Tropical Grasslands (2008) Volume 42, 112–119

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Intake of tropical grass, legume and legume-grass mixtures by rabbits

G.T. IYEGHE-ERAKPOTOBOR1 AND I.R. MUHAMMAD2

Introduction

1 National Animal Production Research Institute, Ahmadu Bello University, Shika-Zaria, Nigeria 2 Department of Animal Science, Faculty of Agriculture, Bayero University, Kano, Nigeria

The use of forages in rabbit feeding is normal practice, and rabbit producers are advised to feed forages as a supplement to a basic concentrate diet in order to meet the fibre and some of the vitamin requirements. However, inflationary pressures and competition between man and animals for grains used in concentrate feeds have produced a sharp increase in the cost of producing rabbits, especially in the past year (2005–2006). Costs of grains and their byproducts have increased dramatically and they were often scarce. In developing countries, where commercial feeds are either not available or cost-prohibitive, Linga and Lukefahr (2000) advocated raising rabbits on a basic forage diet with an energy supplement. Forages are readily available and cheap in the tropics, and rabbits, being pseudoruminants, have the ability to utilise forages for growth. Though optimum rabbit production has not been sustained on forages alone using most tropical forages, it is possible to reduce the cost of concentrates in the rations by utilising forages that are nutritious and palatable, to achieve a compromise between level of production and cost that is acceptable to producers. Harris et al. (1983) and Aduku et al. (1989) have conducted some studies on preference of rabbits for different forages, but the vast range of forage species in the tropics has not been properly harnessed for this purpose. Since legumes are high in protein, they have potential to reduce the quantity and cost of concentrates for rabbits. However, for rabbits to perform well on forage diets, they need to consume the forages in significant amounts. This study was undertaken to evaluate the acceptance by rabbits of a range of tropical grasses, legumes and legume-grass mixtures.

Abstract Intake of grass and legume forages by growing rabbits, when offered individually or as legumegrass (50:50) combinations with 50 g concentrate, was measured in 2 experiments. Forage grasses used were: Cenchrus ciliaris (buffel grass), Digitaria decumbens (digitaria, woolly finger grass), Brachiaria decumbens (brachiaria), Sorghum almum (Columbus grass), Andropogon gayanus (gamba grass), Pennisetum purpureum (elephant grass), Chloris gayana cv. Callide (Callide rhodes grass), Chloris gayana cv. Katambora (Katambora rhodes grass) and Pennisetum pedicellatum (kyasuwa); while the forage legumes were: Arachis hypogea (groundnut), Phaseolus aureus (green gram), Vigna unguiculata (cowpea), Lablab purpureus (lablab), Centrosema pascuorum (pascuorum), Centrosema pubescens (centro), Stylosanthes guianensis cv. Cook (Cook stylo) and Macrotyloma uniflorum (horse gram). Horse gram, lablab, cowpea and C. pascuorum were fed in 50:50 combination with the grasses. Overall, intakes of elephant grass, Callide rhodes, buffel, digitaria and Katambora rhodes were high, while those of Columbus grass, kyasuwa and brachiaria were medium. All legumes were consumed at medium levels. Intakes of mixtures did not necessarily reflect the intake levels of the separate components. Correspondence: G. T. Iyeghe-Erakpotobor, Rabbit Research Unit, National Animal Production Research Institute, Ahmadu Bello University, PMB 1096, Shika-Zaria, Nigeria. E-mail: [email protected] or [email protected]

Intake of tropical grass, legume and legume-grass mixtures by rabbits

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Materials and methods

Experiment 1

Study site

Growing rabbits were used to evaluate the acceptance of grass and legume forages fed individually or in combinations of legume and grass. The rabbits weighed 1.25 kg (range 0.80–1.70 kg). Grasses tested were: Cenchrus ciliaris (buffel grass), Digitaria decumbens (digitaria, woolly finger grass), Brachiaria decumbens (brachiaria), Sorghum almum (Columbus grass), Andropogon gayanus (gamba grass), Pennisetum purpureum (elephant grass), Chloris gayana cv. Callide (Callide rhodes grass), Chloris gayana cv. Katambora (Katambora rhodes grass) and Pennisetum pedicellatum (kyasuwa); while the forage legumes were: Arachis hypogea (groundnut), Phaseolus aureus (green gram), Vigna unguiculata (cowpea), Lablab purpureus (lablab), Centrosema pascuorum (pascuorum) and Macrotyloma uniflorum (horse gram). All forages were offered individually and, in addition, horse gram, lablab, cowpea and pascuorum were fed in a 50:50 combination with Columbus grass, elephant grass and Katambora. Other grasses were not included in the grass-legume mixtures because insufficient biomass was available. The forages were offered fresh. Each day, a single forage was offered for 5 hours from 08.00 h to 13.00 h to all 18 rabbits (n=18 rabbits/forage) individually. The forages were chopped and 100 g fresh forage was offered according to the methods of Harris et al. (1983) and Omokanye et al. (2001). After 5 hours, the uneaten forage was weighed and the total amount consumed recorded. After withdrawal of the forage, the rabbits were offered 50 g of concentrate meal (Table 1), which was consumed by evening. When legumes were offered in combination with grasses, the forages were mixed together and offered in earthen pots. This reduced the opportunity for selection of the individual forages in a mixture and particular plant parts by rabbits. Forages were tested from Monday to Friday each week and the rabbits were fed their normal ration of high concentrate (100 g) and low forage (20 g) on Saturdays and Sundays. Forage acceptance was calculated as (forage consumed/forage offered) × 100, and was classified into 3 classes as follows: (1) 70–100%, high; (2) 50–69%, moderate; and (3) 0–49%, low acceptance. The study lasted 7 weeks.

The study was conducted at the National Animal Production Research Institute, Shika, Nigeria, located in the Northern Guinea Savanna ecological zone (10°11′N, 7°8′E; 650 m asl). The climate of the study location has defined wet and dry seasons, which are typical for the subhumid tropics. The area receives an annual rainfall of 1100 mm, spread between April and October (wet season). The mean minimum (night) and maximum (day) temperatures were 20°C and 34°C, respectively, during the study, with relative humidity ranging between 85% and 50%. Mean day length was 12 h. Animals The experimental animals were crossbred New Zealand White × California rabbits, which were housed individually in metal cages (60 × 40 × 50 cm) in a completely walled house with open windows covered with poultry wire mesh and mosquito netting. Forage planting Irrigated forage evaluation trials were conducted in the late dry season (March–June). Following ploughing and harrowing of the site, legumes and grasses were established in 3 m × 4 m plots in a randomised block design with 3 replications. All legumes received 20 kg/ha P at planting, while grasses received 100 kg N, 50 kg P and 50 kg K per hectare in split applications. All plots were irrigated at planting and at 3-day intervals until germination was completed (within 2 weeks). Thereafter, irrigation was applied at 10-day intervals. At the full vegetative stage of physiological maturity (less than 5% booting), the forage was harvested with sickles daily and whole plants (stems and leaves) fed to rabbits fresh. Subsamples of each batch of forage material were taken, and oven-dried at 100°C overnight for dry matter determination. Forages were allowed to regenerate.

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G.T. Iyeghe-Erakpotobor and I.R. Muhammad

Table 1. Composition of concentrate supplement fed to grower rabbits. Ingredient Maize Groundnut cake Maize offal Bone meal Salt Vit./Min. premix1 Total Crude protein (%DM) Crude fibre (%DM)

Proportion (%) 39.2 42.3 15.0 3.0 0.25 0.25 100.0 21.9 10.1

1 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 g, Calcium D-Pantothenate 0.01mg, 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.

stages of the study because insufficient biomass was available. Grasses were offered at 100 g fresh forage on Day 1, 150 g on Day 2 and 250 g daily subsequently, while legumes and legumegrass combinations were offered at 250 g daily throughout. All forages were chopped and offered fresh. The rabbits were offered 50 g of concentrate meal (Table 1) (22% CP; 2500 kcal ME/kg) daily in the morning at 08.00 h with the forages. Nutrient composition of some of the forages offered is shown in Table 2. Concentrate and forages were offered in separate earthen feeders and were available for 24 hours. Forage remaining and wastage were weighed daily before feeding. At the end of each feeding period of 5 days, the rabbits were fed 100 g concentrate and 50 g grass hay daily for Saturday and Sunday. Rabbits were weighed at the start and end of each feeding period. The study lasted 4 weeks.

Experiment 2 Data analysis Fifty-four rabbits were used to investigate acceptance of grasses, legumes and legume-grass combinations (n=6 rabbits/forage) in a completely randomised design. The rabbits weighed 1.5 kg (range 0.9–1.8 kg). Grasses fed were: buffel, digitaria, brachiaria, Columbus, gamba, elephant, Callide rhodes, Katambora rhodes and kyasuwa; while the forage legumes were: groundnut, green gram, cowpea, lablab, pascuorum, Centrosema pubescens (centro), Stylosanthes guianensis cv. Cook (Cook stylo) and horse gram. Lablab and pascuorum were fed in a 50:50 combination with the grasses. Grasses, legumes and legume-grass combinations were fed for 5 days except for pascuorumgrass combinations, which were fed for 4 days. Callide rhodes grass, Katambora rhodes grass and Columbus grass were not included in some

Data obtained were collated using Microsoft Excel package of Windows XP and subjected to analysis of variance for a completely randomised design and significant means separated by the pair-wise difference method (SAS 1987). Results Experiment 1 Table 3 shows intakes of grasses and legumes by rabbits. Among the grasses, intake rankings were: high — buffel; moderate — digitaria, brachiaria, Columbus and gamba; and low — elephant, Callide rhodes and kyasuwa. Intake rankings for

Table 2. Nutrient composition (% DM) of some forages offered to rabbits.

Digitaria Brachiaria Columbus grass Gamba Elephant grass Rhodes grass Katambora Lablab C. pascuorum C. pubescens Cook stylo

Dry matter % (as fed)

Ash

Crude protein

Crude fibre

48.4 45.4 48.3 33.0 45.6 47.0 48.4 49.5 62.5 57.7 60.3

9.0 10.6 5.1 8.9 11.1 16.7 7.6 19.3

19.4 12.9 6.3 10.8 17.4 15.3 15.9 13.4

28.8 25.6 29.2 26.6 25.4 20.6 25.2 28.4

4.1

16.1

28.9

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Table 3. Relative intakes (RI) of grasses and legumes by rabbits when offered 100 g individually for 5 hours then 50 g concentrate (Experiment 1). RI1

Grass

76.7a2 63.3b 58.3b 53.9b 49.2c 39.4c 36.6c 26.4d 4.42

Buffel grass Digitaria Brachiaria Columbus grass Gamba grass Elephant grass Callide rhodes grass Kyasuwa s.e. 1

Legume

RI

Groundnut Green gram Cowpea Lablab C. pascuorum Horse gram

81.7a 63.9b 61.7b 56.1bc 44.2cd 36.4d 4.36

RI = (forage consumed/forage offered) × 100.

legumes were: high — groundnut; moderate — green gram, cowpea and lablab; and low — pascuorum and horse gram. Intakes of legume-grass mixtures (Table 4) showed significant differences within horse gram-grass (P