Division of Agricultural Sciences J* I "V- * UNIVERSITY OF CALIFORNIA c t ,r>;«\<.! by J. M. TUCKER • D. R. CORDY • L. J. BERRY • W. A. HARVEY • T. C. FULLER if Ml W ■~.:, X NITRATE POISONING LIVESTOCK CALIFORNIA AGRICULTURAL Experiment Station Extension Service CIRCULAR 506 FIDDLENECK MILK THISTLE Nitrate accumulation in plants presents a poten- tial danger to livestock which feed on them. Vari- ous factors can affect such accumulations, and different plants are known to be capable of accu- mulating nitrates in appreciable or even lethal amounts. This circular, which brings together much data which has been widely scattered, dis- cusses these factors (pages 3, 4, and 5), lists plants known to accumulate nitrates (pages 5 through 9), and suggests approaches to the con- trol of losses from nitrate poisoning (page 9). DECEMBER, 1961 The Authors: J. M. Tucker is Associate Professor of Botany and Associate Botanist in the Experiment Station, Davis; L. J. Berry is Assistant State Director, Agricul- tural Extension, Davis; W. A. Harvey is Extension Weed Control Specialist, Agri- cultural Extension, Davis; T. C. Fuller is Botanist, Division of Plant Industry, California Department of Agriculture; D. R. Cordy is Professor of Veterinary Pa- thology and Pathologist in the Experiment Station, Davis. NITRATE POISONING IN LIVESTOCK J. M. TUCKER • D. R. CORDY * L. J. BERRY * W. A. HARVEY * T. C. FULLER What is nitrate poisoning? Nitrates, absorbed from the soil by most plants, serve as a source of nitrogen which plants convert into proteins and other nitrogen-containing compounds. Normally functioning plants usually con- tain relatively small amounts of nitrate because the nitrate is converted into other nitrogenous compounds almost as soon as it is absorbed. Under certain con- ditions, however, some plants may accu- mulate fairly high concentrations of ni- trate. While these concentrations are not toxic to the plant itself, animals feeding on such plants may sometimes suffer fatal poisoning. Nitrate itself is not very toxic, but is readily converted into nitrite. Probably most of the conversion of nitrate to ni- trite takes place in the animal digestive tract, although some field studies indi- cate that nitrite may already be present in the plants before they are eaten. Ni- trite converts the hemoglobin in red blood cells to methemoglobin, which can- not transport needed oxygen from the lungs to the body tissues. Thus, animals affected with nitrate poisoning show gen- eral symptoms of oxygen deficiency. Animals most often affected Ruminants, particularly cattle, are the principal victims of nitrate poisoning be- cause of the large amounts of plant mate- rial they eat and the action of micro- organisms in the rumen. Sheep and swine are less susceptible, and sheep and horses have been known to suffer no ill- effects from oat hay that was poisonous to cattle. However, one case of poisoning in sheep in California has come to the authors' attention (see table 1) and other cases have been reported in Wyoming. In New Zealand, a case in which 200 pigs succumbed to nitrate poisoning after eat- ing mangels (Beta vulgaris var. rapa) is on record. There appear to be few recorded cases of horses dying from nitrate poisoning under pasture or range conditions. De- spite this, it has been demonstrated ex- perimentally that horses can be fatally poisoned by nitrate and that the mode of action of the poison is the same as in cattle. Symptoms of poisoning The symptoms most frequently ob- served in nitrate poisoning are depres- sion, weakness (often appearing sud- denly), rapid pulse, and respiration which is often very noisy and labored as though the animal were in great pain. Mucous membranes become dark in color. The recumbent animal may show convulsive movements of the legs. Death is due to asphyxia and in acute cases may occur within a few hours after the plant is eaten. The animal's blood is often dark and sometimes chocolate brown. The fourth stomach and the intestine are sometimes congested due to the direct irritating action of high levels of nitrate. Cows not fatally poisoned may abort dead calves. [3] Table 1. Recent Cases of Nitrate Poisoning in California Date of NlTEATE OCCUR- Location Animals Plants involved ANALYSES AS KN0 3 ON DRY RENCE lost WEIGHT BASIS ( MAXIMUM VALUES) August, Sacramento calves (num- Rough pigweed 4.30% 1952 Co. ber not recorded) (Amaranthus retroflexus) May, 1953 Yolo Co. 9 Shorthorn heifers Milk thistle (Silybum marianum) 10.30% March, Stanislaus Co. 1 Holstein Miner's lettuce 1.97% 1954 calf {Montia perfoliata) Fiddleneck (Amsinckia sp.) Popcorn flower {Plagiobothrys sp.) 1.16% 0.87% Spring, San Bernardino 12 heifers Sudan grass "exception- 1956 Co. (Sorghum sudanense) ally high levels of nitrate" June, 1957 Yolo Co. 2 head of cattle Sudan grass (Sorghum sudanense) 2.00% November, Alameda Co. 21 head of Lamb's-quarters 8.66% 1957 cattle (Chenopodium album) February, Los Angeles 40 sheep Coast goldenbush 3.40% 1959 Co. (Haplopappus venetus) Soap plant (Chenopodium calif ornicum) California chicory (Rafinesquia calif ornica) 2.60% 4.90% September, Marin Co. 5 dairy cows Pigweed* 4.48% 1960 lost (Amaranthus sp.) 15 aborted Alfalfa* (Medicago sativa) 1.22% * These plants were in hay grown at Isleton, Sacramento County, cut in May, 1960 Factors affecting nitrate accumulation in plants Much remains to be learned about the factors responsible for the accumulation of high levels of nitrate in plants. This capacity seems to vary widely among dif- ferent species. Many familiar plants — crop plants as well as common weeds — are capable of accumulating appreciable amounts of nitrate ; evidently many other plants cannot ordinarily do so. The stage of the plant's growth is an important factor. In a study involving 25 different weed species, one investigator found that the pre-blooming period was nearly always the time of highest accumulation and that by full maturity the nitrate con- [4] centration had dropped to very low levels. This pattern was shown both by species that accumulated considerable amounts and by those that had only very small amounts at most. An ample supply of available nitrate in the soil is evidently of primary im- portance among factors in the plant's external environment which promote high nitrate accumulation. But other soil factors also have an important influence. An adequate moisture supply, for ex- ample, tends to promote soil nitrate for- mation and plant absorption of the ni- trate. Despite this fact greenhouse ex- periments with oats suggest that in plants under drought conditions nitrate accu- mulation may be higher than in well- watered plants. Other studies indicate that although drought during flowering may result in increased accumulation, plants grown continuously under dry conditions contained low nitrate concen- trations. An acid, rather than an alkaline, soil solution tends to promote nitrate absorp- tion from the soil. Sulfur deficiency, for example, has been shown to result in high nitrate accumulation. An excess of phosphate tends to retard nitrate absorp- tion. When nitrogen fertilizers are used to increase forage production in range or pasture improvement programs, ade- quate amounts of phosphorus and/or sul- fur should also be applied, if these ele- ments are deficient, to enable the plants to utilize the nitrogen. Relatively low temperatures (around 55°F.) also tend to promote nitrate ac- cumulation. At such temperatures ab- sorption of nitrate apparently is not de- creased to the same extent as is its reduction and utilization; hence, the net effect is an accumulation of nitrate. The amount of shading a plant receives during its growth can be very important with some species. Experiments with oats in- dicate that reduction in light intensity results in a considerable increase in ni- trate accumulation. Similarly, high ni- trate accumulation has frequently been recorded under short day (as compared with long day) conditions; light appar- ently is an important or even essential factor in nitrate reduction and utilization. The reduction process is evidently an en- zymatic reaction, and the activity of this particular enzyme has been shown to decrease in complete darkness, and even- tually to stop altogether. Since nitrate accumulation in danger- ous amounts may be related to many con- ditions and situations, it is not possible to predict where or when poisoning may occur. Plants involved in nitrate poisoning Cases of fatal poisoning in cattle re- sulting from eating oat hay or straw have been known for many years in the west- ern plains, both in the United States and in Canada. It was not until the late 1930's, however, that this type of poison- ing was shown to be a result of nitrate accumulated in the plant tissues. More re- cently, certain other plants have been in- volved in this type of poisoning. One of the most spectacular series of losses re- corded to date was presumably caused by a common California range weed, fiddle- neck (Amsinckia) . Reliable reports in- dicate that between 2,000 and 3,000 head of cattle were lost in the upper Salinas Valley as a result of eating this plant dur- ing the winter and spring of 1952, and field observations and laboratory tests by the California Department of Agriculture pointed to nitrate as the main killer. Other instances of nitrate poisoning in California which have come to our atten- tion in recent years are summarized in table 1. In addition to plants which have been involved in actual cases of nitrate poison- ing, many others are known to be capable of accumulating appreciable — possibly toxic — amounts of nitrate. One recent survey in Australia revealed that out of a total of 589 plants tested, 55 different species gave strong positive tests for the [5] presence of nitrate. The following list, compiled from several sources, includes plants that have been involved in cases of poisoning, and also many that have been shown to be capable of accumulating sizeable amounts of nitrate. Some of these reports are well confirmed and quantita- tive, others are based on presumptive clinical observation or equivocal chemi- cal determination. The list is offered only to indicate the wide range of plant species which are capable of nitrate ac- cumulation. All of the plants in the list occur in California, although relatively few of them have been involved in cases of livestock loss in this state. Plants Which Have Been Involved in Nitrate Poisoning or are Capable of Accumulating Appreciable Amounts of Nitrate PLANT Amaranthus blitoides A. graecizans A. retro flexus Ammi majus Amsinckia douglasiana A . intermedia Apium graveolens A vena saliva Beta vulgaris B. vulgaris var. rapa Bidens jrondosa Brassica campestris B. napobrassica B. napus B. oleracea vars. B. rapa Bromus catharticus Chenopodium album C. ambrosioides C. californicum C. murale Cirsium arvense Cleome serrulata Conium maculatum Convolvulus arvensis Cucumis sativa Cucurbita maxima Daucus carota Eleusine indica Euphorbia maculata Glycine max Gnaphalium purpureum Haplopappus venetus Helianthus annuus COMMON NAME Prostrate pigweed Tumbling pigweed Rough pigweed Bishop's weed Douglas' fiddleneck Common fiddleneck Celery Oats Sugar beet Mangel Beggar-ticks Turnip Rutabaga Rape Brocolli, Kale, Kohlrabi Turnip Rescue grass Lamb's-quarters Mexican tea Soap plant Nettle-leaf goosef oot Canada thistle Rocky Mountain bee plant Poison hemlock Wild morning-glory Cucumber Hubbard squash Carrot Goose grass Spotted spurge Soybean Purple cudweed Coast goldenbush Common sunflower FAMILY Amaranthaceae Amaranthaceae Amaranthaceae Umbelliferae Boraginaceae boraginaceae Umbelliferae Gramineae Chenopodiaceae Chenopodiaceae compositae Cruciferae Cruciferae Cruciferae Cruciferae Cruciferae Gramineae Chenopodiaceae Chenopodiaceae Chenopodiaceae Chenopodiaceae Compositae Capparidaceae Umbelliferae Convolvulaceae Cucurbitaceae cucurbitaceae Umbelliferae Gramineae euphorbiaceae Leguminosae Compositae Compositae Compositae [6] PLANT Helianthus tuberosum Hordeum vulgar e Kochia americana Lactuca sativa L. scariola Linum usitatissimum Malva parvi flora Melilotus officinalis Montia perfoliata Panicum capillare Parkinsonia aculeata Pastinaca sativa Plagiobothrys sp. Rafinesquia calif ornica Raphanus sativus Salsola kali Secale cereale Silybum marianum Solarium carolinense S. nigrum Sonchus asper S. oleraceus Sorghum halepense S. sudanense S. vulgare Thely podium lasiophyllum Tribulus terrestris Triticum aestivum Verbesina encelioides Zea mays COMMON NAME Jerusalem artichoke Barley Fireball Lettuce Prickly lettuce Flax Cheeseweed Yellow sweet clover Miner's lettuce Witch grass Horse bean Parsnip Popcorn flower California chicory Radish Russian thistle Rye Milk thistle Carolina horse nettle European black nightshade Prickly sow-thistle Common sow-thistle Johnson grass Sudan grass Sorghum California mustard Puncture vine Wheat Crownbeard Corn FAMILY compositae Gramineae Chenopodiaceae COMPOSITAE COMPOSITAE LlNACEAE Malvaceae Leguminosae portulacaceae Gramineae Leguminosae Umbelliferae Boraginaceae compositae Cruciferae Chenopodiaceae Gramineae Compositae solanaceae solanaceae Compositae Compositae Gramineae Gramineae Gramineae Cruciferae Zygophyllaceae Gramineae Compositae Gramineae Potentially dangerous nitrate accumulations In the past, plants containing more than 1.5% nitrate (expressed as potas- sium nitrate) on a dry weight basis have been considered potentially danger- ous. Recently, however, subclinical poisoning (inconspicuous ill effects) has been attributed to nitrate levels below this percentage, and any amount over 0.5% in the total ration has been con- sidered a possible source of trouble. Toxi- cologists often express the amount of nitrate present in plant tissue as if it were potassium nitrate (KN0 3 ). Agronomists and agricultural chemists usually express nitrates in terms of actual nitrogen de- rived from nitrates present in the tissue; this is referred to as nitrate nitrogen (NO3-N) . These different methods of ex- pression have led to considerable con- fusion as there may appear to be contra- diction in the amounts of nitrate re- ported, depending on the method of ex- pression used. For example, plants are considered by some investigators as po- tentially toxic if they contain nitrate [7] *** , v ,o * X [8] amounting to more than 1.5% expressed as KN0 3 on a dry weight basis. This means 15,000 ppm KN0 3 or 2078 ppm actual N (nitrate-nitrogen). Whether or not poisoning will result in the animal depends not only upon the amount of high nitrate material con- sumed, but also upon conditions in the animal's rumen which favor reduction of nitrate to nitrite. Control of losses from nitrate poisoning An early, accurate diagnosis is impera- tive. Methylene blue in sterile aqueous solution is used intravenously in treating affected animals. Preparations containing sodium nitrite should be avoided. Treat- ment must be prompt. Affected animals must not be forced to exercise and must not be excessively handled during treat- ment, as they may die from oxygen de- ficiency. A laxative should be given if it can be administered without undue stress. Certain investigators have shown that there are marked differences in nitrate accumulation between different plant species even when grown under similar conditions. The small grains, such as wheat, oats, barley and rye, and some weeds, have been found to contain several times the nitrate content found in timo- thy, certain brome grasses, orchard grass, and Ladino clover. This may indicate why only a few cases of apparent nitrate poisoning have been observed on Cali- fornia irrigated pasture and native ranges which have been regularly treated with high rates of nitrogen fertilizer. Livestock operators can reduce some of the danger of nitrate poisoning by exercising certain precautions. Forage containing a high percentage of plants known to be probable nitrate accumu- lators, or which has been treated with high amounts of nitrogen fertilizer, should not be harvested or grazed during, or immediately following, the climatic conditions mentioned previously in this leaflet. Hay having a relatively high nitrate content can be utilized if a sup- plement with high sugar content (such as molasses) is added to the ration. High nitrate forage can also be reduced to safe levels by mixing with liberal quantities of feed known to be safe. Field sampling for nitrate accumulation Occasional plants of a species may ac- cumulate toxic amounts of nitrate while only a short distance away in the same field other plants of the same species may contain mere traces. Therefore, in sampling a field to check for nitrate accumulation two points should be ob- served : 1. Ten or more individual plants or samples should be collected from all over the field, particularly from areas of luxuriant growth. 2. The plants collected should be ana- lyzed as separate samples, not as a single, composite sample. By using this method, any dangerous accumulation in plants in one part of a field will not be masked in a composite sample, which could easily happen if the other collections were quite low in nitrate. Photo 1 , Fiddleneck (Amsinckia) a native orange-flowered spring an- nual, common on rangeland and as a roadside and grain field weed in California. Fiddleneck was presumably the cause of heavy cattle losses in the upper Salinas Valley during the late winter and spring of 1952. [9] #.1 .; •:■ [10 Photo 2, Milk Thistle, Bull Thistle, or Variegated Thistle (Silybum ma- rianum). This weed, naturalized from Europe, was the cause of nitrate poisoning in cattle near Davis in 1953. The name, Milk Thistle, refers to the conspicuous white mottling of the leaves. How the University of California Works with Agriculture As one of the nation's Land-Grant institutions, the University of California plays a multiple role in service to agriculture. This involves teaching, research, and conveying the facts developed by research to those who may put them to good use in the best interest of all the people. These activities are combined in the University's Division of Agricultural Sciences. This statewide framework includes: The College of Agriculture providing instruction in agriculture and related sciences on campuses at Berkeley, Davis, Los Angeles, and Riverside. The Schools of Forestry and Veterinary Medicine function as separate professional schools within the Division but are closely related to the College of Agriculture. The Agricultural Experiment Station conducting research on the four campuses mentioned above as well as on numerous field stations, experimental areas, and farms throughout the state. Closely allied with the Experiment Station are the Giannini Foundation of Agricultural Economics and the Kearney Foundation of Soil Science. The Agricultural Extension Service with 53 offices serving 56 counties carrying out the responsi- bility of "extending" research results to the people. The Service cooperates with the Experiment Station in local research on thousands of farms. It also conducts youth educational activities through the 4-H Club program. In order that the information in our publications may be more intelligible it is some- times necessary to use trade names of products or equipment rather than complicated descriptive or chemical identifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended, nor is criticism implied of simi- lar products which are not mentioned. 12m-12,'61(C3537)V.L. How to do it . . .in photos New (and sometimes old) techniques are described and illustrated for better understanding of, at times. complicated subjects. The rule is, "If it can't be described, use a photo; if a photo won't do, draw a picture." -•* 4 Some Systems Work; Some Don't Scientists at the University of California are constantly trying new plant varie- ties, new growing techniques, new machinery, in an effort to improve the State's agriculture. Their findings are reported and, when possible, illustrated in tech- nical, semi-technical, and popular publications that are available to anyone. Perhaps the answer to your farming problem is in one or more of these pub- lications. For a catalog, write to: AGRICULTURAL PUBLICATIONS University of California • 207 University Hall Berkeley 4