| Table 1: Composition of blocks, % | |
| Ingredients | |
| Molasses | 40 |
| Wheat bran | 35 |
| Cottonseed meal | 10 |
| Cement | 7 |
| Mineral mixture | 5 |
| Salt | 2 |
| Livestock Research for Rural Development 12 (1) 2000 | Citation of this paper |
This paper reports digestibility coefficients and growth and conversion parameters in rabbits fed with commercial rabbit pellets supplemented by 15 or 30 g daily of multi-nutrient mini-blocks (MNB). The treatments consisted of a control (commercial rabbit pellets), a treatment using 15 g/day MNB + pellets ad libitum and another using 30 g/day of MNB + pellets ad libitum. Eighteen rabbits were kept in individual cages and were randomly allocated to the three treatments. The parameters investigated were digestibility of dry matter (DM), organic matter (OM), protein, ether extract (EE), neutral detergent fibre (NDF) and energy during a period of 11 days. Subsequently, growth rates were measured over a 55 day period.
Compared to the pellets, the MNB had a higher amount of ash and fibre but were lower in crude protein and energy. Digestibility of dry matter and organic matter was highest for rabbits supplemented with 30 g MNB followed by those with 15 g MNB. The crude protein and ether extract digestibility did not differ significantly. There was a difference (P<0.05) in the NDF digestibility in favour of the diets with supplementary MNB.
In the growth trial, rabbits in treatments MNB15 and MNB30 had higher (P<0.05) dry matter (DM) intake (127 ± 18.8 and 125 ± 9.86 g/head/day, respectively) than those on the control treatment (104 ± 11.4 g/head/day). The average weight gains for rabbits fed only pellets was 14.8 ± 5.82 g/head/day, significantly less than for the MNB15 and MNB30 treatments (23.4 ± 3.5 and 26.4 ± 6.3 g/head/day, respectively). There were no differences in feed conversion among the treatments.
The beneficial effect of the multi-nutrient blocks was reflected in the improved growth rate, reduction in the time required to reach slaughter live weight and lower cost of production.
The basal diet of most rabbits in Mauritius is based on crop residues and roadside grass. These feeds are nutritionally poor and imbalanced for rabbits (Cheeke and Raharjo 1988). To overcome this problem feed supplements are normally provided. Cereal-based feeds are generally too expensive for use as supplements (Hulman 1988). Alternative non-cereal feed supplements have been successfully developed for many livestock species using locally available agro-industrial by-products. In Mauritius, these include 'melabag' a proprietary supplement for deer (Curumtally 1992; Domingue and Rajkumar1992) and salt licks for sheep and cattle (Bheekee, personal communication). Since quite some time, multi-nutrient blocks (MNB) have been developed for ruminants (Sansoucy 1986, 1988, 1995) but no such feed supplement has been devised for rabbit in Mauritius, although successful use of a molasses-based "cake" has been reported from Vietnam (Dinh Van Binh et al 1991) and Perez (1990) has recommended this technology as an appropriate feed strategy for rabbit production in tropical countries.
This study reports data on the effects of multi-nutrient blocks (MNB) on digestibility and growth in rabbits fed a basal diet of commercial pelleted feeds. It complements the work reported by Ramchurn and Raggoo (2000) which described the ingredients and method of preparation of the blocks according to the conditions in Mauritius.
Eighteen rabbits, the progeny of 12 does, 45 days-old, and of local non-descript breed were housed individually in cages (50x30x30cm) arranged in a three tier battery system. Water was freely available in semi-automatic drinkers.
The experiment consisted of three treatments:
The MNB were prepared at the University Farm, Mauritius as described by Ramchurn and Raggoo (1999). Their composition (parts by weight) is indicated in Table 1:
| Table 1: Composition of blocks, % | |
| Ingredients | |
| Molasses | 40 |
| Wheat bran | 35 |
| Cottonseed meal | 10 |
| Cement | 7 |
| Mineral mixture | 5 |
| Salt | 2 |
The experiment was done in two parts. The first was a digestibility trial carried out over a period of 11 days. This was followed by a growth study over a period of 55 days.
The feed intake and the amount of faeces voided were recorded daily and samples taken for analysis. Feeds and faeces samples were analysed for dry matter, organic matter, protein, ether extract, neutral detergent fibre, calcium, phosphorus and energy. Dry matter was found by drying (70°C) the samples in a MEMMERT fan convection oven while the organic matter was found by burning in a muffle furnace (Carbolite furnace CWF 12/13) (AOAC1975). Protein was determined by the Macro-Kjeldahl technique and fat was found using a Goldfisch Fat Extractor Model . Neutral detergent fibre, acid detergent fibre and acid detergent lignin were determined by an automated fibre determination system (FIBRETEC M System; Tecator, Sweden) (Van Soest 1963). Calcium and phosphorus content were measured by flame photometer (410, CORNING, England ) and spectrometer (Cecile CE 2010, UK), respectively. The energy content was found by using an adiabatic bomb calorimeter.
The growth patterns of the rabbits were determined by weighing them individually every week early in the morning before feeding over a total period of 55 days. The intake of feed was determined daily for each rabbit by weighing amounts offered and refused. Representative samples of the fresh feed and refusals were dried at 70 °C until constant weights were observed. Proximate analyses were carried out on feed samples taken at the start, middle and end of the experiment using conventional methods (AOAC 1975).
A completely randomised design was used with six rabbits on each treatment. One way analysis of variance was used. Comparisons of means were performed using the Fisher's Protected LSD test.
| Table 2: Average composition of rabbit pellets and multi-nutrient blocks (means ± SE; n = 9)) | ||
Nutrient (% ) |
Rabbit pellets |
MNB |
Dry matter |
90.9
± 0.2 |
84.5
± 0.28 |
Organic matter |
90.6
± 0.14 |
79.5
± 0.44 |
Ash content |
9.4
± 0.14 |
20.5
± 0.44 |
Protein |
19.5
± 1.40 |
12.8
± 0.51 |
Lipids |
2.6 ± 0.20 |
1.7 ± 0.31 |
Neutral detergent
fibre (NDF) |
10.8
± 0.19 |
19.0
± 0.44 |
Acid detergent
fibre (ADF) |
4.8
± 0.09 |
8.6
± 0.29 |
Acid detergent
lignin (ADL) |
1.7
± 0.21 |
1.8
± 0.11 |
Cellulose # |
3.0
± 0.03 |
6.9
±0.23 |
Hemicellulose ## |
5.9
± 0.12 |
10.4
± 0.32 |
Phosphorus |
0.7
± 0.35 |
1.0
± 0.11 |
Calcium |
0.4
± 0.43 |
0.8±
0.02 |
Energy (MJ/kg DM) |
15.0
± 0.01 |
12.3
± 0.23 |
| # calculated as % ADF - %
ADL; ## calculated as % NDF - % ADF |
||
Table 2 shows the average chemical composition of the pellets and the MNB. The MNB had higher calcium and phosphorus contents compared to the pellets. The pellets had a maximum of 19.5% crude protein to allow growth and maintenance but on the other hand, the MNB contained only 12.8% crude protein. The dry matter, organic matter and gross energy content were found to be lower in the MNB. However, the MNB had a higher NDF content of 18.9 % in DM compared to 10.8 % DM in the pellets. The lignin content in the MNB was low implying that the fibre in the blocks would be highly digestible.
Digestibility of dry matter and organic matter increased with amounts of MNB offered. The difference between MNB30 and the control was significant. This tendency was even more marked for NDF the digestibility of which increased progressively (P<0.05) as the level of MNB was increased. There were no differences between the treatments in the digestibility of the protein and ether extract nor in total energy.
| Table 3: Coefficients of apparent digestibility of the proximate constituents in the three diets (means ± SE) | |||
Nutrients |
Control |
MNB15 | MNB30 |
Dry matter (%) |
69.2 ± 1.62 a |
71.0
± 0.63a |
74.3
± 1.96 b |
Organic matter (%) |
69.9
± 2.05 a |
72.1
± 2.42 a |
74.7
± 2.56 b |
Crude protein |
74.2
± 2.23 |
75.5
± 2.76 |
76.0
± 2.85 |
Ether extract (%) |
81.7
± 1.26 |
82.4
± 2.07 |
83.1
±1.39 |
Neutral detergent fibre, % |
36.5
± 3.42 a |
42.8
± 6.06 b |
49.7
± 3.92 c |
Digestible energy, MJ/kg DM |
9.9
± 0.26 |
10.8
± 1.11 |
10.7
± 0.25 |
| abc: Means with different superscripts in the row are significantly different at 5% level. | |||
The growth curves of the rabbits show a major difference between the control diet of commercial rabbit pellets and the diets of pellets with supplementary MNB. The difference became progressively more marked as the trial progressed, the response being almost linear on the MNB diets and decidedly curvilinear on the control diet (Figure 1).
 |
The consumption of the pellets did not seem to be affected when the MNB was fed thus the total intake of dry matter was higher (P<0.05) for treatments MNB15 and MNB30 (Table 4). The apparent improvement in dry matter feed conversion on the MNB treatments was not significant.
| Table 4: Performance traits (means ± SE) and feed costs for growing rabbits fed pelleted concentrates partially replaced by multi-nutrient blocks | ||||
| Control | MNB15 | MNB30 | Probability | |
| Feed intake, g/day | ||||
| Pellets | 118 | 128 | 111 | |
| MNB | 0 | 15 | 30 | |
| Total dry matter | 104 ± 11.3a | 127 ± 18.8b | 125 ± 9.86b | 0.05 |
| Liveweight gain,g/day | 14.8 ± 5.52a | 23.4± 3.51b | 26.4 ± 6.33 | 0.05 |
| Feed conversion (DM basis) | 7.8 ± 3.67 | 5.1 ± 0.73 | 4.8 ± 1.13 | NS |
| Feed cost, Rs/day | 0.85 | 1.10 | 0.96 | |
| Feed cost, Rs/kg LWt gain | 57.0 | 43.0 | 36.3 | |
The chemical composition of feeds gives an indication of the potential nutrient supply but determinations of digestibility provides an estimate of the nutrients available to the animal. The growth rates of the animal reflect both differences in digestibility and in feed intake, the latter being mainly determined by the balance of nutrients, especially of protein in relation to energy, for metabolism (Preston and Leng 1987).
Compared to other domestic animals, the rabbit does not differ in its ability to digest starch and sugars, which are the principal nutrients in "concentrates" (Fielding 1991). It is the crude fibre in the diet which is poorly utilised by the rabbit compared with ruminant animals. The MNB had a higher NDF content (19% in DM) compared to the pellets (10.8% in DM), therefore a lower overall digestibility was to be expected on the MNB15 and MNB30 diets. In fact the recorded trend was the opposite. The implication of these findings is that the MNB, and perhaps specifically the molasses component, provided stimulants for microbial growth. In ruminants soluble sugars may depress fibre digestion as both nutrients are fermented simultaneously in the rumen. By contrast, in rabbits and other hind-gut fermenters, the sugars are digested by gastric enzymes in the small intestine prior to the digesta entering the caecum and large intestine thus competition for substrate is avoided. It is postulated that the non-sugar nutrients in molasses would thus be available to stimulate microbial action in the hind-gut with the end result of improving fibre digestion as was noted in this experiment. The data on nutrient composition show a lower lignin: NDF ratio in the blocks compared with the pellets which would also favour fibre digestion in the MNB diets.
The improvements in fibre digestibility when the pellets were supplemented with MNB were reflected in the growth rates of the rabbits which were significantly higher on the two MNB diets. According to Lebas (1983) the energy content of the diet is one of the main factors affecting the level of feed intake in rabbits. This was not the case in the present experiment since the concentration of digestible energy was similar on all diets. The lower gross energy content of the blocks than the commercial pellets (12.3 ± 0.23 compared with 15.0 ±0.01 MJ/kg DM) was compensated by improved digestibility of the energy and specifically the fibrous fraction.
It should be noted that the growth performance on the commercial pellets was much lower (15 g/day) compared to studies carried out by Awotarowa (1992) where rabbits fed commercial pelleted feeds gained 30 g/head/day. The performance on the commercial pellets as the only feed indicates that the MNB supplied nutrients that were deficient in the pellets. The fact that the increase in liveweight gain due to the MNB (by 60 and 80% respectively, on MNB15 and MNB30), was much greater than the increase in the intake is a further indication that the overall diets on the MNB treatments were better balanced nutritionally than the pellets.
The MNB thus appeared to have a synergistic effect on intake and growth despite their apparently lower content of major nutrients compared with the pelleted concentrate. The highly digestible fibre (from the wheat bran) and presence of microbial growth factors (from the molasses) are likely to be the major causes of this synergism. The final outcome is that the diets with supplementary MNB offered a better balance of essential nutrients which, as stated earlier, is the major determinant of feed intake and therefore of growth rate.
The costs to produce 1 kg of blocks were calculated taking into account the needs for transport, equipment and labour, using unit charges normally allocated by the Agricultural Research and Extension Unit (AREU) (Bheekee, personal communication) for preparation of blocks for ruminants. The total cost to produce the blocks was estimated (Table 5) to be Rupees (Rs) 5.40/kg (1 US$ = 25 Rs, 1999 exchange rate) compared with Rs 7.20/kg for the commercial pelleted feed.
From an economic standpoint, there were distinct advantages from feeding the multi-nutrient blocks. Feed costs per unit gain in liveweight were lower by 25 and 36% for treatments MNB15 and MNB30, respectively (Table 5).
| Table 5: Cost elements for 1 kg of blocks | |
| Items | Rs |
| Ingredients | |
| Molasses | 0.3 |
| Wheat bran | 0.9 |
| Cottonseed meal | 0.5 |
| Mineral mixture | 0.5 |
| Salt | 0.1 |
| Cement | 0.1 |
| Labour | 1 |
| Transport | 1 |
| Equipment | 1 |
| Total | 5.4 |
The encouraging results from feeding molasses-based multi-nutrient blocks to rabbits as a supplement to a commercial pelleted feed are in agreement with findings in Vietnam (Dinh Van Binh et al 1991). The next step is to determine if the blocks, made from local resources, can be used as a supplement to local forages with the aim of replacing completely the commercial pelleted concentrates which are based mainly on imported ingredients.
Valuable help was received from Mr. Bheekee (Research Officer, Agricultural Research and Extension Unit). The authors wish to acknowledge the technical support of Mr. Chamroo, former acting farm manager and Messrs Baba and Khidaruth (stockmen) of the University Farm.
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Received 30 July 1999