Chapter 2: Protein sources from plants and microbes

The tropics are rich in plant and microbial protein resources which could be used for livestock production (Ly, 1993). Unfortunately, several of these resources contain compounds, known as anti-nutritional factors, that can depress animal performance. One such compound, a trypsin inhibitor, interferes with the proteolytic activity of the digestive enzyme, trypsin; other inhibitors, such as, hemagglutinins, goitrogens, saponins and lipoxidase are not as well understood but are thought to also affect growth. The trypsin inhibitor and the hemagglutinins are destroyed by heat; however, overheating often changes the amino acid availability while underheating produces a bitter taste which affects palatability and therefore feed consumption. Even though most of this book deals with potential energy sources for pigs, such as sugar cane, oil palm, tubers and plantains, this chapter hopes to emphasize that one major constraint to developing alternative pig feeding systems in the tropics is directly related to optimizing the use of existing protein resources.

NON-OIL LEGUME SEEDS

Canavalia beans

Canavalia ensiformis is a good example of an alternative tropical legume for pigs. It can produce an annual yield of up to 6 t/ha of shelled beans and 10 t/ha of residues that could mean an annual yield of 3.6 t/ha of protein (Escobar et al., 1983). However, because of anti-nutritional factors, the general use of this legume for pigs is best limited to no more than 5% of the diet. Ensiling or autoclaving the bean to reduce the inhibitors has been partially effective (Risso, 1984, cited by Escobar et al., 1983); soaking and cooking do not help (Moncada et al., 1990) and extrusion results in low intake and reduced average daily gains in young pigs (Risso, 1989). The chemical composition of canavalia beans is given in Table 2.1.

Table 2.1. The chemical composition of canavalia beans (% DM).

Form CP Ash CF EE Source
Raw 28.4 - - - León et al. (1990) a
Extruded 27.9 - - -
Raw 31.0 - - 4.0 Mora (1983) b
Raw 29.6 3.0 9.7 4.0 ICA (1988) c
Cooked 27.1 2.8 8.3 3.5
Raw 35 - 10.5 - Garcia and Pedroso (1989)
Autoclaved 28.7 4.5 14.6 - Dominguez and. Ly (1992) d

a cited by Michelangeli et al. (1990); b cited by Escobar et al.(1983); c cited by Moncada et al. (1990); d unpublished data The amino acid composition of canavalia beans and other non-oil legume seeds is shown in Table 2.2.

Table 2.2. The essential amino acid composition of non-oil legume seeds (%DM).

Amino acid Canavalia bean Pigeon pea Cow pea
Arginine 1.56 1.28 1.52
Histidine 0.80 -* -*
Isoleucine 1.12 0.78 0.92
Leucine 2.00 1.63 1.78
Lysine 1.43 1.42 1.57
Methionine + cystine 0.50 0.57 0.62
Phenylalanine + tyrosine 2.42 1.85 1.19
Threonine 1.09 0.83 0.88
Tryptophan -* 0.25 0.34
Valine 1.26 0.94 1.09.

Source: D'Mello et al. (1985); CPNSA (1991); * not reported

Pigeon pea

Pigeon pea, a valuable legume consumed by both humans and animals, is cultivated extensively in India, Southeast Asia, parts of Africa and the West Indies. Although, the seeds and leaf meal contain adequate levels of nitrogen, the foliage has a high level of crude fibre (FAO, 1993). There is little information concerning the use of pigeon pea leaf meal for pigs, however, several studies have determined the feeding value of the seeds. Growing pigs fed raw pigeon pea seeds performed poorly (Castro et al., 1984; Visitpanich et al., 1985a) mainly due to the trypsin inhibitor, which can be reduced by sterilizing (Visitpanich et al., 1985b). Different ways of treating pigeon peas and the effect on the digestion of pigs have been thoroughly studied in Brazil (see Table 2.3).

Table 2.3. Chemical composition and digestibility of cow pea and pigeon pea.

Composition (% DM) Digestibility (%)
CP Ash CF EE N Energy
Cow pea: raw 30.3 5.0 7.6 1.6 66.1 78.0
cooked 26.2 3.7 5.9 1.4 78.2 80.5
toasted 25.7 4.1 7.1 1.4 69.4 73.8
Pigeon pea: raw 23.8 4.3 10.6 1.4 71.5 77.4
cooked 23.0 3.4 10.3 1.1 81.6 83.4
toasted 22.4 3.9 10.6 0.9 76.3 83.4

Source: Fialho et al. (1985)

Cow pea

The cow pea is a short-cycle legume that has not been sufficiently studied as a protein source for pigs. This may be because it has normally been used as grain or forage for ruminants (Das et al., 1975). Table 2.3 shows data from Brazil related to the chemical composition and digestibility of the raw, cooked or toasted cow pea. Cooking involved either boiling for 40 minutes or sterilization at 100C for 20 minutes. The digestibility study by Fialho et al. (1985) clearly indicates that, when cooked or toasted, there is an improvement in the digestion of nitrogen and energy. Pigs fed toasted cow pea, in the form of meal and as the sole protein source, performed the same as pigs fed soya bean meal based diets. Other studies indicated that methionine supplementation of cow peas had no effect on pigs (Maner, 1971). The data in Table 2.4 support the idea that the trypsin inhibitor present in the seeds can be destroyed by cooking. With respect to on-farm trials, Gerpacio (1988) reported that cow pea meal could be included up to 30% in the diet.

Table 2.4. The effect of raw or cooked cow peas supplemented with methionine for growing/finishing pigs.

AD feed intake (kg/d) ADG (g) AD feed conversion
Soya bean meal plus maize 2.02 799 2.53
Raw cow pea 1.89 551 3.43
Raw cow pea plus methionine 1.49 483 3.09
Cooked cow pea 2.04 816 2.50
Cooked cow pea plus methionine 1.98 815 2.43

Source: Maner (1971)

OIL LEGUME SEEDS

Groundnut

The groundnut is cultivated for its oil and for human consumption. The seeds contain a trypsin inhibitor which is neutralized by heat during oil extraction. After oil extraction the resulting cake contains 40 to 45% protein of medium biological value (Table 2.5).

Groundnut meal lacks sufficient lysine and, even though it contains adequate amounts of methionine, threonine, tryptophan and nonessential amino acids (Green et al., 1988), it cannot be used as the only protein source for pigs. The nutritive value of whole groundnuts and groundnut meal can be seriously affected by contamination with Aspergillus mould, particularly if the seeds or the meal are not carefully dried prior to storage. The resultant aflatoxin, produced by the mould, can seriously affect pig performance including loss of appetite. The composition of the essential amino acids of the groundnut is given in Table 2.6.

Table 2.5. The chemical composition of different forms of ground-nut.

Composition (% DM) Source
CP Ash CF EE
Ground-nut meal: solvent 51.8 6.1 11.0 1.5 CNPSA (1991)
Ground-nut meal: screw press 45.3 4.5 4.7 8.3 Knabe et al. (1989)
Ground-nut cake: hulled

with hulls

49.5

46.5

5.7

5.2

5.9

18.5

6.9

2.1

Morrison (1956)

Table 2.6. Composition of the essential amino acids in ground-nut meal (%DM).

Amino acid Ground-nut meal Amino acid Ground-nut meal
Arginine 6.07 Methionine + cystine 1.30
Histidine 1.25 Phenyalanine + tyrosine 4.95
Isoleucine 1.95 Threonine 1.46
Leucine 3.40 Tryptophan 0.54
Lysine 1.87 Valine 2.37

Source: INRA (1984)

Table 2.7 offers an excellent example of amino acid supplementation of groundnut meal for growing/finishing pigs. The addition of both lysine and methionine to the meal produced a feed conversion comparable to that of soya bean meal. In order that the trypsin inhibitor does not affect performance, no more than 20% of full fat groundnut should be used.

Table 2.7. The use of ground-nut meal supplemented with different amino acids for pigs (22-90 kg).

AD feed intake (k/d) ADG ( g) AD feed conversion
Soya bean meal 2.46 700 3.54
Ground-nut meal 2.86 540 5.28
Ground-nut meal plus lysine 2.39 600 4.01
Ground-nut meal plus lysine and methionine 2.40 670 3.57

Source: Brooks and Thomas (1969)

Soya beans

Soya beans, first used in China for human consumption, were brought to America in the early 1800s for the purpose of hay or silage for domestic animals, and as a green cover crop. Later, interest began to focus on their oil content (Table 2.8). The favourable amino acid composition (Table 2.9) of soya bean meal, or adequately treated whole soya beans, complements that of cereals, particularly maize, in pig and other livestock feeding systems often used in temperate countries; in fact, soya bean meal now accounts for approximately 80% of total protein supplements used in non-ruminant feeds (Herkelman and Cromwell, 1990).

Table 2.8. The composition of whole or solvent extracted soya beanseed (%DM).

Parameter Whole seed Solvent extracted seed
toasted cooked 42% CP 45% CP 48% CP
Crude protein 41.5 43.0 48.0 50.8 54.7
Ether extract 17.6 19.6 2.3 2.0 1.6
Crude fibre 7.8 7.7 6.3 6.5 7.0

Source: CNPSA (1991)

The potential use of derivatives of sugar cane and oil palm, and of roots and tubers as alternative energy feed sources for pigs has provoked new interest in the use of the whole boiled seed (Sarría and Preston, 1992; Sarría, 1994) or even the ensiled soya bean plant (Chinh et al., 1993) for pig production. In the former case, pigs from 30 to 96 kg, fed boiled soya beans, sugar cane juice and concentrated distillery solubles, grew at 810 g/day, similar to the average daily gain of 834 g/day reported by Pérez (1993) for pigs also fed a restricted amount of boiled soya beans but only free-choice cane juice. When fed silage made from the entire soya bean plant, Chinh et al. (1993) were able to substitute from 25 to 37% of the dietary protein for growing pigs and from 20 to 30% for finishing pigs. The authors also emphasized that the yield of 8.1 t/ha of green soya bean foliage, about 70 days' growth, would represent 360 kg of crude protein, the same amount normally produced from one hectare of dry soya beans.

Table 2.9. The composition of the essential amino acids of soya bean products (% DM).

Amino acid Soya bean meal Cooked whole soya beans Roasted whole soya beans
Arginine 3.45 2.58 3.21
Histidine 1.41 - 1.22
Isoleucine 1.98 1.77 1.67
Leucine 3.29 3.04 3.09
Lysine 2.90 2.27 2.37
Methionine + cystine 1.15 1.53 1.35
Phenylalanine + tyrosine 3.63 1.76 3.46
Threonine 1.71 1.52 1.72
Tryptophan 0.90 0.91 0.56
Valine 2.15 1.87 1.87

Source: CPNSA (1991)

The use of raw soya beans can affect the digestion and absorption of protein and fat (Combs et al., 1967; Collins and Beaty, cited by Herkelman and Cromwell, 1990) and thus influence the performance of growing/finishing pigs. Pond et al. (1972) and Crenshaw and Danielson (1985a) showed that raw soya beans fed to growing pigs can reduce the average daily gain as well as increase feed conversion by more than 50 percent. Following that, Crenshaw and Danielson (1985b) studied the effect of raw soya beans on three consecutive parities and concluded that the raw, untreated bean can be effectively used during gestation. During lactation the sows were fed a 15% protein maize/soya bean meal ration.

The use of the raw bean during lactation has also been studied. There were no deleterious effects on first-litter sow reproductive traits when a mixture of soya bean meal and cottonseed meal was replaced by 10.4% of raw soya beans (Osorio and Buitrago, 1985, cited by Buitrago, 1987). Likewise, Newman et al. (1987) found that the reproductive performance of first-litter sows was not affected by feeding raw soya beans during both gestation and lactation.

Table 2.10. The effect of soya bean meal or whole soya beans on the performance traits of growing pigs (19-50 kg).

Composition: Soya bean meal Whole soya beans *
maize 82.8 - - -
C molasses - 30.0 40.0 30.0 40.0
sugar cane - 36.8 26.8 26.8 16.8
soya bean meal 14.0 30.0 30.0 - -
whole soya beans * - - - 40.0 40.0
AD feed intake, kg/d 1.78 2.12 2.23 2.25 2.33
ADG, g 600 6l0 670 720 640
AD feed conversion 2.96 3.47 3.33 3.13 3.64

Source: Buitrago et al. (1977); * Cooked 30 min. and sun-dried

Although several heat treatment methods such as toasting or extrusion been developed to neutralize the anti-nutritional factors contained in the raw bean, one simple method is to soak the bean overnight in water (1 part bean to 3 water) and boil the mixture for 15 minutes (Pérez, 1993). Another method is, without soaking, to boil the bean for 40 minutes (Sarría and Preston, 1992; Sarría, 1994). It has also been reported that pig performance was not affected when the whole soya bean was cooked for 30 minutes, and immediately sun-dried (Table 2.10). The author is presently performing observation trials using the entire soya bean plant, in late-milk stage, some 80 days' growth, for growing/finishing and gestating animals. The diet is diluted B molasses and from three to five soya bean plants, daily, depending on the category and size of the pigs.

NON-LEGUME OIL SEEDS

Sunflower seeds

Sunflowers do not contain the toxins found in legumes and although the principal producers of sunflower are found in the temperate climates, it can well adapt to the tropics (Sistach and Díaz, 1974). There are two main problems related to the use of sunflower seed meal for pigs: its high fibre content and the low level of lysine and threonine, the latter which varies according to the method of processing. The composition of different sunflower-derived feeds is presented in Table 2.11.

Table 2.11. The composition of different sunflower seed-derived feedstuffs.

Composition, % DM Source
CP Ash CF EE
Sunflower seeds 18.8 3.9 15.4 42.4 Hartman 1983, cited by Wahlstrom (1985)
Sunflower seeds: non-dehulled, oil extracted 32.2 6.0 26.7 1.5 CNPSA (1991)
Sunflower heads 7.1 10.6 16.6 2.9 Gowd et al. (1987)
Sunflower seed kernels 26.4 3.3 3.4 50.4 Sistach and Díaz (1974)
Sunflower meal: hulled, expeller 44.1 7.3 14 8.2 Pond and Maner (1974)
Hulled, solvent extracted 50.3 8.3 11.8 3.1

One example of the value of sunflower meal, in soya bean meal-based diets, including the effect of correcting the amino acid profile by adding lysine, may be seen in Table 2.12.

Table 2.12. The substitution of soya bean meal by sunflower meal supplemented with lysine for pigs (29-95 kg).

AD feed intake, kg/d ADG (g) AD feed conversion
Soya bean meal (control) 2.36 720 3.26
Sunflower meal, 25 % in diet: 2.67 780 3.5
plus lysine 2.46 740 3.33
50% in diet 2.44 700 3.49
plus lysine 2.46 740 3.35
75% in diet 2.15 580 3.69
plus lysine 2.38 690 3.44
100% in diet 2.20 610 3.59
plus lysine 2.40 760 3.13

Source: Baird (1981), cited by Aherne and Kennelly (1983)

The necessity for lysine supplementation of sunflower-based diets is fully illustrated by the data in the previous table and by the amino acid status of this protein source (Table 2.13). Perhaps, the full-fat sunflower seed, correctly supplemented with lysine, could be more widely employed as an alternative protein source for feeding pigs in the tropics if sugar cane juice was the energy source. Hulling the seed to diminish the indigestible fibre fraction might be unnecessary, however, information is lacking. In conventional cereal diets that contained up to 50% sunflower seeds (Laudert and Allee, 1975, cited by Wahlstrom, 1985), growth performance, but not feed efficiency, was affected.

In spite of its potential, one of the primary difficulties related to the production of sunflower in the tropics is the problem of harvesting, and more important, storage, particularly during the wet season. The author has preserved the entire sunflower head in molasses, a technique similar to the preservation of fish and fish wastes (see Chapter 6). Storing the entire sunflower head in this way inhibits the growth of mould, the main reason for having to dry the seeds for storage.

Table 2.13. Composition of the essential amino acids in sunflower seeds (%DM).

Amino acid Sunflower seeds Amino acid Sunflower seeds
Arginine 2.16 Methionine + cystine 0.50
Histidine 0.73 Phenyalanine + tyrosine 1.22
Isoleucine 1.27 Threonine -
Leucine 1.81 Tryptophan 0.34
Lysine 1.02 Valine 1.74

Source: CPNSA (1991)

Cotton seed

Cotton seed contains 25% crude protein and 25% of oil and, after the extraction of the oil, the resultant meal contains slightly more than 40% crude protein (Table 2.14). However, both the cotton seed, and the meal, contain gossypol, a toxic pigment to which the pig is very sensitive. Although dietary levels of 0.01% are harmless for older animals (Aherne and Kennelly, 1983) levels as low as 0.02% can kill young pigs (Hale et al., 1958).

Although various reviews about the use of cottonseed meal for feeding pigs are available (Buitrago et al., 1977; Aherne and Kennelly, 1983; Tanksley, 1990), one of the most practical suggestions is to include less than 10% of the seed in diets for young pigs, increasing this amount in older animals and breeding stock (Buitrago et al., 1977). The amino acid composition of cotton seed is shown in Table 2.15.

Table 2.14. Composition of cottonseed meal (% DM).

Parameter Screw press Pre-press solvent Solvent
Dry matter 91.4 89.9 90.4
Ether extract 3.7 0.6 1.5
Ash 6.2 6.4 6.4
Crude protein 4.0 41.4 41.4
N solubility 36.8 54.4 69.4
Lysine 1.59 1.71 1.76
Crude fibre 13.5 13.6 12.4
Free gossypol 0.04 0.05 0.03
Total gossypol 1.02 1.13 1.04

Source: Buitrago et al. (1977)

Table 2.15. Composition of the essential amino acids in cotton seeds (% DM).

Amino acid Cotton seeds Amino acid Cotton seeds
Arginine 4.53 Methionine + cystine 1.52
Histidine 1.15 Phenyalanine + tyrosine 3.38
Isoleucine 1.45 Threonine 1.52
Leucine 2.63 Tryptophan 0.62
Lysine 1.70 Valine 1.95

Source: CPNSA (1991)

Coconuts

Two principal feeds can be produced from coconuts. One is the byproduct of the extraction of the oil from the seed, known as coconut oil meal, coconut cake or copra meal and which represents approximately 34 to 42% of the weight of the nut (Hutagalung, 1981). The other is the broken kernel, usually known as raw copra. The main difference between the two products is the amount of protein and fat (Table 2.16)

Table 2.16. Composition of coconut products.

Composition (% DM) Source
CP Ash CF EE
Coconut oil meal: solvent extracted 24.6 6.2 10.8 0.4 Thorne et al. (1989)
expeller 21.9 5.4 10.0 9.1
Coconut oil meal: expeller 20.9 5.8 10.5 5.8 Creswell and Brooks (1971)
expeller 20.0 - 13.0 9.0 Hutagalung (1981)
expeller 25.4 5.8 12.6 17.1 CNPSA (1991)
Raw copra 7.6 1.2 3.5 66.2 Thorne et al. (1989)

Butterworth and Fox (1963) referred to the poor digestibility of coconut oil meal for pigs. Later, Hutagalung (1981) reported a higher value, 74%, for the digestibility of the protein in coconut oil meal. Recent Brazilian data reported levels as low as 67% and 63% for the digestibility of the nitrogen and the energy in expeller-pressed, coconut oil meal, respectively (CNPSA, 1991). It has been shown that coconut oil meal, at a dietary level of 30%, supports adequate performance in growing/finishing pigs (Grieve et al., 1966; Malynicz, 1973) and if certain amino acids are added, it may be used up to a level of 40 percent (Table 2.17)

.

Table 2.17 The use of 40% coconut oil meal (COM) supplemented with different amino acids for pigs (18-93 kg).

AD intake

(kg/d)

ADG

(g)

AD feed

conversion

Maize/soya bean meal 2.21 740 2.98
Coconut oil meal 2.10 560 3.76
COM + lysine and methionine 2.09 640 3.27
COM + lysine, methionine and threonine 2.08 650 3.19
COM +lysine, methionine and tryptophan 2.09 650 3.24
COM + lysine, methionine, threonine and tryptophan 2.12 710 3.00

Source: Yuthana (1986), cited by Argañosa (1987)

The low level of lysine and other essential amino acids in coconut oil meal is summarized in Table 2.18.

Table 2.18. Compositionof essential amino acids in coconut oil meal (%DM).

Amino acid Coconut oil meal Amino acid Coconut oil meal
Arginine 2.96 Methionine + cystine 0.65
Histidine 0.51 Phenyalanine + tyrosine 1.51
Isoleucine 0.89 Threonine 0.77
Leucine 1.71 Tryptophan 0.37
Lysine 0.72 Valine 1.24

Source: CPNSA (1991)

Rubber seed

Rubber seed meal is produced in substantial amounts in Southern Asia and parts of Africa where it is a valuable source of protein (Babatunde and Pond, 1988). Estimated annual yields of the seeds, which contain up to 25% crude protein, are 0.1 t/ha (Table 2.19). Rubber seed meal is relatively poor in the amino acid methionine, while the levels of lysine and cystine are somewhat better. However, the main constraint to using rubber seed meal is the presence of hydrocyanic acid in the seeds, about 9 mg/100g, which, according to Devendra (1989), can be reduced by heat or storage.

Table 2.19. Composition of rubber seed products.

Composition (% DM) Source
CP Ash CF EE
Rubber seed meal 38.0 5.3 3.9 12.6 Devendra (1979)
Rubber seed meal 28.0 - 13.9 11.5 Hutagalung (1981)
Hulled, solvent 31.2 - - 31.8 Babatunde and Pond (1988)

Limited studies have been carried out using rubber seed meal as pig feed. Ong and Yeong (1977) reported a reduction in growth when pigs were fed diets containing more than 20% of the meal (Table 2.20). Devendra (1989) also considered 20% as optimum.

Table 2.20. The effect of rubber seed meal on pigs.

% in diet AD intake (kg/d) ADG (g) AD feed conversion
0 1.73 500 3.51
5 1.83 500 3.58
10 1.80 490 3.69
15 1.80 480 3.73
20 1.82 470 3.83
25 1.76 410 4.33

Source: Ong and Yeong (1977)

In Sri Lanka, Ravindran (1983) found impaired performance traits with pigs fed more than 10 percent. However, this effect was attributed to a deficiency of lysine and methionine rather than to the cyanogenic glucoside present in the meal. This is fully illustrated in Table 2.21. More recently, Fuller (1988) suggested that with correctly treated meal, the diet could contain up to 40 percent. He also concluded that since rubber seeds slowly lose hydrocyanic acid, storage for a minimum of four months, or detoxification by roasting (350C for 15 minutes), or soaking, in hot water or in a 2.5% ash solution for 12 hours, could solve this problem. These methods would eliminate the anti-nutritional factors and improve palatability.

Table 2.21. Composition of the essential amino acids in rubber seeds (%DM).

Amino acid Rubber seeds Amino acid Rubber seeds
Arginine 2.86 Methionine + cystine 0.99
Histidine 0.74 Phenyalanine + tyrosine 2.37
Isoleucine 1.15 Threonine 1.12
Leucine 2.75 Tryptophan 0.36
Lysine 0.73 Valine 1.23

Source: Babatunde and Pond (1988)

FODDER TREES AND SHRUBS

Data concerning the feeding of fodder trees and shrubs for pigs is relatively scarce. Certain negative characteristics of these feeds, anti-nutritional factors and high levels of crude fibre, are known to affect performance, irrespective of the level of their inclusion (D'Mello, 1992). Also, in contrast to ruminants, most pigs are unable to "self-harvest" the foliage, meaning that the farmer has to cut and carry the feed for the animal.

Leucaena leucocephala is a good example of the difficulty of using fodder trees and shrubs as pig feed. Leucaena leucocephala contains mimosine, a free toxic amino acid. Practical methods of detoxification aimed at reducing the mimosine content of the leaf meal have been studied by researchers in Thailand (Kassumma, 1987). Since mimosine is a water soluble amino acid, water soaking and washing the leucaena leaves for one day before sun drying and grinding was reported as an economical way to improve their nutritive value (Table 2.22). Interestingly, however, the best performance was obtained by simply sun-drying the leaves prior to use.

An attempt to increase the level of soaked leucaena leaf, dried and prepared as a meal, from 15 to 25% in the diet, by adding 0.2% ferrous sulfate was unsuccessful. Pig performance tended to decline when more than 15% of treated, soaked meal was fed (Sanchisuriya, 1985, cited by Kassumma, 1987).

Table 2.22. The effect of including 15% Leucaena leaf meal for pigs (30-60 kg).

Form of administration AD intake (kg/d) ADG (g) AD feed conversion
Dried leucaena leaves 2.09 770 2.71
Soaked 24 hr, before drying and grinding 1.91 680 2.81
Ground, before soaking for 24 hr 2.00 690 2.90
Fresh, unsoaked leaves 1.67 540 3.06

Source: Ruengpaibul (1984), cited by Kassumma (1987)

Trichantera gigantea, perhaps the most promising fodder tree from the point of view of yield, palatability, and source of protein (Gómez and Murgueitio, 1991) contains 18% crude protein in dry matter (leaves) and can produce, annually, from 40 to 60 t/ha of fresh foliage. Sarría et al. (1992) reported a decrease in the growth rate of pigs when Trichantera gigantea provided up to 25% of the dietary protein in a sugar cane juice/soya bean meal feeding system, and it was suggested that performance was related to the lower nutrient digestibility or an imbalance of the essential amino acids in the foliage. This result was in contrast to an earlier observation that, as a source of protein for gestating sows, the use of up to 75% fresh Trichantera gigantea leaves was possible (Mejía, 1991, cited by Preston and Murgueitio, 1992).

Recently, Sarría (1994) concluded that there were no significant differences in the productive parameters of weaned piglets when the sows, during gestation, were fed a restricted amount of sugar cane juice, either soya bean meal or cooked soya beans, and up to 30% of daily protein requirements in the form of fresh Trichantera leaves, about one kilogramme per day.

AQUATIC PLANTS

Floating aquatic plants (macrophytes) can contribute to the protein content of the diet and, if grown in the liquid slurry of pig wastes (runoff) which have been treated anaerobically, may also contribute to the recycling of nitrogen. The protein content of some aquatic plants such as Lemna minor and Azolla spp is as high as 29 and 24%, in dry matter, respectively. Annual yields of water hyacinth can fluctuate between 3 and 15 kg of DM /m 2 (Steward, 1970) whereas yields of Azolla filiculoides have been reported as 3.9 kg DM/m2 (Becerra et al., 1990). Although aquatic plants have the capacity to double their biomass every 3 to 4 days, the use of water plants for pigs is limited due to their relatively high content of fibre and minerals (Table 2.23).

In the Philippines, Azolla, the traditional green manure of rice fields, is fed both fresh and ensiled to pigs (Table 2.24). In Colombia, where researchers have successfully used palm oil to replace sorghum as the only energy source in growing-finishing diets, Azolla has been used to replace 10% of the protein, provided by 500 g of soya bean meal, in the growing and 20% in the finishing phase, respectively (Ocampo, 1994).

Table 2.23. Compositionof some floating aquatic macrophytes (%DM).

DM CP Ash CF Source
Water hyacinth: chopped 3.8 11.3 23.0 - Baldwin et al. (1975)

        pressed

10.0 10.6 17.3 -
Water hyacinth: fresh - 26.7 l3.0 l7.4 Bonomi et al. (1981)
Water hyacinth: fresh 8.0 11.0 14.7 22.3 Mishra et al. (1987)
Azolla: dried, milled microphilla - 23.7 28.7 15.0 Alcantara and Querubin (1989)
Azolla filiculoides - 23.7 - - Becerra et al. (1990)
Lemna minor: fresh" - 29.6 17.0 9.7 Bonomi et al. (1981)
" 6.5 33.0 15.0 - Lincoln et al. (1986)

Table 2.24. Performance traits of pigs fed Azolla spp.

Form of feeding and % in diet Liveweight (kg) ADG (g) AD feed conversion Source
Meal: 0

15

16-25

"

223

267

3.40

3.33

Alcantara and Querubin (1989)
Meal: 0

30

35-60

"

557

520

4.11

4.42

Alcantara and Querubin (1989)
Silage: 0

20

30

33-59

"

"

701

778

748

3.22

3.16

3.18

Querubin et al. (1988)
Fresh,

wilted

0

30

24-89

"

482

454

4.73

5.26

Becerra et al. (1990)
Fresh 0

12.6

20-90

"

526

452

2.10*

2.20*

Ocampo (1994)

* DM feed conversions; raw palm oil as basal diet (See Chapter 4)

The amino acid profile of Azolla is given in Table 2.25.

Table 2.25. Compostion of essential amino acids of Azolla microphylla (%DM).

Amino acid Freeze-dried Oven-dried Amino acid Freeze-dried Oven-dried
Arginine 1.54 1.29 Methionine + cystine 0.61* 0.58*
Histidine 0.50 0.48 Phenyalanine + tyrosine 2.80 2.29
Isoleucine 1.46 0.80 Threonine 1.17 1.42
Leucine 3.25 2.27 Tryptophan -** -**
Lysine 2.03 1.16 Valine 1.59 1.45

Source: Querubin et al. (1988); * cystine was not reported; ** not determined

MICROBIAL PROTEINS

Microalgae

Recently, Ly (1993) emphasized that an integrated plant-animal production system could provide a viable contribution to protein-deficient animal feeding systems in the tropics. According to this author, aquatic floating plants and microalgae (microphytes) should be given first priority. Their production would rely on substrates such as pig wastes. This would prevent environmental contamination, at the same time would permit the recycling of valuable nutrients, particularly nitrogen compounds. An attractive strategy is the bio-transformation of manure into methane gas for fuel through inexpensive, simple techniques like those developed in Taiwan (Chung et al., 1978), followed by the use of the effluent from the generation of methane to produce microalgae. The composition of some microalgae are described in Table 2.26.

One of the main constraints in producing microalgae is the difficulty of separating the biomass from the water. However, Lincoln et al. (1986) have claimed that due to their high yields and dense stand, 2 to 12 t DM/ha, an economically sound strategy would be to harvest the algae by flotation or sedimentation techniques, followed by chemical floculation. Moreover, Fuller (1988) has suggested that some of the algae can be separated by simple filtering methods.

Table 2.26. Composition of some microphytes.

Microphyte Composition, % DM Source
CP Ash CF
Spirulina 67.7 7.5 - Ishizaki 1
" 60.5 6.9 - Ross (1990)
" 62.9 - - Chung et al. (1978)
" 58.3 9.8 4.5 Février and Seve (1976) 2
Chlorella 55.5 8.3 3.1 Lubitz 3
" 63.1 - - Chung et al. (1978)
Scenedesmus 22.2 - -
Mixed culture
Various 4 24.9 21 1.6 Harrison et al. (1981)
Various 5 50.9 6.2 6.2 Hintz et al. (1966)

1 Cited by Hugh et al. (1985); 2 Values corresponding to the sample named M6; 3 Cited by Ocio et al. (1973); 4 Chlorella spp, Scenedesmus obliquus and S. quadricauda; 5 Predominantly Synochocystis spp

The filamentous algae, Spirulina, seems to be the most promising microphyte. Although researchers have evaluated this microalga as a protein replacement in pig diets, the maximum level of algal protein is yet to be established (Hugh et al., 1985). Protein digestibility can be depressed in young pigs if the level of Spirulina in the diet is elevated (Février and Seve, 1976). Hintz et al. (1966) suggested that the complex algal cell wall was resistant to digestive enzymes. However, trials did not support his assumption. Contradictory results were also reported by Février and Seve (1976), who assumed that the digestive disadvantages related to the introduction of algae in the pigs diet were largely compensated for by improved metabolic utilization of the absorbed nutrients. The amino acid composition of some microphytes is presented in Table 2.27.

Table 2.27. Composition of essential amino acids of some microalgae (%DM).

Amino acid Spirulina Chlorella Scenedesmus
Arginine 2.73 2.15 0.54
Histidine 0.55 1.40 1.08
Isoleucine 1.05 1.29 1.83
Leucine 3.01 3.44 4.09
Lysine 1.68 3.33 2.90
Methionine + cystine 1.02 1.08 1.40
Phenyalanine + tyrosine 2.96 4.73 3.76
Threonine 1.79 3.23 3.76
Tryptophan -* 0.97 0.86
Valine 1.19 2.26 3.12

Source: Ako (1985), cited by Hugh et al. (1985); INRA (1984); * not reported

Yeast

Strictly speaking, yeasts do not depend on climatic conditions for their production. Therefore, they are not natural tropical protein feed resources, unless, of course, the substrate defines their origin. In such case, yeasts can be obtained from derivatives of tropical crops such as sugar cane.

Saccharomyces yeast is a byproduct of the alcohol industry. There are a considerable number of Brazilian studies concerning the utilization of Saccharomyces (brewers) yeast in pig production (Miyada, 1990). Likewise, torula yeast from sugar cane molasses has been widely used in Cuba (Figueroa and Ly, 1990). The composition of these yeasts is shown in Table 2.28.

Table 2.29 presents the results of including graded levels of Saccharomyces yeast in the diets of growing/finishing pigs. According to the data from Miyada et al. (1988) cited by Miyada (1990) only the highest level, 25% dry matter of Saccharomyces yeast, affected the average daily gain, and this was perhaps due to a decrease in feed intake. This same result was not observed when Saccharomyces yeast completely substituted fish meal in cane C molasses-based diets (Lezcano and Elías, 1975). Possibly, the low palatability of the yeast was masked by the sweetness of the molasses.

Table 2.28. Composition of yeast produced from sugar cane C molasses (% DM).

Type of yeast CP Ash CF EE Source
Saccharomyces yeast: type A 34.9 4.1 0.5 0.2 Fialho et al. (1985)
type B 37.0 5.5 0.7 0.3
Saccharomyces yeast average 31.6 10.3 0.8 1.0 Miyada (1990)
Saccharomyces yeast: average 34.8 10.2 1.0 0.9 CNPSA (1991)
Torula yeast: average 45.7 9.0 - - IIP (1988) *
Torula yeast: low CP 34.7 - 2.5 - García and Pedroso (1989)
medium CP 40.4 - 2.5 -
high CP 49.1 - 2.5 -

* Cited by Figueroa and Ly (1990)

Table 2.29. The use of Saccharomyces yeast for pigs ( 23-93 kg).

% DM in diet DM feed intake (kg/d) ADG (g) DM feed conversion
0 2.66 810 3.28
5 2.57 820 3.16
10 2.71 850 3.23
15 2.62 830 3.16
20 2.56 800 3.21
25 2.41 740 3.23

Source: Miyada et al. (1988), cited by Miyada (1990)

Both Saccharomyces and torula yeast contain a high level of lysine and other essential amino acids, except methionine plus cystine. If low amounts of yeast are included in the diet, a complementary sulfur-containing, amino acid-rich protein supplement or synthetic DL-methionine might be included in the ration. However, the beneficial effect of the inclusion of methionine for growing/finishing pigs fed high amounts of Saccharomyces (Ceballos et al., 1970), or torula yeast (Lezcano et al., 1992), has not been demonstrated. The amino acid composition of yeast is offered in Table 2.30.

Table 2.30. Composition of the essential amino acids of yeast (% DM).

Amino acid Saccharomyces Torula
Arginine 1.51 2.04
Histidine 0.77 0.71
Isoleucine 1.64 1.95
Leucine 2.41 3.00
Lysine 2.30 2.57
Methionine + cystine 0.91 0.76*
Phenyalanine + tyrosine 2.29 3.24
Threonine 1.75 2.19
Tryptophan 0.58 -
Valine 1.97 2.29

Source: Anon (1985); CPNSA (1991); methionine

Throughout the life-cycle of the pig the use of torula yeast as a protein source is as effective as Saccharomyces yeast (Figueroa and Ly, 1990). Table 2.31 shows a good example of substituting a conventional protein source (fish meal) with dry torula yeast for growing/finishing pigs in Cuba.

Table 2.31. Comparison of fishmeal to dry torula yeast as the only source of protein for growing/finishing pigs * (34-90 kg).

% DM in diet DM intake (kg/d) ADG (g) DM feed conversion
Fishmeal, 24 2.38 680 3.50
Dry torula yeast, 33 2.28 650 3.60

Source: Lezcano (1980), cited by Diaz et al. (1985); * fed C molasses as the energy source

Approximately, one-half of the fuel needed to produce torula yeast is used in drying the yeast cream. One innovative technique involves mixing, on a dry matter basis, 30% of plasmolyzed cells of liquid torula yeast with 70% of cane B molasses. The resulting liquid diet is called "protein molasses" (ICIDCA, 1988). It contains 36% dry matter and between 13 and 14% protein, also in dry matter, and has been used in Cuba as a commercial diet for growing/finishing pigs (See 3.3.2.5).

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