MATERIALS AND METHODS

Location
This study was carried out from April to July, 2006 at the Delta State University Teaching and Research Farm, Asaba Campus, Asaba in Nigeria (6°14`N and 6° 49`E).

Test Ingredient and Experimental Diets
Fresh, young Gliricidia sepium leaves were harvested, dried under shade for several days, milled to obtain Gliricidia Leaf Meal (GLM) and incorporated into five rabbit diets in which soybean meal was replaced with GLM at 0% (control), 5, 10, 15 and 20%. The diets (Table 1) were formulated to contain approximately 17% crude protein and 2340 kcal kg^-1 Metabolizable Energy (ME). Dry samples of GLM and the experimental diets were analysed for their proximate composition using standard procedures by AOAC (1990).

Animals and Their Management
Twenty-five Dutch rabbits of mixed sexes, aged 5-6 weeks, were weighed individually and randomly assigned to the five dietary treatments with 5 rabbits per treatment. Each rabbit was regarded as a replicate. The rabbits were housed singly in cages in two rows of hutches. Each of the cages measured approximately 70x60x54 cm. The hutches were raised approximately 80 cm from the floor in a house with 1 m high dwarf walls, which permitted sufficient ventilation. The experimental diets and clean drinking water were provided the rabbits ad libitum for 8 weeks.

Table 1:	Composition of the experimental diets (g kg-1 DM)
GLM = Gliricidia Leaf Meal

Data Collected
At the end of eight weeks, two rabbits chosen at random from each treatment group were starved overnight, stunned, sacrificed by cervical dislocation and dissected in accordance with guidelines of the World Rabbit Science Association (WRSA). The carcasses were then eviscerated and the vital internal organs carefully removed and weighed and expressed as percentages of the dressed weight.

Data on body weight, feed intake, feed conversion and costs and the weights of the major internal organs of the rabbits were taken.

Data Analyses
Data collected were analysed by the one-way analysis of variance procedure using the IRRISTAT for Windows (Version 5.0.) computer software. Significantly different means were separated by the Duncan`s Multiple Range Test procedure (Duncan, 1955).

RESULTS AND DISCUSSION

The proximate composition of Gliricidia Leaf Meal (GLM) is presented in Table 2. The values obtained fell within the range of nutrients earlier reported for Gliricidia sepium in the tropics by Göhl (1981), Chadhokar (1982) and Adejumo and Ademosun (1983). Its protein content was, however, lower than those reported for the forage by Herbert (1998) and Ifut and Inyang (2007) (19.30 and 25.63%, respectively) while its crude fibre and ash contents were higher than those reported by Herbert (1998) (19.00%) due, perhaps, to differences in edaphic characteristics to which the plants were exposed and to possible variations in plant age, processing procedures and climate.

Table 3 shows the energy and proximate composition of the experimental diets, while the performance characteristics and feed costs of the rabbits fed the experimental diets are presented in Table 4. The energy and proximate values of the diets fell within recommended ranges of nutrients required by rabbits in the tropics for optimum growth and performance (Aduku and Olukosi, 1990) (12-17% Crude Protein; 20-25% fat; 10-20% Crude Fibre; 2.39-2.50 kcal g^-1 Digestible Energy).

Although body weight gains and feed intake tended to decline as the level of GLM in the diets was increased, which is a reflection of the increasing levels of fibre in the diets, the differences were non-significant. The body weight gains observed in this study are in agreement with the reports of studies on rabbits in Nigeria by Omole (1982) and Aduku et al. (1988) and are an indication that the use of up to 20% GLM in rabbit diets does not adversely reduce tissue synthesis.

Table 2:	Energy and proximate composition of gliricidia leaf meal (GLM)

Table 3:	: Energy and proximate composition of the experimental diets

Table 4:	Performance and feed costs of rabbits fed the experimental diets Mean ± SEM)
Within each row, means with the same superscripts are not significantly different

Table 5:	Organ weights of rabbits fed the experimental diets (Mean ± SEM)
Within each row, means with the same superscripts are not significantly different

Feed conversion ratio, though numerically higher for the 10, 15 and 20% GLM diets when compared to the control treatment (Table 4), was not significantly affected by dietary treatments.

The economic indices showed significant reductions in cost kg^-1 of feed and in cost kg^-1 body weight gain. This implies that inclusion of GLM at moderate levels of up to 20% can substantially reduce feed costs without significantly reducing feed intake, feed conversion and growth in rabbits.

Changes in the organ weights of the rabbits with variations in the level of dietary GLM are shown in Table 5. Variations in the heart and lung weights with dietary treatments were not significant whereas the kidney and liver weights tended to increase as the proportion of GLM in the diets increased. The weights of some internal organs like the liver and kidney are commonly used in animal feeding experiments as evidences of toxicity (Ahamefule et al., 2006). Bone (1979) reported that increased metabolic rate of the organs in attempt to reduce toxic or anti-nutritional factors in livestock feeds to non-toxic metabolites may cause abnormalities in their weights. Gliricidia leaves contain some anti-nutrient factors such as condensed tannins and cyanide (Chadhokar, 1982; Ahn et al., 1989; Herbert, 1998). This may have accounted for the significantly higher weights of the kidneys and liver of rabbits fed the 15 and 20% GLM diets. Kidney fat weight decreased gradually but significantly as the level of dietary GLM increased thus reflecting the effect of increasing proportions of dietary fiber.

The findings of this study indicate that incorporation of GLM up to 20% level in the diets of weaner rabbits does not significantly reduce tissue synthesis in the rabbits. However, there is significant reduction in the cost of feeding weaner rabbits in the tropics. This probably increases detoxification activities in the liver and kidneys of rabbits when used at levels beyond 10% in rabbit diets (Table 5).