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Research in Veterinary Science 1992, 53, 116-121

Bracken po i son ing and enzoo t i c haema tu r i a i n ca t t l e i n Ch ina

L . R . X U , Department o f Anim al and Veterinary Sciences, Guizhou Agricultural College, Guiyang,Guizhou, 550025 People's Republic o f China

A c u t e b r a c k e n p o i s o n i n g a n d e n z o o t i c h a e m a t u r i aa r e b e l i e v e d t o h a v e o c c u r r e d i n c a t t l e i n C h i n af o r a l o n g t i m e . I t i s o n l y in t h e p a s t 1 0 y e a r s ,h o w e v e r , t h a t t h e s e d i s e a s e s a s s o c i a t e d w i t h t h ec o n s u m p t i o n o f b r a c k e n f e r n s h a v e b e e n s t u d i e di n d e t a i l a n d t h i s p a p e r r e v i e w s t h e s e r e c e n t s t u d i e s .

B a s e d o n a l a rg e s c a le s u r v e y, b o t h c o n d i t i o n sw e r e f o u n d t o b e s e r i o u s p r o b l e m s w i t h a w i d eg e o g r a p h i c a l d i s t ri b u t io n , e s p e c i a l ly i n t h e m o u n -t a i n o u s r e g io n s o f s o u t h w e s t C h i n a . E p i d e m i o -l o g i c a l a n d e x p e r i m e n t a l w o r k r e v e a l e d t h a t t w os p e c i e s o f b r a c k e n f e r n s ,P t er i d i u m a q u i l i n u ma n dP t er i d i u m r e vo l u tu m , w e r e a s s o c i a t e d w i t h t h e s ed i s e a s e s , b u t t h e la t t e r s e e m s m o r e i m p o r t a n t inC h i n a .

T H E b r a ck e n f er n(Pteridium aquilinum)is a veryanc ien t p lan t and a l so one o f the mo s t success fu lweeds in the wor ld . I t i s wide ly d i s t r ibu tedth roughou t the wor ld inc lud ing China and con-t inues to sp read by ex tend ing i ts rh izomes andreleas ing i t s spores .

The tox ic ity and ca rc inogen ic i ty o f b rackenfern for l ives tock, especia l ly for ca t t le , and var iousspecies o f l abora to ry an imals, have been o f pa r-t i cu la r in te res t and resea rch has demons t ra tedt h a t c o n s u m p t i o n o f t h e p l a n t(P aquilinum)c a u s e d b o t h a c u t e b r a c k e n p o i s o ni n g a n d e n z o o -t ic haem atur i a in ca t t le (Evans and M aso n 1965,Evans 1987, Fenwick 1988) . Fur thermore , a pos-s ible r i sk to human heal th has been discussed(Evans 1987, Fenwick 1988, Evans and Galpin1990) . Cons ide rab le e ffo r t has been devo ted toisola t ing and ident i fy ing the toxic substances inbracken and na tu ra l com ponen t s o f b racken havebeen isola ted and ident i f ied as carc inogens , buto the r compounds con t r ibu t ing to the tox ic i tyand carc inogenic i ty o f brac ken are st il l und erinvest igat ion (Hiron o 1985, H opk ins 1986, Eva ns1987, Fenwick 1988).

O n t h e m a i n l a n d o f C h in a , w o r k o n b r a c k e n

toxic i ty and carc inogenic i ty s tar ted in the ear ly1960s (Chang and Fen g 1964). Bracken poisoningin cat t le was f i rs t recorded in Sichuan province ,bu t was no t invest igated ser iously unt i l the 1970s.A g roup o f work ers in Guizhou p rov ince s tud iedenzoo t ic haem atur ia of ca tt le , which is a ser ious

disease in the mo unt aino us region (Xu e t a l 1979,1983a,b , 1984a,b) and demonstra ted that twospecies of bracken ,P aqu ilinuman d P revoIutum,possessed s imi lar carc inogenic i ty. Both speciesof fe rn caused b racken po i son ing and enzoo t i chaem atur ia (Xu e t al 1983b, 1984a,b , Xu 1989b)bu t un l ike o the r a reas in the wor ld , the l a t t e rspecies seemed to be more imp or tan t in Ch ina.Th i s b r i e f r ev iew dea ls w i th s tud ies o f b rackenpo i son ing and enzoo t i c haematur i a in ca t t l e inChina.

B r a c k e n p o i s o n i n g i n c a t t l e i n C h i n a

Field disease

The toxic effect of bracken fern on cat t le hasat t rac ted the a t tent ion of veter inary sc ient is ts fornearly a cen tury, since i ts f irst description as 'veg-etable poiso ning' (P enbe rthey 1893, Stor rar 1893).In that year a drought las ted through spr ing in tosumm er in Eng land and b racken fe rn became theon ly food ava i l ab le fo r the ca t t l e . A number o fca t t l e su ffe red f rom a haemor rhag ic syndromewith high fever, which was s imi lar to anthrax.The nex t yea r, Alm ond (1894) demo ns t ra ted tha tthe haemor rhag ic syndrom e cou ld be rep roducedexper imental ly by feeding bracken and th is wasconf i rmed by Stockman (1917) . Fol lowing thesef indings, m any work ers over the world hav e inves-t igated the natura l and exper imental d isease andacu te b racken po i son ing has been repor ted f rommany countr ies including China.

I t i s cer ta in that there was a long his tory ofb racken po i son ing o f cat t le in Ch ina be fo re thef i r st r ecorded occur rence o f the d i sease was

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Bracken poisoning in cattle

repor ted by Chang and Feng (1964) in ca t t l e inS i c h u a n p r o v i n ce . T h e y r e p o r t e d f e v e r a n dhaem or rhages in a he rd o f g raz ing cows on afa rm b e long ing to S ichuan A gr icu l tu ra l Co l l ege .T h e o u t b r e a k o f t h e di se a se t o o k p l a c e a b o u t

one mo nth a f t e r the t r ans fe r o f the he rd to ab r a c k e n - i n f es t e d p a s t u r e . Tw e n t y - e i g h t o f 36cow s (78 per cent) were affected an d 19 (53 percen t ) d ied . Bracken po i son ing was d iagnosedf rom the typ ica l c l in ica l , haemato log ica l andpatho logica l fea tures . In the 1970s , a large dai ryfa rm was es t ab l i shed in Lanshan , a supposed lyi d ea l m o u n t a i n o u s a r e a o f H u n a n p r o v i nc e a n da l a rge num ber o f g rowing ca t tl e were in t roducedto the f a rm f rom Be i j ing , Shangha i and o the rb i g c it ie s. U n f o r t u n a t e l y, b r a c k e n p o i s o n i n goccur red ab ou t one mon th a f t e r they en te red thi s

region and las ted several mo nths . T hree-hund red-a n d - t w e n t y c o w s w e r e a f f e c t e d a n d 7 0 d i e d ,a l though a l l t he a ffec ted an imals had been t r ea tedby he te ro the rapy (Deng 1977) .

In G uizho u p rov ince , a ca t t le d i sease cha rac -t e r ised by feve r and b loo dy swea t ing , ca l led ' t i nyb loo d d rop d i sease ' by na t ive peop le , has occur redfor a long t ime . A n ep idemio log ica l su rvey sug-ges ted tha t th is d i sease o f unk now n ae t io logymigh t be as soc ia ted wi th b racken in take (Xu e ta l 1979, Wang e t a l 1984) . Recent ly, brackenpo i son ing occur red in a he rd o f da iry cows inZhen j i ang p rov ince and was assoc ia ted wi th ahigh incidence of abor t io ns (Z hu 1987); th is con-f i rmed an anc ien t des igna t ion o f b racken as ana b o r t i f a c i e n t ( C u l p e p e r 1 6 5 2 ) . I n G u a n g x ip r o v i n c e , a b u f f a l o w i t h h i g h f e v e r a n dhaemor rhage f rom the nose , ea r s , eyes , vu lvaand con junc t ivae , and haematur i a and b lo od c lo t sin the faeces , was diagnosed as suffer ing f rombracken poisoning (Li 1987) .

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sal ivat ion, petechia l s pots on the vis ib le m uco saeand skin , b lo od y sweat , b leeding f rom the nost r il s ,haem atur i a an d dysen te ry. Tow ards the t e rmina ls tage, o ther c l in ical s igns were seen and theseincluded pal lor of the vis ib le mu cosae , anorexia ,

c e s s a t i o n o f r u m i n a t i o n a n d h e a r t f a i l u re .L e u c o p e n i a a n d t h r o m b o c y t o p e n i a w e r e c o n s t an thaemato log ica l f ea tu res ; the re was a lmos t com-p le te d i sappearance f rom the b lood o f a l l t hewhi te b loo d ce ll com pone n t s excep t lymphocy tes .Th rom bocy tes dec reased a t f ir s t, t hen l eucopen iaoccur red as g ranu locy tes dec reased and f ina l lyd i s ap p e a re d . N u m b e r s o f l y m p h o c y t e s i nc r e as e drela t ive to granulocytes . To wa rds the f inal s tage ,e ry th rocy tes dec reased g radua l ly and som et imesan i socy tos i s was p resen t . Inc reas ed cap i l l a ryf rag i l i ty, p ro longed b leed ing t ime , inc reased

b loo d coagu la t ion t ime and de fect ive c lo t r e tr ac -t ion were found in some cases . Pos t mo r tem exam-ina t ion show ed incomple te b lood coagu la t ion andh a e m o r r h a g e s a n d o e d e m a in a lm o s t a ll t h eorgans and t i ssues o f the body. T he connec t iveand ad ipose t i ssues becam e ge la t inous and degen-e ra t ion o f l ive r, a t rop hy o f sp leen and u lce ra t ionsof the mu cosae w ere obse rved in some cases.M arked changes occur red in bone mar row; ye l lowb o n e m a r r o w b e c a m e g e l a t i n o u s a n d r e d b o n em arrow inf i l tra ted wi th fa t . His tological and cy to-l o g i c a l e x a m i n a t i o n s s h o w e d a p l a s i a o f t h ehaem atopoie t ic t i ssues , especia lly the granulocy t icand th rombocy t i c se r i e s , ind ica t ing depress ionof bone m ar row ac t iv i ty, l ead ing to b lood dy sc ra -sia.

These f indings in exper imental animals wereessen ti a lly in ag reement wi th those o f bo th f i eldand exper imen ta l cases desc r ibed by p rev iousworke rs (Evans and Evan s 1949 , Chang and Fe ng1964, Evans 1964, 1968).

Exper imental d isease

A c u t e b r a c k e n p o i s o n i n g w a s r e p r o d u c e dexper imen ta l ly in ca t t le in Guizho u , Shangx i andH un an provin ces separate ly. In 14 calves, typicala c u t e b r a c k e n p o i s o n i n g w a s p r o d u c e d i n t h r e emonths by feed ing a d ie t con ta in ing 30 to 40 gd-1 kg-1 bodyweight of f resh bracken fern , har-ves ted loca l ly f rom the mo unta ins dur ing M archto July, whi le a l l the control animals remainedcl in ical ly normal (Deng 1977, Wang e t a l 1984,Xu e t a l 1984b) . The c l in ica l man i fes ta t ionsincluded high fever (40.5 to 42.5C) , dul lness ,

E n z o o t i c h a e m a t u r i a o f c a t t l e in C h i n a

Field and experimental disease

Enzoo t i c h aem atur i a o f ca tt l e is cha rac te r i sedb y h a e m a t u r ia , u r i n a r y b l a d d e r t u m o u r s a n dh a e m o r r h a g e s i n t h e b la d d e r m u c o s a . T h e m o s tprominent c l in ical s ign is chronic in termit tenthaematur i a bu t the c l in ica l s igns va ry wi th thes tage o f the d i sease , the behav iour o f the tum ourand the p resence o r absence o f compl ica t ions .Th i s d i sease i s ve ry com mo n in ce r t a in pa r t s o fthe wo r ld and i ts occur rence has been assoc ia ted

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1 1 8 L . R .

wi th the geograph ica l d i s t r ibu t ion o f b rackenfern (P aquilinum).Enzoo t i c haematur i a o f ca t tl eusua l ly occurs in h igh land a reas w here b rackenfern is present ; whe reas i f brac ken fern is absent ,usual ly in lowland areas , the disease is absent .

Ros enberg er and Heesch en (1960) were the f ir s tto r ep roduce enzoo t i c haem atur i a exper imen ta llyin cat t le , by con t inuous feed ing o f g reen and d ryb r a c k e n . L a t e r, o t h e r w o r k e r s f ed d i f f e r e n tam ounts o f b racken fo r d i ffe ren t pe r iods o f t ime(Pamukcu e t a l 1976) and conf i rmed tha t p ro -longed feeding o f bra cke n fern (2 to 3 g d-1 kg-1bodyw eigh t , mean : 550 days ) p rod uce d a d i seasetha t was ind i s t ingu i shab le f rom the na tu ra l lyoccur r ing cases o f long t e rm po i son ing in thebracken- infes ted areas .

Ear ly in 1928 , a Japanese worker, Miyamoto ,repor ted enzo o t i c haem atur i a o f ca t t le in Ta iw anand s tud ied a l a rge num ber o f cases in na t iveca t tl e and buffa lo . The f i r s t r epor t o f enzoo t i ch a e m a t u r i a o f c at tl e o n t h e m a i n l a n d o f C h i n aw a s s u b m i t t e d b y H u n a n w o r k e r s i n 1 95 8. T h e yfound a d isease o f unk now n ae t io logy, cha rac -t e r ised by in te rmi t t en t haem atur i a and u r ina ryb ladder tumours , and f i rs t nam ed 'bov ine haema-tur ia ves ical is due to turnouts ' .

F rom the l a t e 1970s , a g roup in Guizhouprov ince as we l l a s o the r s f rom o the r p rov inces ,con t inued to s tudy the d i sease and made someprogre ss in th is subject (Xu e t a l 1979, Xu 1986).

A s u r v ey s h o w e d t h a t e n z o o t ic h a e m a t u r i a o fca t t l e in Ch ina was d i s t r ibu ted main ly sou th o ft h e Ye l l o w R i v e r a n d w a s f o c u s e d i n G u i z h o uand a d jacen t p rov inces , such as S ichuan , Hun an ,Yun nan , Guan gx i and Shangx i . Al l the endemica reas a re loca ted in the mounta inous reg ions1000 to 3000 m above sea level . In these areas ,two spec ies o f b racken occur,P aquilinum an dP revolutum. T h e f o r m e r i s f o u n d t h r o u g h o u tChina and the l a t t e r on ly occurs in a reas whereenzoo t i c haem atur i a o f ca t tl e is endemic . Th i sinteres t ing coincidence suggested thatP revolu-turn w a s t h e c a u s e o f e nz o o t ic h a e m a t u r i a o fcat t le in China (Xu 1986) .

E n z o o t i c h a e m a t u r i a w a s f o u n d t h r o u g h o u tGu izhou p rov ince , wi th an inc idence o f 18 .4 pe rcent (256 of 1390) in s laughtered cat t le (Xu e ta l 1983a,b) . In o ther provinces where enzoot ichaem atur i a o f ca t tl e was endem ic i t was d i s t ri -bu ted in h igh land a reas and the inc idence wasbe tween 0 .8 pe r cen t and 16 pe r cen t (Zhao andH u 1981, Fen g 1982, X u 1986). In som e regions

Xu

( G u a n g x i, T a i w a n a n d G u i z h o u ) w a t e r b u f f a l osuffe red f rom the d i sease and the inc idence wasbetw een 0-57 per cent and 5 .2 per c ent (X u 1986).The a ffec ted an imals were usua l ly four to 12years o ld and the re was no b reed o r sex p red is -

pos i t ion . Y oun g an imals le s s than two yea r s o ldwere no t invo lved .

Pathology

Tu m o u r s a r e r e c o g n i s e d f r e q u e n t l y i n t h eur ina ry b ladder a t pos t mor tem examina t ion .Their shape, s ize , weight , colour and n um ber areex t remely va r i ab le , depend ing on the type o ftumour, whe the r i t i s ben ign o r ma l ignan t andon i t s vascular isa t ion. The larges t one col lec tedin Guizhou we ighed 6 kg (Xu 1986) .

In a s tudy and his to logical c lass i f ica t ion of354 cases o f bov ine u r ina ry b ladde r tum ours co l -l ec ted f rom Gu izou p rov ince (X u e t al 1983a ,b ,Xu 1985, 1988, 1989a), there was, in more thanhalf (53-3 per cent , 178 of 354) o f the cases ,haem or rhage in to the tum our and , o r, the mucosaof the u r ina ry b lad der and in some cases nec rosi sand u lce ra t ion were found . In f i l tr a t ion o f theb ladder wa l l and metas tas i s were the m os t impor-t an t cha rac te r i s t i c s in ma l ignan t tumours . One-h u n d r e d - a n d - n i n e o f 2 2 4 m a l i g n a n t t u m o u r s(48.7 per cent) inf il t ra ted the subm uco sa, laminapropr ia , m uscu la tu re o r even the se rosa o f theur inary blad der and 35 (15-6 per cent) of thetu rnou t s me tas tas i sed to lymph nodes and , o r,o the r o rgans . Lympha t i c sp read was the mos tcom m on rou te o f tum our m e tas tas i s (34/35), b u thaematogenous sp read occur red . Implan ta t ionmetas tas i s to the su r faces o f o the r abd om ina lo rgans , an unusua l m e thod b y which u r ina ryb ladder tumours sp read , was a l so no ted in twoof 35 cases.

A v ar ie ty of h is to logical types were recognisedin a su rvey o f u r ina ry b ladde r tumo urs (Xu e ta l 1983a, Xu 1989a) . One-hundred-and- thi r ty of354 cases co l lec ted f rom Gu izhou dur ing the pas t10 yea rs (36-7 per ce nt) w ere epithelial , 161 (45.4per cent) w ere mesenchym al , f ive cases consis tedof two types o f neop las t i c mesenchymal t i s sueand 62 (17-5 pe r cen t ) were mixed tum ours con-s is ting of neoplas t ic epi thel ia l and m esenchy ma lt issues . Ninetee n per cen t (67 of 354) of tum our swere o f musc le o rig in and mo s t were ma l ignan tt u m o u r s , i n c l u d i n g l e i o m y o s a r c o m a ( 4 6 ) a n drhabdomyosarcoma (19) . These f ind ings were

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Bracken poisoning in cattleTA B L E 1 : H is t o g e n yof tumo urs o f the u r ina ry b ladder o f ca t t led e s c r i b e d i n t w o r e p o r t s

StudyHistogeny Pamukcu et a11976 Xu et a11989a

Epithelial tissue 49/139 130/354

(35%) (36.7%)Mes enchym al tissue 13/139 161/354(9%) (45.4%)

Mixed epithelial and 75/139 62/354mes enchym al tissue (54%) (17.5%)

Mixed mesenchymal tissue - 5/354(1-4%)

very d i ffe ren t f rom those o f Pam ukc u e t a l (1976)(Table 1) .

I t i s poss ib le tha t whereas the d i s t r ibu t ion andinc idence o f tum ours o f the u r ina ry b ladde r o fc a t t l e a r e a s s o c i a t e d w i t h t h e g e o g r a p h i c a ld i s t r ibu t ion and dens i ty o f b racken fe rn , the h i s-t o lo g i ca l t y p e o f t u m o u r s o f t h e u r i n a ry b l a d d e rm ay va ry w i th the spec ies o f b racken fe rn con-sumed . T h i s i s sugges ted by a comp ar i son o f theresu lt s o f two g roups o f workers (Tab le 1 ) whichshows tha t the h i s togeny o f tumo urs o f the u r i -na ry b ladder desc r ibed in ca t t l e consuming Paquilinum(Pam ukc u e t a11976) was d i s tinc t f romt h a t i n a n i m a l s c o n s u m i n gP revolutum (X u1989a) . H ow ever, the breeds o f ca t t le that werea ffec ted wi th b ladder tum ours in the two exper-imen t s were d i ffe ren t and th is cou ld acco un t fo rthe di fferences .

S ign i f i cance o fP revolutu m

Deduct ions f r om epidemiological survey

Unt i l now , a lmos t a l l r e sea rch on b racken tox-ic ity has focused on one spec ies o f b racken fe rn ,P aquilinum,and a causal re la t ionship w i th brack-en po i son ing and enzoo t i c haematur i a in ca t t l ehave been de f ined c lea r ly (Hi rono 1985 , Evans1986, 1987, Fenwick 1988). In Australia,P escu-lentum,a brack en fern c losely re la ted toP aquil-inure, caused the same acu te tox ic i ty syndromeas P aquil inum as d id ano the r f e rnCheilanthessieberi (McKenz ie 1978) . The ep idemio log ica lsu rvey o f b racken po i son ing a nd enzoo t i c haema-tu r i a in ca t tl e in Ch ina , sugges ted tha t a no the rspec ies o f b racken fe rn ,P revolutum, seemedmore impor tan t in ce r t a in a reas (Xu 1989b) .

B o t h P revolutuma n d P aquil inum be long tothe sam e genus,Pter id ium Scopli . The y resemblee a c h o t h e r i n s o m e a s p e c ts o f m o r p h o l o g y, b u t

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the i r geograph ica l d i s t r ibu t ions a re d i ffe ren t .P aquil inumis wide ly d is t r ibu ted in ma ny pa r t so f the wor ld , ma in ly loca ted be tw een 200 and1200 m above sea level, whereasP revolutumisl imi ted to the sou th o f Ch ina , Japan , Ind ia ,

Phi l ippines , growing between 570 and 3000 mabo ve sea level.I t was very in teres t ing that in China, enzoot ic

haem atur i a o f cat t le was foun d in a lmos t a l l t heprov inces whereP revolutum occur red and thed i sease has no t be en repor ted ou t s ide o f thesereg ions . Fur the rmore , in a reas where enzoo t i chaem atur i a is found , the d i sease usua l ly occursi n h i g h l a n d o r m o u n t a i n o u s a r e a s a t 9 5 0 t o2000 m a bov e sea level whe re condi t ions are sui t -ab le fo r the g rowth o fP revolutum (Xu 1986,1989b). Th i s f ind ing p rom pted Chinese workers

to feed th is species of brac ken fern to ca t t le andl a b o r a t o r y a n i m a l s i n a n a t t e m p t t o r e p r o d u c eenzoo t i c haema tur i a and t e s t fo r ca rc inogen ici ty.

Exper imen ta l work

Cows . H a e m a t u r i a a n d t u m o u r s o f t h e u r i n a ryb l a d d e r w e r e p r o d u c e d b y p r o l o n g e d f e e d in g o fa die t conta iningP revolutumto na t ive cow s inGuizhou (Xu e t a l 1984a) and S ichuan (Zhao e ta l 1988). Smal l am oun ts o f dr ied , pow der ed Prevolutum (3 to 5 g d -1 k g I bodyweigh t ) werefed to cow s fo r be tween two and th ree yea rs . TheP revolutumhad been ha rves ted dur ing the pe r iodM a r c h t o A u g u s t f r o m r e g i o n s w h e r e b o v i n ee n z o o t ic h a e m a t u r i a w a s e nd e m i c. Tu m o u r s a n d ,o r, haemor rhag ic l e s ions were p roduced in theur ina ry b ladder o f 13 o f 15 cows , an inc idenceof 86.7 per cent . T hese les ions were indis t inguish-ab le f rom those o f na tu ra l ly occur r ing enzoo t i chaematur i a , bo th c l in ica l ly and pa tho log ica l ly.D e p r e s s i o n o f b o n e m a r r o w f u n c t io n w a s n o t i c e din som e t reated animals (X u e t a l 1984a). I t w asdeduce d f rom these re su lt s tha tP revolutumw assimilar to P aquil inum in that i t possessed car-c inogen ic i ty fo r the b ladder and was tox ic to theb o n e m a r ro w.

Guinea pigs. H a e m a t u r i a a n d u r i n a r y b l a d d e rtum ours were p roduced in gu inea p igs by feed ingP aquil inum (Evans 1968) . In the authors ' longte rm bracken feed ing exper imen t , bo thP aquil-inure a n d P revolutuminduced neop lasms in theguinea pig ' s ur inary bladder. The incidence oftumours was inc reased wi th the dura t ion and

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amou nt o f bracken fed. In the group fed P aquil-inum the incidence of turnou ts was 9-1 per cent,28.5 per cent and 76.9 per cent during 201 to400, 401 to 600 and 601 to 769 days after thestart of admini strat ion, respectively, while in the

P revolutumgroup, tumours occurred 1000 daysafter the start o f administration , with an incidenceof 44-4 per cent (Xu et al 1983b).

Ra t s . Rats have been used comm only for testingbracken carcinogenicity. Prolonged feeding of Paquilinumproduced multiple ileal adenocarcino-mas and urinary bladder carcinomas in variousstrains of rats (Hirono 1985, Evans and Mason,1965, Evans 1968, Fenwick 1988). Small amount sof P revolutum or P aquil inum (harvested from

areas of Gu izhou province where enzootic haema-turia of cattle occurred) were fed to Wistar ratsfor 20 weeks and Sprague-Dawley rats for oneyear (Li 1986). Surviving animals were killed fornecropsy one year after the start of administra-tion; five out of seven Wistar r ats (71.4 per cent)and eight out of 10 Sprague-Dawley rats (80 percent) fed P aquil inum as well as four out of six(66.6 per cent) Wistar rat s a nd five out of 10 (50per cent) Sprague-Dawley rats fed P revolutumhad developed turnouts. Most of the tumourswere adenomas or adenocarcinomas o f the ileum

and p apilloma or transitional cell carcinomas ofthe urinary bladder. In addition to tumours, adecrease of bodyweight , depression of bone mar-row fu nction and degeneration of visceral organswas also found in both groups o f bracken-treatedanimals (Li 1986).

It ma y be deduced from these studies with ratsand those in guinea pigs, described above, thatP revo lu tum is less toxic than P aqui l inum.Consequently, the less toxic species might be morelikely to cause the chronic disease of enzootichaematuria because cattle could consume the

bracken fern for long periods without dying ofacute bracken poisoning.

Mice. An aqueous extract of the fronds of Prevo lu tum produced ocular lesions includingexophthalmos, blindness and severe haemor-rhages in the urinary bladder in mice (Y. M. Li,personal communication) but the aqueous extractgave a negative response in the Ames test withSalmonel la typhimuriumTA97, TA98, TA100 andTA102 (Hu and Li 1988).

X u

Sheep, goats and rabbits.There are no reportsfrom China t hat bracken fern can induce tumoursin sheep, goats or rabbits. Zhao et al (1988)reported that long term P revolutumfeeding togoats (30 to 50 g d -1 per an imal for 595 days)

and rabbi ts (20 g d -1 per an imal for 516 days)did not produce tumours or other significantlesions. It may be considered that goats and rab-bits and possibly sheep are more resistant tobracken carcinogens than other species.

Acknowledgements

The author is grateful to Dr I. A. Evans,University College of North Wales, Bangor; DrG. R. Fenwick, Agricultural and Fo od ResearchCouncil Institute of Food Research, Norwich;Professor I. Hirono, Fujita-Gakuen HealthUniversity, Japan; Professor Li Yingman,Lanzhou Veterinary Institute, China, forgenerously providing useful information; Dr G.A. Hall and Mr K. R. Parsons, AFRC Institutefor Animal Health, Compto n, for their valuableadvice and revising the paper and Miss S. J.Cook for typing the manuscript. He also wishesto thank his colleagues for their cooperation inthe past 10 years.

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Received June 25, 1991Accepte d February 3, 1992