This paper reviews the development of multi-nutrient blocks (MNB) for rabbits in Mauritius with special emphasis on the choice of ingredients, formulation and preparation. In Mauritius, the most appropriate ingredients are: molasses, wheat bran, cottonseed meal, cement, mineral mixtures and common salt. Selection of the final formula and casting procedure was arrived at by an empirical method of trial and error. The final product was a mini-block weighing 15 g.
Multi-nutrient blocks (MNB) are a commonly used feed supplement for ruminants (Leng 1984; Sansoucy 1986; Garcia and Restrepo 1995). They provide fermentable energy (usually from molasses), non-protein nitrogen (usually from urea), essential minerals and occasionally vitamins. Mini-blocks for rabbits have been made in the past (Perez 1986; Cheeke and Raharjo 1988). Feeding such blocks to rabbits has several advantages since they can be distributed on the ground or the floor of the cage, without the need of a specialised feeder and without wastage (Fillippi et al 1992). Mini-blocks can be a complete feed for rabbits by including a source of forage in the formulation (Perez 1990). An experiment carried out in Vietnam by Dinh Van Binh et al (1991) showed that MNB based on molasses could be fed successfully as a partial substitute for cereal-based concentrates for rabbits during all phases of production.
In different countries, various formulations have been tested according to the different ingredients available and their prices. At the University of Mauritius Farm, a programme was established with the main objectives: to choose locally available ingredients for the preparation of MNB for rabbits, to prepare the MNB in a form acceptable to the animals, and at a later stage to determine the utilisation of MNB by the rabbits.
This paper describes the ingredients that were used and the procedures for making the blocks.
In this study, the ingredients used for the MNB were molasses, wheat bran, cottonseed meal, cement, a commercial mineral mixture and common salt. Features of these ingredients that are relevant to rabbit nutrition are:
Molasses is a liquid feed derived from the extraction of sucrose from sugar cane. It is usually the cheapest source of energy for livestock in countries where sugar cane is a major crop (Hulman 1989). It is rich in soluble sugars (sucrose, glucose and fructose) and in minerals. It contains neither fibre nor lipids and the nitrogenous fraction is low, soluble, and in a non-protein form (Huque and Stem 1994, Perez 1997). Its vitamin content is not very high but it does contain a series of water-soluble vitamins. It is also a source of trace elements such as cobalt and copper (Paturau 1985; Preston 1995). It can be an important source of sulphur when this element is used in the process of clarification of the sugar cane juice.
It is not feasible to feed liquid molasses to rabbits, hence the idea of the solid block or cake in which the molasses is mixed with fibrous by-products (Preston 1995). Molasses is highly palatable and it increases the acceptability of feed to rabbits.
Wheat bran consists of the outer covering of the wheat kernel and is a by-product of manufacture of flour. It is locally available in almost all countries. Its content of fibre (about 10%) makes it a good absorbent for molasses and thus a logical component of multi-nutrient blocks. Wheat bran is rich in phosphorus (>2%) but low in calcium (<0.5%). It is also a source of B-vitamins and is highly palatable.
Cottonseed seed meal is a by-product from the extraction of edible oil from cottonseed (Gossypium spp). It is usually the cheapest protein supplement in most tropical countries and is highly appropriate for ruminants as it is a good source of "bypass" or "escape" protein (Preston and Leng 1987). The presence of the toxin "gossypol" limits its use for rabbits to relatively low levels.
The main constituents of ordinary cement, according to Arora and Bindra (1996), are lime and silica with lesser quantities of oxides of aluminium, iron, magnesium, sulphur and potassium and sodium. Aluminium oxide gives cement the "gelling" characteristic which makes it an important ingredient in MNB. To a major degree, the hardness of MNB can be controlled by varying the proportion of cement (Amici and Finzi 1994). Cheeke et al (1987) showed that cement does not affect growth rate or cause enteritis in the rabbit.
Salt is an essential nutritional element but, at the 5% level, acts to deter livestock from ingesting too much of the block at any given time (Huque and Stem 1994). The multi-nutrient block is an excellent vehicle for supplying minerals.
Initially, flower pots made from synthetic materials having 500ml capacity were used
for casting the blocks. However, these pots were found to produce
blocks which were too large for the rabbits to bite. The size of the pots was then
reduced, via trial and error, arriving at a capacity of 15ml. However, these
small pots were difficult to obtain. This led to the choice of plastic egg trays and
eventually to trays of synthetic material used for germinating seeds. These were cheap and
readily available in the local market and were used to produce blocks weighing 15 g. It
was found that "mini-blocks" of this size and form were the most acceptable to
the rabbits. During casting, a thin plastic sheet was placed in the moulds to facilitate
removal of the blocks after setting. This prevented the MNB from sticking directly to the
moulds. The plastic sheet was also used to wrap the blocks, thus
preventing loss of moisture and facilitating storage. The MNB were stored in covered
plastic pails to safeguard against rodents and insects while avoiding exposure to factors
such as high temperature, humidity and fungal growth. The blocks were found to keep well
for at least two months.
Table 1 shows three different formulations. The first one was designed and manufactured for ruminants by the Ministry of Agriculture. The second one was the first formulation tried for rabbits, while the last one was the final choice.
|Table 1: Formulations for multi-nutrient blocks (parts by weight)|
|Cotton seed meal||5||10||10|
|* : blocks too hard; ** : formulation used for experimentation|
The sequence of mixing the ingredients was found to be very important. For the preparation of 60 mini-blocks (each block weighing 15 g) the procedure was as follows:
All the ingredients were weighed separately according to the formulation and placed in different containers. Three other containers of different capacities (250 ml, 2 litres and 5 litres) were used for mixing.
a) In the smallest container (250 ml), cement was mixed thoroughly with half the portion of common salt. This would later help in avoiding formation of lumps.
b) In the second container (2 litres), the cottonseed meal and the remaining common salt were mixed thoroughly.
c) The third container was large enough (5 litres) to receive all the ingredients. Molasses and mixtures (a) and (b) above were mixed together. Finally, the wheat bran was added and all the ingredients were mixed thoroughly to obtain a homogeneous product.
e) The moulds were kept for setting in a dry and shaded place, protected from rodents and insects.
f) The moulds were transferred into plastic pails and covered.
Investigations by Balestral et al (1992) on the technological characteristics of MNB as supplements for the rabbit showed that the intake is linked to size, shape, composition and hardness of the blocks. Experience in preparing the mini-blocks at the University Farm confirmed the need for small size (15 g) and that intake declined with increasing block hardness. Studies on the effects of the blocks on digestibility and growth parameters are described in a companion paper.
We are grateful to the following persons for assistance: Mr H. Beekhee, Scientific Officer, Agricultural Research and Extension Unit, Food and Agriculture Research Council; Mr K Chamroo, Acting manager, University Farm; Mr A. Ruggoo, Faculty of Agriculture, University of Mauritius.
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