Recycling organic wastes for commercial pig production is not a new idea (Williams and Cunningham, 1918; Hunter, 1919; Ashbrook and Wilson, 1923; Hultz and Reeve, 1923). The utilization of kitchen wastes from institutions such as hospitals, schools or hotels, and the use of distillery wastes, fish-processing, abattoir wastes and agricultural residues, if used to feed livestock, would help to reduce the increasingly important, problematic question of environmental pollution. Organic wastes are subject to rapid deterioration and contamination by microorganisms, some of which are extremely pathogenic. However, it has been shown that by ensiling, or by thermal treatment, preferably complete sterilization, organic wastes can be completely decontaminated and safely used as alternative feedstuffs. This chapter discusses different alternatives for processing organic wastes as well as their nutritional value when fed to pigs.
The nutritive value of kitchen wastes for pigs is adequate with respect to protein and energy, however, its low dry matter content tends to affect growth due to a reduction in total dry matter intake, principally in younger animals, fed ad libitum (González et al., 1984). The digestibility of the nutrients contained in kitchen wastes is variable and somewhat related to the source. Kornegay et al. (1970) in reviewing the performance of pigs fed heat-treated garbage residue from different sources concluded that it should be supplemented with a 15 to 18% crude protein concentrate in order to improve the daily liveweight gain (to more than 600 g/day) and feed efficiency. No marked difference in carcass quality was observed when garbage residues were fed to pigs. The chemical composition and the digestibility of kitchen wastes is given in Table 6.1.
Table 6.1. Composition and digestibility of kitchen wastes.
|Medium composition (% DM)||Digestibility (%)|
|Nitrogen free extract||50.9||35.0||95.8||88.6|
|Gross energy, MJ/kg DM||-||23.1||-||87.8|
|Digestible energy, MJ/kg DM||-||-||-||23.9*|
Sources:(a) Woodman and Evans (1942); (b) Balazs et al. (1971) ; * Differs from the mean value for gross energy which suggests a higher energy content for this sample
The experience during the 1970s of one sub-tropical country, Cuba, to consolidate a nationwide pig feeding strategy based on the collection of organic wastes from all major institutions will serve to illustrate the concept of industrial swill used throughout this chapter. Private kitchen wastes are excluded; however, all institutionally-produced organic wastes, including agricultural residues and fish wastes are collected daily in specially designed trucks and brought to the processing plants, generally adjacent to the pig units. Once in the processing plant, any undesirable material, particularly metal objects, are removed and the wastes are ground in a hammer mill to a particle size of 80 mm. Following that, they are sterilized in an autoclave at 121C and 1.0 to 1.5 atmospheres for 30 minutes (del Rio et al., 1980). This process converts the organic wastes into a heterogeneous feeding material known as "processed" swill which is mixed with molasses to produce a final product called "terminal" swill. The "terminal" swill is pumped directly from the processing plants to the feed troughs in the nearby feedlots. Each ten thousand head feedlot requires 80 tons of organic wastes, daily.
Industrial swill, known in Cuba as "processed" swill, contains between 14 and 19% dry matter, and contains in dry matter: 18-22% crude protein, 6-12% crude fibre, 6-10% fat and 10% ash. It has a gross energy value of about 18.0 MJ/kg dry matter (Domínguez, 1985). The mineral composition of processed liquid swill is offered in Table 6.2.
Table 6.2. Mineral composition of processed liquid swill.
Source: Domínguez et al. (1983)
The composition of the essential amino acids of processed swill is presented in Table 6.3. The level of methionine is insufficient and although the amount of lysine appears to be suitable, its precise availability is unknown due to the technology used in treating the organic residues, particularly the effect of heat. Even though tryptophan was not determined, Maylin (1983) has reported a level of 0.3% in processed swill.
Table 6.3. Amino acid composition of " processed" Cuban swill, %.
|Amino acids||Grau et al. (1978)||Maylin (1983)||Amino acids||Grau et al. (1978)||Maylin (1983)|
ND: Not determined
The digestive utilization of the main nutrients of processed swill is slightly lower when compared to cereals (Table 5.9). Nevertheless, the digestive indice of nitrogen, gross energy and digestible energy, the latter with an average value of 15.3 MJ/kg dry matter, shows that processed swill offers considerable potential as an alternative feed resource for pigs in the tropics (Table 6.4).
Table 6.4. Digestibility of processed swill.
|Digestive energy (MJ/kg DM)||Source|
|Dry matter||Organic matter||Nitrogen||Gross energy|
|79.8||84.0||83.7||-||16.16||Grau et al. (1976)|
|85.3||87.9||83.6||85.4||16.15||Maylin and Cervantes (1982)|
|80.7||-||76.8||79.7||14.37||González et al. (1986)|
|78.4||-||76.0||77.1||14.60||Domínguez et al. (1987)|
It has been shown (González et al., 1984) that for growing/finishing pigs processed swill can be used to substitute up to 50% of the dry matter of cereals. There was no affect on feed conversion; however, it was emphasized that due to its low dry matter content, 14 to 19%, younger animals could not obtain sufficient nutrients (Table 6.5).
Table 6.5. Performance of growing/finishing pigs fed different proportions of cereal and "processed" liquid swill in ad libitum rations (% DM).
|Initial liveweight, kg||26.0||26.6||26.8||27.1||26.1|
|Final liveweight, kg||95.1||95.8||94.3||94.3||92.4|
|DM feed intake, kg/d||2.06||2.07||1.89||1.97||1.75|
|DM feed conversion||3.47||3.75||3.45||3.76||4.04|
Source: González et al. (1984)
When Cuba first began to develop a national pig feeding only treated organic wastes, known at that time as "processed" swill, was used for feeding grower/finishers. The average daily amount fed to pigs weighing between 25 and 90 kg was 12 kg. It contained 18 to 22% dry matter depending on the quality of the product in each processing plant. The average daily gain was never more than 450 g and the dry matter feed conversion was approximately five tons of "processed" swill to one ton of liveweight gain (Pérez et al, 1987).
The idea of using molasses in "processed" swill for pigs caught on quickly after ruminants, in Cuba, were successfully fed diets containing in dry matter up to 70% C molasses (see Chapter 3). However, the addition of C molasses diluted the energy and the protein in the final mixture, known as "terminal" swill, and this resulted in increased, therefore poorer, feed conversions (Domínguez, 1985). The immediate solution was to mix a dry cereal concentrate with the "terminal" swill before it was pumped to the feedlot, or add it directly to the "terminal" swill in the trough.
Gradually, therefore, the major commercial pig feeding system used in Cuba from 1975-1985 for pigs from 25 to 90 kg consisted of (dry matter basis): 37% organic wastes, 33% C molasses and 30% concentrates (Pérez et al., 1982). Depending on the quality of the product produced in each of the more than 20 processing plants, the daily ration was 8 to 10 kg of "terminal" swill and 0.8 kg of a dry concentrate ration. Eventually, between 400 and 500 thousand pigs were fed on this system, daily.
After a time, it was noted that the addition of C molasses, followed by the addition of a cereal-based concentrate produced no major change in feedlot performance. Moreover, in a review of eleven experiments to determine the effect of supplementing "terminal" swill with concentrates, Domínguez (1988) showed that there was no positive effect on performance: the average daily gain remained unchanged while the dry matter conversion fluctuated from 4.14 to 6.88 with an average value of 5.17.
An effort was made to improve the performance traits of pigs fed this system and different additives were studied; however, none of them caused sufficient improvement to merit their commercial application, even the experimental results of Domínguez and Lan (1985) which had shown that the addition of copper sulfate would improve gains by some 50 g/day, as well as improve dry matter feed conversions by 10% (Table 6.6). As mentioned, the problem involved almost half a million growing/finishing pigs, daily.
During this same period, 1980-1985, that Cuban researchers studied different additives to improve the performance of pigs fed "terminal" swill, another type of molasses, B molasses, was first extracted from the sugarmills and promoted as an energy feed resource for swine, particularly for use with processed swill (Table 6.7).
The data in Table 6.8 show the performance of pigs fed processed swill and C or B molasses, with or without additives as growth promoters. The utilization on an experimental basis of these additives significantly improved performance; however, the conversion to B molasses, besides improving the average daily gain and feed conversion by 17 and 15%, respectively, was seen from a commercial perspective as easier to implement since it only involved the extraction of a different type of molasses from the sugarmills. The infrastructure was already in place, therefore, by the mid-to-late 1980s, the major commercial pig feeding system in Cuba based on "processed" swill was converted to B molasses (see Chapter 3). Most interestingly, as observed in this same table, the performance of pigs fed the swill/concentrate ration with B molasses, and additives, differed little from that of the performance obtained with a typical maize/soya bean meal ration!
Table 6.6. Performance of growing/finishing pigs fed a ration of: processed swill/C molasses/ cereal concentrate and different additives.
|Additive/ level||Initial LW, kg||Final LW, kg||ADG (g)||DM feed conversion||Source|
|Sodium bicarbonate (%)|
|Domínguez et al. (1980)|
|Domínguez and Lan (1985)|
|Copper + vitamin E (ppm)|
|Domínguez et al. (1981)|
a as CuSO2.5H2O; b Variable level
Table 6.7. Performance of pigs fed processed swill and different types of cane molasses.
|Type of molasses||% DM||Initial LW (kg)||Final LW (kg)||ADG (g)||DM conversion||Source|
|Figueroa et al. (1985)|
|Pérez et al. (1987)|
* Syrup-off = end product produced upon centrifuging the final massecuite in a raw sugar refinery
Table 6.8. Performance of pigs fed processed swill, cereal concentrate and C or B molasses, with or without additives.
|no additives||additives *||no additives||additives *|
|Initial liveweight, kg||26.3||26.4||26.2||26.3|
|Final liveweight, kg||88.7||95.3||94.5||96.7|
|DM intake, kg/d||2.47||2.71||2.52||2.75|
|DM feed conversion||4.78||4.01||4.07||3.89|
Source: Domínguez et al. (1988); * additives = 200 ppm of copper sulfate and 1% of a vitamin/mineral premix to provide requirements according to NRC (1979)
Meat meal, and meat and bone meal, byproducts from slaughter houses contain: hair, hoof, hide, trimmings, blood, intestinal tracts and condemned carcasses. If the dry rendered product contains more than 4.4% of phosphorus, it is designated as meat and bone meal. The processing method is important, since high temperatures can cause the destruction of sulphur-containing amino acids and reduce the availability of lysine (Atkinson and Carpenter, 1970). The chemical composition of meat and meat and bone meal is given in Table 6.9.
Table 6.9. Chemical composition of meat meal and meat and bone meal (% DM).
|Parameters||Meat meal||Meat and bone meal||Parameters||Meat meal||Meat and bone meal|
|Ether extract||8.7||9.7||DE ( MJ/kg DM)||10.1||9.5|
Source: NRC (1988)
Table 6.10. Composition of essential amino acids in meat meal and meat and bone meal (%).
|Amino acid||Meat meal||Meat and bone meal||Amino acid||Meat meal||Meat and bone meal|
Source: NRC (1988)
Jorgensen et al. (1984) studied the digestibility of various nutrient components of meat and bone meal. The digestibility of dry matter, 87%, and organic matter, 91%, was satisfactory, while that of nitrogen, 79%, was inferior to that of soya bean meal, 92 percent. The apparent ileal availability of the essential amino acids averaged 72% for meat and bone meal as compared to 80% for soya bean meal. Likewise, the ileal availability of lysine in meal and bone meal, 65%, was significantly lower than that of soya bean meal, 80 percent. The amino acid composition is given in Table 6.10. Meat meal is of lower quality than fish meal or soya bean meal (Atkinson and Carpenter, 1970; Beames and Daniels, 1970) and should not be used as the only source of protein in diets where the source of energy is sugar cane products, roots, bananas or oil palm derivatives. Perhaps, a level of meat meal similar to that proposed when "protein paste" is used would be adequate (See below).
Although blood represents approximately three percent of total liveweight, loss during slaughter can reduce the total amount saved to less than one percent. Fresh blood contains approximately 20% dry matter of which 80% is crude protein; the essential amino acids are given in Table 6.11. Blood meal produced by conventional vat-cooking and drying processes has been found to be of limited use in pig rations because of poor palatability and the low availability of lysine. Spray and flash drying procedures have significantly improved palatability and more importantly, lysine availability, increasing its potential value for swine (Miller and Parsons, 1981; Parsons et al., 1985). The concentration of isoleucine remains a limiting factor; however, with proper supplementation flash-dried blood meal can be used at a level of 5-6% for adult and growing/finishing pigs (Wahlstrom and Libal, 1977). The chemical composition of spray-dried (NRC, 1988) and flash-dried (Miller and Parsons, 1981) blood meal is, in % air-dry: dry matter, 93 and 90; crude protein, 86 and 83; ether extract, 1.2 and 1.5; crude fibre, 1.0 and 1.5 and digestible energy, 12.5 and 15.1 MJ/kg, respectively.
Table 6.11. Essential amino acids in spray and flash-dried blood meal (%).
|Amino acid||Spray-dried *||Flash-dried **||Amino acid||Spray-dried *||Flash-dried **|
Source: * NRC (1988); ** Miller and Parsons (1981)
Barbosa et al. (1983) substituted blood meal for soya bean meal in a sorghum-based diet with no difference in average daily gain but with an increase in the conversion (Table 6.12). When Itori et al. (1984) substituted soya bean meal for combinations of peanut meal and flash-dried blood meal in maize-based diets, the average daily gains and feed conversions were similar, suggesting similarity in the apparent biological value of the protein sources.
Table 6.12. Performance of growing/finishing pigs * fed flash-dried blood meal.
Level of blood meal (% DM)
|DM intake kg/d||2.14||2.14||2.28||2.38|
|DM feed conversion||3.06||3.21||3.22||3.39|
Source: Barbosa et al. (1983); * liveweight 25-95 kg; basic diet: sorghum/soya bean meal
Although feather meal is one of the most protein-rich feedstuffs available, more than 90% crude protein, it is poor in some essential amino acids like methionine, lysine, histidine and tryptophan (Table 6.13). Therefore, the proportion of feather meal that can be used in the ration will depend on the content and the quality of the protein in the other components of the diet. Whereas steam cooking at 3.2 atmospheres can produce a good quality product, Eggum (1970) reported that acid hydrolysis (HCl at pH 6 for 20 hours) can also be used to produce a meal of high digestibility and similar biological value. The chemical composition of feather meal, in % dry matter, is: crude protein, 92.7; ether extract, 2.7; ash, 4.7; crude fibre, 0.1 (Boda, 1990). This same author also reported that feather meal had a dry matter content and in vitro digestibility of 96 and 46%, respectively.
Table 6.13. Composition of the essential amino acids in steam and acid-treated feather meal (g/16 g nitrogen).
|Amino acid||Steam-treated||Acid-treated||Amino acid||Steam-treated||Acid-treated|
Source: Eggum (1970)
Although different feeding trials have shown that 5 to 7% hydrolyzed feather meal can replace soya bean or fish meal for growing/finishing pigs (Hall, 1957; Lavorenti et al., 1983), when Combs et al. (1958) used 10% to supplement a maize diet, all major performance parameters were affected. Table 6.14 shows that feather meal should not be regarded as a full-value protein feed and its use should be restricted to low levels if maximum growth and efficiency of feed utilization by pigs is the objective.
Table 6.14. Performance of growing/finishing pigs fed hydrolyzed feather meal.
|Level (%)||ADG (g )||DM feed conversion|
Source: Lavorenti et al. (1983)
In many tropical countries, the slaughter of livestock is accompanied by the loss of a considerable amount of raw material which could be used as a protein supplement for feeding pigs. The most important sources are: blood, hair, viscera and bones, and sometimes even the entire carcass. In the more developed countries, animal slaughter is often associated with processing plants and slaughter residues are generally converted into tankage and meat meal. However, frequently in the tropics, because such procedures are often complicated or expensive, these products are simply discarded. And in most cases, dead animals are simply buried or incinerated.
In Cuba, a system has been designed to process abattoir wastes and dead animals into a high-quality protein paste-like material (Pineda et al., 1986). The technology is simple; the processing plants are integrated with the "terminal" swill processing plants adjacent to the commercial pig fattening units (see 6.2). The main equipment needed is a horizontal autoclave designed for interior mechanical movement. An average temperature of 130 C and a pressure of 2 atmospheres during 60 minutes can convert all of this material, including sectioned, large, dead animals, into a feed resource for pigs of substantial biological value, known as "protein paste".
The chemical composition of "protein paste", which can be preserved several days using either inorganic acids, or molasses, is given in Table 6.15. Preserved in molasses (20%), it has the disadvantage of a slightly reduced protein level, however, it is more palatable than that which is preserved with inorganic acids (Domínguez, 1990).
The digestibility of the nutrients in protein paste preserved with inorganic acids was evaluated in diets using cane refinery "syrup-off" (see Chapter 3) as the sole energy source. The protein digestibility was similar to that of soya bean meal and superior to that of meat meal or torula yeast. In addition, nitrogen retention was higher than that of the other protein sources studied (Table 6.16).
Table 6.15. Chemical composition of protein paste (% DM).
|sulphuric acid||type C molasses (20%)|
Source: Domínguez (1990)
Table 6.16. Digestibility of nutrients in diets * supplemented with conventional sources of protein compared to "protein paste" (%).
Source of protein:
|soya bean meal||torula yeast||meat meal||protein paste|
Source: Domínguez et al. (1986); * cane refinery "syrup-off" as energy source
Table 6.17 shows the performance of two groups of growing/finishing pigs fed protein paste preserved with C molasses. The paste contributed 25 or 50% of total dietary protein in a basal diet of cooked sweet potatoes. The control group was fed a diet of cooked sweet potatoes and torula yeast, only. At a level of 25% of dietary protein in the form of "paste" there was no significant difference in performance compared to the control ration. It was emphasized, that even though the pigs fed 50% protein in the form of "protein paste" showed an inferior performance, the average daily gain and feed conversion were still very satisfactory when compared to the average performance of pigs in the tropics fed the more conventional cereal diets (Domínguez et al., 1990).
Table 6.17. Use of protein paste to replace torula yeast in basal diet of cooked sweet potatoes for pigs (30-90 kg).
% crude protein from:
|control||25% level||50% level|
|DM intake, kg/d||2.36||2.30||2.33|
|DM feed conversion||3.03||2.95||3.33|
Source: Domínguez et al. (1990)
The production of distilled liquors and alcohol from cereal grains includes grinding, cooking and the addition of enzymes to hydrolyze the starch to simple sugars prior to the addition of yeast, which is used to ferment the sugars to alcohol. After fermentation, the alcohol is distilled and a residue remains that can be used for livestock feeding. It contains yeast and other unidentified nutrients and is known as "stillage". The coarse grain fraction, usually removed from the whole stillage and dehydrated, is called dried distillers' grains. The water soluble materials and remaining fine particles, upon dehydration, form dried distillers' solubles. Another variant, following the removal of ethyl alcohol by distillation, is to produce distillers' dried grain with solubles. Currently, this is the major grain distillery byproduct used as a commercial feedstuff for swine.
The nutritional value of distillers' feeds may be influenced by the type or form of cereal employed in the fermentation process. The chemical composition of maize distillery byproducts compared to ground maize is shown in Table 6.18.
Table 6.18. Chemical composition of grain distillery byproducts (% AD).
|DDG a||DDS b||DDGS c||Maize|
|Digestible energy (MJ/kg DM)||14.2||13.9||15.2||14.8|
Source: NRC (1988); a DDG = dried distillers' grains; b DDS = dried distillers' solubles; c DDGS = distillers' dried grain with solubles
Distillery feeds are relatively high in crude fibre which could limit their use as an energy source. However, their relatively high content of fat means that the amount of digestible energy compares favorably to that in maize. Generally, distillery feeds are a good source of phosphorus, water-soluble vitamins and vitamin E, but they are low in calcium. The composition of the essential amino acids in several sources of distillery byproduct feedstuffs, compared to maize, is presented in Table 6.19.
"Distillers' dried grain with solubles" has been used in rations for both weaners and grower/finishers. For weaners, the feed intake and average daily gain were slightly improved by the addition of 2.5% in the diet, while at a level of 5% no additional benefit was observed (Orr et al., 1981). Harmon (1975) fed a maize-soya bean meal ration to 10 kg weaners in which "distillers' dried grain with solubles" substituted 9, 18 and 27% of the control diet. The average daily gain decreased as the level of "distillers' dried grain with solubles" increased. The data in Table 6.20 suggest that this residual material can serve better as an alternative source of energy and protein for growing/finishing pigs.
Table 6.19. Composition of the essential amino acids in distillery byproduct feeds compared to maize (% AD).
|DDG a||DDS b||DDGS c||Maize|
Source: NRC (1988); a DDG = dried distillers' grains; b DDS = dried distillers' solubles; c DDGS = distillers' dried grain with solubles; d ND = not determined
Table 6.20. Performance of growing/finishing pigs fed " distillers' dried grain with solubles".
|% DM in diet||ADG (g)||DM feed conversion||Source|
|Cromwell et al. (1984)|
|Livingston and Livingston (1966)|
"Distillers' dried grain with solubles" were used at levels of 17.7 and 44.2% in substitution of a maize-soya bean meal diet for feeding pregnant gilts. Litter size and average piglet weight at birth were similar for all three treatments (Table 6.21). During lactation, the sows received a fortified 16% crude protein ration. Litter size, average piglet weaning weight and sow weight changes were similar for all groups and it was suggested that "distillers' dried grain with solubles" can partially replace, on a lysine equivalent basis, a diet of maize-soya bean for pregnant sows (Thong et al., 1978).
Table 6.21. Reproductive performance of gilts fed "distillers' dried grain with solubles" (DDGS).
DDGS (% DM in diet)
|Average no. piglets born alive||8.8||8.6||8.2|
|Average piglet birth weight, kg||1.4||1.4||1.4|
|Average no. piglets weaned||7.3||7.4||7.3|
|Average piglet weaning weight, kg||6.5||6.7||6.6|
Source: Thong et al. (1978)
Rum is produced by the fermentation by yeast of the sugars in cane C molasses into alcohol. After the alcohol is distilled, a residue, known as "molasses distiller's solubles" remains; it contains only 7% dry matter. Molasses distiller's solubles are a good source of vitamins and are reported to contain unidentified growth factors (FAO, 1993); however, due to their low dry matter content they are generally discharged, untreated, into the surrounding ecosystem. If concentrated or dehydrated to 45-50% dry matter, they are known as "concentrated distillers' solubles" (Table 6.22). In either case, the yeast, which converts the sugars to alcohol, tends to settle as a thick sludge at the bottom of the fermentation vats. It tends to spoil quickly, therefore, most often, it is dried and bagged for use in concentrate feeds.
Table 6.22. Chemical composition (% DM) of molasses distillers' solubles (MDS) and concentrated molasses distillers' solubles (CMDS).
|MDS *||CMDS **|
|Nitrogen free extract||60.8||-|
Sources: *FAO, (1993); ** Gorni et al. (1987)
"Concentrated molasses distillers' solubles" can serve as an alternative source of energy and protein for growing/finishing pigs. Gorni et al. (1987) added 12% of concentrated molasses distillery solubles, of 50% dry matter, to a sorghum/soya bean meal diet and obtained identical performance. García et al. (1991) used dehydrated molasses distillery solubles in a cereal-based feeding system, while Sarria and Preston (1992) improved performance by adding, on a dry matter basis, up to 20% of concentrated molasses distillery solubles, containing 60% dry matter, to a sugar cane juice-soya bean meal feeding system (Table 6.23).
The major problem with fresh molasses distillers' solubles relates to its extremely low dry matter content, about 6 percent. The author has used the same sun-dried filter-press mud, three times, in an attempt to absorb the nutrients present in this material, prior to mixing the filter-press mud in a concentrate ration.
Table 6.23. Performance of growing/finishing pigs fed different forms of molasses distillery solubles (MDS): concentrated or dehydrated.
|% MDS||ADG (g)||DM conversion||Source|
|Gorni et al. (1987) *|
|Sarria and Preston (1992) **|
|García et al. (1991) ***|
* MDS of 50% DM and level in sorghum/soya bean meal diet as % AD; ** MDS of 60% DM and level in sugar cane juice/soyabe an meal diet as % DM; *** dehydrated MDS of 94-95% DM and level in sorghum/soyabe an meal diet as % AD
The technique for making fish silage is cheap and simple. It can be made from by-catch (scrap fish) or fish wastes (offal), preferably chopped or ground prior to the addition of acids (Cervantes, 1979), or carbohydrates (Tibbets et al., 1981). The action of the endogenous enzymes break down the protein causing the tissue to liquefy. The presence of mineral or organic acids, or the result of the fermentation of the added carbohydrate, decreases the pH, which in turn inhibits the growth of bacteria enabling long term storage of the material. An additional way to preserve fish wastes is to mix and store it directly in molasses. A brief description of all three methods follows:
Acid fish silage is one in which by-catch or fish wastes, preferably chopped or ground and placed in non-metallic vats, are mixed with an acid solution and stirred several times daily, three to five days, until liquefied. The lowered pH prevents bacterial putrefaction permitting the fish tissue to be stored for several months, preferably in protected or closed vats. Reportedly, the best acids to use in this process are the organic acids, propionic and formic (Wiseman et al., 1982; Rattagool et al., 1980, cited by Green et al., 1983), and certain mineral acids, either sulphuric (Cervantes, 1979), or hydrochloric (Machin, 1990).
In Cuba, Alvarez (1972) used a concentrated solution of sulphuric acid and water (1:1 ratio by volume) in order to determine the optimal proportion of acid solution to use in preserving fish wastes obtained from a processing plant. The residues were not chopped and the quantities of acid solution used were: 20, 30, 40, 50, 60, 70, 80 and 90 ml/kg of fish residue. The amount of 60 ml of acid solution/kg of fresh fish waste (residue) was selected as optimum. The final pH of the material was 1.8 and prior to use it was neutralized to a pH 5 by the addition of calcium carbonate. Following that, Cervantes (1979) observed that if fish wastes were ground prior to the addition of the acid solution, then the amount of 30 ml/kg of raw material was sufficient. Domínguez (1988) stated that one general rule using other types of acid might be to adjust the pH to below four.
As earlier mentioned, during storage, the protein of fish silage is broken down by enzymes to low molecular weight peptides and amino acids and this results in high levels of free, soluble amino acids which appear to be stable (Green et al., 1983). In fact, it has been shown that less than 8% of the amino nitrogen is released as ammonia in fish silage stored for up to 220 days. Degradation under normal storage conditions does not appear to be of great importance; however, at temperatures exceeding 30o C, tryptophan, methionine and histidine are most likely to decompose (Gildberg and Raa, 1977).
The principle of fermented fish silage is similar to that of acid silage, however, in the case of fermented silage, preservation is due to the acidity arising from the growth of lactic acid producing bacteria. By-catch or fish wastes, preferably chopped or minced, are placed in nonmetallic vats and mixed with a carbohydrate source such as, cassava, sweet potatoes or molasses, or a mixture of them, and stored airtight. The immediate addition of a small amount of molasses, 20% (Domínguez, 1988), or 30% (Green et al., 1983) is recommended in order that fermentation begins rapidly. However, if the objective is to produce a balanced or complete silage ration, using roots as the principal source of carbohydrates and fish wastes as the source of protein, then the following proportions, in air-dry, should be used: roots, 50-30%; molasses, 10% and fish wastes, 40-60% (Domínguez, 1988).
Molasses, alone, can be used for the preservation of by-catch or fish offal which have preferably been chopped or ground, and drained, prior to mixing in a minimum 1:1 ratio, by weight, with molasses. A weighted wire netting should be placed on the surface of the fish/molasses mixture in order that the raw material is kept completely submerged in molasses. This is particularly important if whole by-catch is used. Although the osmotic pressure of the molasses causes an initial dehydration of the raw fish residue, an acidic fermentation also occurs which tends to preserve this material. The mixture should be stirred daily until the pH lowers to below five (Domínguez, 1988).
The chemical composition of fish silage prepared from different substrates is presented in Table 6.24. This information suggest that fish silage produced using by-catch, surprisingly, does not exhibit a higher nutritional value than that produced from only wastes (offal). Although fish silage is considered primarily a protein supplement, it can also contain energy provided by residual oil.
The amino acid composition of fish silage is presented in Table 6.25. Lysine, threonine and sulphur-containing amino acids are present in high levels, as they are in fish meal, and as a consequence fish silage would appear to be an excellent protein supplement in the pig diet. In fact, Whittemore and Taylor (1976) reported that the digestible energy and digestible nitrogen were higher in diets containing fish silage than in those of fish meal.
The results of substituting the protein in fishmeal for that of acid fish silage for growing/finishing pigs, where processed swill and C molasses were the major components of the ration, are presented in Table 6.26. It was stated that at the highest level of substitution, the palatability (acidity) of the ration was probably responsible for the reduction in feed intake which undoubtedly affected growth performance. Emphasis was placed on the need to neutralize this material to a pH of five prior to use, particularly when used in rations based on processed swill which, in themselves, tend to be acidic (Cervantes, 1979).
Table 6.24. Chemical composition of different types of acid fish silage (% DM).
|Rattagool et al. (1980)
Green et al. (1983)
Tatterton & Windsor (1974) *
|Whittemore and Taylor (1976)
Tatterton & Windsor (1974) *
Disney et al. (1978) *
Green et al. (1983)
|Mixture||Cuba: by-catch & fish wastes||37.0-70.2||6.1-12.3||4.0-11.1||Penedo et al. (1986)|
* cited by Green et al. (1983)
Table 6.25. Amino acid composition * of fish silage (%).
|Amino acid||Smith and Adamson 1976||Whittemore and Taylor 1976||Amino acid||Smith and Adamson 1976||Whittemore and Taylor 1976|
* Penedo et al. (1986) reported the presence of lysine, methionine and cystine in the leftover liquid portion (6% DM) as 3.3, 1.3 and 0.6 g/kg, respectively
Table 6.26. Replacement of protein in fishmeal (FM) for acid fish silage (AFS) * in diets based on processed swill and C molasses for growing/finishing pigs (% DM).
|FM 100%||FM/AFS (75:25)||FM/AFS (50:50)||AFS 100%|
|Initial liveweight, kg||25.5||25.3||25.5||25.20|
|Final liveweight, kg||78.2||78.8||77.9||68.9|
|DM feed consumption, kg/d||2.1||2.1||2.1||1.9|
|DM feed conversion||4.10||4.00||4.00||4.40|
Source: Cervantes (1979); * fish wastes, ground, preserved with 30 ml/kg acid solution (see 6.5.1)
Information related to the feeding of low-fat, by-catch fish silage to both weaners and grower/finishers is shown in Table 6.27. Similar to the results in the previous table, a reduction in feed intake could have caused lowered average daily gains when the highest level was fed. Smith (1977) reported that when fish silage with a low oil content was used, it was possible to include levels as high as 10% dry matter in the diet for growing/finishing pigs without negative effects on performance or carcass quality; however, herring fish silage fed at the same rate reduced performance and produced an unacceptable carcass. Although the use of fish silage in growing/finishing rations sometimes results in '"off-flavors" in the pork, this can be easily controlled by reducing the amount fed or removing the silage from the ration 20 days prior to slaughter.
Table 6.27. Performance of weaner and grower/finisher pigs fed diets containing fermented fish silage. *
|% DM in diet||
|DM feed intake, kg/d||ADG (g)||DM feed conversion||DM feed intake,kg/d||ADG (g)||DM feed conversion|
Source: Tibbetts et al. (1981); * fermented silage: by-catch, 60%; ground maize, 30%, molasses, 5% and lactobacillus culture, 5 percent
More recently, in Vietnam, the nutritional value of fermented silage made from shrimp heads, blood and molasses was compared to fishmeal in 17% crude protein rations for growing pigs (AHRI, 1993). The silage material and fishmeal had similar protein contents in dry matter, 46.2 and 45.8%, respectively. The objective was to study the effect of replacing 10% fishmeal (dry matter basis) by silage, which after a period of ten days' fermentation had a pH of 4.3-4.5 (Table 6.28). A reduction in growth, when the silage replaced 100% of the fishmeal, was assumed to be related to a reduction in feed intake, possibly caused by lowered palatability. Acidity might have been the factor responsible for the reduction in consumption. It was concluded that silage could replace 75% of the fishmeal and that other protein-containing materials, such as, small fish, crabs, silk worms and animal offal might be similarly processed for use as animal feeds.
Fish silage, neutralized to a pH of five prior to feeding, should be an excellent source of protein to complement energy feed resources such as sugar cane juice or molasses, bananas, cassava, sweet potatoes or the African oil palm. In this regard, Pérez (1993) even suggested that the preservation of whole or chopped by-catch or fish wastes directly in B molasses, in a proportion of two parts by weight of molasses (air-dry basis) to one of fish, would constitute a complete ration consisting of between 8 and 10% protein in dry matter for fattening pigs.
Table 6.28. Replacement of fishmeal (FM) with shrimp's head, blood and molasses fermented silage (SHS) for pigs (% DM).
|FM (100%)||FM/SHS (50:50)||SHS (100%)|
|Initial liveweight, kg||13.9||15.2||14.50|
|Final liveweight, kg||72.8||76.0||73.0|
|DM feed intake, kg/d||1.95||1.89||1.74|
|Average daily gain, g||491||523||487|
|DM feed conversion||3.97||3.61||3.57|
Source: AHRI (1993); basic diet (% DM): ground maize, 58; rice bran, 20; fried soya beans, 5; soya bean meal, 5; fishmeal, 10; minerals and vitamins, 2.
Finally, Green et al. (1983), in their review of the use of fish silage in pig diets, emphasized that the major cause of discrepancy amongst researchers in defining performance has been attributed to diversity with respect to both the type of fish tissue and the silage method employed. They concluded that in experiments where the same amount of lysine, and in which the levels of other essential amino acids were adequate, fish silage diets have produced better feed conversions than soya bean meal diets. Perhaps, one of the problems, not mentioned, is the need to put more of these ideas into practice!
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