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6 Aquatic Plants INTRODUCTION Aquatic plants occur throughout the world in oceans, saltwater marshes, rivers, lakes, and waste-treatment ponds. Seaweeds, especially kelp, have been used as medicinals for centuries, but little use has been made of other aquatic plants. These plants have been regarded more as problems than resources. A National Academy of Sciences report pointed out that the problem of aquatic weeds was reaching alarming proportions in many parts of the world (National Research Council, 19761. The report pointed out the following adverse effects of these plants: blocking canals and pumps in irrigation projects, interfering with hydroelectric production, wasting water by evapotranspiration, hindering boat traffic, increasing waterborne dis- ease, interfering with fish culture and fishing, and impeding drainage, which results in flooding. The problem seems to be more severe in tropical areas. Aquatic plants may foster mosquitoborne diseases because small sheltered pools formed between floating plants are well adapted for mos- quito breeding. Recently, aquatic plants have been recognized as potentially valuable resources for animal feed and other uses. The production per hectare may be quite large. Problems exist in harvesting and processing these plants for animal feed, since they are grown in water and are very high in moisture content. Nevertheless, they appear to be valuable resources for use as feedstuffs for production of meat, milk, and eggs. 211
212 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS QUANTITY Information is available on seaweed production by countries known to harvest seaweeds (Naylor, 19761. The values by countries for 1960, 1967, and 1973 are given in Table 59. The total tonnage harvested is not very large, especially considering the low dry-matter content of the harvested seaweed. Data are not available on total quantity of other aquatic plants; however, there is potential for very large quantities. For example, growth rates of 800 kg dry matter/ha/day have been recorded for water hyacinth (National Research Council, 1976~. If such growth could be expected for even 6 months a year, a yield of 146 tons dry matter/ha would be achieved. Yields of 17.8 tons dry matter/ha were reported for duckweeds, compared to 4.4 to 15.9 tons for alfalfa for hay (Hillman and Culley, 1978~. Standing crops of microalgae have yielded up to 1,130 g dry weight/m2 surface pond (Boyd, 1 973a). This would amount to 1 1 .3 tons dry matter/ha. PHYSICAL CHARACTERISTICS The physical characteristics of aquatic plants present problems in har- vesting and processing. Algae are small (5 to 15 ~m) and have low specific gravity (Golueke and Oswald, 19651. Kelp varies in length, from very small to 6 to 9 m long (Hart et al., 19784. Water hyacinths consist of a short rhizome, roots, rosulate leaves, and inflorescence and stolons that connect different plants (Pieterse, 19781. Duckweed is a tiny free-floating vascular plant (Rusoff et al., 19801. Harvested plants usually consist of a slippery, tangled mass that is difficult to handle mechanically. Water hyacinths grow rapidly and may present problems by blocking water flow, thus interfering with rice production. In Bangladesh, rafts of water hy- acinths weighing up to 300 tons/ha float over rice paddies (National Re- search Council, 1976~. A common physical characteristic of all water plants is a low dry-matter content, varying from 5 to 15 percent (National Research Council, 19764. Kelp contains approximately 12 percent dry matter (Hart et al., 1978~. The low dry-matter content of algae in ponds is an even more serious problem; algae harvested from ponds contains only 1 to 2 percent solids (Golueke and Oswald, 19651.
Aquatic Plants 213 TABLE 59 Production of Seaweeds and Aquatic Plants Thousands Metric Tons (wet weight) Continent Country 1960 1967 1973 Africa Egypt 3.8 Morocco17.018.08.0 Senegal- (1.0) South Africa 43.024.1 Tanzania0.52.00.5 North and Canada188.8.131.52 Central Mexico15.528.936.9 America United States(91.0)2.31.1 South Argentina0.932.824.4 America Brazil (103.0) Chile7.232.526.5 Peru (1.0)(1.0) Asia China(250.0) (700.0) India(1 5)(3 5)(5 5) Indonesia 16.6 Japan386.1534.3654.2 Republic of Korea29.787.8224.2 Philippines(0.1)1.62.8 Thailand 0.3 Europe Denmark15.627.510.9 France45.776.360.2 Iceland(20.0) (20.0) Ireland69.1(54.0)(44.0) Italy (0.6) Norway 61.0(75.0) Spain15.536.047.0 United Kingdom(18.0)23.124.1 USSR (100.0) Oceania Australia (7.0) New Zealand(0.4)(0.5)(0.6) World Total 117118862402 NOTE: Numbers in parentheses are estimates. SOURCE: Naylor (1976). Courtesy of the Food and Agriculture Organization of the United Nations.
214 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS NUTRITIVE VALUE Chemical Composition Algae Crude protein content of algae (see Appendix Table 1) ranges from 31 to 68 percent, dry-matter basis. The levels of essential amino acids indicate that algae protein is of high quality (see Appendix Table 41. Algae are also rather high in ether extract and low in crude fiber, indicating fair energy value. Values given for required minerals indicate that algae are good sources of these (see Appendix Table 21. Other Aquatic Plants The crude protein content of other aquatic plants ranges from 11 to 32 percent, dry basis (see Appendix Table 1 J. These levels would be satis- factory for ruminants and for most classes of swine if the amino acid pattern is satisfactory. Aquatic leaf protein was lower in lysine and me- thionine than meat proteins (Boyd, 19681. The fiber level appears to be lower in duckweed than in other aquatic plants. Aquatic plants are also rich in required minerals (see Appendix Table 21. According to Bagnall et al. (1973) 3 kg dry water hyacinths would supply an excess of the major minerals for 450 kg steers. None of the other minerals were present at high levels (see Appendix Table 31. Nutrient Utilization Algae The protein efficiency ratio (PER) in rats was lower for dried algae than for casein (Cook, 19621. Autoclaving algae lowered the PER, and cooking for 30 minutes or 2 hours had no effect. However, cooking improved true digestibility of protein and net protein utilization (NPU). The PER of protein in three species of algae was lower than that of soy protein and casein for chicks and rats, respectively (McDowell and Leveille, 19631. Supplementing algae protein with methionine increased the PER for rats but not to the value for casein. Including cellulase, diastase, and alpha amylase at 1 percent of the diet increased the digestibility of nitrogen by laboratory rats. In swine, digestibility of the protein in algae was 72 percent, whereas the digestibility of energy was only 34 percent (Hintz and Heitman, 1967~. PER, biological value, and apparent digestibility of
Aquatic Plants 215 nitrogen were lower for algae protein than for casein in growing rats (Chung et al., 1978~. Dry-matter digestibility by sheep of dried or dehydrated algae was 54.2 percent, calculated by difference (Hintz et al., 19661. Energy digestibility was 58.7 percent. In cattle, energy digestibility of algae was 59 percent. Seaweed Incorporation of 20 percent seaweed in a concentrate mixture did not affect digestibility of protein, but lowered the TDN (67.9 versus 70.6 percent) of a calf diet (Shukla et al., 19741. Digestion coefficients in pigs were 12 percent for energy and negative for nitrogen in seaweed residue that had been extracted for alginate (Whittemore and Percival, 19754. The authors indicated that the nitrogen fraction was largely insoluble. They indicated that the low energy digestibility resulted from a loss of soluble energy through the extraction process. Water Hyacinth Organic matter and crude protein digestibility were lower for ensiled water hyacinth and dried citrus pulp (4 percent) than for pangolagrass and citrus pulp (Bagnall et al., 19741. Values for organic-matter digestibility were 40 and 48 percent for water hyacinth silages and 54 percent for pango- lagrass. Crude protein digestibility averaged 51 percent for ensiled water hyacinth-dried citrus pulp for hyacinth from oxidation pond water, com- pared with 53 percent for hyacinth from lake water. Addition of 2 percent acetic acid, propionic acid, or a combination of these prior to ensiling was necessary to get a pH below 5 from ensiling partially dried aquatic plants (Linn et al., 1975a). Adding 5 percent corn grain did not lower the pH to less than 5. Dry-matter digestibilities were 43.8 and 43.4 percent for dried aquatic plants (two species), compared with 50.8 percent for dehydrated alfalfa (Linn et al., 1975b). Respective values for energy digestibility were 53.7, 47.4, and 49.2 percent. Digestibility of ensiled aquatic plants was 41.4 percent for dry matter and 51.4 percent for energy. Crude protein digestibility was 58.3 percent for dried material and 33.0 percent for the ensiled material. Replacing 35 percent of alfalfa meal with dried aquatic plants depressed dry-matter digestibility from 77 to 72 percent in sheep and 66 to 64 percent in goats (Heffron et al., 1 9771. In vivo digestibilities of dry matter, organic matter, and crude protein were lower for ensiled water hyacinth than ensiled pangolagrass (Baldwin et al., 19751. Values for pangolagrass and water hyacinth, respectively, were 54.0 and 35.0 percent for dry matter,
216 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS 53.6 and 39.6 percent for organic matter, and 76.1 and 52.8 percent for crude protein. Digestibility of amino acids in duckweed by channel catfish varied from 38 percent for glycine to 64 percent for tyrosine (Robinette et al., 19801. Animal Performance Algae Chicks could tolerate only up to l O percent algae meal in the diet if residual alum was present, but could tolerate up to 20 percent of aluminum-free algae meal (Grau and Klein, 19571. Algae was found to contain substantial amounts of xanthophyll, which can be utilized in the chick for shank and skin pigmentation. Performance of chicks and rats fed algae-supplemented diets was lower than that of comparable animals fed soybean-protein and casein-supplemented diets (McDowell and Leveille, 19631. Supplemen- tation of algae-containing diets with seven essential amino acids increased growth rate 49 percent and feed efficiency 47 percent in chicks, indicating amino acid deficiency in algae protein. Including up to 10 percent algae in swine diets did not alter rate of gain or feed efficiency (Hintz et al., 19661. Supplementing lambs on summer range in California with pellets in which 50 percent of the nitrogen was supplied by algae and 50 percent by alfalfa resulted in higher weight gains than supplementing only with alfalfa pellets. Rate of gain was similar for pigs fed diets supplemented with algae or fishmeal if certain B-vitamins were also supplemented (blintz and Heitman, 19671. Performance was lowered if the diets were supplemented with only algae. In a subsequent trial, evidence was obtained that the effect of B-vitamin supplementation was due at least partly to vitamin By. Seaweed Including 20 percent seaweeds in the concentrate of a calf diet tended to lower rate of gain, but the difference was not significant (Shukla et al., 19741. Feeding concentrate mixtures with up to 30 percent seaweed did not alter milk yields and fat-corrected milk yields in dairy cows (Desai and Shukla, 19751. Body weights tended to be lower if the level of seaweed meal exceeded 15 percent in the concentrate. Including up to 15 percent dried seaweed meal did not affect feed intake and weight gain in sheep (Herbert and Wiener, 1978~. Diarrhea was observed in swine fed a diet containing 50 percent dried residue of seaweed after extraction of alginate (Whittemore and Percival, 1975~.
Aquatic Plants 217 Water Hyacinth Body weights and shank pigmentation score of chicks fed a diet containing duckweed were similar to those of chicks fed diets containing alfalfa (Truax et al., 19724. Cattle preferred water hyacinth silage containing the highest level of preservative, 4 kg dried citrus pulp and 1 kg sugarcane molasses/100 kg plant residue (Baldwin et al. ? 1974J. The silage preference was negatively related to pH and ash in silage. Cattle and sheep readily consumed com- plete diets with processed water hyacinth (Bagnall et al., 1974J. Dry- matter intake of pangolagrass silage by sheep was higher than that of water hyacinth silage (Baldwin et al., 1 9751. Intake of a diet by sheep and goats in which dried aquatic plant was substituted for 35 percent of the alfalfa meal was similar to that of the control diet (Heffron et al., 1977~. Rate of gain of dairy heifers fed diets containing duckweed was equal to or higher than that of heifers fed control diets (Rusoff et al., 1977~. PROCESSING Harvesting and processing water plants would result in reduction of weeds in waterways in addition to providing a resource that could be used as animal feed. There are problems with harvesting and processing. Since weeds are located in water, specially adapted harvesting equipment is essential. The high water content (up to 95 percent) adds volume and weight to the process and means some of the water may have to be removed. Algae Harvesting algae involves three steps: (1) initial concentration, (2) de- watering, and (3) final drying (Golueke and Oswald, 19654. The solids content of pond water is increased to 1 to 2 percent in the initial concen- tration. Chemical precipitation and centrifuging appear to be most prom- ising for the initial concentration. Suitable floculating agents were alum, lime, and synthetic organic polyvalent cationic polymers. Optimum pH for alum precipitation was 6 to 7. Optimum pH for precipitation with lime was 11.2. Excellent dewatering was achieved by using a modified industrial grav- ity filter with two batch-type centrifuges and with a continuous solid-bowl centrifuge. In the gravity filtration, at maximum production of slurry of 14 m3/ha/day, a bed width of 24 m would be required to process the yield from each 0.4 ha of pond.
21 8 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS Golueke and Oswald (1965) suggested minimum exposure to high tem- peratures during drying in order to maintain quality. They suggested flash drying, a process similar to alfalfa dehydration procedures. A high-grade product was obtained using a steam-heated drum dryer. These workers used an inexpensive method of sand bed dewatering and drying of algae. An area of 1,470 m2 would be required/ha of pond. Seaweed The greatest problem facing the seaweed industry is the need for improved efficiency in harvesting (Naylor, 1976J. Hand collection still accounts for most seaweed harvested. Few mechanized methods have been developed successfully, the principal exception being the California Macrocystis beds. Compared with the brown algae, red algae are much smaller and occur in deeper water, making their harvesting slower and more costly. Red algae are usually collected by hand or by using rakes or grapnels. Along the eastern seaboard of the United States and Canada, Chondrus crispus (Irish moss) is normally harvested by use of long-handled rakes from small boats. After harvesting, the bulk of seaweed must be reduced by drying before further processing, since the wet material deteriorates in quality (Naylor, 19761. Most seaweed is dried naturally by exposure to sun and air, but there has been increased use of mechanical dehydration. In the case of natural drying, the washed seaweeds are spread thinly on portable racks, wooden platforms, or areas of flat rock. Under favorable drying conditions 1 or 2 days are sufficient to reduce the moisture level to 18 to 20 percent. The problems and uncertainties of the weather have stimulated the development of artificial drying, especially the use of rotary flame-heated air driers. The use of this method of drying also results in a more uniform product. A process has been developed to reduce water and ash content of kelp and increase its caloric and bulk densities (Hart et al., 1978~. The process consists of chopping the kelp in a silage cutter, then grinding in a vertical- shaft hammermill. After addition of calcium chloride the mixture is heated and pressed, with removal of 75 percent of the moisture and 65 percent of the ash. The level of calcium chloride was 0.5 percent. Following calcium chloride treatment, kelp could be pressed successfully after 15 minutes at 90°C or 30 minutes at 77°C. The process is shown diagra- matically in Figure 14.
Aquatic Plants 219 Fresh Kelp AL my= Juice | Aqueous I- Chemical Additive Juice to Recovery Operations for Organic Solids KCI Pulp Press Cake Ju ice to · Fermentation · Marine/Terrestrial Animal Feeds · Human Food FIGURE 14 Flow diagram of kelp dewatering process. SOURCE: Hart et al. (1978). Other Aquatic Plants Aquatic plants may be harvested from a site at the water's edge or with a self-propelled floating harvester (National Research Council, 1976~. Small moving boats can be used to mow aquatic plants (see Figure 15~. A harvester for submerged plants is shown in Figure 16. Stationary con- veyers (see Figure 17) may be used to remove aquatic plants from the water and transport them to processing or transportation equipment (Bryant, 1973). Approximately 50 percent of the water in aquatic plants can be removed simply by pressing since it is on the surface or contained loosely in the vascular system (National Research Council, 1976~. This press water contains only about 2 percent of the plant solids. Heavier pressing is necessary for further reduction in water. Approximately 10 to 30 percent of the solids may be removed by further pressing. The complete process may remove up to 70 percent of the water in hyacinth, reducing the moisture level from about 95 to 65 percent. This moisture level would enable ensiling of the aquatic plant. Bagnall and Hentges (1979) produced cattle feed by harvesting, chopping, pressing, and ensiling water hyacinth. Production energy and cost were less and the ensiled product was more acceptable to cattle than dried feed. It appears that artificial drying of aquatic plants is not economically feasible because of the high-moisture content of these materials. In areas of low rainfall, solar drying may be feasible.
220 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS FIGURE 15 Harvester for water hyacinth. An experimental harvester lifts, breaks, and throws water hyacinth by grasping and pulling on aerial parts of the plants, protecting the high-speed harvesting mechanism from damage by sudden underwater obstructions. SOURCE: National Research Council (1976). UTILIZATION SYSTEMS The high protein and mineral levels in algae indicate that these materials could be dried and used in limited amounts in swine and poultry diets. They have been used at levels of 10 to 20 percent of the diet in these animals (Grau and Klein, 1957; Hintz et al., 19661. The lower protein and energy value of the other materials would make them more likely to be used for ruminants. Seaweeds are usually used as sources of minerals and vitamins rather than of protein and energy (Stephenson, 1973~. It is probable that ensiling would be more economically feasible than dehy- dration. ANIMAL AND HUMAN HEALTH Feeding a diet containing 18.3 percent algae (Arthrospira) to male rats for 14 days did not produce gross pathological or histopathological effects in liver, kidney, heart, lungs, spleen, stomach, intestines, testes, or lymph nodes (Chung et al., 19781. Feeding this diet to female rats from weaning
Aquatic Plants 221 FIGURE 16 Floating harvester for submerged aquatic plants. Large, complete floating harvesters for submerged aquatic plants are impressive but expensive and have modest capacity. SOURCE: National Research Council (1976). until the second week of lactation did not alter reproduction and lactation. The livers of these females were histologically normal. Feeding high levels of water hyacinth (Eichhornia crassipes) for three generations affected reproduction in rats (Chavez et al., 19761. During the first two generations little difference was noted in number of dams that littered when fed diets containing 0, 10, 20, and 30 percent dehydrated water hyacinth. During the third generation 75 and 38 percent of the females littered on the 20 and 30 percent hyacinth diets, respectively. The number of offspring weaned in the first generation was lower for females fed 30 percent hy- acinth and was lower for females fed 20 and 30 percent hyacinths during the second or third generations. In all three generations, gains of rats from 5 through 13 weeks of age were lowest for those fed 30 percent hyacinth. The gains for those fed 10 and 20 percent hyacinth were lower than for the controls during the second and third generations. The nitrate, oxalate, and tannin content of hydrilla and water hyacinth did not appear to be a hazard in cattle diets (Stephens et al., 19731. Data are not available concerning pathogens in water plants. The main potential problem appears to be in plants harvested in waste-treatment
222 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS FIGURE 17 Hyacinth control station. SOURCE: Bryant ( 1973). Courtesy of Aquamarine Corp. Crown Copyright. 1973. Controller of Her Britannic Majesty's Stationery Office. ponds and lagoons. Data on mineral composition do not implicate a serious heavy metal threat (see Appendix Table 2), but this aspect needs to be explored further. REGULATORY ASPECTS There are no specific regulations concerning feeding water plants except those related to algae feeding. More data are needed before sound regu- lations can be formulated. RESEARCH NEEDS More critical experiments are needed to define the utilization of protein and energy in aquatic plants, especially seaweeds and water hyacinths.
Aquatic Plants 223 This should include research on parts of plants, aerial versus submerged; stage of maturity; and palatability. The most serious void is in development of economical mechanical harvesting and processing methods. The research should be with seaweed, algae, water hyacinths, and duckweed. In the case of algae, hyacinths, and duckweed, equipment needs to be developed for handling plants from lakes and waste-treatment ponds. Research should be directed toward developing controlled production, harvesting, processing, and quality for use as animal feed. Research should be directed toward the health aspects of utilizing these resources. The presence of pathogens and methods of destroying these should be studied. Data should be collected on pesticides, mycotoxins, and heavy metals in these resources. SUMMARY Aquatic plants occur throughout the world and may present problems in irrigation projects, hydroelectric production, boat traffic, fish culture, and drainage. They are potentially valuable resources for different uses, in- cluding as animal feed. Yields of dry matter per hectare are usually higher for these plants than for conventional forage and grain crops. The physical characteristics, including varying size and high water contents, present problems in harvesting and processing the plants. Generally, algae are high in crude protein and ether extract, and low in fiber. Water hyacinths are fairly high in fiber, indicating limited energy value, and are lower in protein than algae. Efficiency of utilization of protein in algae is good, although lower than in casein. The energy value of water hyacinths is lower and ash content much higher than for con- ventional roughages. Including 10 percent algae in diets of chicks and swine did not alter performance. Including limited levels of seaweeds in ruminant diets has not altered performance. Water hyacinths have been ensiled successfully, and the silage was consumed readily by cattle and sheep. The location of water plants and their high water content present prob- lems in harvesting and processing. Equipment has been developed for processing various aquatic plants, but generally efficiency and capacity are low. Drying algae and ensiling the other aquatic plants probably are the most feasible processing methods at present. Feeding 18 percent algae did not produce harmful effects in male and female rats. Feeding 10 percent dehydrated water hyacinths did not affect reproduction in female rats during three generations, but feeding 20 or 30 percent lowered reproductive rates. There is no evidence of harmful levels of minerals in aquatic plants.
224 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS LITERATURE CITED Anonymous. 1970. State of development of the IFP Algae Process at December 1970. Report to FAOtWHO/UNICEF Protein Advisory Group. Institut Francais du Petrale. Bagnall, L. O., and J. F. Hentges, Jr. 1979. Processing and conservation of water hyacinth and hydrilla for livestock feeding. In Aquatic Plants, Lake Management, and Ecosystem Consequences of Lake Harvesting. Proceedings of Conference at Madison, Wisconsin, Feb. 14- 16, 1979. Madison: University of Wisconsin. 367 pp. Bagnall, L. O., R. L. Shirley, and J. F. Hentges. 1973. Processing, chemical composition and nutritive value of aquatic weeds. P. 40 in Water Resources Research Center Pub. 25. Gainesville: University of Florida. Bagnall, L. O., T. de S. Furman, J. F. Hentges, Jr., W. J. Nolan, and R. L. Shirley. 1974. Feed and fiber from effluent-grown water hyacinth. Pp. 116- 141 in Wastewater Use in the Production of Food and Fiber. EPA Paper No. 660/2-74-041. Washington, D.C.: U.S. Government Printing Office. Baldwin, J. A., J. F. Hentges, Jr., and L. O. Bagnall.' 1974. Preservation and cattle ac- ceptability of water hyacinth silage. Hyacinth Control J. 12:79-81. Baldwin, J. A., J. F. Hentges, Jr., L. O. Bagnall, and R: L. Shirley. 1975. Comparison of pangolagrass and water hyacinth silages as diets for sheep. J. Anim. Sci. 40:968- 971. Boyd, C. E. 1968. Fresh-water plants: A potential source of protein. Econ. Bot. 4:359. Boyd, C. E. 1973a. Summer algal communities and primary productivity in fish ponds. Hydrobiologia 41:357-390. Boyd, C E. 1973b. Amino acid composition of freshwater algae. Arch. Hydrobiol. 72: 1- 9. Bryant, C. B. 1973. Control of aquatic weeds by mechanical harvesting. Pestic. Art. News Serv. 19:601 -606. Chavez, M. I., R. L. Shirley, and J. F. Easley. 1976. Effects of feeding hyacinths to rats for three generations. Soil Crop Sci. Soc. Fla., Proc. 35:74-76. Chung, P., W. G. Pond, J. M. Kingsbury, E. F. Walker, Jr., and L. Krook. 1978. Pro- duction and nutritive value of Arthrospira platensis, a spiral blue-green alga grown on swine wastes. J. Anim. Sci. 47:319-330. Clement, G., C. Giddey. and R. Menzi.1967. Amino acid composition and nutritive value of the alga Spirulina maxima. Sci. Food Agric. 18:497-501. Cook, B. B. 1962. The nutritive value of waste-grown algae. Am. J. Public Health. 52:243 251. Culley, D. D., Jr., and E. A. Epps. 1973. Use of duckweed for waste treatment and animal feed. J. Water Pollut. Control Fed. 45:337-347. Dam, R., S. Lee, P. C. Fry, and H. Fox. 1965. Utilization of algae as a protein source for humans. J. Nutr. 86:376-382. Davis, I. F., M. J. Sharkey, and D. Williams. 1975. Utilization of sewage algae in as- sociation with paper in diets of sheep. Agric. Environ. 2:333-338. Desai, M. C., and P. C. Shukla. 1975. Effect of feeding seaweed to lactating cows on body weights and milk production. Indian J. Anim. Sci. 45:823-827. Golueke, C. G., and W. J. Oswald. 1965. Harvesting and processing sewage-grown plank- tonic algae. J. Water Pollut. Control Fed. 37:471. Grau, C. R., and N. W. Klein. 1957. Sewage-grown algae as a feedstuff for chicks. Poult. Sci. 36: 1046- 1051. Hart, M. R., D. de Fremery, C. K. Lyon, and G. O. Kohler. 1978. Dewatering kelp for fuel, feed, and food uses: Process description and material balances. Trans. ASAE 21:186-189.
Aquatic Plants 225 Heffron, C. L., J. T. Reid, W. M. Hascheck, A. K. Furr, T. F. Parkinson, C. A. Bache, W. H. Gutenmann, L. E. St. John, Jr., and D. J. Lisk. 1977. Chemical composition and acceptability of aquatic plants in diets of sheep and pregnant goats. J. Anim. Sci. 45:1166-1172. Herbert, J. G., and G. Wiener. 1978. The effect of breed and of dried seaweed meal in the diet on the levels of copper in liver, kidney and plasma of sheep fed on a high copper diet. Anim. Prod. 26:193-201. Hillman, W. S., and D. D. Culley, Jr. 1978. The uses of duckweed. Am. Sci. 66:442- 451. Hintz, H. F., and H. Heitman, Jr. 1967. Sewage-grown algae as a protein supplement for swine. Anim. Prod. 9:135-140. Hintz, J F., H. Heitman, Jr., W. C. Weir, D. T. Torell, and J. H. Meyer. 1966. Nutritive value of algae grown on sewage. J. Anim. Sci. 25:675-681. Linn, J. G., E. J. Staba, R. D. Goodrich, J. C. Meiske, and D. E. Otterby. 1975a. Nu- tritive value of dried or ensiled aquatic plants. I. Chemical composition. J. Anim. Sci. 41 :601-609. Linn, J. G., R. D. Goodrich, D. E. Otterby, J. C. Meiske, and E. J. Staba. 1975b. Nu- tritive value of dried or ensiled aquatic plants. II. Digestibility by sheep. J. Anim. Sci. 41:610-615. McDowell, R. E., and G. A. Leveille. 1963. Feeding experiments with algae. Fed. Proc. 22: 1431-1438. National Research Council. 1971. Atlas of Nutritional Data on United States and Canadian Feeds. Washington, D.C.: National Academy of Sciences. National Research Council. 1976. Making Aquatic Weeds Useful: Some Perspectives for Developing Countries. Washington, D.C.: National Academy of Sciences. Naylor, J. 1976. Production, Trade and Utilization of Seaweeds and Seaweed Products. FAO Technical Paper No. 159. Rome: Food and Agriculture Organization of the United Nations. Pieterse, A. H. 1978. The water hyacinth (Eichhornia crassipes): A review. Abstr. Trop. Agric. (Roy. Trop. Inst., Amsterdam) 4(2):9-42. Robinette, H. R., M. W. Brunson, and E. J. Day. 1980. Use of duckweed in diets of channel catfish. Thirty-Fourth Annual Conference, Southeast Association of Fish and Wildlife Agencies. Nashville, Tenn.: Association of Fish and Wildlife Agencies. Rusoff, L. L., D. T. Gantt, D. M. Williams, and J. H. Gholson. 1977. Duckweed A potential feedstuff for cattle. J. Dairy Sci. Suppl. 1. 60:161. Rusoff, L. L., E. W. Blakeney, Jr., and D. D. Culley, Jr. 1980. Duckweed (Lemnaceae family): A potential source of protein and amino acids. J. Agric. Food Chem. 28:848. Shukla, P. C., P. M. Talpada, and B. M. Patel. 1974. Utilization of seaweeds in the concentrate ration of growing calves. Indian J. Anim. Sci. 44:428-431. Stephens, E. L., J. F. Easley, R. L. Shirley, and J. F. Hentges, Jr. 1973. Availability of nutrient mineral elements and potential toxicants in aquatic plant diets fed steers. Soil Crop Soc. Fla., Proc. 32:30-32. Stephenson, W. A. 1973. Seaweed in Agriculture and Horticulture. 2nd ed. East Ardsley, England: E. P. Publishing. Truax, R. E., D. D. Culley, M. Griffith, W. A. Johnson, and J. P. Wood. 1972. Duckweed for chick feed? La. Agric. 16:8-9. Whittemore, C. T., and J. K. Percival. 1975. A seaweed residue unsuitable as a major source of energy as nitrogen for growing pigs. J. Sci. Food Agric. 26:215-217.