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Abstract Summary The current work was conducted to test the effect of different dietary energy and protein levels on growth performance, carcass traits, blood parameters, cecal contents, digestion coefficient of nutrients, nitrogen balance and economical efficiency of growing rabbits. Sixty male (45 days old) New Zealand White rabbits were obtained from a local commercial source and divided randomly to five groups, twelve rabbits in each. Rabbits were housed individually in batteries (galvanized wire cages that allowed separation of feces and urine) provided with feeders to provide free access to feed and automatic drinkers (nipple waterers), fresh and clean water ad libitum. The experiment lasted for 10 week. Control diet was designed according to NRC (1977) to meet the nutritional requirements of growing rabbits, and had a classical energy and protein content (16% CP and 2500 kcal DE / kg diet). High and low energy diets (3007&2059 kcal DE / kg diet) were formulated to contain about 500 kcal DE / kg diet higher and lower, respectively than control. While high and low protein diets (20&12.15 % CP) were formulated to contain 4% CP higher and lower, respectively than control. Growth performance including body weight, weight gain, feed intake and feed conversion indices was calculated. Mortality rate was recorded during the experiment. Three randomly selected rabbits from each group were slaughtered at the end of the experimental period for measurement of carcass traits, blood parameters, cecal parameters and for chemical composition of meat. At the end of the experiment, three rabbits from each group were kept to be used in the digestibility experiment. The feed intake was recorded individually and total faecal excretion was collected daily in the same individual bag and stored at - 18°C or less. For each rabbit, the apparent digestibility coefficient of different nutrients was calculated. Urine was collected daily from each rabbit during the digestibility trial and nitrogen concentration was determined using Kjeldahl apparatus for determination of nitrogen balance. Monetary value was calculated and experimental crude data were subjected to statistical analysis. The following results were obtained: 1. The group of rabbits fed high protein diet recorded the best body weight and weight gain. 2. The highest feed intake values were recorded by group of rabbits fed high protein diet followed by rabbits fed high energy diet then control one. 3. The best feed conversion was recorded by high protein diet and the worst feed conversion was recorded by low protein one. Groups of rabbits fed control diet and high energy one recorded nearly equal feed conversion ratio. 4. The highest dressing % was recorded by high protein group followed by high energy one, while the lowest dressing% was recorded by low protein group followed by low energy one. 5. Regarding chemical composition of meat, no significant differences were detected among groups of rabbits in DM content of either the breast or the thigh meat. While there were significant differences in CP, EE and ash in the breast and thigh of meat between the different groups. 6. There were significant differences in the cecal parameters between the different groups. Regarding pH value, the highest value was recorded by high protein diet. While the highest value of total volatile fatty acids and highest number of total bacterial count were recorded by high energy diet. 7. No significant differences were detected in serum total protein, albumin, globulin, cholesterol and glucose. While there were significant differences only in the serum urea and serum triglycerides between the different groups. 8. There were significant differences in digestion coefficients of DM, OM, CP, CF, EE, NFE and Ash between different groups due to different levels of dietary energy and protein. 9. There were significant differences between different groups in nitrogen intake, faecal nitrogen, urinary nitrogen, total excreted nitrogen, absorbed nitrogen, absorbed nitrogen percentage, retained nitrogen, nitrogen retention of intake % and nitrogen retention of absorbed %. 10. Rabbits fed diets containing high energy and low protein levels, respectively had no mortality during the whole experimental period, while control, low energy and high protein diets were accompanied by 8.33, 16.67 and 16.67 % of mortality, respectively. 11. The best economical value was recorded by the group fed high protein diet followed by the group fed high energy diet. |