Page 1013 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Nitrate and Nitrite Toxicity Chapter | 65 945

VetBooks.ir diagnostic of poisoning (Burrows and Tyrl, 2001). In toxicoses. The potential for nitrate accumulation as well
as the factors that can predispose to nitrate accumulation
abortion and stillbirth situations, interpreting bovine fetal
in weeds and forages intended for feeding or grazing and
ocular fluid nitrate levels is more problematic because
normal concentrations may approach 20 ppm in weak or the risks this poses to ruminants, especially cattle, should
stillborn calves (Johnson et al., 1994). A content of be pointed out to farmers and ranchers. Cutter blades can
greater than 30 ppm or content greater than 20 ppm with be raised to reduce the amount of edible stalk in harvested
additional diagnostic information such as high forage forages if conditions suggest the possibility of high nitrate
nitrates may be needed to confirm nitrate abortion in the stalks and stems. Prefeeding testing of potentially
(Casteel and Evans, 2004). In an alpaca nitrate poisoning high-nitrate forages is very important, especially when
case, aqueous humor from two adults contained 25 ppm environmental conditions predispose to accumulation.
nitrate and that from the fetus contained 10 ppm Feeding cattle an energy source such as corn can increase
(McKenzie et al., 2004a). the rate of nitrite reduction by rumen flora and decrease
Clinical history may be suggestive of nitrate poison- the potential for poisoning. Other management strategies,
ing. However, identification of diagnostic concentrations such as ensiling or allowing weathering of stalks, can be
of nitrate in the ocular fluid, serum, or plasma is needed beneficial, but it is still essential to test prior to utilizing
for confirmation. Since nitrite is short lived in biologic the forage materials.
samples, nitrate analysis is much more reliable. All
sources of forages, weeds, water, feed supplements, and REFERENCES
fertilizers to which the animals had access should be
determined and sampled for nitrate analysis. Allison, M.J., Reddy, C.A., 1984. Adaptations of gastrointestinal bacteria
in response to changes in dietary oxalate and nitrate. In: Klug, M.J.,
TREATMENT Reddy, C.A. (Eds.), Current Perspectives in Microbial Ecology.
American Society for Microbiology, Washington, DC, pp. 248 256.
Care must be taken to minimize stresses to nitrate poi- Bhikane, A.U., Singh, B., 1990. Diphenylamine blue test for diagnosis of
soned animals. These animals will be clinically hypoxic experimental nitrite poisoning in crossbred calves. Indian Vet. J. 67,
and subject to sudden death. 808 812.
Bhikane, A.U., Singh, B., 1991. Diazotization test for diagnosis of exper-
Treatment is with intravenous methylene blue in a 1%
imental nitrite poisoning in cross bred cattle. Indian J. Anim. Sci.
or 2% aqueous solution at a rate of 4 15 mg/kg body wt
61, 61 62.
(Burrows, 1980). Risk of toxic effect from this treatment
Boermans, H.J., 1990. Diagnosis of nitrate toxicosis in cattle, using bio-
are low. The response to intravenous treatment of a 2% logical fluids and a rapid ion chromatographic method. Am. J. Vet.
solution of methylene blue at a dosage of 20 mL/100 kg Res. 51, 491 495.
body wt is rapid, with reversal of the clinical signs within Bruning-Fann, C.S., Kaneene, J.F., 1993. The effects of nitrate, nitrite, and
several minutes (Burrows and Tyrl, 2001). In severe N-nitroso compounds on animal health. Vet. Hum. Toxicol. 35 (3),
cases, treatment at a lower dose can be repeated. 237 253.
Methylene blue has a serum elimination half-life of about Burrows, G.E., 1980. Nitrate intoxication. J. Am. Vet. Med. Assoc. 177,
1.5 h, but some tissue accumulation has a much longer 82 83.
elimination time. Methylene blue serves as an electron Burrows, G.E., Tyrl, R.L., 2001. Toxic Plants of North America. Iowa
State University Press, Ames, IA, pp. 934 941.
carrier for an NADPH-dependent system to reduce methe-
Burrows, G.E., Horn, G.W., McNew, R.W., et al., 1987. The prophylac-
moglobin to hemoglobin. Methylene blue is most effec-
tic effect of corn supplementation on experimental nitrate intoxica-
tive in humans and ruminants (Burrows and Tyrl, 2001).
tion in cattle. J. Anim. Sci. 64, 1682 1689.
Tissues in the treated animals are stained, and the urine
Casteel, S.W., Evans, T.J., 2004. Feed associated toxicants: nitrate.
becomes dark green. Treated animals should not be sold In: Plumlee, K.H. (Ed.), Clinical Veterinary Toxicology. Mosby, St.
for slaughter for 180 days. Other dyes, such as tolonium Louis, MO, pp. 127 130.
chloride (tolonium blue), are effective in reducing methe- Clay, B.R., Edwards, W.C., Peterson, D.R., 1976. Toxic nitrate accumu-
moglobin to hemoglobin but have a narrow therapeutic lation in sorghums. Bovine. Pract. 11, 28 32.
index (Gupta et al., 1992; Cudd et al., 1996). Crawford, R.F., Kennedy, W.K., Davidson, K.L., 1966. Factors influenc-
ing the toxicity of forages that contain nitrate when fed to cattle.
Cornell. Vet. 56, 3 17.
CONCLUDING REMARKS AND FUTURE Cudd, L.A., Burrows, G.E., Clarke, C.R., 1996. Pharmacokinetics and
DIRECTIONS toxicity of tolonium chloride in sheep. Vet. Hum. Toxicol. 38,
329 332.
Safe use and storage of nitrate containing fertilizers is Geurink, J.H., Malestein, A., Kemp, A., et al., 1979. Nitrate poisoning in
essential if accidental poisoning of livestock, especially cattle. 3. The relationship between nitrate intake with hay or fresh
ruminants, is to be avoided. Use of liquid fertilizer tanks roughage and the speed of intake on the formation of methemoglo-
to deliver water to livestock is a documented hazard for bin. Neth. J. Agric. Sci. 27, 268 276.