Page 1010 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

942 SECTION | XIV Poisonous Plants

VetBooks.ir TABLE 65.1 Common Nitrate Accumulating Plants fertilizer, or where waste accumulations occur in holding
pens may accumulate excessive nitrates. A variety of fac-
tors that diminish plant growth or photosynthesis can
Pigweed
Amaranthus spp.
inhibit utilization of accumulating nitrates, such as dam-
Amskinckia spp. Tarweed
age to leaves by disease, wind, hail, or herbicides, as well
Ambrosia spp. Ragweed as drought, decreased sunlight, or nutritional inadequacies
Avena sativa Oats in plants (Whitehead and Moxon, 1952; Hicks and
Peterson, 1976). For example, molybdenum is a compo-
Beta vulgaris Beets
nent in enzymatic reactions of nitrate reductase in plants,
Brassica spp. Rutabaga, rape, broccoli, turnip so molybdenum deficient plants can accumulate nitrates
Chenopodium spp. Lamb’s quarters due to poorer utilization. These factors can decrease the
further processing of the nitrates into plant proteins,
Cirsium arvense Canada thistle
resulting in a build-up of potentially toxic concentrations.
Convolvulus spp. Bindweed
A major reason plants accumulate nitrates is drought.
Datura spp. Jimsonweed During periods of drought, the growth of forages and
weeds is reduced, but the roots can continue to collect
Daucus carota Wild carrot, Queen Anne’s lace
nitrate resulting in high nitrate in plant materials. This is
Eleusine indica Goose grass
particularly true of well-fertilized sorghum hybrid
Eupatorium purpureum Thoroughwort (Sorghum spp.) and millet (Pennisetum spp.) forages
Glycine max Soybean grown for temporary summer grazing and for hay produc-
tion (Clay et al., 1976). Corn, oats, sorghum, millet and a
Gnaphalium purpureum Purple cudweed
variety of weeds are well known to accumulate nitrates
Helianthus annuus Sunflower
during drought. Shortages of forage caused by a 2-year
Hordeum vulgare Barley drought in Kansas were further exacerbated by increases
of nitrate and cyanide in those forages based on analyses
Ipomoea batatas Sweet potato
of samples submitted to a diagnostic laboratory (Pickrell
Kochia spp. Firebush
et al., 1991).
Lactuca serriola Prickly lettuce Plants may accumulate nitrates during periods of
Linum spp. Flax reduced sunlight. Sunlight is needed to drive photosynthe-
sis and the energy-dependent nitrate reductase system in
Malva parviflora Small mallow
plants. Forage or weeds growing in the shade of trees
Melilotus officinalis Sweet clover may be subject to nitrate accumulation. Nitrate poisoning
Panicum capillare Panic grass is occasionally a problem in areas of the United States
where winter grazing for cattle consists of fertilized pas-
Polygonum spp. Smartweed
tures of ryegrass (Lolium multiflorum), oats (Avena spp.),
Rumex spp. Dock
turnips (Brassica rapa), or wheat (Triticum spp.). During
Salsola iberica Russian thistle extended periods of overcast weather, perhaps several
Secale cereale Rye days, the nitrate content of the forage may increase to
potentially toxic concentrations. Accumulation is more
Solanum spp. Nightshades, potato
likely when temperatures are mild, or where growth slows
Solidago spp. Goldenrods or stops but the roots continue uptake of nitrate, which is
Sorghum spp. Johnson grass, milo, sudangrass stored in the stems until there is adequate sunlight for
growth to resume. Generally, a day or two of sunlight
Stellaria media Chickweed
with temperatures above 55 F allows plant growth to con-

Tribulus terrestris Puncture vine
tinue, converting excess stored nitrate into plant protein.
Triticum sativum Wheat Within a given field or pasture, forage nitrates may
Urtica dioica Stinging nettle vary considerably, requiring multiple forage samples for
testing to achieve accurate assessment of the risk of
Verbesina encelioides Golden crownbeard
nitrate nitrite intoxication. Determining the nitrate status
Zea Mays Corn of bales of stored hay can be a challenge because only the
forage growing in a portion of a hayfield may have been
affected. Obtaining a representative sample requires using
a hollow handheld commercial tool that cuts through to
the center of the bale and recovers a core sample. At least