Table of Contents
Cook, C.G. and G.A. White. 1996. Crotalaria
juncea: A potential multi-purpose fiber crop. p. 389-394. In: J. Janick
(ed.), Progress in new crops. ASHS Press, Arlington, VA.
Crotalaria juncea: A Potential Multi-Purpose Fiber Crop
Charles G. Cook and George A. White
- ECONOMIC IMPORTANCE
- BOTANICAL DESCRIPTION
- CULTIVATION AND MANAGEMENT
- SEED PRODUCTION
- MAJOR DISEASES AND OTHER PESTS
- GENETICS AND BREEDING
- SUMMARY AND FUTURE
Sunn hemp (Crotalaria juncea L.) is one of the earliest and most
distinctly named fibers of India. Past research efforts have shown that the
soft, lignified fibers produced in the stem of sunn hemp could be utilized in
the manufacturing of pulp and paper, and more recent efforts have indicated
that other potential products can be developed from these fibers. Additional
characteristics that enhance the value potential of sunn hemp as a nonwood,
fiber crop are low nitrogen fertilization requirements, the ability to fix
nitrogen and to grow in marginal soils, drought resistance, and resistance to
root-knot nematodes. Unlike kenaf (Hibiscus cannabinus L.), another
potential nonwood fiber crop, which produces consistently greater yields and is
less susceptible to lodging, sunn hemp is highly resistant to root-knot
nematodes and the stalks dry out more rapidly after a killing frost prior to
harvest. Past and present research efforts have identified sunn hemp as a
potential nonwood fiber source that could be used in the manufacturing of
several products, including newsprint, specialty papers, and as a component of
commercial nursery potting media. This paper reports on the potential use of
Crotalaria juncea as a nonwood source of fiber.
Sunn hemp, a member of the legume family (Fabaceae), has great potential as an
annually renewable, multi-purpose fiber crop. It is the most important species
of the Crotalaria genus, which is comprised of over 350 species located
in the tropics and subtropics of both hemispheres. As one of the most widely
grown green manure crops throughout the tropics, sunn hemp is often grown in
rotation with several different crop species (Kundu 1964; White and Haun 1965;
Lai et al. 1967; Purseglove 1968; Srivastava and Pandit 1968; Barros Salgado et
al. 1972; Mascarenhas et al. 1980; Rotar and Joy 1983). The stems of sunn hemp
are composed of two fibers, the bast and woody core. The bast fibers, which
are located in the outer bark, are much longer than the core fibers, but the
two fiber widths are very similar (Cunningham et al. 1978). The proportion of
bark in the total stalk, by dry weight, generally ranges from 15% to 20%.
Kundu (1964) reports that the actual proportion of bast fiber in dry stalks
ranges from 6.4% to 10.5%.
Research with sunn hemp has been conducted in the United States since the
1930s, where it was reported to be an excellent soil-improving crop. It
produced high organic matter yields, was able to fix nitrogen, and could reduce
the build-up of root-knot nematode populations (Breitenbach 1958; Dempsey
1975). However, the difficulty in producing seed caused many farmers to
abandon the growing of this crop. Interest in growing sunn hemp was renewed
during World War II, as C. juncea was added to the list of critical war
materials in 1942 because of its potential use as cordage fiber, especially for
Marine Oakum. Attention again focused on sunn hemp from the late 1950s through
the 1960s. This was the result of efforts to identify annually renewable
sources of nonwood fiber which could be used in the manufacture of paper and
pulp. Although research showed that sunn hemp possessed good pulping
characteristics and that high macerate yields could be obtained (Nieschlag et
al. 1960; Nelson et al. 1961), most research eventually concentrated on kenaf.
Kenaf received more attention because of its ability to produce consistently
greater yields and have less lodging, which could reduce yields and harvest
efficiency. A more recent report by Cunningham et al. (1978) indicates that
sunn hemp may be superior to kenaf for some fiber properties, including bast
fiber length (3.79 vs. 2.62 mm) and width (24.3 vs. 19.7 µm). They concluded
that sunn hemp possessed the following properties that made it an excellent
candidate for papermaking: (1) good yields of bleachable sulfate pulps, (2)
pulp strength properties that are equal to or greater than those of mixed
southern hardwood pulp, and (3) bast fiber length to width ratio that is
greater than those of wood fibers. A study by Scott and Cook (1994) indicated
the potential yield advantage of sunn hemp compared to kenaf when grown in
soils infested with the southern root-knot nematode [Meloidogyne
incognita (Kofoid and White) Chitwood]. In tests conducted under growing
conditions in South Texas, Kansas, and South Carolina total stalk yields have
been reported to range from 14,800 to 18,450 kg/ha (White and Haun 1965; Scott
and Cook 1994; Scott et al. 1991).
Most of the present-day sunn hemp production is located in India, Bangladesh,
and Brazil, where it is grown as a green manure crop, a fodder crop, or for the
bast fibers. The bast fibers are utilized for the manufacture of cordage and
high quality paper. In addition to the uses as a green manure crop and as a
fiber source, research is being conducted in Texas to determine if the shorter
core fibers of sunn hemp can be utilized in the manufacture of soil-less
potting media for commercial nursery application.
Crotalaria juncea is generally considered to have originated in India,
where it has been cultivated since prehistoric times (Montgomery 1954). The
genus name Crotalaria means rattle and is indicative of the noise made
by the seeds shaken in the mature pods (White and Haun 1965). The species name
juncea was given to this plant by Linnaeus because of its resemblance to
Spartium junceaum L., the Spanish broom of the Mediterranean region with
its green rushlike, scantily-leaved branches (Kundu 1964).
Crotalaria juncea is the most important and fastest growing species of
the Crotalaria genus. Although generally considered to be a tropical or
subtropical crop, it is drought resistant and has a wide range of adaptation to
soil types. For fiber production, a light loam, moderately rich, well-drained
soil is preferred (Montgomery 1954; Kundu 1964). Vigorous growth can be
achieved on clay or low lying soils; however, the bast fiber may be coarser and
yields lower. The major sunn hemp growing areas of India and Brazil are
characterized by high humidity, an average temperature of 23.0° to
29.4°C, and a rainfall of 170-200 mm during the growing season (Dempsey
1975). Sunn hemp is typically photoperiod-sensitive and flowering occurs in
response to short days (White and Haun 1965).
Sunn hemp is a short-day, erect shrubby annual, generally 1 to 4 m in height.
The stems are cylindrical and ribbed. Branching in the upper portion is
minimized with dense plantings. The simple, elliptic to oblong shaped leaves,
are spirally arranged on the stem. The root system is characterized by a long,
strong taproot, well developed lateral roots, and much branched and lobed
nodules, up to 2.5 cm in length. The inflorescence is a terminal open raceme
to 25 cm in length with deep yellow flowers. Flowering is indeterminate.
Extensive cross-pollination occurs in sunn hemp and self-pollination takes
place after the stigmatic surface has been insect or mechanically stimulated
(Purseglove 1968). Seeds are small, flattened, kidney-shaped, and contain
approximately 35% protein. Due to cultivar and environment, seed weight is
highly variable, ranging from 18,000 to 30,000 seed per kg (Dempsey 1975).
'Tropic Sun', a Hawaiian cultivar, was reported to have 30,000 to 35,000 seed
per kg (Rotar and Joy 1983).
Good land preparation should be made before planting sunn hemp for fiber
production (White and Haun 1965; Ghumary and Bisen 1967; Barros Salgado et al.
1972). Although reports on fertilization requirements vary, additions of P are
generally recommended for low phosphorous soils (Barros Salgado et al. 1972;
Rotar and Joy 1983). Sunn hemp is fast growing and generally suppresses weed
populations due to dense canopy shading (Burnside and Williams 1968). However,
early season weed control has been shown to improve yields when sunn hemp is
grown for fiber (White and Haun 1965). No herbicides are currently registered
for use in sunn hemp production. However, several preemergence herbicides
(most notably clomazone at 1.38 kg a.i./ha) recently have been identified as
causing minimal phytotoxicity and providing efficient weed control (J.R. Smart
and C.G. Cook, unpubl.).
Recommendations for seeding rates vary greatly among production areas. In the
1995 South Texas commercial planting, seeds were sown at 17 kg/ha in
double-drilled rows spaced 1.02 m apart (G. Kinney pers. commun). White and
Haun (1965) recommended seeding rates of 16.8 to 22.4 kg/ha in rows spaced 30.5
to 35.6 cm apart. For fiber production in Brazil, Lovadini et al. (1970)
advocated 60 kg/ha of seed in rows spaced 50 cm apart, while Barros Salgado et
al. (1972) suggested a seeding rate of 35 to 40 kg/ha. Ghumary and Bisen
(1967) report that the broadcast seeding rate in India is 66.5 to 88.5 kg/ha.
However, when drill-planted on rows spaced 30 cm apart, they reported that a
seeding rate of 6.6 kg/ha can yield 10% more fiber than the higher broadcast
rate. Preliminary results from studies conducted at Weslaco, Texas indicate
that plant height and total stalk dry yield was not changed for four different
seeding rates of ca. 4.9, 6.8, 8.7, or 10.8 kg/ha on rows spaced 1.02 m
Planting dates also differ among locations; however, adequate soil moisture and
frost-free, warm weather conditions will provide rapid emergence and the
highest yields (Kundu 1964; White and Haun 1965). In Kansas, White and Haun
(1965) reported a 40% decrease in yield due to a two-week delay in a 1962
planting. However, a two-week delay in 1963 did not affect yields.
Preliminary results in South Texas also indicate that significant decreases in
yield, plant height, and stalk diameter may occur when planting is delayed by
two, four, or six weeks. Later harvest dates do not appear to improve yields
of late planted crops and delaying harvest may actually result in lower yields.
To obtain the highest quality fiber, harvesting should be done at the optimum
time. Although opinions differ, the general recommendation is that harvesting
should take place during the seed pod stage (Medina et al. 1961; Kundu 1964;
Purseglove 1968). Mechanized harvests will be necessary for large-scale
commercial plantings. White and Haun (1965) reported that although forage
harvesters had been successfully used, precision cutting was difficult to
obtain and the chopped material was bulky to handle. A whole stalk kenaf
harvester that was designed using sugarcane technology will be used to harvest
the South Texas sunn hemp crop. This harvesting system is adjusted to cut the
stalks slightly above ground level and to remove the very upper foliar portion
of the stalk, which may be necessary if the fiber is to be utilized in the
manufacture of paper. The experimental harvesting of small research plots in
1994 with this machinery indicated that this method of harvest should be
successful. However, more efficient, rapid, and specifically designed
machinery for harvesting and processing may be necessary for large-scale
commercial operations, since it was reported by Scott et al. (1991) that
increasing the growing season beyond six months may not be beneficial and may
actually result in declining fiber yields.
Sunn hemp is generally photoperiod-sensitive and flowering commences in
response to short days (White and Haun 1965). Because of the lateness in
flowering, with the exception of Texas, very little seed production has
occurred in the continental United States. The primary sources of seed for the
sunn hemp grown in the continental United States are from Hawaii and South
America (most notably Brazil and Columbia). The short-day, frost-free
environments of these locations allow for reliable and excellent yields of good
quality seed to be produced. Small-scale seed production has occurred in South
Texas, but the possibility of early frost always poses a threat of reducing
yields of seed crops grown in the continental United States. Recommended seed
rates vary from 3 to 5 kg/ha in Hawaii (Rotar and Joy 1983) to 17 to 22 kg/ha
in South Africa (DeToit 1946).
Seeds are ready for harvest when pods begin to turn yellow in color and the
seeds rattle in the pods (DeToit 1946; Rotar and Joy 1983). For mechanical
harvest, a combine with the header raised as high as possible without leaving
the seed pods on the stalk should be used. This technique will result in
cleaner seed, less moisture, and maintain the speed of the combine harvesting
operations. Seed yields are variable between locations. DeToit (1946)
reported 450 to 900 kg/ha could be produced in South Africa, while Baird et al.
(1957) found that yields in Columbia ranged from 555 to 1000 kg/ha. Rotar and
Joy (1983) indicated that 1460 to 2240 kg/ha could be produced in Hawaii.
Many species of Crotalaria contain toxic pyrrolizidine alkaloids in the
seeds. In C. juncea, trichodesmine was identified as the principal
toxic alkaloid (Zhang 1985). Studies have indicated that poisoning can occur
in both horses (Nobre et al. 1994) and pigs (Zhang 1985) when C. juncea
seed are ingested.
No serious diseases have developed in South Texas and few have been reported
for the United States. However, the soils of South Texas are naturally
infested with Phymatotrichum root rot, incited by Phymatotrichum
omnivorum Duggar [= Phymatotrichopsis omnivora (Duggar) Hennebert],
a fungal pathogen that attacks over 2,000 plant species (Streets and Bloss
1973). Sunn hemp is reported to be susceptible to attack from this fungal
pathogen (Streets and Bloss 1973; Cook and Hickman 1990). However, laboratory
studies have indicated that sunn hemp is more resistant to P. omnivorum
than kenaf (Cook and Hickman 1990). Control of this pathogen can be achieved
through cultural practices and crop rotations (Streets and Bloss 1973). Other
pathogens of sunn hemp that have been reported from the United States are a
powdery mildew, caused by Microsphaera diffusa Cook and Peck, and a root
and stem rot, incited by Sclerotium rolfsii Sacc. (Farr et al. 1989).
Serious diseases of sunn hemp grown in India are anthracnose, caused by
Colletotrichum curvatum Briant and Martyn (Mitra 1934; Whiteside 1955)
and a wilt, caused by Fusarium udam E.J. Butler f. sp.
crotalariae (G.S. Kulkarni) Subramanian (Mitra 1934; Kundu 1964;
Purseglove 1968). Fungicide seed treatments and crop rotations are the most
recommended and practiced disease control measures (Mitra 1934; Whiteside
1955). Sources of resistance to anthracnose have been reported by Dey et al.
(1990), indicating the potential to reduce disease losses through the
development of anthracnose resistant varieties. A fungus (Ceratocystis
fimbriata Ellis & Halst) that causes a wilt disease of sunn hemp in
South America has been reported by Barros Salgado et al. (1972) and Malaguti
(1951). In addition to implementing crop rotations for disease control, sunn
hemp germplasm which possesses resistance to C. fimbriata has been
reported (Ribeiro et al. 1977).
The major insect pests of sunn hemp in the United States are reported to be the
lima bean pod borer, Etiella zinckenella Treit. and bella moth,
Utetheisa bella L. (Seale et al. 1957). In Florida, these insect pests
were reported to attack the fruiting pods, with little to no seed being
produced. In India, the two major insect pests of sunn hemp are the sunn hemp
moth (Utethesia pulchella L.), which feed on the leaves and seed pods,
and the top-shoot borer (Laspeyresia pseudonectis Meyr.), which bores
into the apical tip of the plant, causing excessive branching and cessation of
growth (Kundu 1964). Dempsey (1975) reports that significant shoot borer
resistance has been identified.
Other insect pests that are reported to periodically attack sunn hemp are the
leaf feeding catapillars, Argina cribraria Clerck and A. syringa
Cramer. Additional stem or shoot borer species include Laspeyresia
tricenta Meyr., Cymotricha tetraschema Meyr., and Selinas
monotropa Gaert. Dempsey (1975) and Reddy (1956) also report that the sunn
hemp mirid (Ragmus importunitas Distant), flea beetle (Longitarsus
belgaumensis Jac.), and stink bug (Nezara viridula L.) will attack
sunn hemp. In 1995, the silverleaf whitefly (Bemisia argentifolii
Bellows & Perring) was observed to feed and reproduce on the lower surface
of sunn hemp leaves. Although no actual damage was quantified, premature leaf
defoliation appeared to occur.
Sunn hemp, 2n = 16, is generally reported to be a self-incompatible
plant. Cross-pollination is extensive and self-pollination occurs only after
the stigmatic surface has been stimulated by insects or some other means (Kundu
1964). More recently, successful efforts in breeding for self compatibility
have been reported (Ribeiro et al. 1977). The development of self compatible
germplasm should accelerate the development of true breeding, stable pure
According to Purseglove (1968) and Dempsey (1975), most of the sunn hemp
cultivars have originated from selection of improved types suited to specific
localities, rather than by breeding procedures. These selections generally
focused on early maturity, improved fiber yield, and resistance to pests.
Dempsey (1975) provides lists of improved sunn hemp cultivars that have been
selected for the growing conditions of India, Brazil, and Taiwan. Past
attempts to develop strains from interspecific crosses among Crotalaria
have not been successful (Kundu 1964).
In more recent years, genetic research and breeding procedures have been
conducted on sunn hemp in Brazil (Ribeiro et al. 1977; Miranda et al. 1989;
Miranda 1991). Miranda (1991) conducted a genetic study in 1990 to determine
the inheritance pattern of seed yield and plant height for sunn hemp. Results
indicated that the estimation of the dominant effect was nine times larger than
the additive effect. Since pollination generally can be controlled in sunn
hemp due to the self incompatibility factor, these findings indicate the
possibility of exploiting heterosis. Ribeiro et al. (1977) described the
breeding methodology used in the development of sunn hemp germplasm possessing
both self compatibility and resistance to C. fimbrata. The presence of
a self compatibility factor in sunn hemp will allow breeders to treat sunn hemp
like a self pollinated crop, ie. single, individual plant selections can
be made and the potential exists for a more rapid development of true breeding,
pure line cultivars. Preliminary results indicate that final plant height and
basal stem diameter are positively correlated with total stalk dry matter,
indicating selections for these traits could result in higher yielding
As the world faces an increased need for fiber, sunn hemp, a nonwood fiber
crop, has the potential to be grown on a large commercial scale. Present known
industrial uses for sunn hemp fiber include the manufacture of pulp, specialty
papers, and as a component of a soil-less potting media. In the past, sunn
hemp bast fiber was used for cordage and for making specialty paper. Today, in
countries outside of the United States, sunn hemp is often grown in crop
rotations as a green manure crop to improve soils and reduce root-knot nematode
infestations. Future efforts should focus on the expansion of product research
and development, the development of harvesting and processing equipment, and
the identification of more efficient crop management strategies. The future of
sunn hemp appears very promising given the fact that worldwide demands for
fiber are increasing and current wood fiber supplies cannot continue to meet
the industrial market demands of the future. Research has shown that sunn hemp
can be successfully grown as a fiber crop and that these fibers can supplement
many of the current fiber market needs.
- Baird, G.B., M. Rodriguez, B. Martinez, and P. Sanchez. 1957. Crotalaria
juncea-a green manure. DIA Boletin de Divulgacion 2. Havana, Cuba.
- Barros Salgado, A.L., L.A.C. Lovadini, M. Pimental, and W. Gimenez. 1972.
Instrucoes para a cultura da Crotalaria juncea. Instituto Agronomico,
Campinas, Brazil. Secao de Plantas Fibrosas Boletim 198.
- Breitenbach, C.A. 1958. Land management practices for kenaf production. p.
97-101. In: Proc. World Conf. on Kenaf. ICA, Havana, Cuba.
- Burnside, O.C. and J.H. Williams. 1968. Weed control methods for kinkaoil,
kenaf and crotalaria. Agron. J. 60:162-164.
- Cook, C.G. and M.V. Hickman. 1990. Response of kenaf and sunn crotalaria to
Phymatotrichopsis omnivora. Guayulero 12:4-9.
- Cunningham, R.L., T.F. Clark, and M.O. Bagby. 1978. Crotalaria
juncea-annual source of papermaking fiber. TAPPI 61:37-39.
- Dempsey, J.M. 1975. Fiber Crops. The University Presses of Florida,
- Detoit, J.J. 1946. Sunn hemp, a valuable fodder crop and soil renovator.
Farmer's Weekly (S. Africa) 72:90-91.
- Dey, D.K., K. Banerjee, R.D.N. Singh, and S.A.K.M. Kaiser. 1990. Sources of
resistance to anthracnose disease of sunnhemp. Environ. Ecol. 8:1217-1219.
- Farr, D.F., G.F. Bills, G.P. Chamuris, and A.Y. Rossman. 1989. Fungi on plants
and plant products in the United States. The American Phytopathological
Society, St. Paul, MN.
- Ghumary, S.R. and M.S. Bisen. 1967. Sunn hemp (Sunn crotalaria) has satisfied
M.P. farmers. Indian Farming 16:17-18.
- Kundu, B.C. 1964. Sunn-hemp in India. Proc. Soil Crop Soc. Florida.
- Lai, M.L., C.C. Yang, and P.S. Ching. 1967. Introduction and selection of the
dual-purpose varieties of sunn hemp and their fiber extraction and paper
manufacturing experiments. Taiwan Agr. Quart. 3:34-46.
- Lovadini, L.A.C., A.L.B. Salgado, and S. Miyasaka. 1970. Efeito de epoca de
plantio e da poda na producao de massa verde e sementes de Crotalaria
juncea L. Bragantina 6:25-29.
- Malaguti, G. 1951. Una podredumbre del tallo de Crotalaria juncea,
causada por Ceratostomella fimbrata. Agronomia Tropical 1:287-292.
- Mascarenhas, H.A.A., N.R. Braga, M.A.C. de Miranda, C.T. Feitosa, and O.C.
Bataglia. 1980. Efeito de adubos verdes e organicos na producao de soja.
Instituto Agronomico, Campinas, Brazil. Boletim Tecnico 63.
- Medina, J.C., D. Ciaramello, and A. Pettinelli. 1961. Resultados experimentals
com a cultura de Crotalaria juncea L. Como planta produtora de celulose
para papel. Bragantia 20:659-668.
- Miranda, M.A.C. de. 1991. Adequacao modelo aditivo-dominante em dois caracteres
de crotalaria. Bragantia 50:195-202.
- Miranda, M.A.C. de, E.A. Bulisani, J.P.F. Teixeira, and H.A.A. Mascarenhas.
1989. Haranca da pigmentacao com antocianina em Crotalaria juncea L.
- Mitra, M. 1934. Wilt disease of Crotalaria juncea Linn. (sunn-hemp).
Indian J. Agr. Sci. 4:701-714.
- Montgomery, B. 1954. Sunn fiber. p. 323-327. In: H.R. Mauersberger (ed.),
Mathew's textile fibers. 6th ed. Wiley, New York.
- Nelson, G.H., H.J. Nieschlag, M.E. Daxenbichler, I.A. Wolf, and R.E. Perdue.
1961. A search for new fiber crops. III. Laboratory scale pulping studies.
- Nieschlag, H.J., G.H. Nelson, I.A. Wolf, and R.E. Perdue. 1960. A search for
new fiber crops. TAPPI 43:193-201.
- Nobre, D., M.L.Z. Dagli, and M. Haraguchi. 1994. Crotalaria juncea
intoxication in horses. Vet. Human Toxicol. 36:445-448.
- Purseglove, J.W. 1968. Tropical crops. Wiley, New York.
- Reddy, D.B. 1956. Sunn hemp and its insect fauna. Proc. Tenth Int. Cong.
- Ribeiro, I.J.A., M.C.A. de Miranda, E.A. Bulisani, L.D'A. Almeida, L.A.C.
Lovadini, M.H. Sugimori, and O.P. Filho. 1977. Melhoramento da crotalaria
I-autocompatibilidade e resistancia a murcha de Ceratocystis fimbriata.
- Rotar, P.P. and R.J. Joy. 1983. `Tropic Sun' sunn hemp, Crotalaria
juncea L. Univ. of Hawaii, College of Tropical Agr. and Human Resources,
Institute of Tropical Agr. and Human Resources Research Extension Series 36.
- Scott, A.W., Jr. and C.G. Cook. 1994. Kenaf, crotalaria, roselle--two year
comparison in South Texas. p. 97-101. In: Proc. Int. Kenaf Assoc. Conf.
- Scott, A.W., Jr., L.N. Namken, and J. Garza. 1991. Kenaf/crotalaria variety
study--1989. p. 44-46. In: Rio Farms, Inc. 50th Anniversary Research Report.
- Seale, C.C., J.F. Joyner, and J.B. Pate. 1957. Agronomic studies of fiber
plants. Fla. Agr. Expt. Sta. Bul. 590:16-17.
- Srivastava, S.C. and S.N. Pandit. 1968. Relative role of sunn hemp for tops and
roots in contributing to the green-manuring benefits of sugarcane. Indian J.
Agr. Sci. 38:338-342.
- Streets, R.B. and H.E. Bloss. 1973. Phymatotrichum root rot. Monogr. 8. The
American Phytopathological Society, St. Paul, MN.
- White, G.A. and J.R. Haun. 1965. Growing Crotalaria juncea, a
multi-purpose fiber legume, for paper pulp. Econ. Bot. 19:175-183.
- Whiteside, J.O. 1955. Stem break (Colletotrichum curvatum) of sunn hemp
in southern Rhodesia. Rhodesian Agr. J. 52:417-425.
- Zhang, X.L. 1985. Toxic components of the seeds of Crotalaria juncea and
their toxicity to pigs. Chinese J. Vet. Sci. Tech. 7:13-17.
Last update June 16, 1997