Review article — Oorsigartikel

Plant poisonings and mycotoxicoses of importance in horses in southern

C J Bothaa* and T W Naudéa

longer, thus promoting saprophytic ABSTRACT growth of P. leptostromiformis. A number Well-known poisonings such as ‘dunsiekte’ (seneciosis) and ‘jaagsiekte’ (crotalariosis) of horses have been poisoned after con- of horses in are briefly reviewed. Relatively unfamiliar mycotoxicoses such suming such mouldy hay (D J Schneider, as stachybotryotoxicosis and perennial rye grass staggers and potentially occurring exotic Regional Veterinary Laboratory, Stellen- intoxications such as equine nigropallidal encephalomalacia and ergot alkaloid poisoning bosch, pers. comm., 1999). Horses suffer- are also discussed. This article is aimed at informing the southern African equine practitio- ing from acute lupinosis exhibit anorexia, ner about probable poisonings that might occur locally in horses. colic, constipation, weakness and icterus. Key words: equine, horses, mycotoxicoses, plant poisoning, toxicity. Mass loss is common in chronically af- fected animals7. Botha C J, Naudé T W Plant poisonings and mycotoxicoses of importance in horses in southern Africa. Journal of the South African Veterinary Association (2002) 73(3): 91–97 (En.). Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, RESPIRATORY SYSTEM Private Bag X04, Onderstepoort, 0110 . Crotalariosis This respiratory affliction is caused INTRODUCTION disease. Horses suffering from acute mainly by Crotalaria dura and C. globifera, In general horses, being fastidious feed- seneciosis exhibit dullness, icterus, which also contain pyrrolizidine alka- ers, are not as prone as ruminants to eat- petechial and ecchymotic haemorrhages loids. Both species occur mainly in ing poisonous ; for instance, it is on the mucous membranes, colic and KwaZulu-Natal. ‘Jaagsiekte’ in horses has well-known that horses can with safety anasarca. The protracted, chronic form of been regarded as of only historical or aca- utilise gifblaar ( cymosum)- the disease, referred to as ‘dunsiekte’, is demic importance, but recently 2 out- infested camps where would suc- characterised by unthriftiness, depres- breaks in KwaZulu-Natal have been cumb. However, under conditions of feed sion (head hanging, drowsy, yawning), reported8. One outbreak was associated shortage, they may also resort to eating incoordinated gait (staggers), emaciation with the feeding of Themeda hay contami- poisonous plants. Stabled horses fed on and occasionally icterus. The nervous nated by Crotalaria dura while the other hay and concentrates, not having access involvement, which also manifests as occurred in horses that had ingested fresh to natural grazing, are particularly prone excitation, is attributed to hepatic green plants (subsequently identified as to poisoning with hay contaminated by encephalopathy. Once affected, the prog- C. globifera or C. dura) in a camp denuded toxic plants. Well-known and lesser- nosis is poor, and horses must therefore of grass by drought and fire. This chronic, known recorded poisonings of horses be prevented from eating Senecio plants progressive respiratory disease is charac- in southern Africa are briefly reviewed. either on the or in hay. A diagnosis terised by undulating fever, increased Unrecorded poisonings and as yet undiag- is confirmed by the characteristic histo- respiratory rate (polypnoea) and forced nosed, but likely to occur, exotic intoxica- pathological changes, especially in the inspiration and expiration (dyspnoea). tions are also discussed. The various con- liver7,17. The most prominent necropsy findings ditions are grouped according to the reported were: pleural effusion (hydro- organs or systems in the body that they Lupinosis thorax), severe pulmonary emphysema affect. Lupins are predominantly cultivated in and hepatisation7, 8. Clinically it may be the Western Cape Province as a green confused with horse sickness and pneu- LIVER compost and fodder crop. Phomopsis monia. Histopathological findings can aid Seneciosis leptostromiformis is a phytopathogen of in making a diagnosis. There are more than 250 Senecio species most lupin species that under favourable in South Africa of which S. latifolius and conditions grows saprophytically on the Ageratina adenophora (= Eupatorium S. retrorsus are the most important. In dead plant host (Fig. 1). The fungus adenophorum) South Africa the toxic varieties, contain- Phomopsis leptostromiformis (= Diaporthe Ageratina adenophora (crofton weed) ing pyrrolizidine alkaloids, have mainly toxica) causes lupinosis when it parasitises (Fig. 2), an alien invader of known toxic- an eastern distribution. Horses may in- various Lupinus species. The cyclic hexa- ity, has recently been implicated as the gest fresh plant material or Senecio-con- peptide, phomopsin A, the principal cause of mortality in 3 horses in taminated hay. This hepatotoxicosis toxin, is relatively stable7. (K van Laeren, Borrowdale Park Veteri- manifests as either an acute or chronic Lupinosis is a hepatotoxicosis of live- nary Hospital, Zimbabwe, pers. comm., stock, including horses, occurring in the 2000). This perennial weed is also present aDepartment of Paraclinical Sciences, Faculty of Veteri- winter rainfall area of South Africa. Some- in South Africa (Fig. 3) where in the winter nary Science, University of Pretoria, Private Bag X04, times farmers sow oats and lupins in the months it grows up to2minheight. Onderstepoort, 0110 South Africa. *Author for correspondence. E-mail: [email protected] same field. When the plants are cut and Horses are the only species affected by Received: March 2002. Accepted: May 2002. baled, the thicker lupin stems stay moist consumption of crofton weed as the plant

0038-2809 Jl S.Afr.vet.Ass. (2002) 73(3): 91–97 91 is palatable to them and they eat it readily. nased in this phase for humane reasons7. They observed mild posterior paresis and After a few weeks of grazing on the flow- At necropsy the brain may be oede- ataxia in mares grazing in a paddock ering plant, animals are observed to matous and yellowish swollen areas that seeded with Lolium perenne (perennial cough frequently. This is quickly followed fluctuate on palpation may be present. ryegrass) on a farm near Somerset West in by reduced exercise tolerance and signs of Macroscopical or microscopical examina- the Western Cape Province. The mares re- chronic emphysema. In severely affected tion of coronal sections of the fixed brain covered following removal from the animals there may be rales on auscul- will reveal focal areas of liquifactive ne- particular paddock. tation and fluid in the pleural sacs. This is crosis and haemorrhage in the subcortical followed by depression and death. On white matter of the cerebrum. Sometimes Stringhalt necropsy, marked interstitial and sub- damage to the liver may also be evident7. Odd incidents of suspected stringhalt in pleural fibrosis and frequently multiple South Africa have come to our attention. abscesses, thrombosis, and/or cavitation Cynanchum poisoning Hypochaeris radicata (hairy wild lettuce, are noticeable16. Cynanchum ellipticum (monkey rope) is a flatweed) is a cosmopolitan weed (Fig. 4) The widespread, seriously invading slender, robust climber which, although that occurs throughout South Africa and trifid weed (paraffienbos), Chromolaena mainly confined to coastal bush, also oc- resembles the common dandelion (Tara- odorata (= Eupatorium odoratum) should, curs inland in wooded valleys. Various xacum officinale), except that the flower because it is closely related to crofton glycosides (‘cynanchosides’) have been stems tend to branch. There is circum- weed, also be regarded with suspicion. isolated from the Cynanchum species7.In- stantial evidence that this plant or fungi gestion of this plant by horses results in a associated with this weed induces string- NERVOUS SYSTEM nervous syndrome. Affected horses may halt in horses in the USA, Australia and rock backwards and forwards, appear to New Zealand. This locomotory disor- Leucoencephalomalacia (LEM) suffer from laminitis and frequently lie der appears in late summer or autumn, Fusarium verticillioides (= F.moniliforme), down (M Terblanche, private practitioner, usually following a dry summer resulting is a common saprophytic cob rot fungus Port Elizabeth, pers. comm., 2001). in sparse grazing and when this weed is on maize. It has a pinkish mycelium, Typically ruminants are hypersensitive abundant in the paddocks. Although especially conspicuous where cobs are and undergo episodes of convulsions fol- axonal degeneration is present, horses damaged by insects7. The mycotoxin, lowed by protracted paresis/paralysis7. generally recover, albeit over an ex- fumonisin B1 causes LEM by altering When removed timeously from infested tended period (several months to years), sphingolipid synthesis1. Leucoence- camps animals usually recover.Treatment when removed from the particular pas- phalomalacia (LEM) is a fatal neuromyco- is symptomatic and supportive. tures1,5. toxicosis of equidae characterised by focal liquifactive necrosis of the cerebral white Annual ryegrass toxicosis (ARGT) Nigropallidal encephalomalacia 7 matter . Fumonisin B1 has also been impli- Various Lolium spp. containing bacterial Continuous consumption of Centaurea cated in the aetiology of anterior enteritis galls in their seed heads may induce solstitialis (yellow centaurea, in the USA in equines15. ARGT in livestock, including horses. referred to as yellow star thistle) (Figs 5, 6) This fungal infection of maize is espe- Rathayibacter toxicus produces coryne- and C. repens, which has purple to pink cially prevalent in wet seasons after toxins which are responsible for the neu- flowers, (Russian centaurea; Russian droughts. In South Africa, outbreaks rological signs9. In South Africa, the knapweed in the USA) induce a nervous occurred where horses had access to condition occurs mainly in the winter disorder known as equine nigropallidal mouldy cobs that remained on the land rainfall area of the Western Cape Prov- encephalomalacia (ENE) in the USA, after hand harvesting or following inges- ince. Following introduction as a pasture Argentina and Australia1,6. Both are exotic tion of infected cracked maize kernels, grass, the different Lolium species have plants introduced into the 3 Cape prov- ground maize and maize chaff. Several spread and hybridised and are now inces, where they generally grow in outbreaks in equidae have been encoun- troublesome weeds on disturbed ground, weedy paddocks or fallow fields. As far as tered especially in the maize producing in orchards, vineyards, fallow lands, next can be ascertained, this condition has not area of South Africa where animals were to roads, etc13. There is a latent period of been diagnosed in South Africa. fed on grossly contaminated material. 4–16 days before clinical signs are seen. Poisoning with Centaurea species is ap- Most maize is infected, but this is of no The signs may be precipitated by disturb- parently restricted to horses ingesting significance as gross infection is needed ing or exercising the animals, especially in large quantities of plant material over a for material to be toxic. mild cases. Hypersensitivity, muscular period. Clinical signs of toxicity appear After a latent period of a week or more twitching, locomotory disturbances (un- suddenly. Drowsiness, difficulty in eating clinical signs of LEM usually appear steady, high-stepping gait) and substan- and drinking and aimless wandering abruptly and the course of the disease is tial mortalities have been reported7,13. with the muzzle to the ground or total in- short. Clinical signs vary depending on Treatment is symptomatic and support- activity have been described. The horses the extent and siting of the lesions in ive, using sedatives such as xylazine have particular difficulty in swallowing, the cerebrum. Changes in temperament (Rompun, Bayer AH) and detomidine which is ascribed to impairment of neural (apathy, agitation, frenzy), hypersensitiv- (Domosedan, Novartis AH). activity of the 5th, 7th and 12th cranial ity, posterior weakness, locomotory dis- nerves. In the USA the common name turbances (ataxia, abnormally short steps, Perennial ryegrass staggers ‘chewing disease’ is apt. Affected horses goose-stepping gait, brushing, stum- Perennial ryegrass staggers is caused by generally die of starvation or dehydra- bling) pushing and colliding with objects lolitrems produced by the endophytic tion1,6. have been reported. Paralysis of the lips, fungus Neotyphodium (= Acremonium) Lesions are commonly found in any of tongue and deglutition muscles have lolii16,22. Only 1 suspected outbreak involv- the following 4 sites in the brain: the often been observed and icterus may be ing horses in South Africa has been re- globus pallidus and substantia nigra of present. Terminal convulsions are often ported (A van Halderen, M Denkhaus, the left and right sides (Fig. 7). The toxic seen and the horses are usually eutha- private practitioners, pers. comm., 1997). principle(s) of Centaurea species, although

92 0038-2809 Tydskr.S.Afr.vet.Ver. (2002) 73(3): 91–97 Fig. 1: Phomopsis leptostromiformis infection of lupine pods and Fig. 2: Ageratina adenophora (crofton weed) (courtesy of S Neser, seeds. Agricultural Research Council, Pretoria).

Fig. 3: Distribution of Ageratina adenophora (courtesy of L Henderson, National Botanical Institute, Pretoria).

Fig. 4: Hypochaeris radicata (hairy wild lettuce) (cour- tesy of B van Wyk, University of Pretoria).

Fig. 5: Centaurea solstitialis (yellow centaurea) (courtesy of R Fig. 6: Yellow star thistle (courtesy of R Poppenga, University of Penn- Poppenga, University of Pennsylvania). sylvania).

0038-2809 Jl S.Afr.vet.Ass. (2002) 73(3): 91–97 93 not yet identified, are believed to be grain. Hay may also be contaminated weeks are required for complete recuper- sesquiterpene lactones1,6. with Datura plant material. Recently, ation; even longer if the animal has young Datura cut, dried and baled with laminitis6. Sorghum cystitis/ataxia syndrome annual grasses, such as tef, was found to Sorghum spp. can accumulate toxic con- be as toxic as the seeds (T W Naudé, C J Stomatitis due to grass seed awns centrations of cyanogenic glycosides. Botha, R Gerber, Faculty of Veterinary Sci- The annual nuisance weed grass, Setaria Grazing especially of young, rapidly ence, Onderstepoort, and S de Kock, SA verticillata (burr bristle grass, klits setaria), growing plants for extended periods (an Jockey Club, unpubl. obs., 2000). These occurs widely in South Africa and the average of 8 weeks) may result in a weeds contain the parasympatholytic seed awns commonly get entangled in sorghum cystitis/ataxia syndrome6.In alkaloids, hyoscyamine (atropine) and the coat of pets. In an attempt to remove plants, cyanide (CN–) is present in the hyoscine (scopolamine)7, which induce the awns, dogs groom themselves by form of cyanogenic glycosides. After intestinal stasis and ileus of the gut result- mouth and the severely retro-barbed hydrolysis, the CN– is detoxified by ing in outbreaks of severe, intractable seed awns, of up to 1 cm in length, may rhodanese (sulphur transferase) to the impaction colic as the dominant sign of lodge in the buccal mucous membrane relatively safe thiocyanate (SCN–). In the intoxication in horses. and may migrate deeply into the underly- absence of sufficient sulphur donation, a ing soft tissues, causing severe irritation relatively minor detoxification pathway is Ornithogalum poisoning and possibly secondary infection. Grass followed to cyanate (OCN–) which is Ornithogalum thyrsoides (chinkerinchee seed awns may also result in painful oral neurotoxic and is suspected of causing or star of Bethlehem) is endemic to the ulcers in horses, which can be confused Nigerian nutritional ataxic neuropathy winter rainfall area of the Western Cape with some equine viral diseases (F Galey, (tropical ataxic myeloneuropathy), the Province, where it usually occurs in damp University of Wyoming, pers. comm., casava-related neurodegenerative disease places such as in marshes or near streams. 2002). of humans2,19. The plant can also occur in open veld if During 1997 a horse was hospitalised the rainfall is adequate. As chinkerinchee CARDIOVASCULAR SYSTEM at the Faculty of Veterinary Science, is a popular cultivated flower, poisoning Onderstepoort, after grazing in a Sorghum of stock often results from plants or bulbs Avocado poisoning field. The horse presented with ataxia, discarded as garden waste in the veld. Three avocado (Persea americana) races hind limb paresis and cystitis, a syndrome Dried chinkerinchee in hay or fresh in are recognised, of which the Guatemalan well described in the literature6. Loss of fodder often causes poisoning. Choles- race is potentially the most poisonous. nerve function to the hind limbs and tane glycosides have been isolated from Popular cultivars such as Hass, Fuerte and bladder was encountered, resulting in this species20. It is extremely toxic, as little Nabal are all examples of the Guatemalan inflammation of the bladder. Bladder as 8 flower heads may kill a horse! Horses race. An unidentified cardiotoxin and paralysis results in overfilling and con- exhibit anorexia, depression (drowsiness) persin (which induces a non-infectious stant leaking of urine which may, in and severe, persistent, watery diarrhoea7. mastitis and agalactia in lactating fe- mares, scald the hind limbs. Bladder in- males), are responsible for the clinical fection is a common sequel. The animals Robinia pseudoacacia poisoning syndrome11. Relatively large quantities of had a normal clinical appearance, but Robinia pseudoacacia (black locust), an plant material need to be ingested for stumbled and/or fell when exercised. introduced invader (Figs 8, 9), is a frost- poisoning to occur. Although the ripe Affected animals may be unable to back- resistant tree occurring throughout South fruit is eaten by humans, several cases of up and complete paralysis of the hind Africa. However, poisoning has to date cardiac poisoning of animals by avocado limbs may develop6. not been recorded here, although it is a , green fruit, seed or bark, have No satisfactory treatment is available. well-known syndrome abroad. Intoxica- been reported locally. Horses have also Nerve regeneration or recovery is not tion follows after grazing of young been poisoned in South Africa after complete. Horses that survive should not sprouts, or nibbling of bark by horses consuming leaves. be worked or ridden. Grazing of Sorghum tethered to trees or chewing bark off fence Signs associated with pastures for extended periods should be posts. Horses may also be exposed to such as respiratory distress, coughing, avoided. The syndrome, however, does pruned or fallen branches. The toxic prin- increased respiratory and heart rates, not develop following consumption of ciple is robin, a toxalbumin or plant lectin cardiac arrhythmias, anasarca of the ven- dry hay6. similar to ricin, and the toxic dose is rela- tral neck and brisket and cyanotic mucous tively low6. membranes have been recorded. In horses, ALIMENTARY TRACT Clinical signs may develop 1–2 h after severe oedematous swelling of the head ingestion. The following clinical signs (masseter region, eyelids, tongue) has Datura poisoning have been recorded: anorexia, stupor, also been reported. Other clinical signs in- Datura stramonium and D. ferox are the depression, weakness with posterior clude anorexia, general weakness and most important species. These intro- paralysis, laminitis, coldness of the recumbency4. An important differential duced, annual weeds occur throughout extremities, mydriasis, dyspnoea, weak, diagnosis in horses that should be ex- South Africa on disturbed soil, being irregular pulse and diarrhoea (which may cluded is ionophore poisoning. To avoid especially troublesome in cultivated contain blood)6. poisoning, horses must be prevented lands with annual crops. Horses are very Avoid using black locust tree trunks from gaining access to avocado groves or susceptible and poisoning may occur with intact bark as fence posts and pro- pruned branches. following ingestion of a concentrate con- vide adequate forage in early spring to taining Datura seed. During combine-har- prevent horses from grazing young Cardiac glycoside poisoning vesting, grain such as maize may be sprouts. For treatment, activated charcoal Plants such as Nerium oleander (olean- contaminated with Datura seeds. Having followed by a saline purgative could der) and Thevetia peruviana (yellow olean- the same specific gravity (SG) as grain, it is be administered and electrolyte fluid der) contain highly toxic cardenolides. difficult to separate Datura seeds from therapy is indicated. Several days to These exotic shrubs are popular garden

94 0038-2809 Tydskr.S.Afr.vet.Ver. (2002) 73(3): 91–97 plants and may be planted next to horse (Iewag) originating from Harrismith in from infested tall fescue in late gestation. stables or as ornamentals adjacent to the the Free State have been established all Annual grasses, such as tef, are particu- paddock. For a variety of reasons horses over South Africa. Recently an outbreak larly prone to nutsedge infestation. Dopa- may nibble on twigs of these shrubs or of typical ‘fescue foot’ (necrosis of the tail mine-receptor blockers such as domperi- even desiccated leaves and garden trim- tip and hooves) was diagnosed in Brah- done and phenothiazine tranquillisers mings may accidentally be fed to them. man cattle grazing this pasture in mid could possibly be used to alleviate the Intoxication has also been reported where winter near Standerton. The grass con- clinical signs18. horses were exposed to Eragrostis hay tained 1700–8170 ppb ergovaline (200– and lucerne contaminated with ‘tulp’(N 400 ppb is regarded as of toxicological SKIN Fourie, Onderstepoort Veterinary Insti- significance). In addition the seed was tute, pers. comm., 1996). ‘Tulp’ (Homeria ergotised, presumably by Claviceps Stachybotryotoxicosis and Moraea species) contains bufadieno- purpurea, and contained 1000 ppb of the The fungus Stachybotrys atra produces lide cardiac glycosides. Cardiac glyco- usual ergot alkaloids. As the endophyte trichothecenes. Two recent outbreaks of sides inhibit Na+/K+ATPase resulting in infection is spread through seed, chances putative stachybotryotoxicosis (tricho- transmembrane ion gradient distur- are that toxic fescue may be widespread in thecene intoxication) in horses have been bances. Animals may die peracutely from the country. (C J Botha and T W Naudé, brought to our attention. Stabled horses cardiac arrhythmia or refuse contami- unpubl. obs., 2001). in the Western Cape Province developed nated feed, tremble, exhibit signs of colic, The equine practitioner should be necrosis around the nostrils and fetlocks. become weak and develop diarrhoea. aware of this potential intoxication which Examination of the bedding in the stables Various cardiac rhythm disturbances, may result from tef contaminated with revealed that the wheat straw was colo- including atrioventricular dissociation ergotised nutsedge as the following nised by Stachybotrys atra (D J Schneider, have been reported3,7. reproductive difficulties, as listed by the Regional Veterinary Laboratory, Stellen- Oregon Tall Fescue Commission, have bosch, pers. comm., 1996). In another REPRODUCTIVE SYSTEM been attributed to fescue toxicosis. incident, horses stabled at the Bloem- • Abortions – Abortions often occur with fontein show exhibited a mucopurulent Ergot alkaloid poisoning mares grazing fescue, usually in late nasal discharge, lesions (eczema) on the Summer syndrome (= hyperthermia) gestation near the normal foaling date. muzzle and slightly swollen heads. Again in cattle is a relatively recent intoxication • Prolonged gestation – mares grazing the bedding was contaminated with the reported from the Western Cape Prov- fescue may carry a foal for 370 days or fungus (J P J Joubert, Onderstepoort ince. The outbreak in cattle was associ- more as opposed to the normal average Veterinary Institute, pers. comm., 1999). ated with the feeding of barley screenings of around 336. (broken and undersized barley and grass • Dystocia – The excessive size of foals Photosensitivity seeds) from breweries, which were born after prolonged gestation often In South Africa, secondary photosensi- heavily contaminated with ergots from causes foaling problems. tisation is a common syndrome of rumi- annual ryegrass (Lolium spp.) seed heads. • Thickened placenta – Abnormally thick nants. Although far less frequent in Claviceps purpurea (a fungus) infects the and/or tough placentas are frequently horses, the condition has been suspected seed heads of many grasses, including associated with mares grazing fescue. of occurring in southern Africa. In the annual ryegrass, and grain. A hard • Foal deaths – Foals, which are large due USA, secondary photosensitivity has been brown-black, elongated, sclerotium to the long gestation period, often die reported in horses grazing in a clover/ (ergot), which replaces the seed, contains before or during parturition. Many foal lucerne pasture parasitised by the fungus the toxic principles. In grain the sclerotia deaths result from dystocia problems. Cymodothea trifolii12. are often confused with rodent faeces14. • Retained placenta – Retained placentas In addition, primary photosensitivity More recently outbreaks on the High- can occur in mares grazing fescue. Asso- induced by Hypericum species and Ammi veld were associated with the feeding of ciated problems (i.e. uterine infection, majus (lace flower) may also occur7. maize silage or tef hay contaminated with laminitis, septicaemia) can cause infer- Cyperus esculentus (yellow nutsedge, tility. Sour grasses ‘geeluintjie’). The nut sedge, contained • Agalactia – Mares that have been graz- Schmidtia kalahariensis (Fig. 12) and to a numerous sclerotia (ergots) of the fungus ing fescue are likely to produce little or lesser extent Enneapogon cenchroides Claviceps cyperi (Fig. 10). These ergots no milk as ergot alkaloids cause a (‘suurgrasse’) secrete microscopic drop- were also brown-black in colour, but precipitous drop in prolactin. This re- lets of an irritant acid during active significantly smaller than those produced sults in starvation and weak foals. growth. The former occurs in the Kalahari by Claviceps purpurea10. Ergots contain Colostrum production, and thus the region of and , various ergot alkaloids of which ergota- transfer of antibody protection to the whereas the latter has a wide distribution. mine and ergocryptine are the most foal, may or may not be affected. Dense stands of these pioneer, annual important. • Mare mortality – Dystocia caused by grasses may occur and are usually Fescue toxicosis in horses in the USA, large foals, and complications associ- avoided by livestock during the acid another form of ergot alkaloid poisoning, ated with retained placentas, some- secretory growth stage. Preliminary in- is associated with reproductive problems times result in death of mares. vestigations revealed that unidentified in mares grazing tall fescue. Festuca elatior • Difficulty in anticipating birth – Mares organic acids can be extracted from the (= F. arundinacea) (Kentucky 31, ‘swenk- often do not exhibit the normal visual grasses and separated by paper chroma- gras’) (Fig. 11) is infected by an endophyte signs of impending birth. There may be tography. Three components (1 in a high Neotyphodium (= Acremonium) coenophia- little or no udder development, swell- concentration and 2 at much lower levels) lum that also produces ergot alkaloids, in ing of the vulva, or other signs that birth were present in S. kalahariensis and 2 at particular ergovaline18. This grass is popu- is imminent. much lower concentrations in E. cench- lar in South Africa as it is green in winter Avoid feeding screenings or contami- roides21. These grasses cause severe irrita- and thousands of hectares of a variety nated hay. Consider removing mares tion of the skin of the face and distal limbs.

0038-2809 Jl S.Afr.vet.Ass. (2002) 73(3): 91–97 95 Fig. 7: Nigropallidal encephalomalacia (courtesy of R Poppenga, University of Pennsylvania).

Fig. 8: Robinia pseudoacacia (black locust).

Fig. 9: Flowers of Robinia pseudoacacia. Fig. 10: Cyperus esculentus (yellow nutsedge, ‘geeluintjie’) con- taining a sclerotium (ergot) of the fungus Claviceps cyperi.

Fig. 11: Festuca elatior (tall fescue, swenkgras). Fig. 12: Schmidtia kalahariensis (sour grass, suurgras).

96 0038-2809 Tydskr.S.Afr.vet.Ver. (2002) 73(3): 91–97 Dermatitis, eczema and alopecia around nostics in California. In Colegate S M, Angelo, Texas, USA, 19–23 May 1997: 133 the muzzle and lower limbs can develop Dorling P R (eds) Plant-associated toxins. 13. Schneider D J 1981 First report of annual Agricultural, phytochemical and ecological ryegrass toxicity in the Republic of South in horses grazing in camps where these aspects. CAB International, Wallingford: Africa. Onderstepoort Journal of Veterinary grasses are very abundant (P Basson & R 101–106 Research 48: 251–255 Grant, State Veterinarians, Namibia, pers. 5. Galey F D, Hullinger P M, McCaskill J 1991 14. Schneider D J, Miles C O, Garthwaite I, van comm., 1990). Outbreaks of stringhalt in northern Califor- Halderen I, Wessels A, Lategan H J 1996 nia. Veterinary and Human Toxicology 33: First report of field outbreaks of ergot-alka- 176–177 loid toxicity in South Africa. Onderstepoort CONCLUSIONS 6. Hall J O, Buck W B, Côté L-M 1993 Natural Journal of Veterinary Research 63: 97–108 Although plant poisonings and myco- poisons in horses. National Animal Poison 15. Schumacher J, Mullen J, Shelby R, Lenz S, toxicoses are not as common in equines Control Center, University of Illinois Ruffin D C, Kemppainen B W 1995 An in- as in ruminants, intoxications should 7. Kellerman T S, Coetzer J A W, Naudé T W vestigation of the role of Fusarium monili- always be considered in differential diag- 1988 Plant poisonings and mycotoxicoses of forme in duodenitis/proximal jejunitis of horses Veterinary and Human Toxicology 37: noses in equines, as a number of these livestock in southern Africa (1st edn). Oxford University Press, Cape Town 39–45 poisoning syndromes occur locally. 8. Last R D, Vorster J H, Burgoyne P,Petersen 16. Seawright A A 1989 Animal health in Austra- Several plants known to induce poison- R, Thompson M 2000 Two outbreaks of cro- lia. Volume 2. Chemical and plant poisons (2nd ing abroad are present in southern Africa talaria poisoning ‘jaagsiekte’ in horses in edn). Australian Government Publishing and cognisance should be taken of them KwaZulu-Natal. Proceedings of the Biennial Service, Canberra as potential sources of poisoning. Congress of the South African Veterinary Asso- 17. Steyn D G 1934 The toxicology of plants in ciation, Durban, South Africa, 20–22 Septem- South Africa. Central News Agency, South ber 2000: 89–91 Africa ACKNOWLEDGEMENTS 9. McKay A C, Riley I T 1993 Sampling 18. Strickland J R, Oliver J W, Cross D L 1993 We thank the South African Veterinary ryegrass to assess the risk of annual rye- Fescue toxicosis and its impact on animal Foundation and the Equine Practitioners grass toxicity. Australian Veterinary Journal agriculture. Veterinary and Human Toxicology Group of the South African Veterinary 70: 241–243 35: 454–464 Association for financial contributions 10. 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