OPUNTIA SPP. - A STRATEGIC FODDER AND EFFICIENT TOOL TO COMBAT DESERTIFICATION IN THE WANA REGION

Ali NEFZAOUI and Hichem BEN SALEM

INTRODUCTION

The West Asia/North Africa (WANA) region contains large areas with rainy winters and hot, dry summers. WANA is characterized by its high population growth, low and erratic rainfall, limited areas of arable land, harsh deserts and limited water resources for irrigation development (Nordblom and Shomo, 1995).

As much as 50% of the arid rangeland may have lost its vegetation since the Second World War, as the human population has increased fourfold (Le Houérou, 1991a). The sheep population has increased by 75% and the stocking rate jumped from 0.25 sheep/ha to 1.0 sheep/ha between 1950 and 1989. The rangeland degradation is simply the outcome of these changes, besides increased cropping activities and increased use of feed grains.

Thus, contribution of rangelands to the annual feed requirements of livestock is diminishing continuously; from 80% three to four decades ago, to less than 25% currently. Overgrazing and the associated range deterioration are the major factors that have forced pastoralists to change their migration and feeding patterns. In some countries, animals are heavily supplemented with barley grain and other concentrate feeds. Table 30 summarizes a typical feed calendar common for agropastoral

Table 30. Typical feeding calendar for small ruminants in the WANA region

Therefore, most of the WANA countries are seeking appropriate tools to prevent rangeland degradation and restore productivity. Some of the improved rangeland techniques include (i) reduction of stocking rates; (ii) controlled and deferred grazing; (iii) periodic resting; (iv) extended water supplies; (v) reseeding; and (vi) shrub planting.

Moreover, productivity can be improved by increasing feed supplies from alternative sources, including (i) legumes or other forage crops grown in place of fallow; (ii) fodder banks of naturally grown legumes fertilized with phosphate; (iii) treatment and suitable supplementation of straw; and (iv) other crop residues and agro-industrial by-products. In addition, a planned government strategy for drought relief should reduce the risk to small ruminant producers and increase production.

The search for appropriate plant species to grow in arid areas is a permanent concern of most people living in harsh environments. Cactus species fit most of the requirements of a drought-resistant fodder crop. According to De Kock (1980), they must:

* be relatively drought resistant, survive long droughts, and produce large quantities of fodder during the rainy season, which can be utilized during dry season;

* have a high carrying capacity;

* supply succulent fodder to animals during droughts;

* not have an adverse effect on the health of the animals utilizing it;

* tolerate severe utilization and have high recovery ability after severe utilization;

* have a low initial cost (establishment and maintenance); and

* tolerate a wide range of soil and climatic conditions, so that they can be planted where the production of ordinary fodder crops is uncertain.

The future of the arid and semi-arid zones of the world depends on the development of sustainable agricultural systems and on the cultivation of appropriate crops. Suitable crops for these areas must withstand drought, high temperature and poor soil fertility. The opuntias fit most of these requirements and they are important to the economy of arid zones, for both subsistence and market-oriented activities (Barbera, 1995).

IMPORTANCE OF CACTI IN ARID ZONES

The increased importance of cacti in arid zones is because of their ability to:

be more efficient than grasses or legumes in converting water to dry matter, based on their specialized photosynthetic mechanism (CAM) (Russell and Felker, 1987a; Nobel, 1989a)

remain succulent during drought;

produce forage, fruit, and other useful products; and

prevent long-term degradation of ecologically weak environments.

It is suggested that cacti, and Opuntia spp. in particular, were introduced into the WANA region by Spanish Moors. Nevertheless, large plantations were not established until the 1900s. These plantations were implemented to create living fodder banks to feed animals during drought and to combat desertification.

CACTI AS A FODDER BANK

Opuntias used for animal feeding are abundant, easy and cheap to grow, palatable and drought tolerant (Shoop et al., 1977). Such characteristics make them a potentially important feed supplement for livestock, particularly during periods of drought and low feed availability. A large portion of opuntia plant biomass is vegetative material rather than fruits, and it can be fed to livestock as fresh forage or stored as silage for later feeding (Castro et al., 1977). The idea of using cactus to feed livestock is not recent. Griffiths (1905) was certain that feeding cactus to livestock started in the USA before the Civil War, and before and after the war, there was extensive freight transportation of cactus pads between Brownsville, Indianola, San Antonio and Eagle Pass in Texas. The plant has become important fodder in many parts of the world, based on natural and cultivated populations. It is cultivated in Africa, Argentina, Bolivia, Brazil, Chile, Colombia, Israel, Italy, Mexico, Spain, USA and Peru (Barbera et al., 1992; Le Houérou, 1979; Brutsch, 1984; Clovis de Andrade, 1990; Curtis, 1979; Pimienta, 1990; Russell and Felker, 1987a; Saenz, 1985).

Large areas are found in Algeria, northeast Brazil, Mexico and South Africa. The opuntia is used all year round, or as emergency feedstock during drought. In many arid areas (Mexico, south Texas, South Africa, Tunisia, etc.), farmers use cactus extensively as emergency forage that is harvested from both wild and cultivated populations to prevent the disastrous consequences of frequent and severe droughts (Le Houérou, 1992).

From the early 1900s in North Africa, several strategies were introduced to reduce water and wind erosion and rangeland degradation, using shrubs (Acacia cyanophylla, Atriplex nummularia and A. halimus) and cacti (Opuntia ficus-indica f. inermis). Large areas have been planted in Algeria, Morocco and Tunisia since the 1950s. It is estimated that in low rainfall areas, some 0.7 to 1 million ha plantings are helping to combat erosion and desertification and provide feed for livestock during drought.

Figure 14. Yield of Opuntia ficus-indica f. inermis in relation to rainfall in Tunisia (adapted from Monjauze and Le Houérou, 1965)

The importance of opuntia became evident when research showed that CAM plants could have high productivity in dry regions. Due to their high water use efficiency (Nobel, 1989a), their aboveground productivity is much higher than any other arid plant species. In Tunisia, under rainfed conditions and with no fertilizer application, spineless cactus yield from 20 t/yr of fresh cladodes in areas with 150 mm/yr rainfall, to 100 t/yr in areas with an average rainfall of 400 mm/yr (Figure 14).

USE OF CACTI AGAINST DESERTIFICATION IN NORTH AFRICA

Marginal lands are fragile ecosystems, and when they are subjected to cultivation and indiscriminate vegetation removal, large-scale degradation and destruction of vegetative cover occurs. The disappearance and scarcity of several plant species indicate the magnitude of genetic and edaphic losses.

To reverse desertification and restore the vegetative cover in those areas, appropriate integrated packages are used for rangeland monitoring, livestock and natural resources conservation. Spineless opuntia (Opuntia ficus-indica) is used in Algeria and Tunisia to slow and direct sand movement, enhance restoration of the vegetative cover and avoid erosion of the terraces built to reduce runoff.

In central and south Tunisia, opuntia plantations provide a large amount of fodder for livestock and play a key role in soil conservation. Terraces are easily damaged by runoff, but opuntia roots help to hold them in place, ensuring stability of the terraces. Two rows of cactus pads are planted on the inner side of the terraces. The moisture stored at the base of the terrace enhances plant growth. In addition, pads are harvested and used as an animal feed during drought spells. Cactus can be used in combination with cement barriers or cut palm leaves to reduce wind erosion and sand movement, maintaining the soil and improving vegetative cover.

USE OF CACTI AS FODDER

Opuntia is not a balanced feed and should rather be considered as a cheap source of energy. Cladodes have low crude protein content and consequently should be supplemented with protein sources. They are also low in phosphorus and sodium.

Chemical composition

Hoffman and Walker (Table 31) analysed Opuntia nutrient content in 1912. These early investigations indicate that spiny and spineless cactus have practically the same chemical composition and are of equal value for feeding purposes (Woodward, 1915). Cladodes have high water content (90%), ash value for feeding purposes (Woodward, 1915). Cladodes have high water content (90%), ash (20% DM), Ca (1.4% DM), soluble carbohydrate and vitamin A. They have low contents of crude protein (CP) (ca. 4% DM), crude fibre (CF ca. 10% DM), and phosphorus (P ca. 0.2% DM) (Nefzaoui et al., 1995).

Table 31. Average chemical composition (as % of DM) of Opuntia engelmannii and O. lindheimeri

Source: Hoffman and Walker, 1912

Table 32. Average chemical composition of Opuntia ficus-indica cladodes produced in Tunisia

Key: DM = dry matter. CP = crude protein. CF = crude fibre. NFE = nitrogen-free extract. P = phosphorus. Ca = calcium. K = potassium. Na = sodium.

Table 32 summarizes nutrient content of cactus pads determined in Tunisia. Water content is high (80-95%) and ash content can reach 33% of DM. The crude protein content is low, often below 5% of DM. Fibre content is also relatively low: its average value is about 9% of DM. These data are similar to those reported in other countries (Table 33).

Table 33. Average chemical composition of cactus cladodes

Key: as for Table 32.
Sources: De Kock, 1965; Lozano, 1958; Morrison, 1956; Teles, 1978; and Theriez, 1965.

Contents of major macro-elements show again very low levels of P and Na and high levels of Ca. Recent investigations (Ben Salem and Nefzaoui, unpublished data) show that cactus cladodes have high oxalate content. Total oxalate is about 13% of the DM, of which 40% is in a soluble form. These oxalates are probably bound to Ca, making this anion less available to animals. This high amount of oxalates may also explain the laxative effect of cactus cladodes when fed to animals.

Crude fibre percentage is a poor indicator of feed fibre status, and improved methods, such as the Van Soest fractionating procedure, are more appropriate. It appears that, compared to alfalfa, cacti have a relatively low fibre content, especially the lignocellulose fraction (Table 34). It is well known that high levels of lignocellulose or lignin are responsible for low digestibility of foodstuffs. According to these data, the digestibility cactus pads could be expected to be high.

Table 34. Average neutral detergent fibre, acid detergent fibre, hemicellulose, cellulose and lignin contents (as % of DM) of some Opuntia species compared to alfalfa

Key: NDF = neutral detergent fibre. ADF = acid detergent fibre.
Source: Ben Thlija, 1987

Ash content of cactus pads is high, ranging from 10 to 25%, mainly because of the high calcium content. Most of the opuntia species have phosphorus levels below animal requirement (Tables 31 and 32).

Water deficiency and high levels of Ca compounds in arid and semi-arid soils lead to cactus accumulating high quantities of Ca solutes in its pads. This process allows the plant to extract, through osmosis, as much water as possible from the soil. In any case, the Ca content of cactus pads well exceeds animal requirements. An excess of calcium is not problematic in itself, but an unbalanced Ca/P ratio requires correction. Most authors report a Ca/P ratio of about 35.

Shoop et al. (1977) working with O. polyacantha, indicated that phosphorus content was below livestock dietary requirements. Calcium levels seemed to be adequate, but the Ca/P ratio, at about 36/1, is too high for optimal livestock performance. According to the same source, the other minerals (manganese, copper, zinc, magnesium and iron) had concentrations within the acceptable range for ruminant diets, except for sodium, which was relatively low (0.02%).

Protein content of cactus cladodes is low, but tends to increase after fertilizer application. Species or varieties also have influence on this parameter. Thus, Gregory and Felker (1992) found that some clones from Brazil had over 11% crude protein.

González (1989) found that N and P fertilizers increased crude protein contents of opuntia cladodes from 4.5% to 10.5% of dry matter. This is rather spectacular. However, in the WANA region, large plantations of opuntia are located in dry areas where poor soil, low rainfall and limited financial resources do not allow fertilizer application. Therefore other methods of increasing nitrogen content of cladodes - through selection, hybridization and inoculation - are very attractive. Protein deficiency can also be solved through appropriate supplementation and/or feed source combination.

Little attention has been paid to the quality of cladode proteins. Investigations conducted in the authors’ laboratory showed that the amino acid composition of cladodes is satisfactory and comparable to that of barley grain (Table 35).

The nutritive quality of opuntia depends on plant type (species and variety), cladode age, season, and agronomic conditions (soil type, climate, growing conditions, etc.). Nutrient content variation is similar for cladodes in their first and second years. The general trend is that dry matter content is high during summer months, while crude protein content is at its lowest level. The trend for ash content is less clear, but seems to be high for spring months. Crude fibre is less variable and seems to be higher during winter (Figure 15).

Table 35. Amino acid composition of Opuntia ficus-indica var. inermis cladodes (g N/16 g N).

Key: CP = crude protein

Figure 15. Variation of chemical composition of opuntia cladodes (Opuntia ficus-indica var. inermis) in the first (a) and second (b) years. Key: MS = dry matter. MM = ash. MAT = crude protein. CB = crude fibre.

The effect of cladode age on nutrient content is quite interesting. It is obvious that dry matter increases as cladodes get older. Analysing data related to this aspect, the authors found that crude protein contents decreased (5 to 3% DM) and crude fibre increased (9 to 20% DM) as cladodes aged from 1 to 5 years. Crude protein content decreased significantly (R2 = 0.6) when cladode dry matter/age increased (Figure 16).

Figure 16. Changes in crude protein content associated with DM (Nefzaoui, unpubl. data)

This trend is similar to other fodder sources, where valuable nutrients decrease with plant age, a result of the relative increase in fibre content. Thus, opuntia behaves like any other conventional fodder where crude protein content decreases and crude fibre increases with age (Figure 17).

Digestibility

Opuntia cladodes are highly digestible. In vivo average values obtained with sheep varied from 60 to 65%, 60 to 70%, 35 to 70% and 40 to 50%, for DM, OM, CP and CF, respectively. An example of digestibility data obtained with sheep is given in Table 36. These coefficients are similar to those observed with common forage crops. Since opuntia should not be used alone to feed animals, digestibility is calculated by difference, assuming no interaction between diet components.

The main difference between cactus and other forage crops is nutrient degradability in the rumen. While forage crops potential degradability in the rumen is often reached after 48 hours, cactus nutrients are rapidly degraded (in between 6 and 12 hours), so it can be assumed that no significant nutrient extraction is operating after 24 hours (Ben Thlija, 1987).

According to Shoop et al. (1977), 80% of the total digestion of Great Plains opuntia (O. polyacantha) occurred during the first 16 hours of a 48-hour incubation period, whereas only 73% and 71% of total digestion for hay pellets and alfalfa hay, respectively, occurred during the initial 16 hours. Comparative dry matter digestibility of these forages is shown in Table 37.

Figure 17. Dry matter (DM), crude fibre (CF) and crude protein (CP) content associated with cladode age (Nefzaoui, unpublished data).

A rapid rate of digestion means a faster passage of the material through the digestive tract. This also means that cactus dry matter remains in the gastrointestinal tract only for a short time, leaving more volume available for further intake. In other words, the gut fill of cactus is low, explaining why an increase of cactus volume in the diet does not reduce the intake of other components of the ration. These findings are similar to those obtained by Ben Salem et al. (1996) in Tunisia.

These results are very important for arid zones where livestock is fed mainly with straw or cereal stubble: both coarse feeds are of poor quality and have low intakes, which lead to poor animal performance.

A USDA report indicated that feeding trials using heifers showed that cactus cladodes are readily and more completely digestible than grass-hay (Agropyron cristatum and Bromus spp.). A study conducted by Rossouw (1961) comparing yield and digestible portion of opuntia and other fodders is summarized in Table 38.

Table 36. Effect of spineless cactus (Opuntia ficus-indica var. inermis) supply on intake, total diet digestibility and water consumption by sheep fed straw-based diets

Note: Means in the same row followed by different letters differ significantly at the 5% level.
Source: Ben Salem et al., 1996

Table 37. Dry matter digestibility (%) in vivo (NBDMD) and in vitro (IVDMD) of singed opuntia, grass-hay pellets and alfalfa

Note: Means in the same column followed by different letters differ significantly at the 5% level.
Source: Shoop et al., 1977

Table 38. Total yield and amount (as fed) of digestible nutrients of some fodders

Source: Rossouw, 1961

EFFECT OF FEEDING CACTUS ON RUMEN FERMENTATION PATTERN

The effect of spineless cactus supply on digestion of wheat straw was studied in rumen-cannulated sheep. Animals received wheat straw ad libitum, with graded levels of cactus (0, 150, 300, 450 or 600 g DM/day). When the level of cactus in sheep diet increased, fibrous feed intake, rumen volatile fatty acids concentration, rumen protozoa number and rumen ammonia concentration increased, while water intake, rumen cellulolytic activity and rumen acetic acid/propionic acid ratio decreased (Ben Salem et al., 1996).

Rumen pH

Rumen pH remained in the range of 6.80 to 7.13, even when animals received the highest level of spineless cactus (Table 39), so pH of rumen fluid was not affected by the presence of spineless cactus in the diet. Even though spineless cactus is rich in highly fermentable carbohydrates, no differences were observed. Consumption of large volumes of spineless cactus probably enhanced salivation as a result of the high level of mineral salts and the abundance of mucilage in cactus, which might explain the discrepancy. Efforts to quantify effects of mucilage on saliva production and rumen buffer would

Table 39. Effect of spineless cactus supply on ruminal pH ammonia nitrogen (NH₃-N), volatile fatty acids (VFA) concentration and protozoa count in sheep fed on straw-based diets

Note: Means in the same row with different superscripts differ (P<0.05).
Source: Ben Salem et al., 1996

Ammonia concentration

Animals supplied with spineless cactus showed an increase in ammonia nitrogen (NH₃-N) concentration in the rumen. Rumen NH₃-N increased (P<0.001) from 4.7 mg/100 ml in the control diet to 11.3, 12 and 10.8 mg/100 ml for diets including 300, 450 and 600 g DM of cactus, respectively (Table 39 and Figure 18).

Ruminal ammonia concentrations were relatively high in animals supplemented with spineless cactus. Even when sheep were fed with straw alone, NH₃-N concentrations in the rumen fluid were quite similar to those reported by Satter and Slyter (1974) as the optimal level for microbial growth and fibre digestion in the rumen.

Figure 18. Cactus intake effect on ammonia, volatile fatty acid (VFA) and protozoa contents in the rumen

(Source: Ben Salem et al., 1996)

Volatile fatty acids

Spineless cactus supply significantly increased (P<0.001) total volatile fatty acid (VFA) concentrations. Highest total VFA concentrations were obtained with 300 g DM of cactus in the diet. Propionate and butyrate proportions increased significantly in animals receiving spineless cactus. Cactus supply resulted in a slight decrease in the acetate proportion in rumen fluid and an increase in propionate and butyrate concentrations. Spineless cactus seems to have the same effect on ruminant digestion as soluble carbohydrates (Table 39 and Figure 18).

Protozoa counts

The positive effect of spineless cactus supply on NH₃-N concentration was coupled with a significant increase in the total protozoa number in the rumen fluid (P<0.001). The average number of protozoa shifted from 3.5 × 10⁴/ml to 13, 17.7 and 13.1 × 10⁴/ml with diets supplemented with 0, 300, 450 and 600 g DM of spineless cactus, respectively (Table 39 and Figure 18).

The higher protozoa count observed in animals supplemented with spineless cactus was associated with high levels of ruminal NH₃-N concentration. It is claimed that protozoa contribute to dietary protein digestion and thus ammonia production (Ushida and Jouany, 1985).

Cellulolytic activity

Increasing the cactus level in the diet increased DM intake of fibrous feeds but decreased fibre digestibility, probably because of the depressing effect on rumen cellulolytic bacteria of large amounts of soluble carbohydrates in cactus pads.

Effective degradability of DM and NDF were significantly decreased by spineless cactus supply (P<0.001), indicating an impairment of cellulolytic activity in the rumen. However, the rate of degradation (c) was not affected by spineless cactus supply (P>0.05) (Figure 19).

Figure 19. Effect of spineless cactus intake on rumen cellulolytic activity.

(Source: Ben Salem et al., 1996)

Cellulolytic activity measured by the in sacco technique clearly shows some depression in fibre degradation (Figure 19). Such a trend is consistent with results reported by Chappel and Fontenot (1968). It is now well documented that ciliate protozoa have a negative effect on the number of bacteria in the rumen and thus on ruminal cellulolytic activity (Demeyer and Van Nevel, 1979). Moreover, the high level of minerals in spineless cactus can be a limiting factor for microbial growth in the rumen, as suggested by Komisarczuk-Bony and Durand (1991).

It may be concluded that a combination of spineless cactus (Opuntia ficus-indica var. inermis) with cereal straw is a nutritionally satisfactory solution for maintaining small ruminants in arid zones. Spineless cactus provides a fodder rich in energy and a water source in drought conditions. Animals receiving cactus reduce water intake substantially and may even stop drinking water. Moreover, this trial indicates that spineless cactus may improve the nutritive value and intake of poor quality roughages. It may be offered to sheep without any risk of digestive disturbances, provided that it is mixed with a fibrous feed. Finally, it is expected that supply of a protein nitrogen source in conjunction with spineless cactus could result in a further improvement of the nutritive value of straw-based diets. Additional work is required to test this hypothesis.

Intake

Generally, cacti are highly palatable. Jersey cows fed on opuntia and supplemented with 1 kg of concentrate feed/day, ate 50.6 kg/day of fresh cactus. Metral (1965) obtained similar results, with cows consuming a voluntary intake of 60 kg when cactus was fed alone. Viana (1965) obtained higher values, with an average voluntary intake of 77.3 kg and 117 kg/day maximum.

Valdes and Flores (1967) observed higher intakes with sheep fed with Opuntia ficus-indica (11 kg/day) than with Opuntia robusta (6.5 kg/day). Monjauze and Le Houérou (1965) reported intake values ranging from 2.5 to 9 kg/day. It is also reported that higher intakes are observed when water content of pads is higher. Similar results were observed in the authors’ work (Nefzaoui and Ben Salem, unpublished data). The gut fill value is low, and, unusually, feeding cactus enhances intake of fibrous feeds like straw (Figure 20 and Table 36). This result is very interesting because straw is the main feed source in the arid environments of the WANA region. It is well established that besides its low feed value, straw intake is low. Combining straw with cactus increases straw intake and consequently animal performance (Figure 20).

Figure 20. Relationship between cactus and fibre intake

(Source: Ben Salem et al., 1996).

Sheep fed with straw were able to consume up to 560 g DM of spineless cactus. This level represents nearly half of the total diet. This beneficial effect of spineless cactus could be explained by the improvement in rumen fermentation conditions. Spineless cactus increased by almost 2.5 times the supply of easily fermentable organic matter (Table 36). Animals receiving diets containing up to 500 g of spineless cactus did not show any digestive disturbance, supporting earlier findings (Cordier, 1947). The response pattern to spineless cactus supply with respect to straw intake is in agreement with those generally observed with soluble-carbohydrate-rich diets. Earlier reports (Preston and Leng, 1987; Rangnekar, 1988) indicated that supplementation of poor quality roughages with molasses increased their palatability. Thus, spineless cactus may have a similar effect. Absence of a negative effect of spineless cactus supply on straw intake presumably lies in the high digestibility of spineless cactus in the rumen and in the rapid outflow rate of this feed from the rumen, as it is rich in water.

CACTUS FEEDING HELPS TO SOLVE THE PROBLEM OF WATERING ANIMALS IN ARID ENVIRONMENTS

Water is scarce in arid zones of the WANA region, and animal watering is a real problem during summer and drought periods. Animals expend a lot of energy to reach watering points, and rangeland degradation is a serious risk in the area surrounding watering points. Therefore, the high water content of cactus pads could help mitigate the problem of watering animals in dry areas. Research clearly shows that water intake is nil when cactus intake by sheep is about 300 g of dry matter (Figure 20). The volume of water consumed by animals decreased from 2.4 litre for the control diet to 0.1 litre when the level of spineless cactus consumption exceeded 300 g DM. Terblanche et al. (1971) reported similar findings.

Feeding cactus helps to solve the problem of animal watering. Sheep fed for a long period (400 to 500 successive days) with large amounts of cactus stopped drinking (Rossouw, 1961; Harvard-Duclos, 1969). Woodward et al. (1915) with Jersey cows reported similar results. However, Cottier (1934) suggested that it is not possible to suppress water in cattle fed on cactus.

Energy content

Gross energy content of most cacti species ranges from 3500 to 4000 Kcal/kg DM. Digestible energy is about 2000 Kcal, which is comparable to a medium quality grass (Ben Thlija, 1987). Thus energy levels of cacti make them a valuable component to include in livestock diets. This energy comes mainly from the high carbohydrate concentration of cladodes.

According to De Kock (1985), the feeding value of spineless cactus is equivalent to 65% TDN, while the authors’ measurements (Nefzaoui, unpublished data) are about 0.7 Milk Forage Unit (MFU).

SOME PRACTICAL CONSIDERATIONS

The method of utilization of spineless cactus will differ from farm to farm according to circumstances, such as available labour, facilities, volume of spineless cactus, etc. It is often recommended to use opuntia for feeding livestock by:

* Grazing of cladodes in situ. Although this is the simplest method, it is not the most efficient, and care should be taken so that the animals do not overgraze and destroy the plants.

* Cutting harvested cladodes into small pieces or strips and feeding them in a confined area to limit unnecessary wastage.

* Making silage. The cladodes are cut into small pieces and mixed with hay or low quality alfalfa. If no fruits are included it is necessary to add molasses. The silage container must be airtight.

* Supplementation in case of emergency. Cactus, fed in any form, will keep the animals alive for long periods. De Kock (1980) emphasized the desirability of supplementing opuntia with a protein-rich supplement of alfalfa or hay (200 g in winter and 100 g in summer) with cactus fed ad libitum. A lick of equal parts by mass of bone meal, salt and fodder lime is recommended by De Kock (1980) to supplement the phosphate and sodium.

STORAGE

Since cacti are evergreen, it is better to store the product in situ to avoid expensive processes like silage or drying, even if they are technically feasible. Chaffed spineless cactus pads can be dried on any suitable surface and then ground in a hammermill through a 6-mm sieve. In the form of meal, the spineless cactus material is not only ingested better, but is also easier to store. A supply of spineless cactus meal can thus be stored for use during droughts.

Good quality silage can be made from spineless cactus by chaffing the pads together with oat straw, low grade lucerne hay or any other roughage on the basis of 84 parts by mass of spineless cactus and 16 parts by mass of roughage, with the addition of 2% molasses meal.

GRAZING VERSUS CUT-AND-CARRY

The easiest way to utilize spineless cactus is by grazing, as it requires very little labour and is therefore also the cheapest method. However, overgrazing must be avoided, particularly on young plants that can be destroyed by sheep. Even older plants can be badly damaged by overgrazing, and subsequent production will be considerably lower. The best method of grazing is to divide the plantation into small paddocks and graze each of them intensively for a short period. Large losses occur during grazing due to wastage.

Direct browsing needs very tight grazing control, otherwise wastage may reach 50% of the fodder produced (cladodes partially eaten and abandoned) and the plantation itself may be destroyed by overbrowsing within a few months of overstocking (Monjauze and Le Houérou, 1965; De Kock, 1980). The advantage of this type of management is its very low cost and the fact that the grass layer between the shrubs is available to the stock. These two advantages result in an economically more efficient system. It is best to utilize spineless cactus in rotation so that a plantation is utilized every three to five years. In this way a plantation can be chopped or grazed each time to the height of one pad higher than the original planting. When spineless cactus are utilized in this manner, the plants recover well, the material available for use is of good quality and the plants are kept within a suitable height range.

Zero grazing or the cut-and-carry technique is more efficient. Loss of feed is virtually nil and risk of over-utilization is considerably reduced. Over-exploitation may occur, however, especially in case of early harvest in young plantations; which is detrimental to future production. But the zero grazing technique is costly, although the method is amenable to the stock. In most cases in North Africa, zero grazing management would be recommended because of insufficient grazing discipline and therefore a high risk of destruction.

SPINES

Cactus pads are valuable feed provided the spines are singed off first, usually through the use of a propane weed burner (Shoop et al., 1977). Other practices were discussed by Griffiths (1905). Steaming to moisten the spines and chopping of the large pads were, and are, very efficient practices to facilitate the use and maximize the amount of cactus eaten by livestock. According to the same author, tools and machines have been built for these purposes.

While in some countries (Mexico and USA) the whole standing plant is burned before grazing, in North Africa individual pads are burned and chopped into small pieces with hand tools or appropriate cutting machines.

LAXATIVE EFFECTS - EASY TO SOLVE

A problem experienced when spineless cactus pads are fed to sheep in any form is the severe laxative action they have. This laxative effect is not a disease symptom, it just happens that the food passes past through the animal’s digestive system faster, and as a result digestion is poorer. It appears that hay as a supplement retards this rapid transit to a certain extent.

A laxative effect appears when the volume of cactus in the diet is high (more than 50 to 60% of the DM intake). This problem is easy to solve, and feeding small amounts of straw or hay prior to cactus distribution is sufficient to have normal transit.

INTEGRATION OF CACTI WITH OTHER ARID ZONES FEED RESOURCES

As stated in the introduction, rangeland areas and productivity in WANA countries are decreasing dramatically and currently provide only a small portion of livestock needs.

Moreover, the seasonality of range production due to climatic conditions results in two feed gaps: one in winter (2-4 months) and a longer one in the summer period (5-6 months). These gaps are very difficult to manage by livestock owners, and require large volumes of imported concentrate feeds to supplement animal requirements. Since it is almost impossible for social reasons to reduce animal numbers, most national strategies aim to increase rangeland productivity, using several techniques, including reseeding, fertilizer application, resting, and establishing shrub plantation. The last option, even if it is not the cheapest one, is the most attractive. Most of these plantations are based on the introduction of highly productive species such as Acacia cyanophylla, Atriplex nummularia (or A. halimus) and spineless opuntia. According to the land tenure system in operation, several techniques are used for planting shrubs and cacti.

* On communal rangeland, introduced species are planted in rows without removal of natural herbaceous or woody species.

* On private land, the alley cropping technique is preferred, where farmers can crop the area between rows when the rainfall conditions are favourable.

* On both categories of land, water and soil conservation techniques are applied. In this case, shrubs and cactus are planted according to the contour lines in order to consolidate the so-called tabias.

* Another approach is related to cactus, and the oldest one is the bosquet type, which is a dense plantation surrounding the house, used for fruit cropping as well as fodder to supplement animals indoors.

Because of these actions, shrubs (i.e. Acacia and Atriplex) and opuntia became an integral part of the livestock production system in North Africa. It is also evident that a better integration of these feed resources with conventional ones is necessary. In the following section, selected examples of resource integration are discussed.

Example 1. Poor quality roughages supplemented with opuntia

Poor quality roughage can be supplemented with cactus. Indeed, the intake of straw increases significantly with the increase of the amount of cactus in the diet (Nefzaoui et al., 1993; Ben Salem et al., 1996). Cactus is also a good supplement to ammonia- or urea-treated straw, since it provides the necessary soluble carbohydrates for the efficient use of the non-protein nitrogen in the rumen (Nefzaoui et al., 1993).

To study the effect of using large amounts of cactus (Opuntia ficus-indica var. inermis) in order to quantify non-protein nitrogen from ammonia- or urea-treated straw, six groups of six Barbarine sheep were submitted to diets that included cactus ad libitum and two levels (300 and 600 g) of untreated, urea- or ammonia-treated straws (Table 40). Results showed that cactus voluntary intake can be high (450 g DM) and remain important when straw daily ingestion increased from 300 to 600 g. Diets containing 64% of cactus caused no digestive disturbance. Data indicated that it is possible to cover sheep maintenance requirements for energy by using diets based on cactus given ad libitum together with 300 g of straw per day. With high levels of straw (600 g/day) it is possible to cover 170 to 190% of maintenance energy requirement. To cover nitrogen maintenance requirements, straw should be treated. Therefore, cacti may be used as a major component of diets containing cereal straws; it is only necessary to add appropriate supplements in order to overcome the nitrogen deficiency and to supply the fibre needed for normal rumen function.

Table 40. Straw supplementation with spineless cactus

Key: US = untreated straw. ATS = ammonia-treated straw. UTS = urea-treated straw. DM = dry matter. OM = organic matter. CP = crude protein. CF = crude fibre. N = nitrogen.

Source: Nefzaoui et al., 1993

Example 2. Atriplex as a nitrogen supplement to cactus

In a first experiment (Nefzaoui and Ben Salem, 1996), Barbarine sheep were randomly allotted into three equal groups, and fed diets (80% of the diet) based on opuntia (Opuntia ficus-indica var. inermis) and atriplex (Atriplex nummularia). Limited amounts of wheat straw (180 g/day) and commercial mineral and vitamin supplement (30 g/day) were distributed. Diet dry matter (DM) intakes were similar for all groups. Digestibility coefficients of organic matter (OMD) and crude protein (CPD) of the three diets were relatively high, averaging 68, 74, and 75%, respectively (Table 41). In contrast, fibre digestibility was low, as the soluble carbohydrates of cactus might have depressed rumen cellulolytic activity. The diets provided about 1.7 times sheep energy and digestible crude protein (DCP) requirements. Diet 1 covered 1.65 and 2.3 times energy and DCP requirements of sheep, respectively. Thus, it provided excess nitrogen and should be supplemented with an energy source such as barley grain. Diet 2 was relatively well balanced in both energy and nitrogen, while diet 3 had excess energy and needed to be supplemented with a nitrogen source (non-protein nitrogen, like urea).

Table 41. Nutritive value of three diets

Notes:
(1) The values (in parentheses) correspond to intakes stated in g DM/kg of LW^0.75.
(2) OMD = organic matter digestibility.
(3) CPD = crude protein digestibility.
(4) Feeding value is expressed in % of sheep maintenance requirements in terms of energy (as digestible organic matter intake (DOMi)) and nitrogen (as digestible crude

Sheep energy and N requirements may be matched using diets based on these two feeds. The level of cactus in the diet can reach 55% on a DM basis without any digestive side effect. It is advisable that small amounts of fibrous feed (straw, hay) be fed to animals before cactus. Better dietetic efficiency can be obtained if the mineral balance is improved.

In another experiment, the effect of nitrogen supplement (urea, soybean meal, Atriplex halimus, Atriplex nummularia) on cactus-pear-based diets, voluntary intake and growth of Barbarine yearlings, was investigated (Nefzaoui et al., 1996). Four iso-nitrogenous and iso-energetic diets (D1 to D4) were offered to four groups with six Barbarine yearlings in each, during 60 days in summer (Table 42). For all diets, freshly cut cactus was fed ad libitum in addition to a limited amount of hay (170 g/day). Diets were supplemented respectively with 8 g/day urea (D1), 770 g/day Atriplex halimus (D2), 740 g/day A. nummularia (D3), and 65 g/day soybean meal (D4). Results showed that cactus based-diets could be supplemented efficiently by Atriplex nummularia. Use of urea and A. halimus led to low growth rates in comparison with diets supplemented with soybean meal or A. nummularia.

The voluntary intakes were 694, 844, 858 and 674 g DM/day, for diets D1, D2, D3 and D4, respectively. The average daily liveweight gains were 55, 58, 74 and 70 g for D1, D2, D3 and D4 respectively. Such diets, using low quantities of cereals (28%) and forage (17%) in the ration, are recommended to cope with feed deficiency in the arid and semi-arid areas prevailing in West Asia/North Africa.

Table 42. Feed intake and liveweight gains

Source: Nefzaoui et al., 1996

Example 3. Can acacia supplement cactus?

Acacia cyanophylla - a widespread, introduced shrub - was used to supplement cactus-based diets. Acacia is rich in crude protein (about 13% of DM). To assess the effect, four Barbarine sheep groups were fed with various diets (R00, R21, R22 and R23) (Table 43). Because of cost, hay was given in limited amounts. The intake of acacia was low (250 g DM/day) because of its high content of condensed tannins (7% DM). These tannins also caused low digestibility of the acacia crude proteins. Such diets need to be supplemented with an appropriate source of nitrogen.

Table 43. Nutritional value of opuntia-based diets supplemented with Acacia cyanophylla

Note: DM = dry matter. OM = organic matter. CP = crude protein. CF = crude fibre.

(1) Feeding value is expressed as % of sheep maintenance requirements in energy (DOMi = digestible organic matter intake) and nitrogen (DCPi = Digestible crude protein intake).

Source: Nefzaoui et al., 1996

CONCLUSIONS

Opuntia cladodes behave like common forage crops:

(i) As cladode age increases, so dry matter and fibre contents increase and crude protein content decreases.

(ii) They have high contents of water (»90%), ash (»20%) and calcium (»1.4%), soluble carbohydrates and vitamin A.

(iii) They are poor in crude protein (»4% DM), fibre (»10 % DM) and P (»0.2% DM).

(iv) Their digestibility can be compared to a good forage crop, with average digestibility coefficients ranging from 60 to 70% for organic matter, 35 to 70% for crude protein and 40 to 50% for crude fibre.

When fed to animals they show some differences with forage crops and behave more like a sugar-rich foodstuff (similar to cereal grain or molasses). Indeed, when the level of cactus cladodes in the diet increases:

(v) there is an increase in the intake of fibre feeds, and the rumen volatile fatty acids, the rumen protozoa count and the rumen ammonia concentration all increase.

(vi) There is a decrease in water intake, rumen cellulolytic activity and the acetic acid/propionic acid ratio.

Cactus cladodes are highly palatable, with average daily consumptions of 6 to 9 kg for sheep and 50 to 80 kg for cattle observed. They have a very low gut fill value, because their intake does not reduce fibrous feed intake and the improved rumen conditions enhance the fibrous feed intake.

The high moisture content of cladodes should be considered a positive factor, because it helps mitigate the problem of animal watering in dry areas. Feed values of spiny or spineless cactus are similar. Spines are not a limiting factor because they can be removed.

When feeding cactus, two simple rules should be observed:

(vii) Cactus is an unbalanced diet and should be fed in association with fibrous foodstuffs (straw, hay, shrubs, etc.). It also needs to be supplemented with an appropriate and cheap nitrogen source.

(viii) Cactus is rich in soluble carbohydrates and Ca, but poor in P. Therefore it is recommended to (a) add molasses to the ration to avoid decreasing rumen cellulolytic activity; (b) limit the amount of grain in the diet for the same reason; (c) feed animals with fibrous feeds (straw, hay, etc.) before giving the cactus. Moreover, a special mineral supplement is required to provide sufficient sulphur (S) to maintain an equilibrium Ca/P ratio.