Abstract—This experiment was conducted to investigate the effect of different levels of dietary chromium yeast (Cr-yeast) on thigh meat quality of broiler chicks reared under heat stress condition. Two hundred and forty Ross male chickens in heat stress condition (33±3°C) were allocated to five treatments in a completely randomized design. Treatments were supplemented with 0 (control), 200, 400, 800 and 1200 μg kg-1 Cr in the form of Cr yeast. Twelve chicks from each treatment were slaughtered at 42 d, to evaluate moisture, protein, lipid, pH and lipid oxidation of thigh meat. Protein, moisture, lipid and pH of thigh meat were not affected by supplemental Cr. Thigh meat lipid tended to decrease in broilers received 1200 μg kg-1. Storage time increased lipid oxidation of meat (P<0.01). Lipid oxidation of thigh muscle for two days of storage were affected by supplemental Cr and decreased (P<0.05). Results of this study showed that dietary Cr-yeast supplementation improved the thigh meat quality of broiler chicks in heat stress condition. Keywords—Broiler, Heat stress, Chromium yeast, Thigh meat quality. I. INTRODUCTION EAT stress has long been recognized as having a detrimental effect on broiler production efficiency and meat yield [1,2]. Exposure to high ambient temperatures has been reported to cause undesirable changes in meat characteristics in broilers [3,4,5]. Trivalent Cr is an essential element in the animal body [6] and is involved in carbohydrate, lipid, protein and nucleic acid metabolic functions [7]. Cr is also a cofactor of insulin, promoting insulin activity [8] and enhancing amino acid uptake into muscular cells for protein synthesis [9]. Stress increased urinary excretion of Cr and may exacerbate a marginal Cr deficiency [10,11]. Dietary Cr supplementation has been reported to have a positive effect on meat quality [12,13] and carcass traits of broiler chicks in natural [14,15] or heat stress condition [16]. The aim of this study was to investigate the effects of 1 * Corresponding Author: Majid Toghyani, Department of Animal Science, Islamic Azad University, Khorasgan (Isfahan) Branch, Isfahan, Iran, E-mail: toghiani@hotmail.com 2 Department of Animal Science, Isfahan Agricultural Research Center, Isfahan, Iran. 3 Young Researchers Club, Islamic Azad University- Khorasgan Branch, Isfahan, Iran. different levels of Cr-yeast on the thigh meat quality of broiler chicks in heat stress condition. II. MATERIALS AND METHOD Two hundred and forty one-day-old commercial Ross male chicks were reared under heat stress condition. During the experiment, the mean value of daily temperature in the house was kept 33 ± 3 °C. Birds were randomly allotted by body weight to one of five treatments (four replicate pens of twelve chicks per pen) in a completely randomized design. Broiler chicks were housed in floor pens. Chicks were maintained on a 23 h light and 1 h dark schedule and allowed ad libitum access to experimental diets and water. The dietary treatments consisted of the basal diet supplemented with 0 (control), 200, 400, 800 and 1200 μg kg-1 Cr of diet in the form of Cr yeast (contain 1000 mg/kg Cr). The birds were fed a corn-soybean meal starter diets until 21 d of age followed by a finishing diet from 21 to 42 day. Ingredients and chemical composition of the starter and finisher basal diets are shown in Table 1. The basal diets were formulated to meet or exceed the nutrient requirements of broilers by the National Research Council [17]. Cr contents were 3.45 and 3.96 mg kg -1 in starting and finishing basal diets, respectively, as measured by atomic absorption spectrometer with a graphite furnace (Perkin- Elmer, AAnalyst 600, USA). On day 42 of the trial, three broiler chicks from each pen were selected according to average body weight within the pen following a 12-h fasting, were weighed individually, killed and eviscerated (abdominal fat pad, liver, intestines, proventriculus, gall bladder, spleen, oesophagus and full crop). Some thigh muscles were immediately stored at −20 °C for assessing crude fat and crude protein, and others were stored individually in plastic bags at 4 °C in refrigerator for 2 and 6 days for analysis of meat lipid oxidation. In order to determine the moisture content, the sample (5 g) was dried at 105°C for 24 h [18]. Intramuscular fat content was determined according to the AOAC (1990) (Soxhlet procedure). The sample was dehydrated (2 g) and subjected for 75 min to a 40–60°C petroleum ether circuit at 80 ºC [18]. The crud protein was determined following the Kjeldahl method. At 12 h after slaughter the thigh muscle pH was measured with a Knick digital pH meter (Broadly Corp., Santa Effect of Dietary Chromium Yeast on Thigh Meat Quality of Broiler Chicks in Heat Stress Condition Majid Toghyani 1 , Abbas Ali Gheisari 2 , Ali Khodami 3 , Mehdi Toghyani 3 , Mohammad Mohammadrezaei 3 and Ramin Bahadoran 1 H International Journal of Biological and Life Sciences 6:4 2010 196