MATERIALS AND METHODS

Site of Study
The experiment was conducted in the Rabbitry of the National Animal Production Research Institute (NAPRI), Shika, Nigeria, located in the Northern Guinea Savanna ecological zone. Shika lies between Latitudes 10° 11’ N and Longitude 7° 8’ E, about 650 m above sea level, with an annual rainfall of 1100 mm, spread from April to October. During the study, the mean minimum and maximum temperature ranged between 28 and 36°C. Relative humidity ranged between 60 and 75%.

Animals and Housing
Thirty 15-week old growing crossbred rabbits of average weight 1.5 kg were used. The rabbits were obtained from mating between New Zealand White, California and Chinchilla rabbits. The rabbits were individually housed in metal cages located in a well-ventilated house. The rabbits were treated in accordance with accepted standards for humane treatment of animals.

Experimental Procedure
The treatments comprised of two concentrate diets and three forages in a 2x3 factorial experiment in a completely randomized design. The concentrates were rabbit meal (21% CP) and soybean cheese waste meal (12% CP), while the forages were groundnut haulms, sweet potato vines and soybean forage. Rhodes grass (Chloris gayana) was fed to all the groups. The rabbits were given 50 g of concentrate, 60 g of Rhodes grass and 40 g of forage in separate feeders and allowed to adjust their intake of the feed offered.

Table 1:	Composition of concentrate diets fed to growing rabbits
*Vitamin/mineral premix content per kilogram ration: Vit. A 1251 IU, Vit. D3 2750 IU, Vit. E 151 IU, Vit. K 0.002 g, Vit. B2 0.006 g, Nicotinic acid 0.035, Calcium D-Pantothenate 0.01 mg, Vit. B6 0.0035 g, Vit. B12 0.02 g, Folic acid 0.001 g, Biotin 0.0005 g, Vit. C 0.025 g, Cholin chloride 0.39 g, Zinc bacitracin 0.02 g, Methionine 0.2 g, Avatec (Lasolocid) 0.09 g, Manganese 0.1 g, Iron 0.05 g, Zinc 0.04 g, Copper 0.002 g, Iodine 0.00153 g, Cobalt 0.000225 g, Selenium 0.0001 g.-Naira. 180 = 1 Euro

Table 2:	Proximate composition of concentrate and forages fed to growing rabbits

All the forages were fed as hay. Groundnut, sweet potato forage and Rhodes grass were harvested, dried, chopped and bagged for the study. Soybean forage used was obtained after harvesting and threshing. Composition of the concentrate diets is shown on Table 1 while the proximate composition of concentrates and forages is shown on Table 2.

Concentrates, grass and forages were weighed and fed separately in flat bottom earthen pots in the morning (08.00 h). Intake of the concentrate meal, grass and forage were monitored daily. Feed and forage leftovers and or wastage were weighed daily before feeding. Water was supplied daily in earthen pots. The rabbits were treated routinely against ecto- and endo-parasites using ivomec (Ivomectin) and coccidiostat (Amprolium). Weekly weights of rabbits were taken during the study. Parameters determined were feed intake, weight gain, feed conversion efficiency (weight gain/feed intake), feed cost and feed cost kg^-1 gain. The study lasted six weeks.

Digestibility Study
Digestibility study was conducted using eighteen rabbits at 19- and 21-weeks old corresponding with the fourth and sixth weeks of the study for four days. Fecal samples were collected daily. Samples collected were stored at -20°C in a deep freezer immediately after collection. At the end of each collection period, the samples were bulked for each animal for proximate analysis according to AOAC (1980) procedures. Nutrient composition of the concentrates, chloris, groundnut haulms, sweet potato forage and soybean forage was also done according to AOAC (1980). Parameters determined were feed and nutrient intake and nutrient digestibility coefficients of rabbits.

Data Analysis
Data collected were subjected to analysis of variance using general linear model procedure (PROC GLM), for factorial experiments in a completely randomized design for the growth and digestibility studies. Effect of age of rabbits on nutrient digestibility was also considered using general linear model procedure. Pair-wise difference (pdiff) method was used to separate significant means (SAS, 1987).

RESULTS

Rabbits on soybean cheese waste meal consumed 6% more (p<0.05) concentrate than rabbit meal (Table 3). Grass, forage and total feed intake, weight gain and feed conversion efficiency were similar for the two concentrate meals. Feed cost and cost kg^-1 gain were 27 and 37% lower (p<0.05) for soybean cheese waste meal than rabbit meal. Nutrient intake and digestibility of rabbits fed the concentrate types is shown on Table 3. Dry matter and nitrogen free extract intakes were similar for the two concentrates. Intake of ash, crude fibre and crude protein were higher (p<0.05) for rabbits fed rabbit meal than soybean cheese waste meal. Ether extract intake was however, higher (p<0.05) for soybean cheese waste meal than rabbit meal. Dry matter, ash, ether extract and nitrogen free extract digestibility were higher (p<0.05) for rabbits fed soybean cheese waste meal than rabbit meal. Crude fibre and crude protein digestibility were similar for the two concentrate diets.

Concentrate and total feed intake were similar for all the forage types (Table 4). Grass intake was 9% lower (p<0.05) for groundnut haulms fed rabbits than sweet potato forage fed rabbits. Forage intake was 6-7% higher (p<0.05) for groundnut haulms than sweet potato and soybean forages. Feed cost was also similar for all the forages while feed cost kg^-1 gain was 18-29% higher for sweet potato forage than groundnut haulms and soybean forage.

Dry matter, crude fibre, crude protein and nitrogen free extractives intake (Table 5) were similar for rabbits fed the forages. Ash intake was higher (p<0.05) for groundnut haulms, while ether extract intake was higher (p<0.05) for sweet potato forage than the other forages. Dry matter, ether extract, crude fibre and nitrogen free extractives digestibility were similar for all the forages. Crude protein digestibility was higher (p<0.05) in soybean forage than sweet potato forage.

Table 3:	Effect of concentrate type on performance, nutrient intake and digestibility of growing rabbits
Means with different superscript along rows are significantly different (p<0.05, *p<0.01); FCE: Feed Conversion Efficiency; SE: Standard Error; 180 = 1 Euro

Table 4:	Effect of forage type on performance of growing rabbits
Means with different superscript along rows are significantly different (p<0.05); FCE: Feed Conversion Efficiency; SE: Standard Error; 180 = 1 Euro

Table 5:	Effect of forage type on nutrient intake and digestibility of growing rabbits
Means with different superscript along rows are significantly different (p<0.05); SE: Standard Error

Table 6:	Effect of concentrate and forage type on performance of growing rabbits
Means with different superscript along rows are significantly different (p<0.05); SE: Standard Error; -Naira. 180 = 1 Euro

Interaction between concentrate and forage was observed in forage intake and feed cost. Concentrate intake was 8-10% lower (p<0.05) for rabbit meal groundnut haulms and rabbit meal soybean forage than the other treatment groups (Table 6). Grass intake was 4-14% lower (p<0.05) for soybean cheese waste meal groundnut haulms and soybean cheese waste meal soybean forage than the other treatment groups. Forage intake was 7-12% lower (p<0.05) for soybean cheese waste meal sweet potato vines than the other groups. Total feed intake was 8-9% (p<0.5) lower for rabbit meal soybean forage than rabbit meal sweet potato vines and soybean cheese waste meal groundnut haulms groups. Daily weight gain and feed conversion efficiency were similar for all the groups. Feed cost was 27-28% lower (p<0.05) for the soybean cheese waste meal forage groups than the rabbit meal forage groups. Feed cost kg^-1 gain was 34-59% higher (p<0.05) for rabbit meal sweet potato vines group than the other treatments.

Table 7:	Effect of concentrate and forage type on nutrient intake and digestibility of growing rabbits
Means with different superscript along rows are significantly different (p<0.05); SE: Standard Error

Table 8:	Effect of age on nutrient intake and digestibility of growing rabbits fed concentrate and forages
Means with different superscript along rows are significantly different (p<0.05, **p<0.01); SE: Standard Error

There was no interaction between concentrate and forage on nutrient intake and digestibility. Dry matter intake (Table 7) was similar for all the groups. Ash intake was lower for soybean cheese waste meal sweet potato and soybean forage groups than other groups. Ether extract intake was low for rabbit meal forage groups while crude protein and crude fibre intake was low for soybean cheese waste meal forage groups. Dry matter digestibility was higher for soybean cheese waste meal forage groups than rabbit meal forage groups. Ether extract and crude fibre digestibility was similar for all the groups. Crude protein and nitrogen free extract digestibility was lower for rabbit meal sweet potato vines than the other treatment groups.

Nutrient intake was similar for rabbits at 19 and 21 weeks except for ash intake, which was higher (p<0.05) at 19 weeks than 21 weeks (Table 8). Dry matter, crude fibre and nitrogen free extractives digestibility were however, higher (p<0.01) for rabbits at 21 weeks than 19 weeks. Ether extract digestibility (p = 0.07) and crude protein digestibility (p = 0.06) were similar for rabbits at 19 and 21 weeks.

DISCUSSION

Higher intake of soybean cheese waste meal than rabbit meal by rabbits in this study, indicates that soybean cheese waste meal is likely more palatable than rabbit meal. Similar weight gain and feed conversion efficiency observed for the two concentrate meals agrees with the findings of Linga and Lukefahr (2000) who observed that final weight and gross feed conversion was not different for rabbits fed molasses blocks and crumbles diets. Considering the lower protein content of the soybean cheese waste meal compared to rabbit meal, it was expected that the rabbit meal group would perform better in terms of weight gain and feed conversion than the soybean cheese waste meal group. However, this was not the case. Higher digestibility of nutrients by soybean cheese waste meal fed rabbits than the rabbit meal group indicates a high potential of soybean cheese as a feed resource for rabbits.

Higher intake of groundnut haulms than sweet potato and soybean forages by rabbits in this study probably indicates that groundnut haulms was more palatable to rabbits than sweet potato and soybean forages. Weight gains obtained for rabbits fed the forages in this study are similar to those reported by Taiwo et al. (1999) for rabbits fed Tridax procumbens, Centrosema pubescens and Calopogonium phaseloides and Phimmmasan et al. (2004) with Stylosanthes guianensis. For all the forages, feed cost was similar and though feed cost kg^-1 gain was slightly higher for rabbits on sweet potato forage than groundnut haulms and soybean forage, any of the forages could be used for feeding rabbits and it agrees with the results of Iyeghe-Erakpotobor et al. (2002) who reported similar weight gain when rabbits were fed groundnut haulms, lablab and mucuna forages. Similar dry matter, ether extract, crude fibre and nitrogen free extractives digestibility obtained for all the forages could explain the similar weight gains observed for rabbits on the three forages. Dry matter and crude protein digestibility obtained in this study are similar to those reported for temperate (Alfalfa and Clover) and tropical (Leucaena leucocephala, Sesbania sesban and Albizza falcata) legumes (Cheeke et al., 1986).

The rate of gain in this study agrees with daily growth rate of 5-10 g reported during the grower phase under tropical conditions (Iyeghe-Erakpotobor et al., 2001). Low growth performance of rabbits as a result of high ambient temperatures has been reported. Significant effect of temperature and day length on rabbit growth performance has been reported (McNitt and Lukefahr, 1993) with rabbits having lowest growth rate in summer and highest growth rates in early spring and late autumn. It is concluded from this study that soybean cheese waste meal has a great potential as a concentrate meal for rabbits. Though rabbits utilized all the forages for growth, feeding groundnut haulms and soybean forage were more cost effective than sweet potato forage.

ACKNOWLEDGMENTS

The author wishes to express gratitude to the Director, National Animal Production Research Institute (NAPRI) for permission to publish this study. Contributions of staff of the Rabbitry for data collection and Central Laboratory Unit for Laboratory analysis are acknowledged. The Federal Ministry of Agriculture and Rural Development funded the study.