This study was conducted to evaluate the effects of different diet structure and protein levels on the growth performance and biometric measurements of male Holstein calves during starter period (from 1 to 60 days of age). In this experiment, 56 Holstein male calves were randomly divided into a 4 × 2 factorial experimental design with 4 levels of diet structure (grinding, nutty, pelleted and grain) and 2 levels of protein (22 and 24%) in a completely randomized design with 8 treatments and 7 replications. The measured traits were: body weight gain, average daily feed intake, body temperature, biometric measurements (height, chest girth, length and width), blood parameters (glucose and beta hydroxyl butyrate), fecal score and rumen fatty acids. The results showed that average feed intake, body weight and glucose and beta-hydroxyl butyric acid concentration in the blood at two levels of protein, had no differences. But the structure of feed mostly influenced traits. Nutty diet showed higher feed intake and body weight. The grinding diet increased volatile fatty acids in rumen of valves. The structure of diet affected biometric measurements, grain and nutty diets increased the body height and chest girth. The fecal score and concentration of volatile fatty acids was variable in different diet structures but the difference was not meaningful. In terms of body temperature, nutty and pelleted diets containing 22% protein increased body temperature spite of the grinding diet that decreased the temperature up to 0.25 ˚C, it is mentioned that changing the structure of diet may be a useful way for controlling heat stress. The findings of this study indicated that nutty starter increased feed intake and significant weight gain compared to grinding, grain and pelleted diets, it is suggested to use nutty starter to increase the growth performance of the production period of calves. تفاصيل المقالة