OPUNTIAE: A STRATEGIC FODDER AND EFFICIENT TOOL TO COMBAT DESERTIFICATION IN THE WANA REGION

A. Nefzaoui and H. Ben Salem
Institut National de la Recherche Agronomique de Tunisie
Rue Hédi Karray, Ariana 2049, Tunisia

Introduction

The West Asia/North Africa (WANA) region contains large areas with rainy winters and hot, dry summers. WANA is characterized by 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 World War II, as the human population has increased fourfold (Le Houérou, 1991). The sheep population has increased by 75 % and the stocking rate jumped from 1 sheep/4 ha to 1 sheep/ha between 1950 and 1989. The rangeland degradation is simply the outcome of these facts beside the increased cropping activities, and increased use of feed grains.

Thus, contribution of rangelands to the annual feed requirements of livestock is diminishing continuously; it went from 80 % 3 to 4 decades ago to less than 25 % at current time. Overgrazing and the deterioration of the range are the major factors that forced pastoralists to change their migration and feeding patterns. In some countries, animals are heavily supplemented with barley grain and other concentrate feeds. Table 1 summarizes a typical feed calendar common for agropastoral systems of arid and semiarid zones of the WANA region.

Therefore, most of the WANA countries were seeking for appropriate tools to prevent rangeland degradation and even to restore their 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 given phosphate fertilizer, (iii) treatment and suitable supplementation of straw, (iv) other crop residues and agro-industrial by products. In addition a planned government strategy for drought relief will reduce the risk to small ruminant producers and encourage increased production. 

The search for appropriate plant species able to grow and to produce in arid areas was of a permanent concern of most of people leaving in harsh environment. Cactus species characteristics fit with most of the requirements of a drought resistant fodder crop as described by De Kock (1980):

As the name implies it must be relatively drought resistant. It must not only be able to survive long droughts, but must also be able to produce large quantities of fodder during preceding times of plenty or periods of favorable rainfall, which can be utilized during periods of drought.

  • Drought resistant fodder crops must have a high carrying capacity.
  • It must be able to supply succulent fodder to animals during droughts.
  • It must not have an adverse effect on the health of the animals utilizing it.
  • Severe utilization must not have an adverse effect on the plants. In other words, the plants must have high recovery ability after severe utilization.
  • The establishment must have a few problems as possible.
  • The establishment and maintenance of the plantations must be economical. It must thus have a low initial cost.
  • The plants must be relatively less fastidious regarding soil and climatic requirements. They must thus be adapted to a wide series of soil and climatic conditions, so that they can be planted where the cultivation of ordinary fodder crops is an uncertain undertaking.
    Table 1. Common feed calendar for small ruminants in the WANA region
Period Physiological stage Area Type of feed Supplement
May- July Mating - early pregnancy Agricultural land Cereal stubble Bran, barley, cactus
August- September Pregnancy Agricultural land,  Cereal stubble, straw Bran, barley, cactus, shrubs (Atriplex)
October- January Late pregnancy - early lactation Rangeland, agricultural land  Fallow, hay, natural grazing Barley, wheat bran, Olive tree by-products
February- April Weaning, fattening Rangeland, agricultural land Natural grazing, fallow, standing barley, straw Olive tree leaves and twigs, barley, bran

The future of the arid and semiarid 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 successfully withstand water shortage, high temperature and poor soil fertility. Cacti, particularly Opuntia, fit most of these requirements and they are important to the economy of arid zones, for both subsistence and market-oriented activities (Barbera, 1995).

1- REASONS FOR THE INCREASED IMPORTANCE OF CACTI IN ARID ZONES

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

  • To grow in "deserts" and are drought tolerant. They indeed possess a highly specialized photosynthetic mechanism that allows being more efficient than grasses or legumes in converting water to dry matter (Russel and Felker, 1985; Nobel, 1989).
  • To produce forage, fruit, and other useful products.
  • To prevent long-term degradation of ecologically weak environments.

  • It is suggested that cacti and Opuntia genus in particular were introduced in the WANA region by Spanish moors. Nevertheless, large plantations were undertaken during this century only. These plantations were implemented to create living fodder banks to feed animals during drought and to combat desertification.
1.1-  Cacti as a fodder bank

Opuntia species used for animal feeding are abundant, easy and cheap to grow, palatable and can withstand prolonged droughts (Shoop et al., 1977). Such characteristics make these species a potentially important feed supplement for livestock, particularly during periods of drought and seasons of low feed availability. The majority of Opuntia plant biomass is pad material rather than fruits and it can be fed to livestock as fresh forage or stored as silage for later feeding (Castra et al., 1977).

The idea of using cactus to feed livestock is not recent. Griffith (1905) was certain that feeding cactus to livestock started in the US before the civil war. He mentioned that before and after this war, there was very extensive freight transportation of cactus pads between some regions of Texas such as Brownsville, Indianola, San Antonio and Eagle Pass.

The literature indicates that this plant has become important for fodder in many parts of the world, as is the utilization of both natural and cultivated populations. It is cultivated in Africa, Italy, Israel, Spain, the United States, Mexico, Colombia, Brazil, Peru, Bolivia, Chile and Argentina (Barbera et al., 1992; le Houérou, 1979; Brutsch, 1984; Clovis de Andrade, 1990; Curtis, 1979; Pimienta, 1990; Russell and Felker, 1987; Saenz, 1985).

Large areas are encountered in South Africa, Algeria, Mexico and Brazil. It is used all year around or as emergency feedstock in case of drought. During drought, cacti remain succulent. In many arid areas (Tunisia, Mexico, South Texas, South Africa, etc.) the 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).

In North Africa and from the beginning of the century several tentative were undertaken to reduce water and wind erosion and rangeland degradation by using shrubs and cacti (Opuntia ficus-indica var. inermis mainly). Acacia cyanophylla and Atriplex nummularia or halimus were the most used. Therefore, from the 50th until now large areas were planted in Algeria, Tunisia and Morocco. They are estimated to be 700,000 to 1 million ha and are located mainly in low rainfall areas and aiming to combat erosion and desertification and to provide feed for livestock during frequent drought periods.

Figure 1. Cactus (O. ficus-indica) yield according to rainfall in Tunisia (adapted from Montjauze et Le Houérou, 1965)

The importance of cacti became evident when research results show clearly that other CAM plants; cacti are capable of developing high productivities in water stress regions. Because of their high water use efficiency (Nobel, 1989) their aboveground productivity is much higher than any other arid plant species. In Tunisia under rainfed conditions and with no fertilizer application, spineless cactus yields were between 20 and 100 tons of cladodes per year, for an average rainfall of 150 and 400 mm per year, respectively (figure 1).

1.2-  Use of cacti to combat desertification in North Africa

Marginal lands, are fragile ecosystems, subjected to ploughing and indiscriminate vegetation removal that resulted in large-scale degradation and destruction of vegetative covers. The disappearance and scarcity of several plant species indicate the magnitude of genetic and edaphic losses.

To revert the desertification trend and restore the vegetative cover in those areas, appropriate integrated packages are utilized for rangeland monitoring, livestock and natural resources conservation. Spineless cactus (Opuntia Ficus-indica), drought and erosion tolerant plant, is being advantageously used in Tunisia and Algeria to slow and direct sand movement, enhance the restoration of the vegetative cover and ovoid the water destruction of the land terraces built to reduce run off. 

In Central and South Tunisia cactus plantations provide a large amount of fodder for livestock and play key role in natural resources conservation. Land terraces are easily damaged by water runoff. Cactus helps by its deep and strong rooting system. Two rows of cactus pads are planted on the inner side of the terraces. The rooting system is enhanced by the availability of the water collected at the base of the terrace. Roots are widely spread on the elevated land part and deeply in the soil to ensure stability of the terraces. In addition, cut and carried pads provide sufficient feed resources during spells. Cactus can be used in combination with cement barriers or cut palm leaves to stop wind erosion and sand movement. It will fix the soil and enhance the restoration of the vegetative plant cover.

2- USE OF CACTI AS FODDER

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

2.1- Chemical composition

Opuntia spp. Cladodes have high contents in water (90 %), ash (20 % DM), Ca (1.4 % DM), soluble carbohydrates and vitamin A. They have low contents in crude protein (CP. ~ 4 % DM), crude fiber (CF ~ 10 % DM), and phosphorus (P ~ 0.2 % DM) (Nefzaoui et al., 1995). 

Hoffman and Walker (table 2) have analyzed Opuntia species for nutrient contents as early as 1912. These early investigations indicate already that spiny and spineless cactus have practically the same chemical composition and are of equal value for feeding purposes (Woodward, 1915).
 

Table 2. Chemical composition (% DM) of O. engelmannii and O. lindermeri (Hoffman and Walker, 1912).
Water  85 Phosphoric acid  0.33
Crude protein  1.4-4.4 Potassium  3.04
Nitrogen free extract  7.85 Magnesium  1.6
Fat  1.55 Calcium  2.84-13.85
Crude fiber  8.65

Table 3 summarizes some relevant nutrient contents of cactus pads measured in Tunisia. It appears that globally the water content is high (80-95 %), the ash content is also high and can reach 33 % of the DM. The crude protein content is low and often below the level of 5 % of the DM. Fiber content is also relatively low, the average value is about 9 % of the DM. These data are quite similar to those reported in other countries (table 4).

Contents of major macroelements show again the very low levels of P and Na and the high levels of Ca. Recent investigations (Ben Salem and Nefzaoui non-published) show that cactus cladodes have high contents in oxalates. The Total oxalate amount is about 13 % of the DM from which 40 % are 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.

Table 3. Average chemical composition of Opuntia ficus-indica cladodes produced in Tunisia
 
DM, %
% of DM
Ash
CP
CF
NFE
P
Ca
K
Na
average
13.48
27.41
3.84
8.55
58.16
0.04
8.66
1.09
0.05
Minimum
8.95
23.11
1.90
7.39
52.60
0.02
7.56
0.43
0.001
Maximum
21.48
33.70
7.51
10.60
63.79
0.07
10.62
1.92
0.17
Standard deviation
4.50
3.77
1.48
1.03
4.02
0.02
1.09
0.45
0.05

(*) DM: dry matter, CP: crude protein, CF: crude fiber, NFE: nitrogen free extract, P: phosphorus, Ca: calcium, K: potassium, Na: sodium.

Table 4. Average chemical composition of cactus cladodes calculated on the basis of the results published by several authors (De Kock, 1965; Theriez, 1965; Lozano, 1958; Morisson, 1957; Teles, 1978)
 
DM, %
% of DM
Ash
CP
CF
NFE
Average
11.01
17.19
4.76
10.91
65.30
Minimum
4.74
8.18
2.5
7.82
56.7
Maximum
17.00
23.53
7.87
14.50
72.67
Standard deviation
3.87
4.61
1.90
2.24
5.25

(*) Idem table 3

Crude fiber measurement is a poor indicator of feed fiber status and improved methods, as the Van Soest fractionating procedure, are more appropriate. It appears that compared to alfalfa, cacti have a relatively low fiber content especially lignocellulose fraction (table 5). It is well known that high levels of lignocellulose or lignin are responsible for low digestibility of foodstuffs. According to these data it is easy to guess that cactus pads organic matter digestibility is expected to be high.

Table 5. Average neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose, cellulose and lignin contents (% of DM) of some Opuntia species (Ben Thlija, 1987)
Species NDF ADF Hemicellose Cellulose Lignin
Alfalfa (ref. sp.) 45.15 29.91 15.24 21.49 7.93
O. engelmannii 31.18 11.29 19.88 7.95 2.89
O. filipendula 33.30 15.31 17.99 10.49 3.97
O. versicolor 39.85 18.98 20.87 13.73 3.86
O. polyacantha 31.16 18.42 12.74 12.69 4.79
O. fragilis 35.08 15.47 19.61 10.97 3.91

(*) NDF :neutral detergent fiber, ADF :acid detergent fiber

Ash content of cactus pads is high, ranging from 10 to 25 %, mainly because of the high calcium content. Most of the Opuntias have phosphorus levels below animal requirement (tables 2 and 3).

High Ca compounds levels in arid and semi-arid soils and the water deficiency pushes cactus to accumulate in its pads high quantities of Ca solutes. 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 is largely higher than animal requirements. An excess of calcium is not problematic in itself, but an unbalanced Ca/P ratio requires to be corrected. Most of authors report a Ca/P ratio of about 35. 

Shoop et al. (1977) working on O. polyacantha, indicated that the phosphorus content was below livestock dietary requirements. Calcium levels seemed to be adequate but the calcium/phosphorus ratio, of 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 range generally suggested to be acceptable in ruminant’s diets. An exception was sodium content which was relatively low (0.02 %).

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

Several investigators (i.e. Gonzalez, 1989) have demonstrate that N and P fertilizers increase crude protein contents of Opuntia cladodes which jump from 4.5 % to 10.5 % of dry matter. This is rather spectacular. But in the WANA region, where large plantations of Opuntia are implemented for fodder production in dry areas where soil quality, rainfall and finances cannot allow fertilizers 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 feeds sources combination. This aspect will be developed in the next chapter.

Little attention was paid to the quality of Opuntia cladodes proteins. Investigations conducted in our laboratory showed (table 6) that the aminoacids composition of Opuntia cladodes is quite satisfactory and is quite comparable to that of barley grain.

Table 6. Aminoacids composition of Opuntia cladodes proteins (g N/16 g N)
 
O.F.I.
CP : 4.24 % DM
O.F.I.
CP: 7.51 % DM
(Ousseltia 12.1975)
O.F.I.
CP : 4.24 % DM (Bourebia)
Barley gain
CP : 11 % DM
Aspartic acid
9.29
11.66
10.98
5.70
Threonin
3.83
4.96
4.22
3.40
Serin
4.19
4.25
4.37
4.20
Glutamic acid
12.88
12.72
13.25
24.80
Prolin
6.38
5.73
7.25
12.80
Glycin
4.66
4.69
4.86
3.80
Alanin
8.19
6.33
8.38
3.80
Cystin
0.94
0.31
0.94
2.40
Valin
7.14
6.52
7.14
4.80
Methionin
1.82
2.33
1.99
1.40
Isoleucin
4.94
5.20
5.25
3.50
Leucin
7.99
8.58
8.43
6.90
Tyrosine
4.01
4.14
4.01
3.13
Phenylalanin
4.76
5.66
4.81
5.40
Lysine
4.86
6.32
6.56
3.60
Histidin
1.89
2.42
2.40
1.10
Arginin
5.60
5.31
5.60
4.90

(*) O.F.I. : Opuntia ficus-indica var. inermis. CP: crude protein, CF: crude fiber

Nutritive quality of Opuntia depends on plant type (species, varieties), cladode’s age, season, agronomic conditions (soil type, climate, growing conditions, etc.).

The trend of nutrient content variation is quite similar for cladodes of 1 and 2 years. The general trend is that dry matter content is highest during summer months, while crude protein content is at its lowest level for the same period. The tendency for ash content is less clear, but seems to be high for spring months. Crude fiber is less variable and seems to be higher during winter (figure 2).

The effect of cladode’s age on nutrient contents is quite interesting. It is obvious that dry matter increases when cladodes get old. Analyzing data related to this aspect, we noticed that crude protein contents decrease (5 to 3 % DM) and crude fiber increase (9 to 20 % DM) when cladode’s age move from 1 to 5 years. Crude protein content decreases significantly (R2=0.6) when cladode’s dry matter/age increases (figure 3)

This trend is similar to other fodder sources, where valuable nutrients decrease with the plant age resulting from the relative increase in fiber content. Thus, cacti behave like any other conventional fodder where crude protein content decreases and crude fiber increases when the plant get old (Figure 4).

Figure 2. Variation of chemical composition of cactus cladodes (Opuntia ficus-indica var. inermis) of the first year (figure 2a) and the second year (figure 2b). MS (dry matter), MM (ash), MAT (crude protein), CB (crude fiber)

Figure 3. Crude protein content decreases when cladodes DM increases (age) (Nefzaoui, non published)

Figure 4. Dry matter (DM), crude fiber (CF) and crude protein (CP) contents variation with cactus (Opuntia ficus-indica var. inermis) cladodes age (Nefzaoui, non-published).

2.2- Digestibility

Opuntia cladodes are highly digestible. In vivo digestibility coefficients average values obtained with sheep are of 60 to 65 %, 60 to 70 %, 35 to 70 % and 40 to 50 %, respectively for DM, OM, CP, and CF. An example of digestibility data obtained with sheep is given in table (table 7). These coefficients are quite similar to those observed with common forage crops.

Since cactus cannot be fed alone, it should be mentioned that these values are calculated by difference, assuming the absence of interaction between diet components.

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

According to Shoop et al. (1977) 80% of the total digestion of Great Plains prickly pear (O. polyacantha) occurred during the first 16 hours of 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 digestibilities of the three forages and shown in table 8. A rapid rate of digestion means a faster passage of the material through the digestive tract. This means also that cactus dry matter remains in the gastrointestinal tract only for a short time leaving more available volume for further intake. In other words the gut fill of cactus is low and explains why the increase of cactus amount in the diet will not reduce the intake of the other components of the ration. This fact is supported by the work conducted in Tunisia by Ben Salem et al (1996).

This result is of very high importance for arid zones where livestock is fed mainly with straw or cereal stubble. These two coarse feeds are of poor quality and have low intakes, which lead to low animal performances. 

Table 7. Effect of spineless cactus (Opuntia ficus-indica) supply on intake, total diets digestibilities and water consumption by sheep fed straw-based diets (Ben Salem et al., 1996).
 level of spineless cactus (g DM / day) 
0 150 300 450 600
DM intake (g/day)
straw 550c 574bc 523 643ab  716a
cactus+straw 550 724 823c 1093 1278a
DM intake (g/ KG M0.75 day) 
straw 43.6 42.2bc 37.7 44.8 54.7a
cactus+straw 43.6e 53.3 59.6 76.3 97.6a
Total diet digestibility
OM 0.453 0.504ab  0.543 0.577 0.587a
CP 0.495 0.550bc 0.537bc  0.585ab  0.643a
CF 0.525  0.508  0.534  0.523  0.468 
NDF 0.504  0.495  0.483  0.523  0.506 
ADF 0.524  0.473 0.473  0.522 0.484 
Digestible OM and CP intakes (% maintenance requirements)†
DOMi  93 123 158 193 212
 DCPi  52 52 64 93 111
Drinking water
consumed (l / day)  2.42 1.49 0.14 0.11c 0c
_______________________________________________________________________
a,b,c,d,e Means in the same line with different superscripts differ (P<0.05).
†DOMi : digestible organic matter intake calculated as (DOMi / 23) x 100, DCPi : digestible crude protein intake calculated as (DCPi / 45) x 100. The numbers 23 and 45 represent the DOMi requirement in g / kg M0.75.day and the DCPi requirement in g /animal according to Institut National de la Recherche Agronomique (1978).
 

A report of US Department of agriculture indicated that feeding trials, using heifers, cactus cladodes are more readily and more completely digestible than grass-hay (Agropyron cristatum and Bromus spp.). In a study conducted by Rossouw (1961) a comparison, of yield and amount of digestible portion, between prickly pear and some other fodders is summarizes in table 9.

Table 8. Dry matter digestibility (%) in vivo (NBDMD) and in vitro (IVDMD) of singed cactus pear, grass-hay pellets and alfalfa (Shoop et al., 1977).
 

NBDMD
IVDMD
Feed  16 hour Incubation 48 hour Incubation 96 hour Incubation
Prickly pear 52.9 66.4 a 63.8 a
Grass-hay pellets 39.3 54.1 c 53.0 b
Alfalfa hay 44.5 62.9 63.7 a
_______________________________________________________________________
(*) Means in the same column followed by different letters differ significantly at 5% level.
 
Table 9. Total yield and amount (as fed) of digestible nutrients of some fodders (Rossouw, 1961)
Crop 
Yield
Amount of digestible nutrients
(t/ha)  (t/ha) %
Prickly pear 80  5.0  6.25
Maize (silage) 25  4.2 16.80
Mangelwurzel 25 3.7  14.80
Lucerne hay 2.5  50.00

2.3- Effect of feeding cactus on rumen fermentation pattern

The effects of spineless cactus supply on digestion of wheat straw were studied in rumen canulated 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 diets increases, fibrous feeds intake, rumen volatile fatty acids concentration, rumen protozoa number and rumen ammonia concentration increase; while water intake, rumen Cellulolytic activity, and acetic acid/propionic acid ratio of the rumen decrease (Ben Salem et al., 1996).

Even when animals received the highest level of spineless cactus, rumen pH remained in the range of 6.80 to 7.13 (table 10).

Rumen fluid pH was not affected by the presence of spineless cactus in the diet. If one supposes that spineless cactus is rich in easily fermentable carbohydrates, we should normally expect a decrease of pH in the rumen, but that was not the case in this study. Such discrepancy may be explained by the fact that consumption of large amounts of spineless cactus had probably enhanced salivation resulting from the high level of mineral salts and the abundance of mucilage in cactus.

Efforts to quantify effects of mucilage on saliva production and rumen buffer would be worthwhile.
 

Table 10. Effect of spineless cactus supply on mean ruminal pH, ammonia nitrogen (NH3-N) and volatile fatty acids (VFA) concentrations and protozoa total number in sheep fed straw based diets (Ben Salem et al., 1996)
 level of spineless cactus (g DM / day) 
0 150 300 450 600
pH 7.16ab 7.03bc 7.19a 7.13ab 6.96c
NH3-N (mg/100ml) 4.7b 7.1b 11.3a 12.0a 10.8a
Total VFA (mmol/l) 43.4c 60.4b 77.6a 60.2b 55.1b
      Acetate 63.7a 57.8b 61.2ab 59.2ab 61.4ab
       Propionate 21.0b 25.4a 24.2a 25.7a 23.6ab
       Butyrate 6.7b 6.8b 8.3a 7.9a 7.9a
       Acetate/
       Propionate
3.29a 2.34b 2.72b 2.55b 2.57b
Protozoa(x 104 /ml) 3.5d 9.3c 13.0b 17.7a 13.1b
___________________________________________________________________________
a,b,c,dMeans in the same line with different superscripts differ (P<0.05).

Ammonia concentration

Spineless cactus supply had a positive effect on ammonia nitrogen (NH3-N) concentration in the rumen. Rumen NH3-N increased (P<0.001) from 4.7 mg / 100 ml for 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 10, figure 5).

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

Volatile fatty acids

Spineless cactus supply significantly increased (P<0.001) total VFA concentrations. Highest total VFA concentrations were obtained with 300 g DM of cactus in the diet. Propionate and butyrate proportions were significantly increased in animals receiving spineless cactus.

In the present study, cactus supply resulted in a slight decrease of acetate proportions in rumen fluid and an increase of propionate and butyrate concentrations. Spineless cactus seems to have the same effect on ruminant digestion as soluble carbohydrates (table 10, figure 5).

Protozoa counts

Positive effect of spineless cactus supply on NH3-N concentration was coupled with a significant increase of total protozoa number in the rumen fluid (P<0.001). Mean number of protozoa shifted from 3.5 x 104 / ml to 13, 17.7 and 13.1 x 104 / ml with diets supplemented with 0, 300, 450 and 600 g DM of spineless cactus, respectively (table 10, figure 5).

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

Cellulolytic activity 

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

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 6). 

Cellulolytic activity measured by the in sacco technique clearly shows some depression in fiber degradation. 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, high level of minerals in spineless cactus can be a limiting factor for microbial growth in the rumen, as reviewed by Komisarczuk-Bony and Durand (1991).

It may be concluded that 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. Spineless cactus would appear on a welcome water source in drought conditions since animals receiving spineless cactus reduce water intake substantially and may even stop consuming 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 offered to animals in conjunction with a fibrous feed. Finally, one could expect that the supply of a protein nitrogen source in conjunction with spineless cactus may result to a further improvement of the nutritive value of straw-based diets. Further work is required to test the latter hypothesis.

Figure 5. Cactus intake increases ammonia, VFA and protozoa contents in the rumen (Ben Salem et al., 1996).

Figure 6. Effect of spineless cactus intake on rumen Cellulolytic activity measured by the in sacco technique (Ben Salem et al., 1996).
2.4- Intake

Generally cacti are highly palatable. Jersey cows fed on cactus and supplemented with 1 kg per day of concentrate feeds ate some 50.6 kg per day of fresh cactus. Metral (1965) obtained similar result, with a voluntary intake of 60 kg when cactus is fed alone to cows. Viana (1965) obtained higher values with an average voluntary intake of 77.3 kg and a maximum of 117 kg per day.

Valdes and Flores (1967) observed with sheep a higher intakes with Opuntia ficus-indica (11 kg/day) than Opuntia robusta (6.5 kg/day). Monjauze and Le Houérou (1965) reported values for intake from 2.5 to 9 kg per day. It is also reported that higher intakes are observed when water content of pads is higher. Similar results were also observed in our work (Nefzaoui and Ben Salem, non-published). The gut fill value is low, and unusually feeding cactus (figure 7 and table 7) enhances intake of fibrous feeds (straw). This result is highly interesting because straw is the main feed source in arid environment of the WANA. It is well established that besides its low feed value straw intake is low. Combining straw with cactus increases straw intake and consequently animal performances. 

Sheep fed straw were able to consume up to about 560 g DM of spineless cactus. Such level represents nearly half of the total diet. This beneficial effect of spineless cactus may be explained by the improvement of rumen fermentation conditions. Spineless cactus increased by ca. 2.5 times the supply of easily fermentescible organic matter (table 7). Animals receiving diets containing up to 500 g of spineless cactus did not show any digestive disturbance. This is in agreement with earlier findings (Cordier, 1947). The pattern of responses to spineless cactus supply with respect to straw intake is in agreement with that generally observed with soluble-carbohydrate-rich diets. Earlier reports (Preston and Leng, 1987; Rangnekar, 1988) indicate that supplementation of poor quality roughages with molasses increased their palatability. Thus, spineless cactus may have the similar effect to molasses. Absence of negative effect of spineless cactus supply on straw intake lies presumably in the high digestion of spineless cactus in the rumen and in the rapid outflow rate of this feed from the rumen as it is rich in water. 

2.5- Cactus may help resolving the problem of watering animals in arid areas

Water is scarce in arid zones of the WANA region. Watering animals during summer time and drought periods is a real problem. Animals spend a lot of energy to reach water points. Moreover, rangeland degradation in the surrounding area of water points is a serious task. Therefore, the high water content of cactus pads is a positive criteria and feeding this species helps solving watering animals in dry areas.

The data obtained in our research show clearly that water intake is nil when cactus intake by sheep is about 300 g of dry matter (figure 8).

Volume of water consumed by animals decreased from 2.4 l for the control diet to 0.1 l when the level of spineless cactus is above 300 g DM. Terblanche et al. (1971) reported similar findings.

Feeding cactus helps to resolve the problem of watering animals. Sheep fed for a long period (400 to 500 successive days) with large amounts of cactus stopped drinking (Roussow, 1961; Harvard-Duclos, 1969). Woodward et al. (1915) with Jersey cows observed the same fact. But Cottier (1934) suggested that it is not possible to suppress completely water for cattle fed on cactus.

2.6- 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 carbohydrates concentration of the cladodes.

According to De Kock (1985), the feeding value of spineless cactus is equivalent to 65 % TDN, while our own measurements are of about 0.7 Milk forage unit (MFU) (Nefzaoui, unpublished).

Figure 7. Cactus intake increases fiber intake (Ben Salem et al, 1996)
2.7- Some practical considerations

The method of utilization of spineless cactus will differ from farm to farm according to circumstances such as available labor, facilities, quantity of spineless cactus etc.

It is often recommended the following ways of utilizing cactus pear for feeding livestock:

  • 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 deplete the plants.
  • Cutting of the harvested cladodes into small pieces or strips and feeding them in a confined area to limit unnecessary wastage.
  • Making of silage. The cladodes are cut into smaller pieces and mixed with hay or low quality alfalfa. If no fruits are included it is necessary to add molasses. Silage must be airtight.
  • Supplementation in case of emergency. Cactus, fed in any form, will keep the animals alive for long periods. De Kock (1983) emphasizes the desirability of supplementing cactus pear 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 (1983) to supplement the phosphate and sodium.
Figure 8. Feeding cactus helps solving watering problem (Ben Salem et al., 1996)
Storage

Since cacti can stand evergreen, it is better to store the product in situ and to avoid expensive processes like silage making or drying, even if they are technically feasible.

Chaffed spineless cactus pads can be dried on any suitable on any suitable surface and then ground in a hammermill through a six-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 two percent molasses meal.

Grazing vs. Cut and carry

The easiest way to utilize spineless cactus is by grazing. It requires very little labor and is thus also the cheapest method. Overgrazing of the plantation must, however, be guarded against. Young plants are especially susceptible to overgrazing and can be killed by sheep. Even older plants can be so badly damaged that the subsequent production will be considerably lower. The best method of grazing is to divide the plantation into small paddocks and to graze each of these intensively for a short period. Large losses occur during grazing due to wastage.

Direct browsing necessitates a very tight control on grazing, 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 very 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 facts result in the much better financial results of this type of management. It is best to utilize spineless cactus in rotation so that a plantation is utilized three to five years. in this way a plantation can be chopped or graze each time to the height of 1 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 usable size.

Zero grazing or the cut-and-carry technique bears the opposite consequences. Loss of feed is virtually nil and risk of overutilization is considerably reduced. Overexploitation may occur , however especially in case of too early harvest in young plantations; this may be very detrimental to the future production potential of the crop. But the zero grazing technique is costly in labor, although the method is amenable to the stock.

In most cases in North Africa the zero grazing management is to be recommended because of insufficient grazing discipline and therefore 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 than burning off the spines were discussed by Griffiths (1905). Steaming to moisten the spines and chopping of the big pads were and are, until now, 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 and regions (Texas, Mexico) the whole standing plant is burned than grazed, in North Africa individual pads of cactus are burned than chopped into small pieces with hand tools or appropriate cutting machines.

Laxative effects : easy to resolve

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, however, not a disease symptom and has, as far as is known, have the disadvantage that the food passes through the animal’s digestive system faster with the result that digestion is poorer. It appears that hay as a supplement retards this rapid transit to a certain extent.

This laxative effect appears when the amount 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.

3- INTEGRATION OF CACTI WITH OTHER FEED RESOURCES

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

Moreover, the seasonability, due to climatic conditions, of range production results in two feed gaps : one in the winter (2-4 months) and a large one in summer period (5-6 months). These gaps are very difficult to manage by livestock owners and require large amounts of imported concentrate feeds to supplement animals. Since it is rather impossible for social reason to reduce animal’s number, most national strategies aimed to increase rangeland productivity using several techniques, as reseeding, fertilizer application, resting and shrubs plantation. The last option, even if it not the cheapest one, is the most attractive. Most of these plantations are based on the introduction of highly producing species as Acacia cyanophylla, Atriplex nummularia (or halimus) and spineless cactus. 

According to the land tenure system several techniques of planting shrubs and cacti are used.

  • On communal rangelands : introduced species are planted in rows without removal of natural herbaceous or woody natural species.
  • On private lands, alley cropping technique is preferred where farmers can crop the area between rows when the rainfall conditions are favorable.
  • On both types of land tenures when water and soil conservation techniques are applied. In this case shrubs and cactus are planted according to the contour lines in order to consolidate (reinforce) the so-called "tabias".
  • Another type is related to cactus and is obviously the oldest one is the "bosquet" type, which is a very dense plantation surrounding the house and used for fruit cropping and as fodder to supplement animals indoors.
For all these reasons, shrubs namely acacia and atriplex and cactus became an integrated part of the livestock production system in North Africa. It is also evident that a better integration of these feed resources to the conventional ones is necessary. In the following chapter selected examples of integrating these resources are discussed. They show the benefit of integrating cactus with other resources in the feeding systems in arid zones.

3.1- Example 1 : Poor quality roughages supplementation with cactus

Poor quality roughage may 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 to 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 valorize non-protein nitrogen from ammonia or urea treated straw, six groups of six Barbarine sheep were submitted to diets including cactus ad-libitum and two levels (300 and 600 g) of untreated, urea or ammonia treated straws (table 11). 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 with 300 g of straw per day. With high levels of straw (600 g/day) it is possible to cover 170 to 190 % 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 bring the fiber needed for a normal rumen functioning.

Table 11. Straw supplementation with spineless cactus (Nefzaoui et al., 1993).
                                          Levels of straw 300 gd-1            600 g d-1
               US              ATS              UTS                 US               ATS              UTS
DM Intake, g
   Opuntia 445 447 425 432 462 439
   Straw 254 242 249 494 466 486
Diets in vivo Digesttibility, %
  OM 67.9 64.0 63.3 66.5 69.8 72.6
   CP 41.1 48.0 43.3 45.9 61.0 77.1
   CF 37.5 30.5 29.2 46.5 49.2 52.7
N retained -0.2 -0.2 -0.6 0.8 2.8 3.9
_____________________________________________________________________
1 US : untreated straw, ATS : ammonia treated straw, UTS : urea treated straw.
2 OM :organic matter, CP : crude protein, CF : crude fiber, N : nitrogen.

3.2- Example 2 : Atriplex a nitrogen supplement to cactus

In a first experiment (Nefzaoui et al., 1996a), Barbarine sheep whether were randomly allotted into 3 equal groups, and fed diets based on (80 % of the diet) cactus (Opuntia ficus-indica var. inermis) and atriplex (Atriplex nummularia). Limited amounts of wheat straw (180 gd-1) and commercial mineral and vitamins supplement (30 g.d-1) were distributed. Diets dry matter (DM) intakes were similar for all groups. Digestibility coefficients of organic matter (OMD) and crude protein (CPD) of the 3 diets were relatively high, averaging 68, 74 %, and 75 %, respectively (table 12). In contrast, fiber digestibility was low, as the soluble carbohydrates of cactus might have depressed rumen Cellulolytic activity. The diets allow to cover about 1.7 times sheep energy and digestible crude protein (DCP) requirements. Diet 1 covers 1.65 and 2.3 times energy and DCP requirements of sheep, respectively. Thus, it provides excess nitrogen and should be supplemented with an energy source such as barley grain. Diet 2 is relatively well balanced in both energy and nitrogen, while diet 3 has excess in energy and needs to be supplemented with a nitrogen source (non-protein nitrogen, like urea).

Energy and N sheep requirements may be matched using diets based on these two feeds. The level of cactus in the diet may reach up to 55 % on DM basis, without any digestive side effect. It is advisable that small amounts of fibrous feed (straw, hay) be fed to animals before cactus. A better efficiency of the diets 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 based diets voluntary intake and growth of Barbarine yearlings, was investigated (Nefzaoui et al., 1996b). Four isonitrogenous and isoenergetic diets (D1 to D4) were offered to four groups of 6 Barbarine yearlings during 60 days (summer 1995) (table 13). For all diets, freshly cut cactus was fed ad libitum in addition to a limited amount of hay (170 g.d-1). Diets were supplemented, respectively with 8 g d-1 urea (D1), 770 g d-1 Atriplex halimus (D2), 740 g d-1 Atriplex nummularia (D3), and 65 g d-1 soybean meal (D4). Results showed that cactus based diets may be supplemented efficiently by Atriplex nummularia. Urea and A. halimus lead to low growth rates in comparison to soybean meal or A. Nummularia supplemented diets.

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

Table 12. Nutritive value of diets (Nefzaoui et al., 1996a)
Diets D1 D2 D3
Total intake g DM d-1 941 (70) 930 (72) 983 (73)
Cactus intake 197 353 550
Atriplex intake 554 391 236
Straw intake  160 159  167
Diet OMD, %  67.7  69.3  74.4
Diet CPD, %  74.5  76.6  75.5
Retailed N, gd-1  4.1 3.9  4.1
Feeding value
    energy 167 174 184
    nitrogen 230 190 167
______________________________________________________________________
1 the values ( ) correspond to intakes stated in g of dry matter (DM) per kg of LW0.75
2 Feeding value is expressed in % of sheep maintenance requirements in energy (DOMi : digestible organic matter intake) and nitrogen (DCPi : Digestible crude protein intake)

3.3- Example 3 : Can Acacia supplement cactus ?

In this example, Acacia cyanophylla wildly spread introduced shrub was used to supplement cactus-based diets. Indeed, Acacia is rich in crude protein (about 13 % of DM). For this purpose, 4 Barbarine sheep groups were fed various diets (R00, R21, R22, and R23) (table 14). Because of cost, hay was distributed in a restricted and limited amount. The intake of acacia is low (250 g DM/day) because of its high content in 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 13. Feed intake and liveweight gains (Nefzaoui et al., 1996b)
Diets D1 D2 D3 D4
Intakes (g DM/d):  
Cactus 241 252 241 228
Atriplex halimus 0 224.2 0 0
Atriplex nummularia 0 0 225.8 0
Soybean meal 0 0 0 57.6
Barley  308.8 243.6 243.6 243.6
Hay  149.0  142.9  147.5  150.6
Urea  8  0  0  0
Total intake  706.8 862.7  857.9 679.8
Average daily gains (g/d)  55 58 74 70
_______________________________________________________________________
Table 14. Diets nutritive value (Nefzaoui et al., 1996b)
Diets R00 R21 R22 R23
Feed intake, g DM/day  
    cactus 0 167 246 267
    acacia 241 373 211 177
Diet digestibility, %
    OM 67.7 76.5 73.9 74.6
    CP 45.8 49.4 34.8 16.9
    CF 62.8 80.5 77.4 79.9
Retained N., g/day  2.77 2.73  0.46  -1.07
Feeding value*        
    energy  147  151  131  116
    nitrogen  75 67  32 10
______________________________________________________________________

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

In summary :

Cactus cladodes behave like common forage crops :

  • When the age increases, dry matter and fiber content increase and crude protein content decreases.
  • They have high contents in water (~ 90 %), in ash (~ 20 % DM), Ca (~ 1.4 % DM), soluble carbohydrates and vitamin A.
  • They are poor in crude protein (~ 4 % DM), fiber (~ 10 % DM) and P (~ 0.2 % DM).
  • They are highly digestible and may be compared to a good forage crop, with an average digestibility coefficients of 60 to 70 % for organic matter, 35 to 70 % for crude protein and 40 to 50 % for crude fiber.
  • When fed to animals they show some differences with forage crops and behave more like a sugar-rich foodstuffs (similar to cereal grain or molasses). Indeed when the level of cactus cladodes in the diet increases :
  • there is an increase of the intake of fiber feeds, the rumen volatile fatty acids, the rumen protozoa numbers and the rumen ammonia concentration.
  • There is a decrease of the water intake, the rumen cellulolytic activity and the ratio acetic acid/propionic acid.
Cactus are highly palatable, an average of 6 to 9 kg for sheep and 50 to 80 kg for cattle. They have a very low gut fill value, because their intake does not reduce fibrous feed intake. At the contrary the improved rumen conditions enhance the fibrous feed intake.

The high moisture content of the cladodes should be considered as a positive factor, because it helps in resolving the problem of watering animals in dry areas.

Feed values of spiny or spineless cactus are similar. Spines are not limiting factor because they are easy to remove.

To feed cactus a few simple rules should be considered :

  • Cactus is an unbalanced diet and should be fed in association with fibrous foodstuffs (straw, hay, shrubs, etc.). It is also needs to be supplemented with an appropriate and cheap nitrogen source.
  • Cactus is rich in soluble carbohydrates and Ca and poor in phosphorus. Therefore it is recommended to (i) avoid decreasing rumen Cellulolytic activity by adding molasses, (ii) limit the amount of grain in the diet for the same reason, (iii) feed animals fibrous feeds (straw, hay, ...) before cactus. Moreover, a special mineral supplement is required (equilibrium Ca/P ratio), to bring sufficient amounts of sulfur (S).
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