Effect of different forages on feed intake, digestibility and growth performance of rabbits

Supharoek Nakkitset, Choke Mikled^* and Inger Ledin^**

Royal Project Foundation, Livestock Extension and Development Section,
65 Moo 1 Suthep Road, Maung, Chiang Mai 50200, Thailand.
inalaw@yahoo.com
* ChiangMai University, Department of Animal Science, Faculty of Agriculture,
Chiang Mai 50200, Thailand.
**Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management,
 PO Box 7024, 75005 Uppsala, Sweden.

Abstract

The performance of growing rabbits fed Ruzi grass, head lettuce residue, Mimosa pigra and water spinach was studied in an experiment using 64 rabbits of 2 breeds, New Zealand White and a crossbred between New Zealand White and native breed, and 2 sexes.

The growth experiment was a 4x2x2 factorial completely randomized design with 3 factors, foliage, breed and sex, and with 4 replications. The rabbits had an average initial weight of 668 g and were about 6 weeks old. They were housed in individual pens and allotted randomly to the treatments. The foliages were fed ad libitum and a basal diet of a commercial concentrate for growing pigs was fed at a restricted level of 2% of body weight on dry matter (DM) basis. In the digestibility experiment the rabbits, 4 per treatment and males only, were fed the same foliages as in the growth experiment but without concentrate.

There were significant differences (P<0.001) in final weight, daily weight gain, total feed intake and feed conversion ratio. Daily weight gain was significantly lower in the group fed Ruzi grass, 14.8 g/day compared to 17.6 g, 18.5 and 18.4 g/day for head lettuce, Mimosa pigra and water spinach, respectively. Feed intake and feed conversion ratio was lowest for the rabbits fed water spinach, 66 g DM/day and 3.6 kg DM/kg live weight, respectively. The New Zealand White breed had a significantly higher daily gain than the crossbred rabbits (P<0.05), 18.0 and 16.7 g/day, respectively. There were no significant differences due to sex.

The digestibility coefficients (%) of DM, organic matter, crude protein, crude fiber, neutral detergent fiber and acid detergent fiber were significantly lower (P<0.001) in the rabbits fed Ruzi grass. Breed had no influence on digestibility.

In conclusion, the rabbits fed head lettuce residue, Mimosa pigra and water spinach as a forage had higher growth rate and digestibility coefficients than the rabbits fed Ruzi grass.

Introduction

Raising of rabbits has started to play an increasingly important role for small farmers in the mountainous areas around Chiang Mai in the northern part of Thailand. Rabbits have potential as a meat producing animal in the tropics due to the characteristics such as small body size, short generation interval, rapid growth rate and ability to utilise forages or agricultural by-products. Mikled (2005) reported that the waste products from product grading before selling to the market, such as vegetables wastes, are well utilized as feed resources for livestock, for example for cattle, pigs, goats and rabbits, and the manure from the animals could be utilized as an organic fertilizer for crops. Production systems with small or large ruminants usually need a long time to give a saleable product and with high cost, especially for feeds. Rabbits have a number of characteristics that make them particularly suitable as meat-producing animals, especially when compared to other herbivores. Rabbits could contribute significantly to solving the problem of meat shortage (Taylor, 1980; Lebas, 1983). Ruiz-Feria (1998) reported that rabbits can subsist on inexpensive diets based on forages under small-scale farm conditions in arid and tropical regions. Agricultural by-products, foliages and weeds such as sugar cane, cassava root meal, rice bran, natural grasses and Leucaena can be used as dietary ingredients for rabbits (Lukefahr and Cheeke, 1991; Ha et al 1996; Ruiz-Feria, 1998). Delgado et al. (1999) reported that the demand for human food from animal products (meat, eggs and milk) is continually increasing. The consumers of today pay great attention to the health aspects of food, such as low fat content and organic origin. Meat from rabbits has a low cholesterol level, high protein/energy ratio and is relatively rich in essential fatty acids (Iraqi, 2003).

Head lettuce (Lactuca sativa) is a vegetable commonly grown by upland farmers in northern Thailand. The residue from head lettuce after grading is a vegetable waste generally found in the project areas.

Mimosa (Mimosa pigra) is a weed that is spread by seeds over many areas in South East Asia. Vearasilp et al. (1981) reported a potential use of mimosa as a livestock feed resource with relatively high protein content, 200 g crude protein (CP)/kg dry matter (DM). Some farmers are already using mimosa as a forage for rabbits in the upland areas. No negative effects were noted in tests run on this thorny plant in Thailand (FAO, 1997). Still, there have been no investigations on the most appropriate use of mimosa as a feed source for rabbits.

Water spinach (Ipomea aquatica) is an aquatic plant cultivated for human food and used for pigs and other animals in Thailand, Cambodia, Vietnam and Laos. The fresh leaves and stems of water spinach have a CP content of between 200 g and 310 g/kg DM (Men et al 2000). Water spinach can be fed as a basal diet to rabbits (Phimmasan et al 2004; Samkol, 2005; Pathoummalangsy, 2005) and appears to have a high potential as a forage source for rabbits (Phimmasan, 2003).

Ruzi grass (Brachiaria ruziziensis) has been promoted as a good grass for improving pastures for cattle in Thailand, and is also present in many pastures in the mountainous areas. According to a report from FAO (1990) this grass can tolerate drought and can grow at altitudes from 100 m up to 1,200 m. The protein content at 45 days of age is reported to be about 75 g CP/kg DM (Narmsilee et al 2003).

The objective of the study was to evaluate the effect of feeding head lettuce (Lactuca sativa) residue, mimosa (Mimosa pigra), water spinach (Ipomoea aquatica) and Ruzi grass (Brachiaria ruziziensis) on growth performance, feed intake and digestibility in rabbits.
 

Materials and methods

Location and climate of the study area

The experiment was conducted at the Demonstration Farm of the Royal Project Foundation, Chiang Mai, Thailand. The climate in this area is tropical monsoon, with a wet season from May to October and a dry season from November to April. Average rainfall during the experiment was around 875 mm and the temperature was about 31^oC in the day time and 23^oC at night. The experiment started in late June and finished in October 2006.

Animals and management

The animals used in the experiment were weaned rabbits of about 6 weeks of age with an average body weight (BW) of 668 (SD=16.5) g.

The rabbit breeds used were pure New Zealand White (NZW) and crossbreds between native rabbits and New Zealand White (NN). There were 32 animals of each breed and equal numbers of males and females. The rabbits were confined in individual cages made from metal net with the size 50x70x60 cm. Before the start of the experiment the rabbits were dewormed using Ivermectin injection, 0.1 ml/kg BW. Four male rabbits from each treatment in the growth experiment were selected when the growth experiment was finished and used in the digestibility experiment.

Feeds and feeding systems

A commercial feed for growing pigs from 30 kg to 60 kg was used as the basal diet in the growth experiment. The CP content was about 160 g/kg DM. Major ingredients in the commercial concentrate feed were maize and rice bran as energy sources and soybean meal and fishmeal as protein sources. The concentrate was fed at a level of 2% (in DM) of BW. The concentrate was bought from a feed shop around 10 kilometres from the farm.

The foliages used in the experiment were Ruzi grass, head lettuce residue, Mimosa pigra and water spinach. Head lettuce residue was collected every day from the packing house of the Royal Project Foundation, which is close to the farm. Before being offered the head lettuce residue was air-dried for about 10-12 hours. Mimosa pigra was collected from the fields around the farm and cut approximately 15 cm from the top, (leaves and stem included), and the leaves from the part >15 cm from the top were also included. Ruzi grass was planted in the farm and was harvested at 45-60 days of age. Mimosa pigra and Ruzi grass were harvested once per day at about 17.00 h. Water spinach was bought fresh every day from a market around 15 kilometres from the farm.

The foliages were hung in the cage and offered ad libitum at a level of 120% of the average individual intake the previous week. Clean water was available at all times.

The diets were fed twice daily at about 7.00 h and 16.00 h with 50% of the feed at each occasion. The head lettuce residue was fed 3 times a day at about 7.00 h, 12.00 h and 17.00 h to increase the level of offer and feed intake because the head lettuce residue had very low DM content and fermented quickly if offered in large amounts at the same time.

In the digestibility experiment the rabbits continued on the same treatment and were fed the same foliages as in the growth experiment, but without concentrate.

Experimental design

The experimental design of the growth experiment was a CRD with 3 factors, 4 kinds of foliage, 2 breeds of rabbit and 2 sexes . The experiment had 16 treatments and 4 replicates.

The treatments were:

• T1 to T4: Ruzi grass (ad libitum) + concentrate feed at 2% DM of BW with 2 breeds (New Zealand White (NZW) and crossbred (NN)and sexes of rabbits (male (M) and female (F)) (control).

• T5 to T8: Head lettuce residue (ad libitum) + concentrate feed at 2% DM of BW, with 2 breeds and sexes of rabbit.

• T9 to T12: Mimosa pigra (ad libitum) + concentrate feed at 2% DM of BW with 2 breeds and sexes of rabbit.

• T13 to T16: Water spinach (ad libitum) + concentrate feed at 2% DM of BW with 2 breeds and sexes of rabbit.

The experimental design in the digestibility experiment was a CRD with 2 factors: 4 kinds of foliage and 2 breeds and 4 replicates. The digestibility experiment had 8 treatments.

Data collection and analysis

The rabbits in the growth experiment were weighed at the beginning of the experiment and then every 7 days, always in the morning before feeding. Feed offered and refused was weighed every day to calculate feed intake and determine feed conversion ratio from DM intake. The feeds and feed residues were sampled every day for analysing the chemical composition. Foliages in the field were sampled every 3 days to analyse DM.

In the digestibility experiment feed offered and feed residues were weighed and recorded every day. Faeces were collected every day. Feed, hair or other contaminations were removed from the faeces. The samples were kept in plastic bags in a freezer until analysed.

The feed, feed residues and faeces were analysed for DM, ash, N, ether extract (EE) and crude fiber (CF) according to AOAC (2000). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) was analysed according to Van Soest and Robertson (1985). The gross energy in the samples was measured by a Bomb calorimeter. Digestible energy (DE) for the concentrate and metabolisable energy (ME) for the foliages and concentrate was estimated according to Noblet and Perez (1993) as mentioned by NRC (1998). DE = 4,151 - (122 x % Ash) + (23 x % CP) + (38 x % EE) - (64 x % CF). ME = DE x (1.003 - (0.0021 x % CP))

Statistical analysis

The data were analysed using the ANOVA GLM option of the Minitab version 14.12 software (Minitab, 2004). Sources of variation were animals (breed and sex), feeding method (different foliages) and error. The means were compared using Tukey's pairwise comparison test. The statistical model for the growth experiment was: Y_ijkl = m + T_i + B_j + S_k + βW_I + e_ijkl where T_i= treatment, B_j= breed and S_k= sex. All interactions were tested and included in the model if they were significant. Initial weight (W_i) was used as a covariate in the model.

The model for the digestibility experiment was the same as for the growth experiment, but since all animals were male, sex was not included.

Results

Chemical composition of the feeds

The chemical composition of the experimental feeds is shown in Tables 1 and 2 for the growth trial and the digestibility trial, respectively. Water spinach, head lettuce residue and Mimosa pigra had a high protein content of 252 g, 188 g and 177 g CP/kg DM, respectively. Ruzi grass had a low protein content of 89 g/kg DM. Both head lettuce residue and water spinach had low DM and fiber contents. The gross energy of the experimental feeds was 14.7 MJ, 15.8 MJ, 17.1 MJ, 19.6 MJ and 19.4 MJ/kg DM for water spinach, head lettuce residue, Ruzi grass, Mimosa pigra and concentrate, respectively.

Chemical composition of the feeds used in the digestibility experiment was similar to the feeds in the growth trial.