelial thickness and surface area for absorption villi were significantly increased in diets containing OLP and/or OLE compared with NC fed birds. Intestinal morphology can reveal some information on gut health. A shortening of the villus reflects villus atrophy and a decrease in surface area for nutrient absorption. The crypt can be regarded as the villus factory, and a large crypt indicates fast tissue turnover and a high demand for new tissue (21). The gastro protective potential of OLE is probably related to its ability to maintain the cell membrane integrity, by its ant lipid per oxidative activity that protects the gastric mucosa against oxidative damage and by its ability to strengthen the mucosal barrier, the first line of defense against exogenous damaging agents (14). The use of OLP and/or OLE as feed additives in diet may affect chick performance and gut health. Although, it seems that further experiments are needed to elucidate the mechanisms underlying the enhanced growth of chickens by OLP and/or OLE.