In an adult (4 to 4.5 kg) or semi-adult (2.5 to 3 kg) rabbit the total length of the alimentary canal is 4.5 to 5 m. After a short esophagus there is a simple stomach which stores about 90 to 100 g of a rather pasty mixture of feedstuffs.
The adjoining small intestine is about 3 m long and 0.8 to 1 cm in diameter. The contents are liquid, especially in the upper part. Normally there are small tracts, about 10 cm long, which are empty. The small intestine ends at the base of the caecum. This second storage area is about 40 to 45 cm long with an average diameter of 3 or 4 cm. It contains 100 to 120 g of a uniform pasty mix with a dry matter content of about 22 percent. The caecal appendix (of 10 to 12 cm) has a much smaller diameter at the end. Its walls are composed of lymph tissues.
Very near the end of the small intestine, at the entrance to the caecum, begins the exit to the colon. The caecum thus appears to be a blind pouch branching off from the small intestine-colon axis (Figure 2). Physiological studies show that this blind pouch-reservoir forms part of the digestive tract: the contents circulate from the base to the tip passing through the centre of the caecum, then return towards the base, along the wall. The caecum is followed by a 1.5 m colon: this is creased and dented for about 50 cm (proximal colon) and smooth in the terminal section (distal colon).
These various organs are shown in Figure 2, which also presents data on the size and features of their contents.
The alimentary canal, which develops rapidly in the young rabbit, is nearly full size in an animal of 2.5 kg, when it has reached only 60 to 70 percent of adult weight.
Two major glands secrete into the small intestine: the liver and the pancreas. Bile from the liver contains bile salts and many organic substances which aid digestion, but has no enzymes. The reverse is true of pancreatic juice which contains a sizeable quantity of digestive enzymes allowing the breakdown of proteins (trypsin, chymo-trypsin), starch (amylase) and fats (lipase).
Generally speaking, the length of the small intestine (3 to 3.5 m) and its relatively small capacity contrast with that of the storage area (the stomach and caecum), which hold 70 to 80 percent of the total dry matter content of the digestive tract. The water content can vary markedly from one segment to the next owing to bodily secretions and water absorption.
Digestive tract and caecotrophy
Feed eaten by the rabbit quickly reaches the stomach. There it finds an acid environment. It remains in the stomach for a few hours (three to six), undergoing little chemical change. The contents of the stomach are gradually "injected" into the small intestine in short bursts, by strong stomach contractions. As the contents enter the small intestine they are diluted by the flow of bile, the first intestinal secretions and finally the pancreatic juice.
After enzymatic action from these last two secretions the elements that can easily be broken down are freed and pass through the intestinal wall to be carried by the blood to the cells. The particles that are not broken down after a total stay of about one and a half hours in the small intestine enter the caecum. There they have to stay for a certain time, from two to 12 hours, while they are attacked by bacterial enzymes. Elements which can be broken down by this new attack (mainly volatile fatty acids) are freed and in turn pass through the wall of the digestive tract and into the bloodstream.
FIGURE 2 The digestive system of the rabbit
The contents of the caecum are then evacuated into the colon. Approximately half consists of both large and small food particles not already broken down, while the other half consists of bacteria that have developed in the caecum, fed on matter from the small intestine.
So far, the functioning of the rabbit's digestive tract is virtually the same as that of other monogastric animals. Its uniqueness lies in the dual function of the proximal colon. If the caecum contents enter the colon in the early part of the morning they undergo few biochemical changes. The colon wall secretes a mucus which gradually envelops the pellets formed by the wall contractions. These pellets gather in elongated clusters and are called soft or night pellets (more scientifically, caecotrophes). If the caecal contents enter the colon at another time of day the reaction of the proximal colon is entirely different.
Successive waves of contractions in alternating directions begin to act; the first to evacuate the contents normally and the second to push them back into the caecum. Under the varying pressure and rhythm of these contractions the contents are squeezed like a sponge. Most of the liquid part, containing soluble products and small particles of less than 0.1 mm, is forced back into the caecum. The solid part, containing mainly large particles over 0.3 mm long, forms hard pellets which are then expelled. In fact, as a result of this dual action, the colon produces two types of excrement: hard and soft. Table 14 shows the chemical composition of these pellets.
The hard pellets are expelled, but the soft pellets are recovered by the rabbit directly upon being expelled from the anus. To do this the rabbit twists itself round, sucks in the soft faeces as they emerge from the anus, then swallows without chewing them. The rabbit can retrieve the soft pellets easily, even from a mesh floor. By the end of the morning there are large numbers of these pellets inside the stomach, where they may comprise three quarters of the total contents.
From then on the soft pellets follow the same digestive process as normal feed. Considering the fact that some parts of the intake may be recycled once, twice and even three or four times, and depending on the type of feed, the rabbit's digestive process lasts from 18 to 30 hours in all, averaging 20 hours.
The soft pellets consist half of imperfectly broken-down food residues and what is left of the gastric secretions and half of bacteria. The latter contain an appreciable amount of high-value proteins and water-soluble vitamins. The practice of caecotrophy therefore has a certain nutritional value.
The composition of the soft pellets and the quantity expelled daily are relatively independent of the type of feed ingested, since the bacteria remain constant. In particular, the amount of dry matter recycled daily through caecotrophy is independent of the fibre content of the feed (Table 7-15). The higher the crude content of the feed and/or the coarser the particles, the sooner it passes through the digestive tract.
On the other hand, this particular function requires roughage. If the feed contains few large particles and/or it is highly digestible, most of the caecal contents are pushed back to the caecum and lose elements which nourish the "normal" bacteria living in the caecum. This would appear to increase the risk of undesirable bacteria developing in this impoverished environment, some of which might be harmful.
It is thus advisable to include a minimum of roughage in the feed, enabling the rabbit's digestive process to be completed fairly rapidly. In theory, roughage is provided by the crude-fibre content of the feed, as this is normally rather hard to digest. However, certain fibre sources (beetroot pulp, fruit pulp in general) are highly digestible (digestibility of crude fibre varies from 60 to 80 percent). Recommendations now made on quantities of indigestible crude fibre to be fed are therefore given below. Table 16 gives the chemical composition of various raw materials which can be fed to rabbits.
Caecotrophy regulation depends on the integrity of the digestive flora and is governed by intake rate. Experiments have shown that caecotrophy starts eight to 12 hours after the feeding of rationed animals, or after the intake peak of animals fed ad lib. In the latter case, the intake rate and hence the function of caecotrophy are governed by the light regime to which the animals are subjected.
Caecotrophy also depends on internal regulatory processes as yet not understood. In particular, the removal of the adrenals halts caecotrophy. Cortisone injections of animals without adrenals causes the resumption of normal behaviour. The digestive process of the rabbit appears to be highly dependent on adrenalin secretions. Hypersecretion associated with stress slows down digestive activity and entails a high risk of digestive ailments.
TABLE 14 Composition of hard and soft faeces: averages and range for ten different feeds
TABLE 15 Intake and excretion of dry matter by growing rabbits eating isonitrogenous feeds containing two levels of straw in place of maize starch
Caecotrophy first starts to function in young rabbits (domesticated or wild) at the age of about three weeks, when they start eating solid feed in addition to mother's milk.
Feeding behaviour studies have basically involved rabbits receiving balanced concentrates or fed ad lib on dry feed (cereals, straw, dry forage).
The feeding pattern of newborn rabbits is imposed by the dam. A doe feeds her young only once every 24 hours (although some does will nurse their young twice). Suckling lasts only two or three minutes. If there is not enough milk the young try to feed every time the doe enters the nestbox, but she will hold back her milk. This behaviour signals insufficient milk production in the doe.
TABLE 16 Chemical composition of different raw materials suitable for feeding rabbits
From the third week of life the young rabbits begin to move about, taking a few grams of mother's milk and a little drinking water if available. In a few days the intake of solid feed and water will exceed the milk intake. During this period the changes in feeding behaviour are remarkable: the young rabbit goes from a single milk feed a day to a large number of alternating solid and liquid feeds distributed irregularly throughout the day: 25 to 30 solid or liquid meals every 24 hours.
Table 17 gives an example of changing feeding behaviour in New Zealand White rabbits, aged from six to 18 weeks.
The number of solid meals, stable up to 12 weeks, tends to decrease slightly thereafter. The total feeding time in a 24-hour period exceeds three hours at age six weeks. It then drops off rapidly, to less than two hours. At any age, feed containing over 70 percent water, such as green forage, will provide rabbits with ample water at temperatures below 20°C.
The consumption of solid and liquid intake fluctuates over a 24-hour period, as shown in Figure 3. Much more liquid and solid feed is consumed in the dark than in the light.
Intake in experimental hutches is very high just before the lights are switched off. As the rabbit grows older the nocturnal nature of its feeding habits becomes more pronounced. The number of feeds during light periods drops and the morning "feeding rest" tends to lengthen. The feeding habits of wild rabbits are even more nocturnal than those of domesticated rabbits.
The intake of feed and water depends on the kind of feed and also on the type of rabbit and its age and stage of production. Taking as a reference animal an adult fed ad lib (140 to 150 g of dry matter per day, for example, for a 4 kg New Zealand White): at four weeks a young rabbit eats a quarter of the amount an adult eats but its live weight is only 14 percent of the adult's. At eight weeks the relative proportions are 62 and 42 percent; at 16 weeks they are 100 to 110 and 87 percent.
A doe's ad lib feeding during the reproduction cycle varies greatly (see Figure 4). The intake during the final days of pregnancy drops off markedly. Some does refuse solid food just before kindling. Water intake, however, never stops completely. After kindling, the feed intake increases very rapidly and can exceed 100 g dry matter/kg live weight a day. Water intake is also high at that time: from 200 to 250 g a day per kg of live weight. A doe that is both pregnant and lactating will eat the same amount as a doe that is lactating only.
TABLE 17 Changing feed habits of nine New Zealand White male rabbits aged from 6 to 18 weeks, given water and balanced feed ad lib in a room kept at 20±1°C
FIGURE 3 Hourly distribution of daily intake of water and balanced pelleted feed of a 12-week-old rabbit aver a period of 24 hours
Feeding and environment
The rabbit's energy expenditure depends on ambient temperature. Feed intake to cope with energy needs is therefore linked to temperature.
Laboratory tests on growing rabbits have shown that at temperatures between 5°C and 30°C intake of pelleted feed dropped from 180 to 120 g a day and water intake rose from 330 to 390 g (Table 18).
A closer analysis of feeding behaviour shows that as temperature rises the number of solid and liquid meals eaten in 24 hours drops. From 37 solid feeds at 10°C the number drops to only 27 at 30°C (young New Zealand White rabbits). The amount eaten at each meal drops with high temperatures (5.7 g from 10°C to 20°C down to 4.4 g at 30°C) but the water intake goes up, from 11.4 to 16.2 g between 10°C and 30°C.
A recent study by Finzi, Valentini and Fillipi Balestra (1992) shows a marked increase in the water/food intake rate at higher temperatures (20°C, 26°C and 32°C), which was already known, but the various ingestion and excretion ratios are also modified (Table 19). The authors propose that these ratios, the easiest to measure locally, be used to identify thermal stress in rabbits.
If drinking water is not provided and the only feed available is dry with a moisture content of less than 14 percent, dry matter intake drops to nil within 24 hours. With no water at all, depending on temperature and humidity, an adult rabbit can survive from four to eight days without any irreversible damage, although its weight may drop 20 to 30 percent in less than a week.
FIGURE 4 Changing intake of balanced concentrate feed (89 percent DM) in a doe during gestation and lactation
Rabbits with access to drinking water but no solid feed can survive for three or four weeks. Within a few days they will drink four to six times as much water as normal. Sodium chloride in the water (0.45 percent) reduces this high intake, but potassium chloride has no effect (sodium loss through urination). The rabbit is therefore very resistant to hunger and relatively resistant to thirst; but any reduction in the water supply, in terms of water requirements, causes a proportional reduction in dry matter intake, with a consequent drop in performance.
The growth performance of rabbits is significantly reduced if they are given salted drinking water with a sodium content higher than 1 percent.
Work in Egypt by Ayyat, Habeeb and Bassuny (1991) showed a 12 to 16 percent slowing of growth speed at sodium contents of over 1.5 percent (Table 20). Solid granulated feed ingestion remained unchanged by water salinity whereas water intake increased slightly with salinity: 14 to 16 percent in the trial by Ayyat and colleagues. However, even at sodium contents exceeding 2 to 4 g (6 g of Rashid salt), no mortality was reported from this eight-week trial, and the rabbits still grew at a rate of 23 g/day:77 percent compared with the control.
Given a choice of several feeds rabbits are often unpredictable. When dehydrated alfalfa and dry grain maize are offered the ratio chosen is 65 percent alfalfa to 35 percent maize. With alfalfa and oats the ratio is 60 to 40. But if the maize grains are rather moist, say with a 14 to 15 percent moisture content which could cause storage problems, the proportion of maize rises to 45 to 50 percent. When rabbits are offered rations containing dehydrated alfalfa with a variable saponin content, which gives the feeds varying degrees of bitterness, they choose the relatively bitter feeds. Such feeds are ignored by rats and pigs, as shown by Cheeke, Kinzell and Pedersen's (1977) tests in the United States.
TABLE 18 Changing feed and water intakes of growing rabbits in changing temperatures
TABLE 19 Impact of ambient temperature on intake and excretion ratios in adult rabbits
TABLE 20 Impact of drinking-water salinity on rabbit growth performance
Feeding rabbits forage plus supplementary concentrate feed raises problems when the forage is not very palatable. The experimental findings in Table 21 demonstrate that in ad lib feeding of both high-bulk (straw, in this trial) and high-energy pelleted feeds rabbits are unable to adjust intake for maximum growth. A breeder faced by such a situation should limit the daily dose of concentrate feed or, generally speaking, the proportion of the more palatable feed. The problem sometimes arises with certain low-value green forages.
The situation changes if the rabbit is faced with two high-energy foods, as in Gidenne's (1986) trial with ad lib feeding of balanced pelleted feed and green banana. In this example, the ad lib trial rabbits grew as much as the control group and their digestible energy intake was identical. However, between weaning at five weeks and the close of the 12-week trial, the banana intake dropped from 40 percent to 28 percent of the daily dry matter intake.
Growing rabbits receiving a pelleted feed lacking in sulphur amino acids or lysine, with access to pure water as well as those missing amino acids in solution, choose the amino acid solution over pure water. Thus they grow as well as control rabbits receiving balanced feed.
Various research experiments carried out in many countries (especially France) in the last 20 years or so have resulted in reliable recommendations for the manufacture of rabbit feeds for meat and milk production in temperate European conditions.
The experimental technique consists of manufacturing feeds in exact but varied mixes, feeding them to rabbits and assessing production by weight gain or number and weight of young in a litter. The best feeds are thus established and the best mixes selected, allowing nutrition experts to draw up recommendations for several categories. The most common feed categories in intensive European rabbitries are for breeding females (lactating does, pregnant or not), young rabbits of weaning age (post-weaning or peri-weaning feeds, the latter also consumed by the mother) and rabbits for fattening. Also included in the range supplied by livestock feed manufacturers is a mixed feed that can acceptably cover the nutritional needs of all rabbit categories providing the breeder's objective is not maximum productivity.
TABLE 21 Feed intake and growth of New Zealand White rabbits aged between five and nine weeks, receiving ad lib a concentrated feed rich or poor in fibre, with and without wheat-straw pellets 5 mm in diameter
These standards have been established for environmental conditions in Europe and are also based on the relative costs of nutrients in European countries. They are reference standards, but can be varied slightly for better economic performance according to locally available cheap feed resources. The upper and lower limits (which should not be exceeded) are listed at the end of this chapter.
Lactating does need the richest, most concentrated feed. They produce a milk three times richer than cow's milk, at the rate of 100 to 300 g per day, and have few reserves in relation to the demand made on them. The next category is growing rabbits (far more research work has been done on this than any other category). Young rabbits are followed by pregnant non-lactating does. Their feed can be slightly less rich than that of young growing rabbits. The last category is bucks, which do not need a rich diet.
Table 22 details the chemical composition of theoretically ideal feeds for each rabbit category. There are four broad classes of standards. First, standards on proteins and protein composition (distribution of amino acids). Proteins must supply the elements to build or rebuild rabbit bodies. The proportion of indigestible fibre serves to provide the slight congestion essential for the proper functioning of the digestive tract. The corresponding proportion of fibre can also be estimated by the acid detergent fibre (ADF) content as per Van Soest or, preferably, indigestible ADF. Energy is needed to regulate body temperature as well as for the general functioning of the body. Minerals and vitamins are building blocks for certain parts of the animal (skeleton, etc.) and for the enzymes which use energy to build and rebuild the body proteins continually. Table 22 also includes a column showing the chemical composition of a mixed feed suitable for all animals in a production unit. Its composition represents a compromise between the requirements of growing rabbits and those of lactating does. The other categories can, in fact, eat a richer feed without suffering any major drawbacks. Further on in the text it will be explained under what circumstances it is desirable to use mixed or more specialized feeds. But, first, the various feed requirements are explored in greater depth.
Nitrogen. The rabbit's response to the quality of the proteins in its diet, long a controversial issue, has now been established beyond doubt. Researchers have found that growing rabbits need feed that contains certain amounts of ten of the 21 amino acids that made up the proteins. These are called the basic or essential amino acids. With two additional amino acids which can partially replace two of the essential amino acids, this is the full list for rabbits: arginine, histidine, leucine, isoleucine, lysine, phenylalanine plus tyrosine, methionine plus cystine, threonine, tryptophane and valine.
Studies on the quantities needed have been virtually confined to arginine, lysine and the sulphur amino acids (methionine and cystine). Expressed as a percentage of the ration, the lysine requirements for growing rabbits are 0.6 and, for sulphur amino acids, 0.7 percent. The lysine intake of breeding does should be considerably higher under intensive milk production to feed nine to 12 young. The arginine intake should be at least 0.8 percent, and a little more for growing rabbits. The toxicity thresholds of lysine and arginine are well above the recommended intake levels. For the sulphur amino acids, however, there is a slender margin between the amount the rabbit needs and an excess dose that would diminish its performance.
TABLE 22 Recommended chemical composition of feeds for intensively reared rabbits of different categories
The recommended amounts of other essential amino acids have been estimated simply on the basis of regular satisfactory diets. Where these essential amino acids are supplied by protein in the diet, 15 to 16 percent crude proteins should be enough for fattening rabbits. Rabbits will always eat more of a balanced feed containing essential amino acids than the same feed without amino acids.
Amino acid balance can easily be achieved with plant protein alone as in almost all balanced European feeds. Proteins of animal origin can be used by rabbits but are absolutely unnecessary: all that counts is the amino acid intake, not the substratum.
The optimum dose of crude protein for the breeding doe seems to be roughly 17 to 18 percent. An increase of protein content to 21 percent leads to higher milk production but slightly reduces the number of young rabbits weaned in a given period.
Lastly, various attempts to replace true proteins by non-protein nitrogen (urea and ammonium salts) have almost all been economic failures, because these sources of nitrogen either degrade or are absorbed too early for the micro-organisms in the caecum to take them up. For a highly nitrogen-deficient ration (30-50 percent below requirements), however, or for a non-protein source which breaks down at average speeds in the intestine (such as biuret), there is a certain amount of uptake. In any case, it is highly recommended that rabbits receive their nitrogen ration in the form of true proteins with balanced amino acids.
Energy and crude fibre. The energy needed for organic synthesizing is usually supplied by carbohydrates and to a lesser extent by fats. Where there is an excess of proteins these also help to supply energy after deamination.
The growing rabbit, like the breeding doe, adjusts its feed intake according to the energy concentration of the feeds offered to it where the proteins and other dietary components are balanced. For a growing New Zealand White or Californian rabbit the daily intake is around 220 to 240 kcal of digestible energy (DE) per kg of metabolic weight (W0.75). For the lactating doe the average amount is 300 kcal DE/kg W0.75 and tops 360 kcal during maximum milk production (15th to 20th day of lactation). So it is hard to set a strict energy requirement, but it has been shown that intake is only correctly regulated between 2 200 and 3 200 kcal DE/kg of feed.
Because of this, concentrated energy feed must also contain all the other required nutrients in concentrated form so that a smaller volume of feed will supply the rabbit's needs.
Energy intake regulation functions well in temperate climates so long as variations in energy content are linked to the presence of fairly digestible carbohydrates (e.g. starch/fibre substitution). At high temperatures (28° to 32°C), however, and/or where more than 10 percent of the digestible energy is provided by fat, regulation may suffer and the animals may easily consume more of the fattier feed owing to the absence of extra heat from the consumption of lipids.
The rabbit is known to have a specific need for essential fatty acids (linoleic acid), but a conventional diet containing 3 to 4 percent fats generally supplies this. The only reason for including more fat in the diet would be to raise the energy concentration, as fats provide approximately twice as much energy as carbohydrates for the same weight. Depending on the kind of basic diet (basic energy level, protein content and quality), such an input of fats might or might not be nutritionally useful. The feed energy for breeding does or growing/fattening rabbits can be supplied in the form of starch. A young rabbit less than 40 days old, however, digests starch poorly as the digestive apparatus has not yet attained functional maturity. For this reason, post- and particularly peri-weaning feeds used for 20- to 40-day rabbits should not contain over 12 to 13 percent starch to avoid digestive problems.
In European feed rations, the poor digestibility of the fibrous parts of raw materials such as alfalfa and straw (digestibility 10 to 30 percent) makes them secondary to starch, for example, in covering energy needs. However, the fibrous components from tender, usually young, plants are much more digestible (30 to 60 percent). They can then provide 10 to 30 percent of energy requirements in favourable conditions.
The fibrous parts have another function: as bulk. Content is generally evaluated on the basis of crude fibre, although this analytical technique is far from perfect. To get enough bulk for growing rabbits a 13 to 14 percent crude-fibre content seems satisfactory. For lactating does a slightly lower content is acceptable (10 to 11 percent). The more digestible the fibrous parts the higher the total input needed to supply at least 10 percent indigestible crude fibre.
Minerals and vitamins. Studies on the calcium and phosphorus requirements of growing rabbits have shown they need much less than lactating does. Does transfer large amounts of minerals into their milk: 7 to 8 g a day in full lactation, of which about one quarter is calcium.
Any sodium, potassium or chlorine imbalance in the diet can cause nephritis and birth accidents. The risk is particularly high when plants used in the feed have been fertilized with high rates of potassium.
Some authors mention improved growth performance with excess intake of copper sulphate: 200 ppm copper. As with pigs, this must be an effect of the growth-factor type.
Even so, the importance of copper sulphate as a growth factor is not universally conceded and some authors have noted negative consequences (higher mortality) with supplements of about 150 to 200 ppm.
Rabbits require water-soluble (B group and C) as well as fat-soluble vitamins (A, D, E, K). Micro-organisms in the digestive flora synthesize sizeable quantities of water-soluble vitamins which are utilized by the rabbit through caecotrophy. This intake is sufficient to cover maintenance requirements and for average production as far as the B group vitamins and vitamin C are concerned. However, fast-growing animals respond favourably to the addition of 1 to 2 ppm of vitamins B1 and B6, 6 ppm of vitamin B2, and 30 to 60 ppm of nicotinic acid (vitamin PP) in the diet. The addition of vitamin C will not influence growth, even at 1 percent of diet, for better or for worse, under temperate conditions.
For fat-soluble vitamins, research has focused more on deficit or excess than on the exact determination of requirements. The recommendations proposed thus comprise a certain safety margin. However, excessive intakes of Vitamin A (100 000 IU/kg of feed) or Vitamin D (3 000 IU/kg of feed) can entail serious disturbances, particularly in breeding females. It is therefore advisable not to feed megadoses of vitamins to rabbits.
Deviating from standard recommendations
Feeds formulated in accordance with the standards given in Table 22 are satisfactory for intensive production. Rabbits can also be reared on feeds only approximating these standards, but the absolute performance level will be lower, although not necessarily uneconomical. Certain indicative values are given in Table 23. Reducing the protein intake of lactating does to 12 to 13 percent of the diet will not affect prolificacy but will cause a regular reduction of milk production and a parallel drop in the weight of the young at weaning.
Additionally, it is better to consider the protein/energy ratio in relation to the intake of bulk fibre, rather than the protein rate in itself.
Some research indicates that rabbits need a certain minimum of fibre for regular digestion: 9 to 10 percent of indigestible crude fibre. Otherwise, there is increasing mortality from diarrhoea, although the low roughage/mortality association is not systematic and may affect experimental lots in random fashion.
TABLE 23 Decline in performance at levels of protein or selected essential amino acids in the feed below recommended values, and minimum acceptable levels
A crude-fibre content of 13 to 14 percent appears sufficient for growing rabbits. It is not possible to establish a reliable relationship between the intake of fibrous parts and mortality in fattening rabbits at rates of 12 to 16 percent of crude fibre.
Finally, as indicated above, excessive fibre intake usually alters the digestible energy content of the feed below the intake regulation threshold.
If this is accompanied by a higher digestible protein/digestible energy ratio, rabbits will suffer energy deficit and protein surplus at the same time, favouring the excessive production of proteolytic digestive flora which produces ammonia and leads to increased digestive problems (Figure 5, curve A).
While an intake of more than 16 percent of fibrous parts is linked to a reduction in digestible proteins, entailing a static or reduced ratio of digestible protein to digestible energy, no harmful effect on the viability of fattening rabbits is observed (Figure 5, curve B). The only alteration is in growth performance due to the energy deficit.
Where a high intake of fibrous parts places the feed exactly at the minimum threshold for energy regulation (2 250 to 2 300 kcal DE), and protein intake is excessive, there is a very high risk of blockage from constipation in growing rabbits. Similarly, mineral bulk can reduce energy concentration.
As for minerals, where calcium and phosphorus in the diet are insufficient, lactating does draw on their bodily reserves, principally those stored in the bones, but the total store is small compared with the amount exported. Under these conditions, intensive production of does is not feasible. As an indication, the minimum and maximum thresholds are given in Table 24 for various minerals, some vitamins and essential amino acids. It should be stressed that the optimum feed rate for some animals is close to the maximum tolerable rate. This is true of vitamin D and phosphorus in breeding does and for sulphur amino acids in growing rabbits. Where too much is supplied performance may drop, to the breeder's surprise, and the risk is particularly high if he or she uses supplements that are added to the feed or drinking-water. Toxicity symptoms can closely resemble the symptoms of deficit, as is true of vitamin A.
In the case of multiple deficiencies, it is difficult to predict the animals' reaction. Direct experiment for on-site measurement of the actual consequences of the proposed feed are recommended in this case. The norms proposed in Table 22 can be used as a reference method of using complementarities meeting the animals' needs.
FIGURE 5 Role of fibre intake in the health of fattening rabbits
Feed manufacture and storage
In Europe, rabbits are fed dry raw materials which complement one another to make a balanced feed. Once the best proportions have been established, the raw materials are weighed and put in a blender. They are usually first crushed into meal for a uniform feed mixture. If the mixture were intended for feeding chickens or pigs it could be given to the animals at this stage, but the rabbit has a very low tolerance for the dust inevitably present in meal. This problem is solved by compacting the mixture in a pelleting machine.
The ideal diameter for ordinary feeds is 3 to 4 mm, 5 mm being the maximum diameter to avoid waste (Table 25). The pellets should be no longer than 8 to 10 mm. The pelleting operation heats the product through friction, which improves nutritional value by some 5 to 7 percent compared with the meal mixture.
Using certain recipes rabbits can actually be fed feed in meal form (Table 26). What must be avoided at all costs is a very fine meal which would disturb the normal functioning of the rabbit's upper respiratory tract which, although a good filter for dust, clogs quickly. Meal must not be given as feed where rabbits drink from receptacles containing water. The water will soon get dirty and the rabbits will immediately stop drinking and eating. A valve-type automatic watering system is recommended where meal is fed. Feeding tests on mash (60 percent meal, 40 percent water) show it is feasible provided the feeding racks are kept scrupulously clean (Table 26).
TABLE 24 Recommended limits for the incorporation of various minerals, vitamins and selected amino acids in rabbit feed
In Europe, depending on local conditions and the size of the production unit, feed is usually delivered in 25 to 50 kg bags or in bulk. Bags are stored in a shed providing shelter from high temperatures and rain, and located near the rabbits but out of their reach. They are stored in piles away from damp ground or walls. The usual solution is a false wooden floor.
TABLE 25 Influence of pellet diameter on growth1 of Californian rabbits aged from 5 to 12 weeks
TABLE 26 Effect of presentation of feed on growth of young rabbits, according to various authors
The room or shed is designed to hold one and a half to two months' supply. Deliveries should actually be made monthly, so feed can be used within one and a half months of manufacture. At delivery, about 10 to 15 days' supply should be left over from the previous month.
For bulk delivery, feed is stored in silos that are filled from the top and emptied from the bottom. They should be completely emptied and disinfected for bacteria, fungi, etc. at least once a year.
Transport costs and, especially, a desirably fast turnover of feed stocks make mixed feed (see Table 22) appropriate for rabbitries with fewer than 200 breeding does. In units with more than 300 does it is preferable to use two or three types of feed: one suitable for lactating and breeding does, one for the weaning period and the last for growing rabbits in all other categories (e.g. young growing rabbits).
Balanced pelleted feeds
The traditional European diet for rabbits used to be cereals, bran and forage (green in summer and dried in winter). In winter, breeders also fed the animals fodder beets or carrots. This style of feeding is definitely on the way out, especially in the big producer countries such as France, Italy and Spain.
In modern production systems, which account for most of the output, the animals are given balanced pelleted feeds conforming to the standards already described. A single feed type is generally used for all categories, corresponding to the mixed feed listed in Table 22. In intensive-reproduction rabbitries, all rabbits except bucks are fed ad lib. Under less intensive regimes, does receive the same feed ration from the weaning of one litter to the birth of the next. The ration is normally 3 to 35 g DM per kg of live weight per day.
Growing rabbits raised in a group are always fed ad lib. One watering point is sufficient for 10 to 15 animals. The watering system must be checked regularly to ensure the animals do not suffer from lack of water because of defective apparatus. One feeding rack is enough for six to ten rabbits, but at least two are needed as a safety measure in case the pellet flow should get blocked. Each feeding place along the rack should be 7 to 8 cm long.
Breeders calculate the quantities of feed for total daily consumption for all animals as follows:
Well-run rabbitries, as in France or Italy, calculate 3.8 kg of pelleted feed consumed for each kg of live weight marketed. This calculation includes breeding rabbits. The best rabbitries use only 3.4 kg of feed to produce 1 kg live rabbit. This represents a feed expenditure of 5.9 to 6.7 kg per kg of carcass. Keeping in mind the protein content of the feed and the carcasses, this means a yield of 190 to 220 g of high-grade animal protein from 1 kg of plant protein, a return of 19 to 22 percent for the best production units.
Forage utilization in developing countries
Pilot trials in Germany have demonstrated that growing rabbits enclosed or penned in a natural meadow receiving no fertilizer can produce 240 kg of protein per hectare (1.2 tonnes of meat) annually in the form of carcasses. This gives some idea of the forage utilization potential of rabbits, although in the trials the rabbits exhibited a modest growth rate (20 to 25 g a day compared with the 30 to 40 g of cage- or hutch-raised rabbits) and a relatively high feed intake.
Climate and soils in most developing countries, however, are very different from those found in Germany. Direct grazing also poses problems of fencing and risks from predators to the point where this technique cannot be recommended. For this reason the authors have reviewed the various wild or cultivable plants used in both tropical and non-tropical regions to feed rabbits reared in confinement. Cereals are intentionally left out as they are needed for human nutrition in most developing countries.
Before reviewing the various plants which rabbits can use, a reminder is needed of rabbits' extreme sensitivity to mould, particularly aflatoxin. The hygiene of the fodder and by-products used must be beyond reproach and it is particularly important to avoid uncontrolled fermentation.
Wild and cultivated fodders suitable for rabbit feed. The following information only concerns plants that have been positively tested in station and other trials for use as rabbit feed. They are listed under their Latin names in alphabetical order. The countries where they are used are indicated where possible.
A "high" nutrient value means the feed has a higher dry matter content than is required for rabbits. Unless otherwise indicated, nutrient content, where shown, is expressed as a percentage of dry matter. For detailed chemical compositions, readers should refer to the general documents in the bibliography, particularly Göhl's work on tropical forages published by FAO (1982). Digestibility of the nutrients has not usually been determined for the rabbit specifically. Lacking these data, reference should be made to forage digestibility for ruminants, but absolute values cannot be transposed, especially for the fibrous fraction.
Alysicarpus vaginalis. A one-leaf clover distributed ad lib to growing rabbits as a supplement to concentrates gave performances not significantly different from the control. This plant, grown in South America, is a good source of protein.
Amaranthus spp. This forage has a 20 percent protein content. It has been tried out in Malawi to supplement a concentrate containing 39.5 percent grain maize, 26 percent maize bran, 34 percent groundnut oilcake and 0.5 percent table salt. Reproduction and growth were satisfactory: 20 rabbits per doe per year; growth of 15 g per day from four to 16 weeks. Amaranthus is routinely fed to rabbits at the Bunda Agricultural College in Lilongwe, Malawi. Modern hybrid varieties conventionally grown for human food can also be used for feeding rabbits.
Arachis hypogaea. Groundnut oilcake is a high protein feed (50 percent). It can be used for feed when not overpolluted by aflatoxins. The whole groundnut can also be fed, but this puts the rabbit into direct competition with people for food so this solution should only be considered under exceptional circumstances. Groundnut tops provide green fodder and hay with a high protein content. This is the conventional use at the Bobo-Dioulasso centre in Burkina Faso. The tops can also be used after harvest, but their protein content is less: about 15 percent before the groundnuts are removed and less than 10 percent after threshing. The proteins in both the tops and the groundnut cake lack the essential sulphur amino acids.
Azolla spp. This family of aquatic ferns can fix atmospheric nitrogen. Trials in Italy have shown that Azolla caroliniana can be incorporated into rabbit feed despite the poor digestibility of the proteins. Other Italian trials on A. filiculoides produced similar conclusions in a trial where this sun-dried fern fully replaced soy cake in the ration at 23 percent. However, the protein content of azolla (30 to 32 percent) is less lysine-rich than soy (4.5 as compared to 5.9 percent protein) and the lignin content is high, reducing digestibility. A. microphylla is comparable to A. caroliniana but A. pinnata, with a lower protein content of 9 percent, is not as palatable.
Bauhinia variegata. Angora rabbits are successfully fed the leaves of this tree as a supplement to concentrates in India. The protein content is 16 percent.
Beta vulgaris. Fodder and fodder sugar beets supply much of the winter feed in traditional European rabbit production. Where they can be grown, beets can supply a good percentage of the energy demand. The fibrous fraction is highly digestible (80 percent). Beet leaves are also good for rabbits. They contain 17 to 18 percent protein, but are very rich in minerals, especially potassium, which can cause digestive problems.
Brachiaria mutica. Fed to breeding does in the Philippines, para grass has proved far more satisfactory than elephant grass (Pennisetum purpureum) or guinea grass (Panicum maximum). However, its low protein content (10 to 13 percent) requires a nitrogen supplement (legumes, supplementary feed).
Brachiaria ruziziensis. In Burkina Faso this forage plant is part of the basic ration produced at the Bobo-Dioulasso centre for its rabbitry. Like all grasses, however, it has a low protein content (8 to 13 percent). For proper utilization it should be supplemented by high-protein feeds. The forage could be grown together with Stylosanthes, for example, for a more balanced feed than either plant can provide alone.
Cajanus cajan. Hay from this tree legume (called "guandu" in Brazil) can successfully be incorporated into balanced feed for growing rabbits as a substitute for alfalfa hay. Pigeon pea hay thus constitutes an interesting source of protein (15 to 25 percent depending on when it is harvested) and fibre (30 to 35 percent crude fibre).
Celtis australis. The leaves of this tree are used to feed Angora rabbits in India. Compared with the dry-matter content, the protein content is low at 12.4 percent as is crude fibre at 14.6 percent, but the fat content is fairly high at 5.7 percent and the 17.7 percent ash content is quite high.
Chamaecrista aeschynomene. This tropical legume is commonly used to feed Creole rabbits in Guadeloupe and Martinique.
Cocos nucifera. Rabbits like the green coconut meat left after the milk has been drunk. In Guadeloupe and Martinique they are fed to rabbits as a bulk dietary supplement. A trial on growing rabbits in Sri Lanka showed that coconut could form 20 or even 30 percent of the diet.
Cucurbita foetidissima. Growing naturally in the semi-desert area of northern Mexico, this member of the gourd family has an enormous root that is 65 percent starch. The crushed root is sun-dried in two or three days and as much as 30 percent can be added to balanced concentrate in place of grain sorghum for breeding and fattening rabbits. Trials at the University of Chihuahua in Mexico demonstrated no toxic effect.
The tops and especially the fruit are rich in protein (12 to 30 percent), but utilization trials have not yet been run on rabbits. Their very bitter taste, which is unattractive to other animals, is not necessarily an obstacle for rabbits. More tests are needed on the possibilities of this interesting semi-desert plant.
Daucus carota. A traditional feed for European farm rabbits, carrots can be grown in many tropical countries. They are used in Zambia, in particular, to feed rabbits. Both leaves and roots have a comparable protein content of 12 to 13 percent, but the leaves - like beet leaves - are very rich in minerals.
Dendrocalamus hamiltonii. The leaves of this tree have been successfully used to feed Angora rabbits in India as a supplement to commercial concentrates. The protein and crude-fibre contents of 15.6 and 23.2 as a percentage of dry matter are fairly low, but the 18.4 percent ash content is particularly high.
Eichhornia crassipes. Rabbits will eat the leaves and bulbs of water hyacinth, but only 24 percent of the energy provided by the green plant is digestible. Incorporating 25 percent water hyacinth meal in a balanced feed gives good results. Amounts of 50 percent or more are less satisfactory. The arsenic content of the rabbit meat (especially the liver and kidneys) in water hyacinth trials raised grave doubts about the plant's potential for feeding rabbits where it grows in polluted water.
In rabbitries located near the Congo River in the Democratic Republic of the Congo, breeders use a local water hyacinth of which the rabbits are very fond. In New Caledonia, a local hyacinth called water lily is also a traditional feed. The whole of the plant -stem, bulb and roots - is eaten.
Erythrina glauca. Rabbits find the leaves of this tree very palatable. A trial in Colombia showed that this (30 percent) protein source produced daily growth rates of 11.5 g as a simple supplement to sugar-cane juice. The proportion of Erythrina leaves actually rose from 50 percent of the daily DM consumption at the onset of the trial to 65 percent eight weeks later.
Grewia optiva. The leaves of this tree contain about 17 percent protein. An Indian ad lib feeding trial to supplement a concentrate produced an Angora wool output equivalent to that of the control fed the concentrate alone.
Gynura cusimba. The leaves of this forage plant, abundant in Nepal in the dry season, contain 27 percent protein. Rabbits like it but cattle, sheep and goats will not touch it. This difference in feed preferences is a reminder that observations valid for one species do not necessarily apply to another.
Hibiscus rosa-sinensis. The branches of these shrubs, which are used as living fences in the Caribbean, can be fed to rabbits, as is now the practice in Haiti. The young shoots contain some 15 percent protein and 16 percent crude fibre. However, a trial on ad lib distribution of hibiscus leaves and a balanced pelleted feed demonstrated very poor nutritional uptake of this fodder.
Indigofera arrecta. This legume grows wild in Mozambique, even during the dry season without irrigation. It is easy to grow from the seeds of the wild plant picked in season. Its high (25 percent) protein content makes it a valuable source of nitrogen for rabbits in Mozambique, especially during the dry season.
Ipomoea batatas. Sweet potatoes are a good source of energy (70 percent starch content) for human consumption and can easily be grown in a family garden. Surplus or specially grown crops could be used as an energy feed for rabbits. The tops when well developed are also a valuable feed because of their high protein content -16 to 20 percent. Sweet potato is used as forage for rabbits in Mauritius, Guadeloupe and Martinique, mainly in backyard rabbitries. A trial in Mozambique produced good performance with sweet potato leaves as a dietary supplement. They are highly digestible, and trials in many tropical countries have confirmed the nutritional value of sweet potato tops.
Ipomoea tiliacea. This convolvulacea grows wild in Guadeloupe and Martinique and is the traditional basic feed for Creole rabbits. It is not planted but simply picked from the hedges where it grows wild.
Lathyrus sativus. Vetch is often grown with oat in North Africa; the vetch/oat duo is used as green fodder for livestock and rabbits like it very much. In ad lib feeding with concentrated feed, it produced acceptable growth or reproduction rates. Much of the food value is lost when the product is stored, however, and rabbits tend not to like it.
Lespedeza spp. These legumes, which provide a protein-rich green forage for rabbits, could also be dried and fed as hay.
Leucaena leucocephala. This is probably the legume most studied in station rabbit trials. Its attraction is its high protein content (28 percent) and the fact that it can be grown during the dry season. Sowing and tillage are no problem in soils where Leucaena grows naturally (e.g. Mauritius). In the absence of symbiotic bacteria, bacterial seeding can be used (Guadeloupe and Martinique).
The presence of the amino acid mimosine, which competes with tyrosine and phenylalanine, is to some authors a limiting factor for Leucaena leucocephala. They suggest that a prudent top ration of this acacia for rabbits would be 25 percent (Mozambique). But growth trials on the island of Mauritius show that Leucaena can replace 40 and even 60 percent of balanced feeds without adversely affecting animal growth or health (Figure 6). In these trials, even where this acacia was used alone, the authors noted no incidence of diarrhoea or symptoms attributable to mimosine.
Other trials in Malawi used Leucaena as a supplementary fodder for a concentrate feed (described in the paragraph on Amaranthus) with good results for both growth and reproduction. Also tested in Malawi as a maize bran supplement, Leucaena proved satisfactory for growth (60 g a week) and better than Tridax procumbens and, especially, Pennisetum purpureum. Used as a supplement to a broiler chicken feed, growth rates of 100 to 110 g a week were recorded.
Despite these encouraging results the problem of mimosine remains. Mimosine toxicity is cumulative and perhaps did not show up in the growth trials, even though these covered the entire fattening period. Several continuous trials in Mauritius, Togo and Malawi, using Leucaena at levels of 10 and 20 percent, have not had any ill effects on growth or reproduction. As mimosine is an amino acid, drying the forage does not reduce its toxicity to animals, although no special rabbit trials have been run on this aspect. The addition of iron sulphate chelates mimosine and considerably reduces toxicity for rabbits as intestinal absorption of the chelated form of mimosine is significantly diminished. The iron sulphate supplement should exceed the mimosine content by a factor of four, comprising 2 to 3 percent of the diet.
FIGURE 6 Weight-gain trends in New Zealand White rabbits aged from 6 to 14 weeks in relation to intake of balanced feed *
Manihot utilissima. Ghana's rabbit development programme includes growing cassava for feed. The inclusion of from 15 to 45 percent cassava meal (87 percent starch and 2.5 to 3 percent protein) in balanced feeds, supplemented by 200 g green forage daily, has given growth and reproduction results comparable to those obtained with the balanced control feed without cassava. But cassava should not be used to feed rabbits except where the human population already has plenty of energy foods, as in Egypt, for example. Additionally, cassava meal requires a protein and crude-fibre supplement. However, cassava peels contain 6 percent protein and 10 percent crude fibre, and the leaves contain 24 to 28 percent protein, so the potential of these two cassava products for rabbit feed should be tested in comparative trials. Cassava does have a slight tendency to produce goitre, which has no practical impact on growing rabbits but is a potential concern for breeders if it comprises over 30 percent of the diet.
Marremia tuberosa. This protein-rich (24 percent) forage, used in Mozambique to feed rabbits, grows during the dry season.
Medicago sativa. Alfalfa is unquestionably the standard rabbit forage, wherever it can be grown. It is grown under irrigation in Mexico, Mozambique and Pakistan. It does not grow in hot tropical areas such as the Caribbean. Breeding and growing rabbits can be fed solely on green alfalfa. The hay is harder for them to ingest. Alfalfa's rather high saponin content makes it especially palatable to rabbits.
Mimosa pigra. No negative effects were noted in tests run on this thorny plant in Thailand. It was used to replace Brachiaria mutica in rabbit feed. Its 22 percent protein content is comparable to that of Leucaena leucocephala.
Morus alba. Mulberry leaves not needed to feed silkworms can be successfully fed to rabbits. Trials in India have even shown that a maintenance diet for adult rabbits can consist exclusively of mulberry leaves. They are used in India to supplement concentrates for Angora rabbits.
Musa spp. Rabbits can be fed on commercial banana rejects. Bananas are rich in energy and poor in protein (5 or 6 percent) and must be supplemented. Rabbit breeders use banana rejects in various African countries and in Guadeloupe and Martinique. The leaves can also be used as green forage (Cameroon, Zambia, Guadeloupe and Martinique). Their protein content is 10 to 11 percent of the dry matter. Data are available on the leaves as rabbit feed, but not on the stems. They contain only 1.5 to 2 percent protein and with a 70 percent nitrogen-free extract could make a useful energy feed. Banana peels can also be used to replace up to 35 percent of the concentrate for growing rabbits.
Neotonia wightii. A trial in Brazil showed that perennial soybean hay can fully replace alfalfa in a balanced ration containing 38 percent of this forage. There is even a marked improvement in the growth rate (41.5 g/day compared with 37.1 g/day with control rabbits fed alfalfa). This legume can be an attractive source of protein and fibre for rabbits.
Opuntia ficus. The aerial part of prickly pear cactus can be fed to rabbits. At levels higher than 40 percent of the feed ration, however, the risk of diarrhoea arises because the fibrous portion is highly digestible.
Oryza sativa. Carefully preserved rice straw or bran can be fed to rabbits. A study in China showed that controlled fermentation of rice straw with bacterial strains of Trichoderma and Azotobacter can boost the food value and serve as a replacement for wheat bran. Uncontrolled fermentation could, however, produce mycotoxins.
Panicum maximum. In various comparison trials with other forages guinea grass made a poor showing, mainly because of its low protein content - 5 to 10 percent of the dry matter according to ripeness. Despite this, guinea grass is part of the basic feed ration for rabbits in Ghana, Guadeloupe and Martinique. Its function is mainly to provide crude fibre and a small amount of energy. There is another use for guinea grass: dried, the plant is sometimes used as straw litter for the nest box when breeding does are raised on a mesh floor.
Pennisetum purpureum. Feed trials with breeding and growing rabbits using elephant grass gave even poorer results than guinea grass, again because of low protein content (6 to 8 percent). A Malawi trial using elephant grass as a supplement for maize bran produced growth rates of only 15 g a week compared with 60 g with Leucaena leucocephala; but it can be used as a source of crude fibre for rabbits, as is done in Guadeloupe and Martinique. A mixed crop where elephant grass supports a climbing legume such as Pueraria is planned in the Democratic Republic of the Congo. The combination gives a much more balanced forage. The dried stems of Pennisetum can be used as straw litter or bedding for the nest box.
Pistia stratiotes. Comprising 30 percent of the diet of growing rabbits, sun-dried water-lettuce meal was used in Nigeria to produce growth rates equal to those of the control.
Populus spp. Green poplar leaves can be used to replace sun-dried alfalfa leaves as a fodder resource for rabbits. The leaves of the older trees are less protein rich (15 percent of the DM) than the leaves of coppiced poplars (20 to 22 percent of the DM). Trials in the United States used up to 40 percent poplar leaves in the diet.
Prosopis chiliensis. The fruits of this drought-resistant South American native have been introduced in Chile as a supplement to balanced rabbit feed, replacing up to 60 percent of the protein in the basic diet. Growth remained unchanged even when the feed contained up to 29.4 percent of the dried Prosopis fruits.
Psilotricum boivinianum. This forage grows without irrigation in the dry season in Mozambique and has a high (20 to 21 percent) protein content, making it an attractive forage feed for rabbits.
Pueraria spp. The legumes of this genus, such as P. phaseoloides and P. javanica, are recommended as rabbit feed in different countries of Africa, especially Ghana. P. javanica is the basic feed of many farm rabbitries in the Democratic Republic of the Congo. Rabbits are very fond of it. Like Stylosanthes, Pueraria remain green even in the dry season.
Robinia pseudoaccacia. Various trials in the United States and India on growing or on Angora rabbits showed that Robinia leaves can easily replace alfalfa in the diet with only a slight drop in performance.
Saccharum officinarum. Sugar cane can be grown in countries with wet tropical climates and is a good rabbit feed, despite its low protein content (1 or 2 percent). In an early trial in Mauritius, coarsely chopped sugar cane was successfully used to re place one half the balanced concentrate feed ration with no consequent drop in performance. In a complementary trial, the same authors found that, fed ad lib, rabbits chose to replace up to 40 percent of their balanced concentrate feed with chopped sugar cane. In a similar ad lib feeding test, Leucaena leucocephala replaced up to 60 percent of the same balanced concentrate feed (see Figure 6). In a New Caledonia trial it was shown that rabbits prefer to eat first the dry leaves, then the green leaves and then the cane itself, chopped small.
Setaria spp. These species of forage are used in Mauritius to supplement concentrated feeds for rabbits. Like all grasses, Setaria are poor in proteins.
Solanum tuberosum. Cooked potatoes can very well be used to feed rabbits, but this puts the animals into competition with humans for food. Potato peelings are part of the kitchen waste in many countries and can be used in feed. However, apart from the fact that the peelings should be fed cooked, not raw, great care must be taken not to use the parings of potatoes which have turned green with exposure to light. Laboratory animals stopped growing when they were given 20 g of green potato peelings a day in addition to their normal feed ration.
Sorghum vulgare. Sorghum tops and grain are a good rabbit feed. They are used in Ghana and Mexico.
Stylosanthes spp. Legumes of this genus can be grown in all wet and dry tropical climates. In dry areas they virtually stop growing during the dry season, but remain green. Different species have been used for rabbits, including S. gracilis (Ghana, the Democratic Republic of the Congo, Burkina Faso) and S. hamata (Martinique).
Taraxacum officinale. The dandelion is among the wild plants conventionally fed to rabbits in traditional European rabbit production. The use of this composite plant as rabbit feed has also been reported in Togo.
Tridax procumbens. Considered a weed on the Malawi grasslands, the advantage of Tridax is that it grows during the dry season. Its 12 to 13 percent protein content also makes it a good rabbit feed. The plant proved satisfactory as a concentrate feed supplement in Malawi. Growth performance trials with Tridax as a maize bran supplement, however, were poorer than trials with Leucaena leucocephala, although more promising than Pennisetum purpureum, probably because of the differing protein content of the three plants.
Trifolium alexandrinum. This Egyptian clover (berseem), typical of the Mediterranean climate, is virtually the only rabbit feed used in the Sudan. Feeding trials in Egypt using the clover alone produced live weights of 1.23 kg at 16 weeks for cross-bred Baladi × Flanders Giant rabbits, with an average weekly gain of 67 g. Like all legumes this clover variety has a high protein content.
Vicia spp. Wild vetches, grown alone or interplanted with grasses, can supply a protein-rich forage attractive to rabbits. The plant grows so quickly, however, that the tendency is to use it as hay, unless planting can be staggered for a continuing crop.
Vigna sinensis. These wild peas of Guadeloupe and Martinique supply nitrogen-rich green forage and grain. Both V. sinensis and V. unguiculata are used as rabbit feed in these islands.
Zea mays. Although maize grain is needed as food for people inmost developing countries, its use as fodder would be feasible in certain regions. The protein content of maize forage is low, so it requires a nitrogen supplement. Maize is used as forage in Burkina Faso, for instance.
This rather lengthy list of plants that have been tested as rabbit feed does not include every usable plant. There are grasses such as the various species of Digitaria, for example, although these are usually poor in protein. Where cabbage can be grown it should be added to the list. Cabbage is a traditional rabbit feed in France. Its 17 to 20 percent protein content is fairly high. Trials in Cameroon suggest that cabbage can form up to 15 percent of the diet.
Agricultural and industrial by-products.
The various agricultural and industrial byproducts will not be reviewed here, as lists of by-products and their composition are usually available for each region. Only a few need special mention. First come the various tropical oilcakes such as groundnut (already described), palm nut and coconut. Cottonseed cake should be used very cautiously, as rabbits are at least as sensitive as pigs to gossypol. However, cottonseed cakes containing up to 700 ppm of free gossypol have been fed to growing rabbits with no problems. In many countries where cottonseed feedcake is available, it is preferable to use it and to accept a drop in performance of 10 to 15 percent compared with a gossypol-free ration rather than attempt to introduce livestock-based meal as a protein source which may be expensive or of poor bacteriological quality. Then there are maize and rice by-products. Brewer's draff and citrus pulp are possible feed sources where the processing plants are not too far from the rabbitry. Rabbits can also be fed waste products from pineapple canneries, as in Côte d'Ivoire, but pineapples are poor in protein.
Brewer's draff from the manufacture of barley-based beer and dolo dregs from millet beer can produce good results. In a test conducted in Burkina Faso, dolo dregs were used as 80 percent of a concentrate feed with 10 percent groundnut cake, 6 percent blood meal and 4 percent bone meal. This was fed with a forage supplement of green Brachiaria or dried groundnut tops. Local rabbits grew faster with this feed (104 g a week with land race) than with an imported balanced feed (83 g). Sun-dried brewer's draff is often also incorporated as a protein source for rabbit rations in the urban peripheries of some African cities.
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