| Livestock Research for Rural Development 12 (2) 2000 | Citation of this paper |
Twelve, forty-five-days old, New Zealand White rabbits were allocated to two treatments and kept in separate cages. The first treatment (control) was ad libitum complete rabbit pellets and the second treatment ( SG) was a combination of Star grass ad libitum along with 50g/day of mash concentrate as supplement. There were no health problems during the experimental period. The parameters measured used were growth, feed conversion and apparent digestibilities of dry matter, organic matter, protein, neutral detergent fibre, cellulose, hemicellulose, lignin and energy.
Growth rate was higher (P=0.001) on the pelleted complete diet (17.2± 2.35 g/day) than on the Star grass and mash (7.7 ± 1.02) reflecting a 30% increase in dry matter intake. Feed conversion also favoured the pelleted diet. There were no differences (P>0.05) in dry matter and organic matter digestibility. Digestibility of protein and energy was higher for the Star grass diet than for the control (P<0.05) but was lower (P<0.05) for all cell wall components.
The rabbit is a non-ruminant herbivorous animal with a satisfactory growth rate and a short production cycle (Wolfgang 1981; Cheeke et al 1987). It is a good source of meat, which is of high quality with low cholesterol and therefore suitable for special diets (Owen 1981). The rabbit has an advantage over poultry and pigs because it can convert locally available plant products and by-products such as Leucaena leucocephala (Awotarowa 1992) and wheat bran (Ramsamy 1993) into animal protein for human consumption. On intensive farms rabbits are normally fed commercial feeds. However, these feeds are too expensive in most developing countries (Hulman 1988). Therefore, in order to reduce the cost of feed, commercial concentrates are often used as supplements for locally available forages.
A common forage in Mauritius is Star grass (Cynodon plectostachyus). It has many advantages, one of them being its high palatability. Also, no toxicity has been attributed to it (Everist 1974). However, information on the nutritive value of star grass under local conditions is lacking and no research has been done on its utilisation by different animals particularly rabbits.
Hence there was the need to investigate the effect on growth and nutrient digestibility of offering fresh Star grass forage as a complement to a fixed allowance of mash, comparing this with the conventional pelleted complete feed.
Twelve 45 days-old New Zealand White rabbits were used for the experiment. The animals were individually caged in a three-tier battery system. Water was available ad libitum. A completely randomised design was used with six rabbits on each of the following two treatments:
The total trial period was 70 days. A digestibility trial was carried out during the last ten days using the total collection method. Feeds and faecal samples were collected daily during that period and analysed for dry matter, organic matter, neutral detergent fibre, acid detergent fibre, acid detergent lignin (Van Soest, 1963) and energy. Dry matter was determined by drying the samples in a MEMMERT fan convection oven while the organic matter was found by burning the samples in a muffle furnace (Carbolite furnace CWF 12/13) (AOAC 1975). Protein was determined by the Macro-Kjeldahl technique. The energy content was obtained by using an adiabatic bomb calorimeter.
For
the slaughter of the animals, the “halal” method was found to be most
appropriate. In Mauritius, as elsewhere generally, the market can have a wider
coverage if it includes consumers of the Islamic faith. After slaughter, the
rabbits were hung, skinned and eviscerated to obtain the carcasses. The dressing
percentage was determined as:
100*Carcass weight (warm)/liveweight
The meat to bone ratio (M: B) of the right limb of each animal was obtained by dissection and weighing these two components. Deboned meat of each rabbit was ground and dried in a lyophiliser (Christ Gefriertrocknungsanlagen, Germany). Analyses were carried out for organic matter (OM), crude protein (CP), fat, calcium (Ca), phosphorus (P) and energy contents using the same methods as for feed analyses.
The growth, carcass and digestibility data were analysed by one-way ANOVA with diet and error as the variables.
Table 1 gives the chemical composition of the feeds used during the experiment.
| Table 1: Chemical composition of pellets, mash and Star grass | |||
| Pellets | Mash | Star grass | |
| Dry matter (g/kg) | 917 | 860 | 194 |
| Ash (g/kg DM) | 90.5 | 114 | 108 |
| NDF (g/kg DM) | 103 | 108 | 487 |
| ADF (g/kg DM) | 46.1 | 49.3 | 236 |
| ADL (g/kg DM) | 14.7 | 18.6 | 24.5 |
| Cellulose (g/kg DM) # | 31.3 | 30.7 | 211 |
| Hemicellulose (g/kg DM) ## | 57.3 | 59.2 | 251 |
| Protein (% of DM) | 17.4 | 18.7 | 22.8 |
| Fat (g/kg DM) | 31.7 | 24.9 | 13.2 |
| Energy (MJ/kg) | 15.7 | 17.5 | 16.6 |
| Calcium (g/kg DM) | 4.9 | 5.1 | 1.8 |
| Phosphorus (g/kg DM) | 7.9 | 8.6 | 1.6 |
| # ADF - ADL,## NDF - ADF | |||
The crude protein content was higher in the Star grass than in the pellets or the mash, but fat, calcium and phosphorus were much lower. The pellets and mash were similar in composition.
| Table 2: Mean values (±SE) for feed intake and growth of rabbits given a pelleted complete diet (control) or Star grass and a "mash" concentrate (SG) | |||
|
Control |
SG |
Prob. |
|
| Feed intake, g/day | |||
|
Fresh matter |
|
|
|
|
Pellets |
105±7.2 |
|
|
|
Grass |
102±8.1 |
||
|
Mash |
50.0±0.5 |
||
| Dry matter | |||
|
Pellets |
96.5±6.6 |
||
|
Grass |
20.2±1.6 |
||
|
Mash |
43.1±0.4 |
||
| Total | 97.0±4.7 | 63.3±4.7 |
0.001 |
| Liveweight, g | |||
| Initial | 1357 | 1176 | |
| Final | 2438 | 1659 | |
| Daily gain | 17.2± 2.35 | 7.7 ± 1.02 |
0.001 |
| Conversion | 6.1 ± 0.92 | 10.9 ± 2.22 |
0.05 |
| Feed cost# | 42.5 | 28.9 | |
| # Rs / kg liveweight gain; US$ 1.00 = Rs 25 (1999 Exchange Rate) | |||
Dry matter intake was more than 30% higher (P=0.001), growth rate was more than doubled (P<0.001) and feed conversion rate halved (P<0.05) on the pelleted complete feed than on the experimental diet of mash and fresh Star grass (Table 2). The growth curves of the rabbits (Figure 1) show the marked superiority of the pelleted diet over the Star grass and mash combination.
| Table 3: Slaughter traits and meat composition of rabbits fed complete pelleted diet or a combination of Star grass and concentrate mash ( Mean ± SE; n=6) | |||
|
Slaughter LWt, kg |
2.4 ± 0.14 |
1.7 ± 0.06 |
|
|
Dressing % |
54.0 ± 0.57 |
44.8 ± 1.16 |
|
|
Meat : bone ratio |
3.2 ± 0.20 |
1.9 ± 0.10 |
|
|
Moisture in boneless meat, % |
71.1 ± 0.68 |
78.1 ± 0.17 |
|
|
Composition of boneless meat, dry matter basis |
|||
|
Protein, % |
65.5 ± 5.38 |
64.9 ± 2.58 |
|
|
Fat, % |
14.8 ± 1.64 |
2.0 ± 0.28 |
|
|
P, g/kg |
2.7 ± 0.25 |
4.0 ± 0.41 |
|
|
Ca, g/kg |
0.8 ± 0.08 |
1.3 ± 0.14 |
|
|
Energy, MJ/kg |
19.3 ± 1.34 |
13.8 ± 0.51 |
|
Rabbits fed the pelleted complete diet were heavier at slaughter, had a higher dressing percentage, and a greater meat: bone ratio than those fed Star grass and mash (Table 3). The boneless meat from the control rabbits was higher in protein and fat and lower in phosphorus and calcium than the meat from the rabbits fed Star grass and mash.
| Table 4: Digestibility coefficients (%) of the main nutrients for the pelleted (control) feed and the combination of Star grass and mash (SG) ( Mean ± SE; n=6) | |||
| Control | SG | ||
| Dry matter | 69.0 ± 0.96 | 68.8 ± 0.69 | |
| Organic matter | 70.0 ± 1.02 | 70.2 ± 0.76 | |
| Crude protein (%N x 6.25) | 77.6 ± 0.82 | 81.3 ± 0.37 | |
| NDF | 42.9 ± 1.33 | 34.6 ± 2.51 | |
| Lignin | 15.7 ± 0.90 | 12.3 ± 0.61 | |
| Cellulose | 19.1 ± 0.80 | 16.1 ± 0.82 | |
| Hemicellulose | 54.9 ± 1.78 | 43.6 ± 1.48 | |
| Digestible energy (MJ/kg) | 10.0 ± 0.28 | 12.7 ± 0.14 | |
The coefficients of apparent digestibility of the main nutrients are shown in Table 4. There were no differences (P>0.05) between diets for apparent digestibility of dry matter and organic matter. Digestibility was higher (P<0.05) for protein and energy for the Star grass diet than for the control but was lower (P<0.05) for all cell wall components. The hemicellulose was the most digestible fraction of the cell wall constituents.
The most important finding was the 30% lower consumption of dry matter on the Star grass and mash diet compared with the pelleted feed. This almost certainly was the reason for the poor growth on this diet, since the digestibility coefficients of the organic matter and the crude protein were similar for both diets. All the slaughter traits, and the meat composition data, reflect the faster growth rate of the rabbits fed the pelleted complete diet and their greater liveweight at slaughter.
Nehring et al (1963) reported that rabbits did not differ from other domestic animals in their ability to digest concentrates but that it was the crude fibre in roughages which is poorly utilised. Thus, it was to be expected that the dry matter digestibility of the Star grass and mash diet should have been lower than for the control. This was not the case due to two possible reasons.
The low dry matter intake on the Star grass / mash combination was probably the reason for the high values of the digestibility coefficients for organic matter and energy on this diet, despite the higher content of cell wall constituents, which normally would be expected to depress digestibility. The Star grass provided to the rabbits during the digestibility trial was of good quality (crude protein and lignin were 23% and 2.4% of the dry matter), consisting of young and fresh grass, having a high proportion of leaves compared to stem and dead material. This would favour digestibility, but not necessarily the feed intake.
The concentration of crude protein was higher in the Star grass diet (20% in dry matter) than in the pellets (17%), thus a higher apparent digestibility of the protein is to be expected (see McDonald et al 1984). The lower values for digestibility of cell wall constituents in the Star grass diet reflect their higher concentrations coming from the grass.
The recommended digestible energy level in the diet of growing rabbits of 4 -12 weeks of age is10.5 MJ/kg DM (Lebas et al 1986). According to Auvergne et al (1987), feeds with less than 9.2 MJ DE /kg DM result in poor performance owing to limited intake capacity. The fact that the DE content of the Star grass and mash combination was higher (12.7 MJ DE/kg DM) than the recommended norm, and yet growth rate was poor, implies that some other factor was limiting intake and hence growth rate.
Despite the poor performance of the rabbits given the Star grass and mash combination, the feed costs were lower. This emphasizes the potential advantages to be gained from the use of local feed resources. The challenge facing researchers is to select the most appropriate local feed resources and to develop ways in which they can be used to support levels of performance that approach the genetic potential of the target animal.
Valuable help was received from Miss J.Raggoo. The authors wish to acknowledge the co-operation of Mr Cupidon, former farm manager and Mr Baba (stockman) of the University Farm.
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Received 30 November 1999