It is possible to cause the development of tolerance in animals, to certain poisonous plants, by drenching them with small and increasing quantities, whilst others do not produce this phenomenon and may even cause sensitisation, or have cumulative effects.
 
 The well known fact that animals, newly introduced to farms infested with poisonous plants, are much more liable to succumb to plant poisoning than animals born and reared on such farms, is most probably partly due to an acquired tolerance developed in the course of time by repeatedly partaking of small quantities of these plants. It is fully realised that discriminate feeding, which is a characteristic of stock reared in areas infested with poisonous plants, plays a very important role in the prevention of plant poisoning in these animals. 
 Theories of tolerance and desensitisation are discussed.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Steyn, D.G.

The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.From the results of experiments conducted upon fourteen rabbits it appears that repeated ingestion of small amounts of slangkop does not induce the development of tolerance but that the plant has cumulative effects. What has been said about gifblaar (Steyn, 1934) in this repect, is also applicable to slangkop.

As the active principle of slangkop belongs to the digitalis series the above findings are not at all surprising

UPSpace at the University of Pretoria

Onders/;eLJOort J ow·nal of Veterinm·p Science and Animal I ndustry , Volmne 4, LYwnbet' 2, April, 1930. P lant Poisoning in Stock and the Development of Tolerance. By DOUvV G. STEY.K, JU:lc., Dr. Med. Vet., D.V .Sc. , Yete1·inary Research Officer, Onrlerstepoort . (Continuerl from Onderstepoort .Jour . Y<-)t . tki . <l ll d .Anim. Iml., Vol. 3, 19~14, pp . 119-124.) TRA~SVAAT, SLANGI\:OP (u- rginea Bm)cc£ lhi~E.H.). I:\" previous experiments (Steyn 18 ~~2, 19:)3 and 1904) it was founrl t hat animals cleYelop a tolerance to C h1·vsocoma tenuijoli11 Berg alld Cen ta1tTea pic1·is ]) C., whilst . .J..sc lezJia s ]Jltysocarzm Sd1lh·. anrl !Hchapetal-u m cy 11w.nun (Hoole) Engl. had r·unmlatiYe pftects. Th f' h1·o latter plants a ppearecl to inrlu ce sensitisation in ~ome animals. H is 11·e ll kno1Yu that ;;tock n•ared in ~ langkozJ m·ea,; 11<-'Yer. o.r r<l rP ly, pa rtake of the plant unle;;,; they are foree d to Llo so owing to ~carcity of edible Yegetation. On t he oth er hand, stock n <->1d5· intro-,lucerl into such <He<lS YPr.\· frequent}:~· fall Yidim s to poiso11iug " ·ith the plant. Some stocl; -o\\·np rs nwintain that ~to c k 1·eared ou slan.r;lwp Yelcl eat the plant 1Yitl1 impunity. IF this statement were true it would mean that auimals, which repeatedly pHI·ta ke of non-toxiC' amounts of the plant, cleYelop a tol eraneP to it. In order to inYe,;tigate this possibility, it was ini.enderl to conduct a n experiment on the following lines: -A . SNcn RalJlJit.s. Eal'h to l"ef ·Pi ,-e : -0·25 gm . (i.e . 1,· ," )I.L.D. ) rlry b11lb three tlinP:; wePkly for bYO Wt-'eks. 0 . ·) g rn. (i. e . ~I.L.D.) dry ,,-eel.::~. hnlb ihree times 11eekly for b1·0 0 gm . ( i .e. 1 ~J.L.D. ) lhy hnlh three ti.mes weeD)· for bYO ± week~ . fl. Seren Rabbit ". Each to r ece1Ye:-0·5 g-m. (i .e. l ~LL.D. ) dry bnlb three tim P,; 11·eeldy for two \veeks. ~ 1·0 gm. (i . (-'. 1 ~I.L ~D. ) clry bnlv three times weekl~· for two ± weeks. 417 )'1. .\~T l'!J I ~USl:\(: IS STOCh: .1.\ I J IJE\· 1-:U ll' .\lE_'\T ()1.- ruu:IL\.\( E . J -,-J g lll . (i.P. ~ M. I. . D . l rlr_, . hnlh t h l'ee limP~ IH'l' kl_,. for (IHJ \1"(-'('k~. 'l' he tulPI':I li<"P I Psi 11·a;; to lJP colll luc iPd (pn <LLyc; a ftl' J' t lw aninwl ,; h;id l'PI 'eiYPtl ( \i p L!.;t r]O~P of -''11/lij/.·o fl. li t t] Jp I'Olll':' t' of t hP t-•s perilllent it " ' ''''· h011E'YP J'. fu 11 J11 l thn t tltP aJIIJ\'P progT <IlllllH' \mel (O ])(' JllOllifiPfl. T h e foll·m· ing table t'llillOdies the rr'~ ult of thP <'); _periJJJPJl1 l'Oll-,] udf'd in orrln to ns<·f'rt:lin " ·het h Pr the.;(' animals a n·· capn lJl <• Ill' d<·I·Ploping· a tol PI'<I II C'P i.o slrmg!.·op : -Hab hit \1-ei).(ht :\0. i l l 1\:. ~. 7 .) I II I I I ll I \ ' :! · JS \ ' 1 I S \ ' II J ·!I \ ' Ill l ·S ----~--1 :\ I ·H:i .\mount of clry -.: lclll ,i!kOp bulb p-i\·cn (>er· K~. hocly -" ·eip;h t. II ·2:) gm . ()Jl li II :;:L 8 II :3:L lll ll :;:L l :l lJ :;:;. :W I I , :;:~. :!:J i lL / :;:;, "2 7 II :n. :2!! 11 ;{;{ , 2 1:2 :n + 12; ;{:J. li ' l :2 :3:L 8 12 :n. 11 12 ;{:L 1 :;; u 1 :;:;, 18; J :11 :;:;, il tl!l 20 112 / :3:; -----D itto . l!itto. IJitLo. Ditto . Dit to . i)i lto. 0 8 g n1. on dat{'~ g i\cn above First f,,fei'IIIII'P fest on '!.7 12; :;:; ( .V .B.- Only !I J li \I.L. I J. g i,·en ) :- Se ,·c· re kympto nl B of po isonill[.! thn·P hour:-i after dreu('l\ing. l~c"m·c red a fler ! \\ ' O da I''· Srrnnd tolemnce /(.,/ 011 '!.:2 1; :;+ ( .\-.B.- Only !) l l(j ~LL.Il. !.!' i,·en ): - ';am e rek nit "' on n 1:2 3:~ . , First toleranct fest 011 :l7/ lt 1 :l :3 (.I'. B.-Unl_~· 9 Hi ~[.L.I!. ,!!i,en) :- Sam e t'e"ltlt '"' in Rabbit Xo. I. .'{e!'onrl tolemnce lest on :!2 I ;q (X. B.- ( ln h-!J I](i ~ [.L l l. g i,·en ) :- Same n ·'!tlt '"' ii1 m h bil ~0. r. Tmatecl in ,;ame wa,; as mbh il,; T a nd II with . ... anH' rc:;.:.1dt. 1- 'irsl loleran!'e /e81 on 27, l:! :;:; (.V./3.- 0nly H 1lli ,\LL. i). g i\' en ) : Dil'd fifteen hour' nftf'r drcnr· hin;:r. I li ed on I:) I I :;:L hdor<' to l(•ranc·t' tc .-< ! \\·a; cond u<'tC'd. /<'irs/ tuleru!ln' test on 27/ 12/ :{:3 (A . N.- Only !l 10 ~I.L .IJ . gi,·en ) : - Di ed n honrs after dt·f'nch i ll .S!. Treated in ;ame wa,; a,; rabbit s J and II 11·ith ~amf' resul t. First tolem•u·,. lest on '27 / 1'2, ;{;3 (A . .b'.- Only !I lli \LL. IJ. gi,·en) :- nicrl + days after drcn"h ing. Ditto. T reatecl in same way as mbhit ,; J and Jl wit It Ditto . same t•esu lt. Treated in sa me way a' rabb its I an 11 with san1e rc .s ul t. 41~ 'l'AnLE.-'l'oLERANCE ExPERB-J ENT-SLAKGKOl'. (Continued.) Amount of dry slangkop bulb given per Kg. body-weight. .Rabbit I Weight No. l m Kg. I ~--------------xi 2 ·+ Ditto. XII 1·8 Ditto. RPsult. First tolerance test on 27/ 12/33 (N.B.-Only 9/16 .i\I.L.D. given) :-Died three clays after drenching. Died at 4 p.m. on l+j l2; :33, before tolerance test was conducted. Ditto. Died on 1 !J; 11 1 :3:3 from purulent plcur·iti> XL\' 2 0 and pneumonia.. 1---------Ditto. Pirst tolerance test on 271 I :2_ 33 (S .B.- Only ----9/ LG :ll.L.D. given) :- Developed sever(' symptoms of poisoning but recovered after 3 clays . Second tolemnce test on 2:2; 1/ 3+ (1\'.B.- Oni,Y 9/16 2\f.L.D. given) :- lliecl about fifteen hours after drench ing. 'l'he slrmyl.:op bulbs, 11·hieb \\·e1·e colleeted in thP 1·iciuity of Hamanshaal, l'retOl'ia District. 11·ere in the post-firl\\'eriHg stage. ~o leaves were present. The bulhs were slir:ecl, rhiell in t h P sun, anrl gTmllld to a fine po,nler, \Yhich '"a~ Yigol'Ousl~· shakr•n in a closed ,·essel in onler to af'hiPW au Pqually cli,;tribn1.ed toxicity. In a rl uplicated expe riment in which twelve rahhit~ were employed the )LL.D. of this llowcler per Kg . rabbit \Yas found to he -±·0 g-m. All the J'abbits in the tolerance experiment exllibitetl ,;light sylll rtomi'i of poisoning (loss of appetite, slig-hi pm·esis, apath~· , accele1·aterl heart-beat and respin1tion) after they had receiYed the first four rlo,;e.-;. Consequently rlrenchi ng was rli .~('Oll ti nued for !'eYen clays. In the .aboYe table the follo"·ing- poi11t,; are noteworthy:-.LL l~ahbit \~ rlierl "·ith symptom~ of s/((.nqlwtJ poisoni11g- aHPl' it had received a total of 1·0 g'lll. slongl.·op ( = <llJpl'Oximately J f ll )LL .D.) in four closeR iu ihe com·,;e d ~eYell days. The post-moriem nppr>m·ance;; resr>mblr>rl those ser>n in slanykop poisonitlg' iu rabbits. This animal npparentl.1· po~c;esc;ed <l hi g hly cleYc>loperl irliosy nnas.\· fOl' t h e plant or hacl become i:Wtt Rit iserl. H. \Yhen th e tolerance test wns r·mHlnf'tecl i he amount of 1101nlered bulb ihat harl to he adminifderecl was too large for oue dofle. Accorcling-ly the total dose for Pach rabhit, which anloUJJted to H )LL.D., was diviclerl i11 two PCJUHl parts 11·hif'h \YerP to 1w aclministered <tt. au inh>rval of four hours. A~ thrr>P houn; aftpr ::~dmini1-dration of the fint dose ( = " / ,(; )LL.D. ) all animnb rlewlopc>d symptoms of poisoning the remaining half of tlw ~LL.D. IYas not given. Rabbits IY, VI, VIII and XI fm cr·umberl to the effeds of "/ 16 )l.L.J)., "·hilst the remaining ::~nimals (I, II, III, Yli, IX, X and XIY J l'ecoverecl after having exhibited severe s.nnptoms of poisonillg. Twenty-six · days after this tolerance test the :';eYen animals , which had recoYered, again received ", ,6 :M:.L.D. sla11.r;lwp with the result that No. XIV clied, whilst the remaining six recowred a few days after having shO\nJ seYere s.nnptomR of poi~oning. PL.IST I'UI S0-:\1.:\<; LS ST OCJ\ .\Sl> ))EY El.Ol')H:: q• OF T OJ.E I/..1:'\'l'E. F1·um thP <th oY e J·e,; nlt :< it i ~ UlJl>aren t t h at t b"' ;tdiYe priuci.ple of sla llqkop lw ~ a t e nfl enc.1· to an·unmlal t> 1n the b od.1· . It i~a lso p o . ..; :-; il>le thn t in ;ultlitiou to ha Yin .~· G t·unnJlatiYe pfte d r f' l> ente(l do~E'~ uf uon-toxi\' amo tutt~ of slan u i•"Ji ('<lli SP progre:;"i.Ye da mag e i n t hP hen rt (<tntlposs ihl_,. i11 i hP c Pnil·;~l ne n on ,; sy:;tem ) thu ,; J·e n<l t>Ting· ilw ;tnim a l more sn . .;(' pptihlt• to th e poison. S Y:IlPT<LIJ S o r S LI-' G I\or P o i S O-:\ t sG 1s H .IHlllTS. TlH' fired ll i,.;c pJ·nible s.\·Jnp tom s in ca,.;p,; of ~I('UtP ]tOi :iOIJ i ng a rP rP stl P~s np ,.;~, <H TP h·ra te cl l'Pspira h on aud a sl owP d lmt fo r ceful ltPart-h t> ;t t. Tlt esP ;1 I'P so oil f n llmYe rl h)· eli n n •si s, a pa t h,1·, pal' E' :-l is a 1Jl1 l~<ll' n l_,..;is . At this .~tagP lhP aniJJlal s lie on Htei1· si cl e.-.: u ua hle t'< J moYe, t he h ead-h t>.a t b ein g ex trem el y a ccel e1·a iP cl <lllU 11·ea k , an (l t he r espira-tio lt lfl hom·e rl. ln muny case:s <1ianhoea is p resen t . T> t>at h m;t y ocnn \Yit h l'OllYl tbion s . Jn l p,.; -; acute c;bes , for exa mple in t h e l' :t,;p of r ah b iL \· . Ylil , Xl and XII, ih e ani mal~ <lie Sll(lrlenl.l·, appa reutl,1 · hom h eart failur e , withont h aYing exhihiterl a ll~ · s trik in g- sym pioms. 01' th e_1· JIW ,. rPm a i 11 in G paral y tir ;-;l'ntt> fm· rla.1·s 1wtore n>r·oYP r~- ,; p h; i n or rl e ;;t h r>r· c- 11 r s . Pos T-)IOHTDl APPLITuscF s . l'rr-ucute und lll'llt e r·a.,cs .- l'ro noun•· Prl rli.ln iation of lwth heart Yen b ·i.clt> ,.; ; pronouiH'ecl h:qJen1 emia of, and haemorrh<li-('P1i iu. g-asho-in te;;;tiJwl muco . ;a; hqJf' ]';lE'mi n of nil p areJH' h.nnato us or g-a ns; oede m ::t o f luug,.; ( rare). Su b-a('11te cmrs .- :JLH];erl h vdr ov eri t oHeu m ;uHl h,1·rh ot l10ntx (nne) ; h,1· pPnwmi a an rl oerl e.1W1 of t h t> lung . ;; Jli 'OJlOll n (' P<1 <li.l n l a t ion of both lt eart Ye ntricles ; c;tlarrhal g-a~ho - Pn i t>ri ti . ..; . A numl wr of <'ases shO\I'Nl no sign,; of anY g-asi 1·o- in t esti n a l init ;ti io n. S L')DfA RY. l'1·o m the r e,.;ults of e:xperimeub :·onrh1 cte rl npm r fo urteen 1·abbits it appears that n >_peat ed ingestion of small amount .-; of .<frrii_IJ h!Ji <lo e,.; not in rlucP the rleYelopllJ eut of t olPntJJ<·e hu t that t he plan t 1w ..; r-1llll11-la tin pffects . \Yhat ha .~ lwPn :;aiel nbout u if/J lour (Si P\ II , }!):$4 ) iu this 1·esped, is abo app1i.r·aLle to slan .l)lcoJ! . . · A s th e GdiYe prin c iple of slrm gko p lwlon g-s io th e diuitulis .<enes tlw ahoYe fi.ncli ng~ are not at all .-.:urpri siug. S'l'EYK, D. G. (1932) . f 'ln.vsoco1n o fe/w. ifoli u Bcr·g. Poi soni ng in A.ngom goat s and t he D eYPlnpme nt of Tol e rance . lRt lt l!epf. D ir . l 'et . Sen . & .4. nim. lnd .. pp. 893-898 . S'l'EY::\ , D. G. ( 10:~ :3 ) . Plaut p o isoni11 g in sto<" k and t ire- n e,·elopment of TolPJ':l.I1Ce . On d erst epoort .TouT. r et. S ci . d:: .l n ·im. . Jnd. , V ol 1 , pp. 149-156. STEY::\ , D. 0. (1 934) . Plant p oisonin g 111 st o"k ancl t he de1·elopm e n t of toleranee . Ond e1·depoort J ou r. F rd. Sei. o 11 d .l lliJII . Ind .. Vol. :l, 1934, pp. 119-12-J . · ~20 

Plant poisoning in stock and the development of tolerance

The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.From the results of experiments conducted upon thirty-two rabbits it appears (a) that the continuous ingestion of leaves or underground stems of gifblaar does not induce the development of tolerance to this plant; and (b) that the active principle of gifblaar has cumulative effects, that is, it is inactivated in the body or excreted at a very slow rate. It is also possible that repeated small doses of the plant may cause progressive damage to organs of vital importance (heart) and that the sum total of these consecutive and progressive lesions is sufficient to cause death in spite of the fact that the active principle has been partly or completely excreted. There also was a certain amount of evidence that some animals became sensitized to the effects of the plant, unless we accept that these animals possessed an idiosyncrasy to gifblaar.mn2015mn201

Onderstepoo1·t Journal of Veterinary Science and Animal l ndu.st1·y, Volume 3, Number 1, July, 1934. Plant Poisoning in Stock and the Development of Tolerance. · By DOUW G. STEYN, B.Sc., Dr .Med.Vet., D .V .Sc., Veterinary R esearch Officer, Onderstepoort. (Continued from Onderstepo01't Jour. Vet. Sci. and Animal I nd., Vol I, 1933, pp . 149-156.) GIFBLAAlt [DichaP'etalum cymosu1n (Home) ENGT,. J In previous publications (Steyn, 1932 and 1933) it was men-tioned that animals develop a tolerance to Chrysocoma tenuifolia Berg and Centaurea piCJ·is D. C., whilst this was not the case with Asclepias physoca.1·pa Schltr. Field observations seem to indicate that gifblaar does not belong to those plants ''"hich induce the development of tolerance when eaten in non-lethal quantities over prolonged periods. In the tables given below the 1·esults of two experiments are recm·cled : -Tolemnce ExP'erinwnt.-Gvfblam· Leaves . Rabbit W gt. No. in Amount of Plan t Given per Kg. Result. ICg . 2 · 8 Body-weight. 0·05 gm. dry leaves from 24/4/33-29/4/33 1 0·1 gm. dry lea.ves from 1/5/33- 5/5/33 0 ·2 gm. dry leaves from 11/5/33-12/5/33 Total amoun t of leaves received = 3 ·36 gm. Died suddenly on 13/5/33 from gifblaar poisoning. ------------------------- -----·--------·- ·----·- --c D E 2·7 0 ·05 gm. dry leaves from 24/4/33-29/4/33 0 ·1 gm. dry leaves from 1/5/33- 5/5/33 0·2 gm. dry leaves f rom ll j5j33-12f5/33 Total amount of leaves received = 3 · 24 gm. 2 · 3 0 · 05 gm . dry leaves from 24/4/33-29/4/33 0 ·1 gm. dry leaves from 1/5/33- 3/5/33 Total amount of leaves r eceived = 1 · 38 gm. 1·9 0 ·05 gm. dry leaves from 24/4/33- 29/4/33 0· 1 gm. dry leaves from 1/5/33- 5(5/33 0·2 gm. dry leaves from 11/5/33-12(5/33 Total amount of leaves received = 2 · 3 gm. 119 Tolerance test on 18/5/33 : Received 1·0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 12 hours after having been drenched. Died suddenly on 3/5/33 from gifblaar poisoning. Tolerance test on 18/•3/33 : Received 1· 0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 10 hours after having been drenched. Tolerance test on 18/5/33 : Received 1 · 0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 6 hours after having been drenched. PLANT POISONING IN STOCK AND DEVELOPMENT OF TOLERANCE. Rabbit Wgt. No. In Kg. F 1 ·5 G 2·1 Amount of Pla.nt Given per Kg. Body-weight. Treated as D . . ...... . ................. . Total amount of leaves received = 1· 8 gm. Treated as D ......... ............. .... . Total amount of leaves received = 2 ·52 gm. Result. I Tolerance test on 18/5/33 : Received 1 ·0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 5 hours after having been drenched. Tolerance test on 18/5/33 : Received 1 ·0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 12 hours after having been drenched. ----- -----------------------------------·-------!------------------------------H 1·8 Treated as D .. . ......... . ... . ..... . .. . . Total amount of leaves received = 2 ·16 gm. I 1 · 8 Treated as ]) .......................... . Total amount of leaves received = 2 ·Hi gm. Tolerance test on 18/5/33: Received 1·0 gm. dry leaves per Kg. body-weight. Died from gifbla>.r poisoning 12 hours after having been drenched. Tolerance test on 18/5/33 : Received 1 ·0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 16 hours after having been drenched. ----- ---- --------------------------·---------1-------J 2·4 0·1 gm. dry leaves from 24/4/33- 29/4/33 0 · 2 gm. dry leaves from 1/5/33- 5/5 /33 0·4 gm. dry leaves from ll/5/33- 12/5/33 Total amount of leaves received = 5 ·56 gm. Tolerance test on 18/5/33 : Received 1·0 gm. dry leaves per Kg. body-weight. Died from gifbbar poisoning 14 hours after having been drenched. ----------I--------------------1----------------K l· 8 0 ·1 gm. dry leaves from 24/4/33-29/4/33 0·2 gm. dry leaves on 1/5/33 Total amount of leaves received = 1· 44 gm. Died suddenly on 1/5/33 from gifblaar poisoning. ----- ----- -------------------·------------1------·------------L 2 ·1 0 · 1 gm. dry leaves from 24/4/33-29/4/33 0·2 gm. dry leaves from 1/5/33- 2/5/33 Total amount of leaves r eceived = 2 ·1 gm. Died suddenly on 2/5/33 from gifblaar poisoning. ----·----1---------------------------------------------------------M 1 · 7 Treated a.R .J .......................... . Total amount of leaves received = 4 · 08 gm. Tolerance test on 18/5/33 : Received 1· 0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 8 hours after having been drenched. --------- -----------------------------------1------------------------------N 1·9 0·1 gm. dry leaves from 24/4/33-29/4/33 0·2 gm. dry leaves on l /5/33 Total amount of leaves received = 1· 52 gm. Died suddenly on l /5/33 hom gifblaa1· poisoning. ------ ----·l---------------------------------1-----------------------------0 2·1 Treated as J ........... . . . ........... . . Total amount of leaves received = 5 · 04 gm. Tolerance test on 18/5/33 : Received 1·0 gm. dry leaves per Kg. body-weight. Died from gifblaar poisoning 5 hours after having been drenched. ------ ·---- -----------------------·---------·--- -----·------------------------p 2 · 0 0 ·1 gm. dry leaves from 24/4/33-29/4/33 0 · 2 gm. dry leaves from 1/5/33- 3/5/33 Total amount of leaves received= 2·4 gm. Died suddenly on 3/5/33 from gifblaar poisoning. - --- ---1-----·-----·-------------- ------------------------Q 2·2 0 ·1 gm. dry leaves from 24/4/33-29/4/33 0·2 gm. dry leaves on 1/5/33 Total amount of leaves received = 1· 76 gm. Died suddenly on 1/5/:{3 from gifblaar poisoning. ----·----·1---------------------------------l---·--------·-----------·--------R 2 · 3 0 ·1 gm. dry leaves from 24/4/33-28/4/33 Died suddenly on 28/4/33 from gifblaar Total amount of leaves received= 1·15 gm. poisoning. 120 D. G. STEYX. The gifblaar leaves used in the above experiment were collected in a very young stage of development on the Magaliesberg, Pretoria North. The leaves ·were air-dried, and ground, and the powder thoroughly mixed before use. The M.L.D. per Kg. body-weight rabbit was found to be 0·75 gm. It was intended to administer the dry leaves as follows:-A. Nine Rabbits (A to I). 0·05 gm. (i.e. 1 / 15 M.L.D.) dry leaves per Kg. body-w·eight from 24.4.33 to 29.4.33 (inclusive). 0·1 gm. (i.e. 2/15 :NI.L.D.) dry leaves per Kg. body-weight from 1.5.33 tot 5.5.33 (inclusive). 0·2 gm . (i .e. 4/15 M.L.D.) dry leaves per Kg. body-weight from 11.5.33 to 12.5.33 (inclusive). B. Nine Rabbits (J to R). 0·1 gm. (i.e. 2/15 M.L.D.) dry leaves per Kg. body-weight from 24.4.33 to 29.4.33 (i,nclusive). 0·2 gm. (i .e. 4/15 ~LL.D.) dry l eaves per Kg. body-weight from 1.5.33 to 5.5.33 (inclusive). 0·4 gm. (i.e. 8/15 M.L.D.) dry leaves per Kg. body-weight from 11.5.33 to 12.5.33 (inclusive). 'l'his manner of dosing was adopted as previous experiments upon rabbits seemed to indicate that the plant has cumulative effects, i.e., that the active principle is inactivated or excreted very slowly. Of the nine rabbits in group A and group B two and six died respectively before the tolerance test could be applied. The remain-ing ten rabbits receivecl 1 · 0 gm. (i.e. I t M.L.D.) dry gifblaar leaves per Kg. body-weight on the sixth day after the preliminary treat-ment with small quantities of dry leaves had been discontinued. Not a single animal survived the tolerance test, thus clearly indi-cating that no decrease in susceptibility to gifblaar had oceurred in the course of the preliminary treatment. It is hardly possible that an increase in resistance had occurred but disappeared in the interval that elapsed between the time of discontinuation of the prelin1inary treatment and the application of the tolerance test. The results reeorded in the above table clearly indicate the difference in susceptibility of the different animals to gifblaar. 'l'hey also bring out the fact that the aetive principle of gifblaar is inac-tivated in, or (ancl), excreted from the body at a very slow rate. The M.L.D. of the dry leaves per Kg. body-weight of rabbit was cletermined as 0 · 75 gm., and yet we find the following noteworthy cases in the above table: (a) Rabbit C (2·3 Kg.) died suddenly after having received only 1· 38 g·m. of dry leaves in the course of ten days. This amount of leaves is less than the M.L.D. given in one dose. This could be regarded as a case of sensitization, unless we 121 PLANT POISONING IN STOCK AND DEVELOP:IIE:t\T OF TOLERANCE. accept that the animal possessed an idiosyncrasy £or gifblaar; (b) Rabbit R (2·3 Kg.) is a case similar to Rabbit C. The forruer died from gifblaar poisoning after having received 1·15 gm. of dry leaves in the course of five days. This amount of plant is much less than the !LL.D. of dry leaves administered in one dose; Rabbits K, L, N, P, and Q died after having received in the course of a numl,er of days amounts of dry leaves slightly higher than the M.L.D. given in one dose. An experiment similar to the above was conducted with the dried underground stems of gifblaar collected by Dr. A. C. Leemann (of the Division of Plant Industry, Pretoria) at Rietondale, Pretoria. Material " ·as collected at intervals of one week from the 17.7.33 when the plant was in the dormant state, to 1.9 .33 when it had produced a large number of leaves. In all, seven collections Wl're made. Each consignment of underground stems \l·ere dried and the M.L.D. per Kg. rabbit determined. Leemann oonsidered it likely that in the dormant state the underground stems of the plant con-tained precursors of the active principle of the plant and that these precursors "·hen brought into the animal body may induce the development of a tolerance to the plant. The first consignment of plant material was given t-o two rabbits, and for each further consignment two rabbits were added, so that for the seven collections fourteen rabbits were employed. In order to explain the manner of rlosing the collections are numbered 1, 2, 3, 4, 5, 6 and 7, and the rabbits A to N. Rabbits A and B received consignment 1 the first week, consignment 2 the second week, and so forth. Rabbits C and D did not receive consignment 1, but all consignments from the second collection omYards. Rabbits E and F did not receive consignments 1 and 2, but all from the third collection onwards, and so forth. Rabbits M and N therefore only received consignment 7. All the rabbits were drenched every alternate day from the time they were placed in the experiment. The initial dose, which was equivalent to one-tenth :NI.L.D. per Kg. body-weight, was slightly increased at ·weekly intervals unt il about ! M.L.D. was reached . Each rabbit was drenched for about six weeks and the tolerance test applied five days after discontinuation of the preliminary drenching experiment. In the tolerance test the animals received 2 M.L.D. of gi.fblaar leaves. The results of this experiment were identical with those described in the former experiment, namely (a) the1·e "·as no evidence of decreased susceptibility to gifblaar after preliminary <losing IYith small quantities of the underground stem; and (b) there was evidence of increased sensitivity to the plant and Yery slow inactivation, or (and), excretion of the active principle. The interesting observation was made that there was a con-tinuous decrease in the M .L.D. of the drierl underground stems per Kg. rabbit from 5·3 gm. on 1.7.33 to 50 gm. on 11.9.33. 'l'l1is phenomenon appears to indicate that the active principle is concen-trated in the underground portions of the plant while in the dormant state and that a high percentage ·of the active principle is passed into the leaves as soon as these appear. A definite opinion in regard to this phenomenon can, however, only be expressed when experiments were oonducted upon the same plant. · l22 D. G. STEYK. SuMMARY . .From the 1·esults of experiments conducted upon thirty-two rabbits it appears (a) that the continuous ingestion of leaves or underground stems of gifblaar does not induce the deYelopment of tolerance to this plant; and (b) that the active principle of gi£blaar has cumulative effects, that is, it is inactivated in the body or ex-creted at a very slow rate. It is also possible that repeated small closes o£ the plant may cause progressive damage to organs of vital importance (heart) :mel that the sum total of these consecutive :md progressive lesions is sufficient to cause death in spite o£ the fact that the active principle has been partly or completely excreted. There also was a certain amount of evidence that some animals became sensitized to the effects ·of the plant, unless >Ye accept that these animals possessed an idiosyncrasy to gifblaar. REFERENCES. STEYN, D. G. (1932). Ohrysocoma tervuifolia Berg Poisoning in Angora Goats and the Development of Tolerance. 18th Rept. Dir. Vet. Sen;. a1ut Anim. Ind. , 1932, pp. 893-898. STEYN, D. G. (1933). Plant Poisoning in Stock and the Development of Tolerance. Understepoort Jour. Vet. Sa. and ilnim. lnd. , Vol. 1, 19ail, pp. 149-156. 123 

The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. 
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.It is possible to cause the development of tolerance in animals, to certain poisonous plants, by drenching them with small and increasing quantities, whilst others do not produce this phenomenon and may even cause sensitisation, or have cumulative effects.
 
 The well known fact that animals, newly introduced to farms infested with poisonous plants, are much more liable to succumb to plant poisoning than animals born and reared on such farms, is most probably partly due to an acquired tolerance developed in the course of time by repeatedly partaking of small quantities of these plants. It is fully realised that discriminate feeding, which is a characteristic of stock reared in areas infested with poisonous plants, plays a very important role in the prevention of plant poisoning in these animals. 
 Theories of tolerance and desensitisation are discussed.mn201

https://repository.up.ac.za/bitstream/2263/54081/3/20steyn1935.pdf

Plant poisoning in stock and the development of tolerance

Abstract

Similar works

Full text

Available Versions

UPSpace at the University of Pretoria

UPSpace at the University of Pretoria

UPSpace at the University of Pretoria