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چکیده
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The objective of this study was to investigate the effects of milk allowances equal to 526 g/d as moderate (MOD) versus 790 g/d milk DM as high (HI) and starter diets containing 18% and 23% crude protein (CP) on growth performance, blood metabolites, and purine derivatives (PD) excretion in the urine of dairy calves. A total of 52 female Holstein dairy calves (40.8 kg body weight) were randomly assigned to the experimental diets. The treatments were (1) calves fed moderate milk and 18% CP starter diets (MOD-18CP); (2) the MOD and 23% CP starter diets (MOD-23CP); (3) calves fed high milk and 18% CP starter diets (HI-18CP); (4) calves fed HI and 23% CP starter diets (HI-23CP). Calves had free access to a starter feed and water and were weaned on day 53 but remained in the study until day 73. Urine samples were collected during the preweaning period (for 6 consecutive days between days 35 and 40) and postweaning period (for 6 consecutive days between days 65 and 70) to investigate urinary excretion of PD. Starter feed intake, β-Hydroxybutyrate (BHB), and blood urea concentrations were reduced; however, average daily gain (ADG) and blood glucose levels increased in calves fed HI before weaning compared to MOD. During the preweaning period, high milk feeding increased total urinary PD excretion but decreased it after weaning. The 23CP diet resulted in higher feed intake and ADG before weaning and higher excretion of allantoin and total excretion of PD compared to the 18CP diet. The HI-23CP treatment resulted in the greatest withers and hip heights at weaning and final measurement, as well as the highest preweaning blood insulin concentrations. In terms of rumen development, MOD-23CP showed the greatest benefits based on starter intake, blood BHB concentration, and urinary excretion of PD. Based on the higher urinary excretion of PD which was found in HI-fed calves before weaning, it is possible that milk feeding overestimates estimated microbial yield. The results sugges
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