Feeding systems for tropical rabbit production emphasizing roots, tubers and bananas
by P.R. Cheeke

INTRODUCTION

Rabbits have potential as meat-producing animals in the tropics, particularly on subsistence-type small farms. Such characteristics as small body size (thus low daily feed requirements), short generation interval, high reproductive potential, rapid growth rate and the ability to utilize forages and fibrous agricultural by-products are attributes in favor of rabbit production (Cheeke, 1986). In spite of these apparent advantages, rabbit production has not yet achieved its potential in the tropics. Productivity is 50% or less of what is typical in temperate areas (a characteristic not unique to rabbits). While heat stress is a major factor accounting for the low productivity, inadequate nutrition is also very important. The limiting nutritional factor is probably digestible energy. Feeding programs that incorporate cull bananas, plantains, cassava, and various tropical fruits, sugar cane products, and agricultural by-products such as rice bran and other grain-milling by-products, should be developed. These materials are excellent sources of digestible energy, and can be used to supplement legume forages (e.g. tree legumes) which are good sources of protein.

Murgueito (1990) has suggested that tropical animal production should become more intensive, with animals managed in confinement. Tropical forest destruction is of global significance, and clearing of rain forests for pasture has contributed significantly to forest destruction. By skillful use of sugar cane products, agricultural by-products and tree forages in an intensive, integrated sustainable agricultural system, animal productivity can be increased and environmental impacts of livestock production reduced. Rabbits, being small, herbage-consuming animals kept in confinement, would seem to be ideal components of intensive livestock production programs in the tropics.

The major nutritional requirements of rabbits of concern in small-scale tropical rabbit production are protein and energy. The rabbit is a small herbivore that has evolved a digestive tract uniquely suited to the utilization of herbage. Some of the characteristics of its digestive tract, which have been described in more detail by Cheeke (1987), will be briefly discussed. The digestive strategy of rabbits is to focus digestive effort on high quality components of plant cells, and to rapidly excrete the less easily digested fibrous material. This is accomplished by muscular activity of the proximal colon. Selective separation of the low density fiber particles and their excretion in the feces occurs, while the high density particles and fluid are transported by reverse peristalsis from the proximal colon to the cecum. Microbial fermentation is accomplished by cecal microorganisms. At least once per 24 hours, the cecal contents are evacuated, covered with a layer of mucus secreted by goblet cells in the proximal colon, and excreted as cecotropes. The cecotropes (soft or night feces) are consumed directly from the anus. Cecotrophy provides the animal with the products of microbial fermentation, such as microbial protein, volatile fatty acids and the water-soluble vitamins. The ability of rabbits to efficiently digest the protein in forages is associated with cecal fermentation and cecotrophy (Robinson et al., 1985).

PROTEIN SOURCES

Because of their efficient digestion of protein in forages and agricultural by-products, rabbits can derive most or all of their protein requirements from these materials. In the temperate countries, Medicago sativa (alfalfa, lucerne) is usually the major ingredient in rabbit diets. It provides protein, cecal-fermentable energy, minerals and vitamins, and is a good source of indigestible fiber. Even though the digestibility of fiber in rabbits is low, fiber is important in the diet because it is necessary for normal gut motility. With low fiber diets, hypomotility of the cecum and proximal colon occurs, leading to disturbances in cecal flora, and a high incidence of enteritis and diarrhea. The standard diets used at the OSU Rabbit Research center are based on alfalfa meal and wheat milling by-product (wheat mill run, middlings, bran or shorts). Excellent performance has been achieved with a diet containing alfalfa meal and wheat mill run as the sole sources of energy and protein (Raharjo et al., 1986a).

I propose that it should be feasible to develop similar types of diet programs for rabbits in tropical countries, using tropical forages in place of alfalfa, and rice bran, cassava, bananas and other fruit, roots, tubers, sugar cane and various by-products as sources of energy. Because of the cecal fermentation processes previously discussed, rabbits can derive more energy from fibrous non-lignified materials such as rice bran and other milling by-products, peels of banana, cassava and sweet potato and other similar products than can swine and poultry. Rabbit production can be successfully based on these products whereas poultry production cannot.

In order to most effectively develop feeding programs for rabbits utilizing tropical feeds, it is necessary to have a data base on their specific feeding properties for rabbits, including digestibility, palatability, nutrient content and effects on gut function and enteric disease. Raharjo (1987) conducted extensive studies of tropical feedstuffs in Indonesia as his Ph.D. thesis; parts of this work have been published (Raharjo et al., 1986a,b; 1988). This work revealed major differences in the digestibility of protein and energy in numerous tropical forages (Table 1). In general, many of the legumes, particularly tree legumes, had digestibilities comparable to those of alfalfa meal. Most tropical grasses, despite their deceptive lush, succulent appearance in some cases, are highly indigestible and should not be considered as suitable forages for rabbit production. In the case of legumes, one of the factors affecting digestibility and intake is their tannin content. Raharjo et al. (1990) found that black locust (Robinia pseudoacacia) leaf meal, a material with a high tannin content, had a very low nitrogen digestibility in rabbits and negative nitrogen retention (Table 2). Various tropical tree legumes such as Leucaena leucocephala and Calliandra spp. contain high levels of tannins, as do cassava and banana leaves. Processing methods such as ensiling and ammoniation should be evaluated for their effects on tannins.

* Cecotrophy was prevented by fitting the animals with a collar that prevented ingestion ofcecotropes.

Tannins are inactivated under alkaline conditions (Price et al., 1979). Other toxins in legume forages may also be of concern. Leucaena contains the toxic amino acid mimosine which causes poor growth, dermatitis and hair loss in rabbits (Ekpenyong, 1985). The relative importance of various toxins in leucaena to animal feeding is not clear (D'Mello and Acamovic, 1989). Dietary additives such as ferric sulfate and polyethylene glycol (PEG) are effective in overcoming growth inhibitory properties of leucaena (D'Mello and Acanovic, 1989) but the practicability of this approach in small scale rabbit production is questionable. The low digestibility of leucaena crude protein in rabbits (Harris et al., 1981; Tangendjaja et al., 1990) has been attributed to tannins by these authors. Tangendjaja et al. (1986) studied the changes in toxin content of leucaena leaves with leaf age. Mimosine was highest in young leaves (4.5%) and decreased to 2% by 10 weeks. There were no changes in fiber, tannin or phenolic concentrations with age, but protein decreased from 31% in young leaves to 14% in leaves 10 weeks of age.

While more complete information is needed on the feeding value of tropical legumes for rabbits, it seems apparent that various legumes could serve as the forage base for small-scale rabbit production. To reduce the likelihood of toxicity problems, use of a mixture of forages rather than a single species is recommended. Leucaena, for example, may be unsatisfactory as the sole forage, but a useful component of a forage mixture. The feasibility of small scale ensiling of forages in plastic bags or containers should be investigated. Ensiling with or without ammoniation may provide a means of detoxifying tannins, mimosine and other toxins, and storage of feed for the dry season. It would also be advantageous in eliminating the daily burden of forage collection. It is necessary to have more data of the type reported by Raharjo et al. (1986) so that only forages with high nutrient digestibility are used.

Besides tree legume forage, many other possibilities exist for the forage component, such as the leaves of sweet potato, ground nut, cassava and other crops, banana, papaya and other fruit crops, and grasses that have been tested to ensure adequate digestibility. Sweet potato foliage is very palatable to rabbits (Raharjo, 1987) and supports good performance (Mutetikka et al., 1990), while Rhodes grass (Chloris gayana) has a very low digestibility (Raharjo et al., 1986a) and does not support good rabbit performance (Mutetikka et al., 1990). Cassava forage contains condensed tannins and cyanogens (Reed et al., 1982) which may reduce palatability (Raharjo, 1987) and probably reduce animal performance. Again, by using a mixture of forages, effects of toxins can be minimized.

In addition to forages, other sources of protein may be needed. Usually, the most suitable protein sources will be those which are somewhat high in fiber, reducing their suitability for use with swine and poultry. Copra meal and palm kernel meal are examples. Groundnut meal, cottonseed meal and other common plant proteins may also be used if economics allow.

Tropical forages can supply a major part of the protein and fiber needs of rabbits. However, feeding forage alone will not support adequate growth and lactational performance. Supplementation with sources of energy is needed. Potential energy sources include roots and tubers (cassava, sweet potatoes), fruit (bananas, plantains, mangos, etc.), rice bran and other grain processing by-products, sugar cane products (whole cane, derinded cane, molasses, juice) and fats such as palm oil. The main apparent disadvantage of roots, tubers and fruit is their high water content. However, this may actually be an advantage. Enteritis in rabbits is provoked by overloading of the cecum with readily fermentable carbohydrate (Cheeke, 1987). Highly concentrated starch sources such as cereal grains promote carbohydrate overload. Although cassava and bananas are high in soluble carbohydrate, their high water content limits rate of dry matter intake and may reduce enteritis by supplying frequent small intakes of starch rather than large intakes of pelleted feed at one time, which is likely to cause carbohydrate overload. By not providing any other source of water, frequent intake of the forage, fruit and roots is promoted.

Omole (1990) has reviewed the use of cassava in rabbit feeding. Both cassava meal and cassava peel meal have supported adequate performance (compared to controls in the same environment) when used at levels up to 30–40% of the diet. In an experiment in Scotland, performed with cassava meal imported from Thailand, Radwan et al. (1985) observed excellent growth rates (41 g/day) of rabbits fed diets with up to 50% cassava meal, substituted for barley. Omole and Sonaiya (1981) noted better growth of rabbits when fishmeal rather than groundnut meal was the protein supplement in diets containing cassava peel meal, reflecting the poor protein quality of cassava protein. Cassava peel meal may contain a moderately high level of cyanogenic glycosides, which can be hydrolyzed to yield free cyanide. Omole and Onwudike (1983) reported evidence that inclusion of 5% palm oil in rabbit diets containing cassava peel meal reduced toxic effects of cyanide and increased the urinary excretion of thiocyanate in the urine. The necessity of processing cassava to reduce cyanide levels before use in rabbit diets has not been established in published work. Because any form of processing adds to feed costs and reduces the practicality of use of cassava on small farms, further research should be conducted with feeding raw cassava roots without processing, to determine the effects on performance and blood cyanide levels. Simple on-farm techniques such as chopping and partial sun-drying may also be adequate in reducing free cyanide in cassava.

Bananas should also have potential as a means of supplementing forages to increase energy intake, although little data has been published on banana feeding to rabbits. Gidenne (1986) fed whole green banana to rabbits fed ad libitum with commercial pelleted diet. Rabbits consumed up to 120 g per day of fresh banana, equal to about 32% of total dry matter consumption. Presumably, if the amount of pelleted diet had been restricted, banana intake would have been greater. Gidenne (1986) estimated the digestible energy value of green banana to be 3640 kcal/kg DM. More research is needed on feeding green and ripe bananas to rabbits as supplements to forage-based diets, using a feeding system that would be appropriate for small scale tropical rabbit production.

Sweet potato is another crop for which there is little data available relevant to rabbit feeding. Raharjo (1987) and Mutetikka et al. (1990) found that sweet potato forage was very palatable to rabbits. If this observation extends to the roots as well, they should be valuable as energy supplements. The use of mixtures of bananas, cassava and sweet potato should also be examined.

Other products with potential as energy supplements for rabbit production in developing countries are sugar cane, sugar cane juice and molasses. Sugar cane might be regarded as the tropical equivalent of grain (Preston and Leng, 1987). If the outer rind is removed, sugar cane is readily consumed by rabbits (Kentor, 1990). Sugar cane juice has also been fed with some success (Solarte, 1989). Molasses is highly palatable to rabbits, and can be mixed with dry ingredients to form a palatable mash that is well accepted (Kentor, 1990). In Haiti, a large commercial rabbitry uses a concentrate supplement of wheat milling by-product mixed with 25% molasses (Kentor, 1990). Sucrose acts as a preservative (mold inhibitor), which is a further advantage of its use in a concentrate supplement.

Grain milling by-products such as rice bran and wheat bran are excellent feedstuffs for rabbits (Raharjo et al., 1986a, 1988). The fiber fraction is not lignified, and has a high digestibility in rabbits. Grain by-products provide useful amounts of protein, energy and fiber, without inducing enteritis problems from carbohydrate overload (Cheeke, 1987). Thus where these products are available, they can form the basis of the concentrate part of rabbit diets. In Indonesia, for example, rice bran is readily available and is used as a moist mash to supplement free choice forages (Cheeke, 1983). In those areas where rice bran and molasses are both readily available, a mixture of these two ingredients will provide a palatable, high energy supplement.

FEEDING SYSTEMS

Where rabbits are raised on a back-yard scale on subsistence-type farms in the tropics, feeding systems should be as simple as possible. In many instances, the feeding system can be based on free-choice forages with a concentrate supplement. Bananas, cassava, sweet potato roots, other starch crops and fruits and sugar cane are products which could be fed without much processing. Since they are succulent, high-moisture materials, they can be fed without the provision of drinking water. Rabbits full-fed on tropical forage may not consume enough to satisfy their water requirements (Jin et al., 1990). Supplementation with roots (cassava, sweet potato) and fruit (banana) may allow the animals to meet their water requirements as well as increasing energy intake.

Thus the simplest feeding system would be the free choice feeding of good-quality tropical forages supplemented with roots, tubers and fruit. The adequacy of this feeding system needs to be established by feeding trials conducted in tropical environments.

Another feeding system is the preparation of a concentrate mash. Mashed roots, tubers and fruit could be mixed with rice bran and molasses to produce a palatable mash or meal-type diet. By adjusting the proportions of bran, a mixture with optimal moisture content could be prepared. Sufficient molasses could be added to inhibit mold growth. Such a mixture could be stored in sealed plastic bags, and prepared at intervals of perhaps once a week.

In some situations, it might be desirable to preserve feed for feeding at a later date, such as conservation of feed for the dry season, or storage of excess cull fruit or tubers. This could be accomplished by the ensiling process. Bananas can be readily ensiled (Le Dividich et al., 1975), because of their high content of readily fermentable carbohydrate. Bananas, sweet potato, cassava, and other fruits could be ensiled with rice bran to produce a high energy concentrate supplement. Silage could be readily prepared on small farms by packing into inexpensive plastic bags. A quantity could be removed for feeding each day, with the bag resealed to prevent spoilage. As a refinement of this system, the forage component could be included in the silage. Tropical forages are often difficult to ensile, because of their structure and low content of fermentable carbohydrate. By combining them with bananas and other products rich in soluble carbohydrates, a complete feed could be prepared as silage. This would facilitate small scale rabbit production by eliminating the daily need for collecting greens. Enough silage could be readily prepared at one time to last several months. It would be stored anaerobically in plastic bags in the shade, and used as needed.

RECOMMENDATIONS

Rabbit production offers great potential as a means of converting tropical forages and agricultural by-products to human food (rabbit meat). However, this potential has not been realized to much extent. With a few exceptions, most rabbit projects in developing countries have failed to be sufficiently productive to have much impact. While there are a number of reasons for this, one of the major ones is nutrition. Feeding programs currently used result in extremely low growth rates, prolonged time for animals to reach slaughter weight, and a lack of reproduction.

I recommend that a pan-tropical series of feeding trials be conducted at a number of research stations, following standard protocols so that the individual trials can be evaluated, analyzed and reported as a single study. Researchers in Africa, Central America, South America and South-east Asia should be identified for participation. The objective is to evaluate the use of common feedstuffs under conditions simulating their use by small farmers. A series of experiments is suggested as a focus for discussion.

1. Evaluation of bananas, cassava and sweet potatoes as supplements to tropical forages.

Objective: To determine the productivity of rabbits fed forage free choice and either cassava, bananas or sweet potatoes free choice, with no processing. This would be the most simple feeding system possible.

Treatments:

1. Control: pelleted diet

2. Banana free choice + forage free choice

3. Cassava free choice + forage free choice

4. Sweet potato free choice + forage free choice

Ten breeding does per treatment would be fed these diets for a period of one year, and production of meat rabbits measured. This would be a sufficient period to demonstrate conclusively if the treatments based on roots, fruit and forage can sustain rabbit production.

The pelleted diet would be a standard commercial diet from North America or Europe, distributed to each investigator. The use of this standard diet would provide a standard of comparison among experiments in different countries. Further, it would help answer a very important question: To what extent is nutrition responsible for poor performance of rabbits in the tropics? In temperate countries, average daily gain (ADG) of market rabbits is 35–45 g. Typical values from experiments reported from the tropics are ADG of nil to about 20 g per day, with 3–8 g being a common range. There has not been a comparison of rabbits in the tropics and in temperate countries fed exactly the same diet, to determine how the animals could perform in the tropics if fed an adequate diet. This experiment would demonstrate what levels of production are possible in tropical environments, so that the responses to diets of tropical ingredients can be adequately assessed.

2. Development of a concentrate supplement using agricultural by-products.

Objective: To prepare a mixed mash-type concentrate based on a dry ingredient (rice bran or other grain milling by-product) with bananas, cassava and sweet potato. The mash could be tested with and without molasses. In sugar cane-producing areas, molasses or cane juice would be beneficial in providng energy and palatability, and retarding mold growth.

Treatments:

1. Control: pelleted diet or other standard

2. Tropical forage ad lib + banana mash^*

3. Tropical forage ad lib + cassava meal

4. Tropical forage ad lib + sweet potato mash

5. Tropical forage ad lib + BCS + mash

^* Mash composition:

+ BCS = equal proportions of banana, cassava and sweet potato in the above mash formula.

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