Pigweed is toxic to Pigs

Pigweed is toxic to Pigs K. Wohlgemuth, G.J. Schamber, A.R. Misek, J.D. CrenshawRedroot pigweed (Amaranthus retroflexus L.) may belethal to pigs .Pigweed is a major agricultural weed throughout NorthDakota; fence rows, farm yards and empty livestock lotstend to have luxurious pigweed growth, especially duringwarm months. A distinct health proble m known as"perirenal edema" may affect hogs (2 ,3) , and sometimescattle (6), fo lloWing ingestion of sufficient quantities of theweed. The term "perirenal edema" describes the appearanceof the kidneys and tissues surrounding them inpigs victims of pigweed poisoning.CAUSE OF KIDNEY DAMAGEPerirenal edema is attributed to ingestion of excessiveamounts of redroot pigweed. In hogs, the problem is commonlyobserved during summer months. Most affe cted pigshave weighed 30 to 120 pounds and the clinical historieshave usually involved sudden access by hogs to pasture orgreen plants following a period of confinement. Clinicalsigns have appeared four to eight days after access to theweed.fluid (Fig. 1), thus the term "perirenal edema." Microscopicexamination of kidney specimens reveals extensive kidneydamage characterized by distention, degeneration andnecrosis of kidney tubules (2) . The clinical signs and grossrenal changes result from kidney damage cause by pigweedtoxin(s) .So far, no effective treatment for this condition is known;prevention is easier. Confined pigs should not be allowed toeat the weed . Interestingly, hogs raised on pasture with freeaccess to red root pigweed seldom if ever become victims ofpigweed toxicosis. This suggests that pasture-raised hogseither avoid the weed or develop reSistance to its toxic prlnciple(s).PIGWEED TOXICITY TO PIGS CONFIRMED ATNDSURain and sunshine provided favorable conditions forabundant growth of redroot pigweed in most North Dakotacounties during the summer of 1986. Previous experimentsRedroot pigweed may accumulate nitrate, but clinicallyperirenal edema bears no resemblance at all to nitratepoisoning. Somehow hogs readily ingest pigweed, evenwhen their normal diet is plentiful. The actual toxic principle(s)in the weed, although not yet identified, appears tospeCificall y damage the tubules of the kidney. Depending onhow much weed a pig ingests, the kidney damage maybecome extensive and severe and cause death from heartfailure (2).CLINICAL SIGNS AND LESIONSClinical signs are of sudden onset and appear four to eightdays after animals started to eat pigweed . Initially I affectedpigs are weak and tremble ; later th ey appear incoordinated,knuckle their pastern joints and eventually become paralyzedin their hind limbs; their attempts to walk fail as they dragtheir rear legs. Their temperature remains normal. Deathusually occurs within two days follOWing onset of clinicalsigns (3) .Postmorte m examination reveals pale-brown kidneys surroundedby abundant jelly- like light-colored material andWohlgemuth is Extension Veterinarian; Schamber is associateprofessor alld Misek is research techniCian , Veterinary Science; andCrenshaw is assistant p rofessor, A nimal & Range Science.Figure 1. Kidneys from piglets victim of pigweed toldcosis. Kidneys are pale and surrounded by abundant edema (arrows). 21

at NDSU had indicated that pigweed was not toxic tolaboratory rats (1) or rabbits (4). A simple test was conductedto determine if pigweed growing in North Dakotawas toxic to pigs .Two young pigs, weighing 8 and 12 pounds respectively,were deprived of feed for 24 hours. They were bled toassess their kidney function, penned together and offered.twice daily, freshly picked, whole redroot pigweed plants astheir only fee d . The plants, collected fro m fields near the·NDSU campus, were lush, about 18 to 24 inches taU and intheir early to mid bloom. During the first day the pigs justnibbled at the plants , but from the second through the fourthday they devoured them without hesitation; only some rootswere left. Both piglets appeared and acted nonnal until themorning of the fifth day when they appeared listless, wererecumbent and unable to stand up. They had lost 1.5 and1.3 pounds respectively. They were killed and laboratoryexaminations performed .The results of these examinations revealed markededema surrounding the kidneys of both pigs (Fig. 2); therewas severe, acute , disseminated dilation and necrosis ofkidney tubules . Analysis of blood sera taken right beforeeuthanasia revealed marked elevation of blood ureanitrogen (BUN) and creatinine levels. These results are consistentwith renal failure in pigs associated with ingestion ofredroot pigweed. Furthermore, the results of this testdemonstrated beyond doubt that ingestion of large amountsof North Dakota varieties of redroot pigweed can be lethal topigs .REFERENCES1. Harrold , R. , Animal Science Dept., NDS U. Personal com­mun ication. Figure 2. Abdominal cavity from pig victim of pigweed tox­Icosis. Kidneys are pale, swollen, and surrounded by abundantedema (arrows).2. Osweiler, G.D., et 01. 1969. "Production of Perirenal Edemain Swine with Amoronthus retrof/exus." Am. J . Vet. Res .,30(4) :557-566.3. Osweiler, G.D., et 01. 1985. "CUnical Veterinary TOXicology,"3rd Ed ., Kendall-Hunt Publishing Co.: 476-481.4. Schamber, G.J . and A.R. Misek. 1985. "Amoronthusre trofl~u~, (redroot pigweed): Inability to cause renal toxicosisIn rabbits . Am. J. Vet. Res ., 46(1):266-2675. Stuart , B.P., et 01. 1975. "Perirenal Edema and ToxicNephrosis in Cattl ,AssocIated with Ingestion of Pigweed ."JAVMA, 167(1 0) :949-950.Continued from page 8The leading re ason affecting land sellers to sell was theneed to reduce debt. Second and th ird reasons wereeconomic conditions or low commodity prices and poorreturn on investment. Lender pressure was listed as fourth ,followed by forced sale , and retirement or health or estatesettlements . Among those listing a second reason , most fre ­quently given were estate settlements , followed byeconomic conditions and the need to reduce debts.Major factors infl uenCing the 1986 farmla nd market includedlow commodity prices, poor conditions of theeconomy, availability of credit, and low return on investment.The leading second reasons Ilste d were availability ofcredit and low commodity prices.Respondent were asked to venture an estimate of howland values a year from now will comp are to current values.The majority, with 65 percent, indicated that November1987 land values will be down by 5 percent or more . Nearlya th ird said that fall 1987 land values will be about the sameas now, and less than 4 percent had the optimism to say thatla nd val ues will be higher at year end.22