Researcher 2010;2(9) Effect Of Partial Replacement Of Berseem Hay By Ensiled And Dried Sugar Beet Tops On Performance Of Growing Rabbits Gaafar, H.M.A.; A.I.A.Abd El-Lateif and Salwa B. Abd El-Hady Animal Production Research Institute, Agricultural Research Center, Dokki, Egypt. Email: dr.gaafar@hotmail.com ABSTRACT: Two experiments were done to study the effect of partial replacement of berseem hay by ensiled and dried sugar beet tops on the performance of growing rabbits. In the first one, 8 mature male NZW rabbits with an average body weight of 2.5 kg and 8 months old were used to determine digestibility coefficients and nutritive values of berseem hay (BH), ensiled sugar beet tops (SBTS) and dried sugar beet tops (SBTH). In the second one, 50 NZW growing rabbits of 60 days of age were used in a complete randomized design experiment with five treatments. The first group fed commercial rabbit diet including 40% BH (control diet), while in the other groups 50 or 100% of BH was replaced by SBTS and SBTH throughout the 70 days of experiment. Results of the first experiment showed that the contents of OM and CF were lower and NFE and ash content were higher in SBTS and SBTH compared with of BH. While, CP was higher in SBTS and lower in SBTH than that of BH. The digestibility coefficients of DM, OM, CF, EE and NFE were significantly higher (P<0.05) for both SBTS and SBTH compared with BH. However, BH had significantly (P<0.05) the highest TDN and DE values followed by SBTS, while SBTH had the lowest values. While, CP digestibility and DCP value of SBTS were significantly higher (P<0.05) than that of BH and SBTH. In the second experiment showed that calculated composition was nearly similar for the different diets except OM and CF decreased and ash increased in diets contained SBTS and SBTH compared with commercial diet. Diet contained 100% SBTS showed significantly (P<0.05) the highest digestibility coefficients of DM, OM, CP, EE and NFE and DCP value. While, commercial diet revealed the highest CF digestibility and TDN and DE values. Rabbits fed 100% SBTS diet had the highest TVFA's and NH 3 -N concentrations and the lowest pH value. Rabbits fed 100% SBTS diet showed significantly (P<0.05) the highest final body weight, total and daily weight gain and the lowest average daily and total DM intake and DM/kg gain, however, those fed commercial diet had the opposite trend. Rabbits fed commercial diet showed significantly (P<0.05) the highest feed cost and feed cost/kg gain, however, rabbits fed 100% SBTS diet showed significantly (P<0.05) the highest total and net revenue and net revenue improvement. Rabbits fed 100% SBTS showed significantly (P<0.05) the highest slaughter weight, carcass weight, dressing percentage, meat weight and percentage and the contents of CP, EE and ash and lowest DM content in meat, but, those fed commercial diet had the opposite trend. [Researcher. 2010;2(9):10-15]. (ISSN: 1553- 9865). Key words: NZW rabbits, SBTS, SBTH, digestibility, body weight gain, feed conversion, economic efficiency, carcass traits. INTRODUCTION It is well that there is a serious shortage in the available feedstuffs for farm animal feeding. There are animal nutritionists are trying every available source of unconventional and/ or agricultural by-product to cover at least a part of this shortage. Poor economic conditions in many tropical countries and associated increase in the shortage of animal protein has turned attention to rabbit production as a ready solution to the problem. This is in view of the rabbit's fast growth and short generation interval. The problem for most producers however, is the high cost of concentrates feed for the rabbits. This has necessitated the need to seek for alternative feed sources in forages. This is especially so because of the greater availability of forages and ability of rabbits to convert forage into meat for human consumption. The high cost of feed has resulted in the search for cheaper ways of producing rabbits. Use of forage and byproducts of agriculture and food processing to substitute concentrate feed may be an alternative means of reducing the high cost of production associated with all concentrate feeding systems (Iyeghe-Erakpotobor et al., 2006). In Egypt, about 168 thousand feddan (feddan = 0.42 hectare) were cultivated in year 2007 with sugar beet. Accordingly, large quantities of sugar beet tops are produced as an agricultural by- product after harvesting the sugar beet crops, which represented about 12.5 tons per feddan (Central Agency for Public Mobilization and Statistics, 2007). Sugar beet tops can be used in the diet of rabbits up to 10%, replacing part of the clover hay (Tag El-Din et al., 2000). Sugar beet tops as hay or silage could be successfully used for growing rabbits 10