Seventy two New Zealand White rabbits (NZW) at 25 days of age were used to study the effect of of different dietary starch and protein levels on productive performance, nutrients digestibility coefficients, carcass characteristics, digestive tract measurements, blood constituents, enzymes activity and economical evaluation. The rabbits were fed on six experimental diets containing 3 levels of starch {16 (LS), 19 (MS) and 22% (HS)} and 2 levels of protein {14 (LP) and 16% (OP)} in a factorial arrangement design. The results obtained are summarized as follows:
- Best results for live body weight (LBW) were obtained for rabbits fed 16% starch and 14% protein diet at the end of growth period (81 days of age). Decreasing of dietary starch and protein levels had a positive effect on average daily body weight gain (DBWG) in overall growth period (25-81 d.). Daily feed consumption (DFC) was affected by different levels of starch, but no protein level. Feed conversion ratio (FCR) was improved at moderate dietary starch and low dietary protein levels. Mortality rate of growing rabbits improved due to decreasing dietary protein levels. However, dietary starch levels had no effect.
- Rabbits fed low levels of starch and protein in their rations significantly increased DM, OM, CP, NFE, starch and sugar digestibility coefficients and nutritive values (TDN and DCP). Neither dietary starch nor protein levels had impact on CF, neutral detergent fiber (NDF), acid detergent fiber (ADF) and EE digestibility.
- There were not significant effects of starch and protein levels on dressing percentage, hot carcass weights (%), blood total protein, albumin, globulin, albumin/globulin ratio, liver activity enzymes (GOT and GPT). While, high starch level in the diet increased significantly liver weight (%) regardless of protein content.
- Blood glucose, triglycerides and total protein content, amylase and protease enzymes activity in the stomach, ileum and cecum were significantly increased, while degree of pH for stomach, ileum and cecum contents was decreased by decreasing starch and protein levels in the diet. In addition, non-significant was observed in the cellulase and carboxymethylcellulase as affected by the different levels of protein and starch in all segents of the digestive tract. The results show that, total VFAs in the cecum and blood were high with 16% starch and 14% protein.
- Economic efficiency and performance index were improved for rabbits fed (MS-LP) diet. However, production efficiency factor was improved for rabbits fed (LS-LP) diet. In growing rabbits, it was concluded that high correlation exists between dietary starch and protein levels which was reflected on productive performance, digestibility coefficients, digestive tract measurements and economic efficiency.