Li ch khi kim sot c mycotoxin * Mathieu Cortyl, Impextraco NV, Singapore Representative Office mathieu@impextraco.com Ti liu ny cung cp bi: Le Vu Thuy Ly, Sales Representative, Business Unit Specialty Raw Materials, Diethelm & Co.,Ltd. Liaison Office, 364 Cong Hoa Str., Tan Binh Dist.,HCMC, Vietnam, Tel. 848 8125848 202, Fax. 848 8125845, Mobile: 0983 690 851, Email add. : ly.vuthuy.le@dksh.com, Web site: www.dksh.com Gii thiu Mycotoxin l sn phm chuyn ha t nm mc v n gy ng c cho ngi v ng vt. c lng trong thc t c khong 300 loi c t nm mc c hi cho ngi v ng vt . Vi s ci thin v cc phng php phn tch, trong tng lai danh sch cc loi c t nm mc s ngy cng tng. Mycotoxin l nguyn nhn gy ra bnh nhim c t nm. c tnh ca c t nm mc ph thuc vo lng n vo ca th, khong thi gian tip xc, loi, ging, tui, gii tnh, tnh trng sc khe v ngoi ra cn c 1 vi thng s khc nh mt nui, dch bnh, nhit , v.v... Nm mc l nguyn nhn chnh trong vic xut hin mycotoxin trn cy trng v nguyn liu thc n. Mycotoxin c th xut hin trc khi thu hoch (hay cn c gi l nm trn ng) hoc trong thi gian lu tr (nm trong thi gian lu tr). Mycotoxin cng xut hin trong thc n hon chnh khi khng c bo qun trong iu kin thch hp. Nm mc khng ch sn xut mycotoxin m chng cn ph hoi ma mng. T chc lng thc v nng nghip th gii (FAO) c lng rng c khong 25% cy trng trn ton th gii c cha mycotoxin. Triu chng in hnh ca heo khi nhim mt s loi c t nm mc Aflatoxins l loi c t ph bin nht v c nhiu ti nghin cu xung quanh loi c t ny. C 4 loi aflatoxin chnh trong nguyn liu thc n: Aflatoxin B1, Aflatoxin B2, Aflatoxin G1, v Aflatoxin G2. Ngy nay, ngi ta cng nhn c 4 loi nm sn xut ra c t aflatoxin. l, A. flavus, A. Parasiticus, A. nomius v A. pseudotamarii (Ito v cng s, 2001; Kurtzman v cng s, 1987; Payne, 1998). Tuy nhin, ch c A. flavus v A. Parasiticus l c thit hi v kinh t nht. Aflatoxin c sn xut trong iu kin dinh dng thch hp v mi trng thun li cho s pht trin (kh hu nhit i v cn nhit i, iu kin lu tr m t). Aflatoxin thng hin din trong cc loi ht ng cc (la mch, bp, k, yn mch, go, la min, la m), ht bng vi, u phng, cy u v u nnh. Aflatoxin xut hin trc khi thu hoch, nhng cng xut hin trong thi

gian lu tr nu cc ht ng cc khng c lu tr ng cch (Tangendjaja, 2002). Aflatoxin c bit nh hng n gan. Khi n vo 1 lng ln c th gy ung th gan, vim gan mn tnh,vng da v x gan. Tip xc vi liu thp trong 1 thi gian di th cng c th mang li 1 s ri ro. heo nhim c t aflatoxin c quan st trn cc giai on: heo theo m, heo choai, heo v bo v n heo ging. Mt vi triu chng in hnh nh l gim lng n vo, tng FCR, gim tng trng, vim gan do c t, hoi t v c th b xut huyt. Aflatoxin c th truyn t t cung ca heo ni qua heo con v lm nh hng n heo con mi sinh. Nhm trichothecenes bao gm 150 loi hp cht c cu trc tng t nhau (Grove, 1988). N c to ra t nm thuc nhm Fusarium, Trichoderma, Stachybotrys, Verticimonosporium, Cephalosporium v Myrothecium. Trichothecene chia lm 2 nhm. Nhm A trichothecenes bao gm c t T-2, c t HT-2 v Diacetoxyscirpenol (DAS). Nhm B trichothecenes l Deoxynivalenol (= DON = vomitoxin), Nivalenol (NIV), v Fusarenon X. Trichothecenes c cc loi cy sinh trng v pht trin vng kh hu m p v n ha, bi v Fusarium l mt nhm nm ln v phc tp n c kh nng thch nghi trong nhiu mi trng sng trn th gii (Summerell v cng s 2001). Fusarium c quan st theo di trn cc loi ht ng cc (la mch, bp, go, yn mch, la m) v u nnh. c t ny cng c tm thy trn mt s loi nguyn liu nh la min, khoai ty, chui, ht m tt, u phng, xoi, ht hng dng v khoai m. c t trichothecenes c th c sinh ra trong khi cn trn ng cng nh trong sut qu trnh lu tr. V d ,nhit ti u nm to ra c t DON l t 20 n 30C. Nhm nm Fusarium l mt trong nhng yu t quan trng gy bnh thit hi trn cy trng. V d nh Fusarium lm ht sn si hoc lm h hng ht, gy thit hi tt c cc loi ng cc nu iu kin kh hu c ma hoc m t trong sut qu trnh ra hoa v bt u kt qu (Abramson 1998). Trung Quc, c tnh din tch la m b h hi ln ti hn 7 triu hecta (chim 28% tng din tch), lm gim sn lng thu hoch khong 20 n 40% (Bai v Shaner 1994). c t Deoxynivalenol v T-2 trong nhm trichothecenes gy tc hi ln nht trn heo. c t T-2 (thuc type A Trichothecenes) c trong thc n vi hm lng khong 200ppm hoc t hn s lm gim hiu sut chn nui. Th nghim trn ni gi (t cung v bung trng b thng tn), cho n thc n c cha 1 n 2 ppm c t T-2. c t DON (trn bp) l nguyn nhn gy nhim c trn heo. Cc ht b nhim nm s lm heo gim tnh ngon ming nn lng n vo gim, tng trng gim, i khi heo b gim trng lng, lm tng mc nhy cm vi bnh v lm ri lon tiu ha (tiu chy). Trong trng hp xu nht l heo b nn ma (DON cn c gi l vomitoxin). chung ni , DON gy

ln ging gi trn ni, lm gim hiu sut chn nui, gy vim ng tiu ho v lm heo con theo m tiu chy cp tnh, nn t l cht cao. Zearalenone cn c gi l ZON, Zea, hay ZEN. c t ny c to ra ch yu t nm Fusarium graminearum. Loi nm ny thng thy nhng ht bp c lu tr mi trng c m cao v thc n vin. Zearalenone thng xut hin kh hu m v n i. Mi trng m t v c nhit t 18 n 30C l iu kin ti u nm pht trin. Nhit lc thu hoch rt thch hp sn sinh ra c t (Cheeke v cng s, 1985). Heo rt nhy cm vi zearalenone. ZON (khong 0.05 n 0.25 ppm trong thc n) gy nh hng ch yu trn ni r v ni hu b, gy ra hi chng ng dc: ZON tc ng n th th oestrogen gy sng m h, nm v sng , ri lon sinh sn. Trng hp cp tnh dn ti sa trc trng, m o. Trn nc, ZON gy sng tuyn v v lm thoi trin t bo tinh. Trong cc tri, c t ZON hu nh khng c quan tm n, nhng n c tc ng r rt n hiu sut sn xut v lm cho tri gim doanh thu. Trong thc n nu c t c nng 1 ppm lm cho heo b n. Zearalenone cng c tm thy trong sa c tiu ho heo con theo m, nguyn nhn gy hi chng ng dc. Chng bt chn heo s sinh nguyn nhn mt phn l do c t ZON . Ochratoxins c to ra t nm Aspergillus (v d: A. ochraceus) v mt vi loi Penicillium. c t nm mc thuc nhm ny gi l Ochratoxin A (= OTA hay OA). C cc phc hp khc trong nhm ny, nhng chng t c hn. Nm Aspergillus ochraceus (to ra c t OTA) thch hp trong iu kin kh hu nng, trong khi nm Penicillium verrucosum to ra c t OTA trong vng kh hu n i. V d A. ochraceus c tm thy Brazil, Chile, Egypt, Senegal, Tunisia, India v Indonesia. Penicillium verrucosum c quan st thy Canada, M, Chu u, v Nam M (theo ngun FAO). Trn heo, OTA gy tn thng thn. This can result in rejection of carcasses at the slaughter house. Thc ra, OTA thu ht cc protein huyt tng bao quanh no, to ra mt hp cht kh bn vng . Hp cht ny c tm thy tht heo v cc sn phm t tht. OTA cng nh hng n s sinh sn ca heo nc. N c truyn qua nhau thai, v c th nh hng n s pht trin ca bo thai. Hin tng cht hng lot heo con mi sinh i khi mt phn l do vi nhim c t OTA. Tronh nhm fumonisins, c 15 c t c tm thy trong bp, ng lu nht l Fumonisin B1 v Fumonisin B2. Fumonisins mi c tm thy gn y (thp k 80) nhng nh hng ca n c nghin cu trn nga t nhng nm 1890. Fumonisins c to ra t nm Fusarium verticillioides (syn., moniliforme) v Fusarium proliferatum. N thng xut hin ng thi vi mt s c t khc, v d nh, aflatoxins, DON v ZON. Ging nh trichothecenes, fumonisins c to ra iu kin kh hu m v n ha. Chng rt ph bin trn bp, chu v Nam M nm Fusarium ph bin trn la m v ht ng cc, v trn go

chu . V d, Fusarium ear root is the most common disease of corn in the Corn Belt in US. Nm pht trin trn cy bp c th cn st li trn phn cn li ca cy sau khi thu hoch, v s gy bnh cho ma v k tip. Cng nh vy, trn cc loi ht thng khng thy cc du hiu nhim nm, nhng thc ra c n hn 50% ht b h hi. Bi v tnh trng trn, ta phi c nhng nghin cu r rng hn v c t Fumonisin khi so snh vi cc c t khc. But it is also true that they are often present in much greater quantities in the commodities. Trn heo, triu chng chnh khi nhim Fumonisin B1 c gi l PPE (sng phi trn heo) n gy nh hng n tim v phi. mc thp hn, ngi ta quan st thy gan v ty b h hi, as well as immunosuppression. Hiu sut chn nui cng b nh hng: gim tng trng (trn 2 ppm), gim FCR, v gim hiu sut chn nui. c t ny lm gim hiu sut chn nui (tht m, phi v gan b h hi). S nh hng ca c t trn s min dch ca heo Chng ti khng lp li cc c ch tc ng sinh ha ca c t ln h thng min dch ca heo (cc bn c th tham kho ti liu ca hi ng khoa hc v k thut nng nghip xut bn nm 2003), nhng trng tm ca vn l hiu qu kinh t trn n heo. C 2 hng quan st: tc ng ca c t nm ln vi khun gy bnh, v tc ng ca chng n hiu qu ca vaccin. T cui nhng nm 70, ngi ta sm xc nh c t khng c nh hng n sc khng ca vi khun gy bnh. Theo bo co ca Hoa k, dch bnh thng hn bng pht do ma thu hoch bp ca vng c xut hin aflatoxins vi nng cao (Miller v cng s,1978). Bo co ca Pfeizer (1994) trn 500 heo tht (trn chung all-in-all-out) khng c tin s c bit v bnh. Khi heo c 55-60 kg, khong 25% b tiu chy v sau c vn v h hp. Tng trng hng ngy gim 25% v lng n vo gim 15%. Nguyn nhn chnh l do Salmonella cholerasuis. C 15% heo bnh b cht, trong khi 10% do ngi chm sc v vic iu tr khng sinh khng hiu qu. C mt s im lm rt ngc nhin. u tin, l tui xy ra dch bnh, bi v hu ht cc vn v bnh thng xy ra trn heo th nghim ch sau mt thi gian ngn sau khi nhp n.. Th hai, trong thc t trc y, chn on trn n heo v tri ny u cha bao gi pht hin ra bnh thng hn. Thc n c o lng cc thnh phn nh calcium, phosphor, m, v Salmonella spp. nh gi thc liu nh mong i v khng c vi khun Salmonella spp. no c phn lp. Khi vic kim tra k hn, tc gi nhn thy rng dch bnh c lin quan n vic s dng t nguyn liu bp mi trong cng thc thc n. Phn tch mu thc n cho thy rng trong mu thc n mi b nhim c t DON (200 ppb) v Aflatoxin (300 ppb) trong khi thc n c khng cha c t nm mc. C s ci thin ng k khi s dng ngun liu bp mi trong 2 tun. Aflatoxin cng lm tng s nhy cm ca heo i vi bnh l (Joens v cng s, 1981). Trong th nghim ny, nhng heo khng b bnh c th nghim cho tip

xc vi heo b mc l sau cho n thc c mc aflatoxin B1 (0.07 n 0.14 mg/kg). Thi k bnh th heo va nhim aflatoxin v Serpulina hyodysenteriae th ngn hn heo ch nhim Serpulina hyodysenteriae. Thm vo , s ngy m heo b nhim bnh v c t c du hiu tiu chy v bnh l di hn nhm heo ch b Serpulina hyodysenteriae. T l cht nhm th nht nhiu hn nhm th hai (xem s 1). Stoev v cng tc vin quan st thy c t ochratoxin A c trong thc n s lm tng nhy cm ca heo i vi bnh thng hn. Th nghim c thc hin trn 18 con heo, c s bc pht tc thi do S. choleraesuis trn ton b s heo cho n vi khu phn c cha 3 ppm ochratoxin A v trn 1/3 s heo cho n vi khu phn 1ppm ochratoxin. Trong cng th nghim, khng c heo no b mc bnh l i chng. S xut hin tc thi ca bnh thng hn c th gii thch rng nu quan st bng mt thng th tt c heo cc tri u kho mnh, nhng thc t th mi c th heo u c nhim S. cholerasuis. Trong mt th nghim khc, tt c cc heo u c tim vaccin chng li S. choleraesuis (nguyn nhn gy bnh hng l). Tuy nhin, c t nm mc li gy bng pht bnh do nh hng ca Serpulina hyodysenteriae v Campylobacter coli (Stoev v cng s, 2000). Mt s tc gi khc (Mller v cng s, 1999; Verma v Mathew, 1998; Baudrimont v cng s, 1994) trnh by v mt s nh hng khc ca Ochratoxin A on trn s min dch ca th: lm gim t bo lympho (t bo min dch), tng apoptotic thc bo (lm cht cc bch cu trung tnh v i thc bo), tng lng bch cu a acid (t bo c lin quan n s p ng min dch), lm tng lng bch cu trung tnh, bch cu a baze v lm gim s thc bo (kh nng tiu dit vi khun ca c th th). Oswald v cng s lm th nghim vo nm 2003 v s tng quan gia c t Fumonisin B1 v Escherichia coli. Trn heo con cai sa c cho n 0.5 mg Fumonisin B1 /ngy/kg trng lng c th (tinh ch hay chit xut th t c t). Trong nhng ngy cui ca th nghim, heo con c truyn E. coli qua ng ming v quan st th trong 24h. Kt qu cho thy s lin quan mt thit gia vic cho th n Fumonisin B1 v s hin din c u th ca E. coli (c trong rut non v rut gi ca th) (xem s 2). S lng vi khun c phn lp t rut non heo th nghim nhiu hn gp 400 n 700 ln so vi heo khng b nhim Fumonisin. Thm vo vi khun cng c tm thy trong phi, gan, v lch ca th th nghim. l i chng, vi khun ch c tm thy trong phi. Tc gi tm ra nh hng ca Fumonisin B1 trn t bo rut (nghin cu trong phng th nghim) v theo l thuyt th Fumonisin B1 lm gim s phc hi ca t bo rut b vim. Tc gi cng kt lun rng c t ny lm tng s pht tn vi khun qua biu m v lm nh hng n hiu qu sn xut v cc t bo rut kho mnh. nh hng ca c t n hiu qu ca vaccin Bnh ng du son trn heo l do vi khun Erysipelothrix rhusiopathiae, vi khun ny c tm thy hu ht cc tri nu khng ni l hu ht cc tri u c.

D nhim bnh nht l trn th ang ln, ni hu b khng tim phng vaccin v up to 4th parity sows. Vi khun pht trin trong c th, ly nhim qua ng mu, v lm nhim trng ng mu. Mc min dch ca th nh hng n cc triu chng ca bnh ca th.

Cysewski v cng s (1978) lm th nghim v nh hng nng c t th n vo trn s p ng min dch ca heo b bnh ng du son. Th nghim c 24 heo c chia thnh 4 nhm. Hai nhm cho n khu phn bnh thng v hai nhm cho n khu phn c nng c t nh nhau. hai nhm trn, trong mi nhm c 1 l c tim vaccin nga bnh ng du son, v 3 tun sau tt c cc heo cho tip xc vi chng virus Erysipelothrix rhusiopathiae. Da trn s p ng min dch ca th, heo s xut hin p ng min dch, mt phn min dch, hoc khng p ng min dch. Kt qu nh sau: Thc n L i chng C cha c t Tim phng vaccin C Khng C Khng Kt qu 3 heo c min dch 2 heo min dch 1 5 heo khng p 6 heo khng 2 heo min dch 1 phn ng min dch ng min dch phn 4 heo khng p 1 heo min dch 1 1 heo khng p ng min dch phn ng min dch (Xem s 3) Taranu v cng s (2005) thc hin th nghim nh hng ca Fumonisin B1 ln p ng min dch ca heo con. Thc hin trn hai nhm heo c trng lng mi con khong 12.3 0.8 kg, cho n khu phn c bn (bao gm bp v kh du u nnh) trong 28 ngy. Trong l th nghim, thc n c cha 8 ppm Fumonisin B1. Trn nhm heo c tim phng Mycoplasma agalactiae ngy th 8 v ngy th 22 ca th nghim. Huyt thanh c ly vo cc ngy 0, 22, 28, v nng khng th c hiu c xc nh bng phng php ELISA. Kt qu c trnh by s 4, kt qu cho thy mt bc sng quang hc dy c (405 nm) (t huyt thanh ca 20 con heo c pha long 1/100 (mean SEM). T nhng d liu trn, h thy rng mc khng th ca 2 nhm heo th nghim (vo ngy 0 v ngy th 22) tng ng nhau. Nhng vo ngy th 28, th c s khc bit r rng, mc khng th trong huyt thanh ca nhm heo cho n khu phn c Fumonisin B1 t hn nhm i chng. H nhn thy rng Fumonisin B1 c tc ng tiu cc n s tng s lng t bo lympho. Theo bo co cho thy tc ng c hiu qu ln s cn bng ca s phn bo gia Th1 v Th2. Khi so snh nhm i chng, s tng phn bo Th1 c quan st trn hch lympho mng treo rut v lch trn heo th nghim, trong khi mc phn bo Th2 (lin quan n p ng min dch c th v sn xut khng th) th gim. It would have been interesting to observe the antibody response on a longer period to analyze if the difference detected at 28 days increases over time. Tc gi lu rng th nghim s khng c chp nhn nu quan st thy c s khc bit v sn xut khng th c hiu influence immunity of the piglets.

Ngn nga v kim sot c t Nu iu kin mi trng thun li th nm s pht trin, v rt kh trnh khi tnh trng thc liu b nhim c t. Tuy nhin nu ngn chn s pht trin ca nm c hiu qu th tt nhin s hn ch c s tc ng ca c t. Vic ngn chn c th c thc hin trc khi thu boch with a good management of preceding crop residues, lun canh hp l, la chn ht ging tt (cht lng ht ging, thch nghi trong nhiu iu kin trng trt), mt trng thch hp, bn phn ng cch, tt nhin ta s ngn chn c cn trng v nm. Thu hoch ng thi gian v trong iu kin tt th s trnh lm h hi sn phm, sau loi cc ht b h v b m, sau d tr cc ht cn li cng sm cng tt. Cui cng, trong sut qu trnh d tr, cn iu chnh ng nhit , m, cn trng, cc loi gm nhm, v s dng hiu qu cht c ch nm mc s ngn chn c c t c trong thc n. Nhng nn lu rng, ngn chn khng c ngha l loi b c c t c trong thc n. C rt nhiu phng php c th nghim nhm loi b c t nm mc trong thc liu. Vn y l khi thc hin cc phng php ny rt tn tin, thng th s c thit hi v c th lm gim ngon ming ca thc n v gi tr dinh dng ca thc liu. Trong cc phng php c thc hin yu cu nh sau: x l vi ammonia, cng vi nhit v p sut (hiu qu trn aflatoxins v trn fumonisins th hiu qu km hn, nhng li pht sinh ra hp cht c t), x l bng ozone, kh chlorine, ammonium hydroxide, hydrogen peroxide, acid hydrochloric v kh sulphur dioxide (chng li c t DON), formaldehyde (chng li c t zearalenone), sy nhit (hiu qu trn c t DON), x l bng tia UV (chng li c t aflatoxins). Cc phng php nh tch v, nh bng, sng lc cng c p dng. Tuy nhin, ngy nay hu nh ngi ta khng cn s dng cc phng php trn na do chng c nhiu hn ch. S dng cht kt dnh c t Khong 20 nm trc, ngi ta thng s dng cht kt dnh t nh l mt phng php tt nht trong vic kim sot c t. Mt trong nhng nghin cu khoa hc l da trn c tnh kt dnh ca t st ca Phillips v cng s (1988). H th nghim trn 38 cht ha hc c c tnh kt dnh c dn xut t aluminas, silicas v aluminosilicates, v cho thy rng mt loi phyllosilicate t st, cn gi l hydrated sodium calcium aluminosilicates (HSCAS) c c tnh kt dnh aflatoxin B1. Thc ra, hp cht aflatoxin-HSCAS n nh nht trong khong pH dao ng t (2-10) v nhit trn 37C (Sarr v cng s, 1990). Nhng nghin cu khc chng minh r hn v HSCAS rt hu ch khi khm ph ra nhim c aflatoxins trn g, g ty, d, b, heo, hoc cu. tuy nhin dng nh HSCAS ch c tc dng mt phn ln zearalenone v ochratoxin A, trong khi chng khng c tc dng trn c t thuc nhm trichothecenes (v d nh, c t T-2 , diacetoxyscirpenol hoc deoxynivalenol, cng nh vomitoxin).

Zeolites, mt loi khc ca hydrated aluminosilicates, c hiu qu trn c t aflatoxins. Trong khi thc hin mt s th nghim trn th, nng zeolite cao trong thc n khng cho kt qu nh mong i (Fukal v cng s 1990, Sova v cng s 1991). Ramos v cng s (1996) c nhng th nghim v hiu qu sodium bentonite (mt loi cht bt kn t thin nhin dng bi vo nhng l thng). n c s dng nh mt tc nhn kt dnh khi sn xut thc n vin. Da trn pht minh ny, cng nh mt vi s liu ca cc nghin cu khc, bentonite c pht hin khng c hiu qu chng li zearalenone, ochratoxin A hay nivalenol v iu ny mu thun vi kt qu c c vi aflatoxins. Nghin cu cng c thc hin trn than hot tnh (l mt dng bt khng ha tan sau khi nhit phn cc hp cht hu c). Mc d than hot tnh c chng minh l c hiu qu khi th nghim trn th, v d nh fumonisin B1 (Solfrizzo v cng s, 2001) hay ochratoxin A, nhng khi thc hin th nghim trong phng th nghim li khng c hiu qu. Thm vo than hot tnh li thng lin kt vi cc cht dinh dng c trong thc n, nh l vitamins, khong v dc phm. Cholestyramine l nha cy thng dng lm gim lng cholesterone cao trong mu. N hot ng bng cch kt hp vi acid mt trong ng rut, kt qu l cholesterone c bin i thnh acid mt trong gan. Ramos v cng s (1996) quan st thy rng nha cy kt dnh zearalenone, trong khi cc th nghim khc chng minh n c hiu qu trong vic chng li fumonisins. Tuy nhin lng s dng li rt ln ( v d nh phi b sung 10 kg/MT thc n nu c s hin din ca zearalenone) nn khng c hiu qu kinh t. Cui cng, polyvinylpyrrolidone (hp cht vinyl polymer), s dng 2 kg/MT thc n c cha deoxynivalenol, khng ci thin tnh trng nhim c t (bo co bi Ramos v cng s (1996). Theo Stanley v cng s (1993), Saccharomyces cerevisiae rt hu ch khi thc liu b nhim aflatoxin, v h kt lun rng thnh t bo kt dnh c t. Santin v cng s (2003) nghin cu nh hng ca thnh t bo nm men chng li c t ochratoxin trn g tht. Kt qu ch ra rng ochratoxin lm gim lng n vo trn g tht, tng trng hng ngy v h s bin chuyn thc n trn gia cm. Thnh t bo nm men khng lm ci thin c cc ch s trn. Yiannikouris v cng s (2004) nghin cu s nh hng ca thnh t bo nm men ln c t zearalenone trong phng th nghim. H kt lun rng cc lin kt khng ng ha tr c c cu rt phc tp, v c s tng tc ho hc nn dng ny gi l ht bm hn l kt dnh. Gii hn ca cht kt dnh c t Da trn mt s cng b c tnh kh thi, chng ta nhn thy rng c mt s im gii hn chnh ca cht kt dnh c t l:

1) Hiu qu ca chng ch gii hn trn mt vi c t. Ni chung, cht kt dnh ch c hiu qu trn nhng c t c cc, nh l aflatoxins. V do cu trc thc t ca c t s quyt nh hiu qu kt dnh. Trong trng hp thc n c nhim cc c t khc, nh l trichothecenes, th hiu qu kt dnh km, nu khng mun ni l hiu qu bng 0. 2) Hiu qu khi thc hin trong phng th nghim khng ging nh khi th nghim trn th. Bi v khi thc hin trong phng th nghim, th mi trng thc hin th nghim thng n gin v khng thay i, khng ging nh trong ng tiu ha ca th. Khi o pH, s tng tc ca thc n hay s tit enzyme th khng tnh ton c, kt qu th nghim c s ri ro. Thc ra, khi c t v cht kt dnh c lin kt khng ng ha tr c nh dng, th s thay i mi trng c th dn n s gii phng c t khi cht kt dnh. 3) Mt vi cht khng c hiu vi c t. Trong trng hp , cht kt dnh tng tc vi thnh phn dinh dng, nh l vitamins, khong v dc phm. Vi s gii hn ny, khi cht kt dnh c tc ng n c t th cng nh hng n hiu sut chn nui. S bin i sinh hc ca c t V qu trnh kt dnh c t nm mc l qu trnh thun nghch, nn hiu qu ca vic s dng cc cht ny ph thuc vo iu kin mi trng. Khi p dng vo thc t cng c s gii hn i vi mt vi loi c t nm mc. V vy kt qu s khng nh mong mun. Nhng nghin cu gn y cho bit rng s bin i sinh hc ca c t nm mc bng cch b sung h vi vi sinh vt hay enzymes c sn s cho nhng kt qu rt kh quan. Shima v cng s (1997) c bo co v th nghim trn vi khun (thuc nhm Agrobacterium-Rhizobium c th chuyn deoxynivalenol thnh mt loi hp cht c c tnh yu hn l 3-keto- deoxynivalenol, v cho bit rng qu chuyn ha sinh hc l do enzyme ngoi bo ca h vi sinh vt ny tit ra (xem s 5). Tng t, Vlkl v cng s (2004) lm th nghim trn hn hp mt s lai vi khun c th chuyn deoxynivalenol thnh 2 sn phm ring bit into two chromatographically separable products, thnh phn chnh l 3-ketodeoxynivalenol. H lp li th nghim v cng b rng qu trnh ny cng c s tham gia cua 3 enzymes ngoi bo. Cc c t khc thuc nhm trichothecenes nhu l 15-acetyl- deoxynivalenol, 3-acetyl- deoxynivalenol v fusarenon-X cng b chuyn ha. Zearalenone c th chuyn sang dng kch dc t yu hn l 1-(3,5dihydroxyphenyl)-10-hydroxy-1-undecen-6-one (Takahashi-Ando v cng s, 2002). Enzyme c xem nh l mt cht gii c c cht hydrolase (cht ny tch c vng lactone trong cu trc phn t) (Xem s 5). Zearalenone nh hng n chu k sn xut ca th v chng gy tr ngi n c quan th cm

hoocmon ng dc ca th ci. Khi cu trc ca c t b thay i do s tc dng ca enzyme th c lc s b mt i. ng dng cc enzymes chuyn i ny ti cc vng chn nui s em li mt c hi mi. Thc ra, enzymes c th c nhng tc dng chuyn bit v phn ng ring, so snh vi s kt dnh, nhng phn ng ny khng c tnh thun nghch. Bng cch gii quyt mi, ta c th ni cht kh c t nm mc khc hn vi cht kt dnh c t nm mc. S kt hp gia cht kt dnh c t nm mc v enzymes tt nhin l c tnh kh thi. hon thin dng sn phm c tc dng lm mt i c tnh ca c t nm mc trong thc n, cng ty Impextrco ca B sng lc rt nhiu sn phm (bao gm c cht kt dnh v enzyme), bng m hnh c thit k tng t nh ng tiu ha. M hnh h tiu ha Kt qu ca cc th nghim khi thc hin mt s php o lng n gin trn mu thc n (trong ng nghim) th khng chng minh c cht no c th kt dnh hay kh c t nm mc, v cc kt qu khng chnh xc. V d nh, nu c t nm mc gn cht vo thc n, nhng c loi thi ra khi c th th chm hn, th cht kt dnh khng c hiu qu. Tng t, nu sn phm kt dnh c t ngay trong c th th (khng trn thc n) th rt hiu qu, nhng hiu qu th kh c th kim chng li. Phn tch hiu qu ca s kh c t trn th l rt kh. Hu ht cc th nghim u quan st trn cc biu hin ca th. Tuy nhin, cc thng s ny nh hng bi nhiu yu t khng kim sot c, nn ng nhin s th th nghim ln v rt tn km. Mt s th nghim thc hin o lng lng huyt thanh, iu ny khng kh thi vi tt c cc loi c t v lng huyt thanh khng phi lc no cng biu th c lng c t m th hp thu. Hu ht cc c t u nhanh chng hp thu hay d tr trong th. Do , lng huyt thanh s tut xung kh nhanh. Thi gian gia vic hp thu trong rut non v lc ly mu trn th l rt quan trng, nhng s khc nhau ph thuc vo tng yu t nh lng n vo, thi gian lu thc n rut non, v.v Cng nh mt s yu t khc nh ging, trng lng c th th, lng nc ung vos to nn s khc bit gia c th th v nh hng n lng huyt thanh. Th nghim trn m hnh h tiu ha ca th s kh tng loi c t khc nhau v kim sot tt c cc yu t khc. Tt nhin, khng c m hnh no tt nh m hnh trn, ng tiu ha c nghin cu rt k cng nhng c mt vi im khng d m phng theo. Tin s. H. Clarijss v nhm nghin cu HAS ti H Lan pht trin m hnh h tiu ha v dng m hnh ny trong vic kim tra v c t nm mc. Mt yu t quan trng trong m hnh l: mi trng k kh, nhit (khng i) trong c th th, pH thay i trong ng rut, thi gian thc n lu li trong ng tiu ho, mt c tit ra, men tiu ha pepsin, cc enzymes rut non v iu chnh m (ph thuc vo ln ca vin thc n).

M hnh m phng theo rut non cho php thc hin cc th nghim c s tng tc gia thc n, c t nm mc v cht bt hot c t trong iu kin nh tht. V m hnh a ra cc iu kin thun li hn so vi cc th nghim c trong phng th nghim ( pH c kim sot v cc thng s khc khng c tnh ton). C s khc bit r rng gia hnh thc th nghim c v trn m hnh h tiu ha . Cht kt dnh c t aflatoxin B1 tt nht (th hin trn mn hnh) (s kt hp ca mt s loi c bit t HSCAS) sau s kt hp vi mt s cht khc, cho ra mt sn phm hon ton khc vi sn phm c c trong iu kin th nghim c. S thm vo mt s cht s cho thm hiu qu. Cht c chn l chitosan (l cht polimer sinh hc) t v ca cn trng v loi gip xc. Cht ny c c tnh kt dnh cc c t c chn lc, v n c chng minh c hiu qu khng khun (No v cng s, 2002). Helander v cng s (2001) cng b rng chitosan c v kt dnh mng ngoi ca vi khun Gram - v ph v c tnh bo v ca mng t bo. Mt s enzymes khc cng c th nghim. Mt vi enzymes c hiu qu trn nhiu loi c t. S kt hp HSCAS, chitosan v enzymes hin ti vn c ng dng (Elitox, Impextraco NV, B). Kt lun c t nm mc rt c hi cho ng vt v c th nh hng rt nhiu n hiu sut chn nui. V c t nm mc rt a dng v c nhiu cu trc ho hc, nn nu gii quyt vn mt cch n gin th khng th c c nhng hiu qu nh . S ngn nga l rt cn thit nhng khng th m bo trong thc n s khng cn c t nm mc. Khi thc liu b nhim c t, th cn s dng mt s bin php x l. Kt hp ng gia cht kt dnh c t nm mc, enzymes lm bt hot c t, v polimer sinh hc s d dng gii quyt vn v n c nh ngha l cht hp ph c t nm mc. S 1: Mi tng quan gia Aflatoxin v Serpulina hyodysenteriae (cho nhim sau 4 ngy, 8 heo trong 1 nhm, theo Joens v cng s, 1981).

18 16 14 12 10 8 6 4 2 0 Thi gian bnh S ngy trung bnh b tiu chy S ngy TB b bnh l S heo cht

Khng c Aflatoxin & Serpulina hyodysenteriae Aflatoxin & Serpulina hyodysenteriae

S 2: Hiu qu khi p dng FB1 trn khun lc (rut heo con) dng E. coli 28CNalr (theo l thuyt) (Theo Oswald v cng s, 2003).Khun lc m qua knh hin vi (CFU/g) Manh trng

10,000,000 1,000,000 100,000 10,000 1,000 100 10 1 Hi trng

I chng + FB1

Kt trng

S 3: nh hng ca Aflatoxin B1 (khi th nghim trn th) n p ng min dch ca heo heo con c chng nga vi erysipelas bacterin v cho nhim sau 21 ngy vi dng virus Erysipelothrix rhusiopathiae (theo Cysewski v cng s, 1978).S heo con

6 5 4 3 2 1 0 i chng AFB1 Khng chng Khng nga chng nga i chng C chng nga AFB1 C chng nga Min dch ton phn Min dch mt phn Khng min dch

S 4: Tc dng ca Fumonisin B1 (8 ppm) trn sn xut khng th c hiu sau khi tim chng vaccin Mycoplasma agalactiae ti ngy th 7 v ngy th 22 (Theo Taranu v cng s, 2005).

i chng

Ngy ly mu mu

S 5: M hnh bin i ca c t nm mc khi c enzymes.