Reducing Livestock Losses to Toxic Plants

B-1499 Reducing Livestock Losses to 'lbxic Plants .. Perennial Broomweed Texas Agricultural Extension Service•Zer!e L. Carpenter, Director• The Texas A&M University System• College Station, Texas TableofContents Diagnosis............. ............................... 3 GrazingManagement................................... 3 SupplementalFeeding.................................. 4 Plant Control..... .............................. 6 BehaviorModification.................................. 7 Management TechniquesToxicforReducingPlant Losses... 8 LiteratureCited........................................ 9 Poisonous Plants of...Texas............................10 Editor: Judy ExtensionWinn, CommunicationsSpecialist TheTexasA&MUniversitySystem. Cover design byRhondaKappler, ExtensionCommercial Artist Reducing Livestock Losses to Toxic Plants Allan McGinty and Rick Machen* More than 100 species of toxic plants in- whether the cause is plant poisoning or in- fest Texas rangelands. These plants affect fectious disease. To do so it is necessary to ranch businesses directly by causing live- carefully observe symptoms exhibited by af- stock death. They also have such indirect ef- fected animals and to have a thorough fects as lower conception rates and weaning knowledge of plants native to the area. weights, increased supplemental feeding Assuming a poisonous plant is respon- costs and reduced production of desirable sible, the next step is to identify the plant. range forage. One toxic plant, perennial Again, symptoms are important when nar- broomweed, is estimated to cause more than rowing the suspected plant to one or a few $30 million in indirect and direct losses per species. It is also helpful to observe whether year in Texas (McGinty and Welch, 1987). any toxic plant species within the pasture have been grazed. Finally, the rumen of a Diagnosis dead animal can be opened and a sample ob- tained of the ingested forage. Careful examination of the rumen contents can assist Some toxic plants produce easily identifi- in identifying the toxic plant responsible. able symptoms. For example, sacahuista causes photosensitization (hyper-reaction to If death has been recent, a post-mortem sunlight), which results in obvious inflam- examination may reveal clues to the cause. mation, swelling and sloughing of the skin. For example, threadleaf groundsel poisoning But accurate diagnosis of poisonous plant produces a hard, yellow liver, while nitrate problems can be difficult. Chronic poisoning poisoning is often identified by chocolate- from perennial broomweed usually causes brown colored blood present for 2 to 4 hours abortion, which may be mistakenly blamed after death. If a layman attempts to perform on improper management practices or dis- the autopsy, he should take adequate ease. Many cases of livestock poisoning are sanitary precautions to prevent self-infec- misdiagnosed and millions of dollars tion in the event the animal died from infec- wasted with improper treatment. tious disease. The time frame over which symptoms Correct diagnosis of a poisonous plant occur adds to the difficulty of diagnosis. death is often a difficult, time-consuming Plants which produce toxic amounts of prus- process. Assistance is available from local sic acid (i.e., sorghum species) can kill veterinarians, the Texas Agricultural Exten- animals within 15 minutes. On the other sion Service, the Soil Conservation Service hand, threadleaf groundsel may not produce or the Texas Veterinary Diagnostic clinical signs or death for 9 to 12 months Laboratory. after consumption. When a sick or dead animal is found, the Grazing Management first step in diagnosis is to determine *Extension range specialist and Extension livestock- Animals grazing rangelands are often ex- specialist, The Texas A&M University System. posed to a wide variety of potentially 3 poisonous plants. Because of this, re- sible to increase livestock numbers within a searchers and ranchers have long recog- problem pasture to a point at which in- nized that grazing management, “the dividual animals cannot obtain a toxic quan- manipulation of livestock to obtain a desired tity of a poisonous plant (Ralphs and result,”can be important in reducing animal Sharps, 1988). Also, if intensive grazing sys- roses to toxic plants. This manipulation of tems use a large number of pastures, it is livestock involves decisions about the stock- easier to avoid pastures with known his- ingrate and grazing system used and the tories of poisonous plant problems during species of livestock grazed. critical times of the year. Rotation timing is critical in intensive Stocking Rate grazing systems because livestock density usually greatly exceeds the annual carrying A rancher’s most important management capacity of individual pastures. If livestock decision is the maintenance of appropriate are left too long in a pasture they will con- “...grazing manage- livestock stocking rates, which involves both sume all desirable forage and are then more ment...can be im- he initial setting of rates and subsequent likely to consume the normally unpalatable portant in reducing seasonal adjustments. Stocking rate toxic plants. Depending on the intensity of animal losses to decisions affect not only individual animal the system, this series of events may occur in toxic plants.” performance (i. e., weaning weights and con- only a matter of days. ception rates) but also livestock consump- The type of grazing system used is not as tion of toxic plants. important as adhering to the principles of When stocking rates are excessive, range good grazing management. Years of re- condition declines. The production and search have shown that regardless of the diversity of desirable plants is suppressed grazing system used, excessive stocking while toxic plants become more numerous. rates cause range condition to deteriorate As a result, the probability that livestock and toxic plants to proliferate will consume toxic plants increases. Livestock Species Grazed Grazing Systems Livestock species differ in both their graz- Because livestock are selective grazers, ing behavior and susceptibility to toxic they often excessively graze the plants they plants. These differences can be managed to prefer. Over time these preferred plants may reduce toxic plant losses. For example, re- decline or disappear from the range. Graz- searchers at the Sonora Experiment Station ing systems which allow rangeland to rest have proved that there are fewer livestock periodically promote the regrowth of losses to western bitterweed when a combina- preferred plants and reduce poisonous plant tion of cattle, sheep and goats is grazed than problems. Research conducted at the Sonora when a single species is grazed (Merrill and Experiment Station compared toxic plant Schuster, 1978). A second example is Woolly deaths in the Merrill three-herd, four-pas- paperflower, a palatable plant in the Trans- ture deferred rotation grazing system with Pecos region of Texas that is toxic to sheep those under continuous grazing. The Merrill but not to cattle. Because of this difference in system reduced livestock losses to bitterweed, susceptibility, cattle can be grazed ahead of oaks and sacahuista over a 20-year period sheep to reduce the quantity of woolly (Taylor, 1990). paperflower available for sheep consumption. Intensive grazing systems (in which individual pastures are grazed intensively for Supplemental Feeding short, infrequent periods) provide flexibility in livestock movement that can reduce toxic plant problems. For example, it maybe pos- Deficiencies in protein, energy, minerals or vitamins may increase the probability 4 that livestock will ingest toxic plants. These also green and relatively high in protein deficiencies can be corrected with sup- during wet winters and may be preferred by plemental feeding programs. livestock. Therefore, supplementation must correct any protein deficiencies in order to When to Supplement? minimize toxic plant consumption. Results of Experiment Station studies indicate that Generally, supplemental feeding is most the form of the protein supplement is also important during the winter and early important. To reduce toxic plant consump- spring when forage quality is fair to poor tion, natural proteins (such as oilseed meals) and most livestock have their highest should be used. Nonprotein nitrogen supple nutrient requirements (last one-third of ges- ments (urea) may aggravate rather than al- tation and lactation). Livestock body condi- leviate toxic plant problems. tion and forage testing can help define Vitamin A deficiency may also increase nutrient-deficient periods. consumption of toxic plants. Vitamin A can be stored by the grazing animal for up to 90 With What to Supplement? days. If no green forage is available for that length of time, it is generally recommended Minerals must receive high priority in any that Vitamin Abe supplemented. supplementation program. For example, phosphorous is considered the most limiting How Much to Supplement? nutrient in most Texas forages. In fact, when rainfall is below normal, forage phosphorus The quantity of supplement to provide is content may never meet basic livestock perhaps the most difficult decision. If too maintenance requirements. Phosphorous much supplement is provided profitability deficiency causes abnormal grazing be- suffers. If not enough is provided individual haviors or cravings, which make livestock animal performance suffers. The correct much more likely to consume normally un- amount

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