The extent and mitigation of mycotoxins in commonly used feed commodities in South African beef feedlots

Thesis (MScAgric)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: The global occurrence of mycotoxins in agricultural commodities, including feed intended for livestock, is a topical concern. Research suggests that up to 88% of global commodities and 89% of South African feed commodities are contaminated with mycotoxins. The exposure to or consumption of these natural contaminants results in detrimental health and production disorders in livestock and cause substantial economic losses. Consequently, mycotoxins pose a significant threat to feed and food safety on a global scale. The presence of mycotoxins in feed commodities is affected by numerous factors, including cultivation methods, environmental conditions, processing, storage, and transportation conditions. As a result, the occurrence of mycotoxins varies between seasons and geographical areas. A national survey was performed to determine the current extent of mycotoxin contamination in feed commodities commonly used in South African beef feedlot diets and the subsequent risk posed to the industry. Five feed commodities, namely maize, maize silage, hominy chop, gluten 20 and wheat bran were sampled from four provinces, including the Free State, KwaZulu-Natal, North-West and the Western Cape. The results showed that the major mycotoxins present in South Africa are deoxynivalenol, fumonisin and zearalenone. The presence and concentration levels of other major mycotoxins observed globally, such as aflatoxin, ochratoxin, and ergot alkaloids were low in the current study. Since the latter toxins are considered storage mycotoxins, this observation can be attributed to optimal handling, transportation, and storage conditions in the local agricultural sector. Overall, 3.33, 6.67, 92.50, 62.90, 10.83 and 67.50% of the feed samples were contaminated with aflatoxin, ergot alkaloids, deoxynivalenol, fumonisin, ochratoxins and zearalenone, respectively. Moreover, most of the mycotoxins were present at medium to high risk levels for beef cattle. A significant interaction (P < 0.01) between the main effects (commodity and province) was observed in co-contamination. There were significant differences (P < 0.01) in the concentration of deoxynivalenol between the respective feed commodities, where hominy chop, followed by gluten 20, had the highest concentration levels. This could be attributed to the uneven distribution of deoxynivalenol in the different milling fractions of maize. In contrast, no differences were found in fumonisin or zearalenone concentrations between the different feed commodities. Finally, despite the varying climatic conditions throughout South Africa, no significant differences in mycotoxin concentrations were observed between the respective provinces. The survey concluded that the current occurrence of mycotoxins in feed commodities in South Africa is significant and poses a meaningful risk to the beef feedlot industry. Although ruminants are considered more resistant to the adversities of mycotoxins, their inherent detoxification ability is variable and satiable. High-producing cattle receive diets rich in energy, which alters their microbial population and increases the feed passage rate, which subsequently decreases the capacity and time available to degrade mycotoxins. Additionally, feedlot cattle are subjected to substantial production stress, which has a depressive effect on their immune system and further increases their sensitivity to mycotoxins. Effective detoxification strategies should thus be implemented to reduce the adversities of mycotoxicosis. Mycotoxin adsorbents or deactivating feed additives have proven efficacy in attenuating or preventing mycotoxicosis in livestock. To determine the effect on feedlot steers, two mycotoxin-deactivating feed additives, namely Mycofix® Secure and Mycofix® Select 5.0 (Biomin [DSM], Getzersdorf, Austria), were investigated. A total of 186 cross- bred steers of similar age and body weights were randomly divided into three treatment groups comprising of 62 animals each. The first group served as a control group, whereas the second and third groups received Mycofix® Select 5.0 and Mycofix® Secure at an inclusion rate of 15 g/head/day. The animals were challenged with the naturally occurring mycotoxin levels throughout the study. The group that received Mycofix® Select 5.0 showed improved body weight gain and feed conversion efficiency over the total duration of the trial, in terms of measured average daily gain (P = 0.03) and calculated Kleiber ratio (P = 0.04). Additionally, both treatment groups had higher (P < 0.01) dry matter intakes as a percentage of their body weight during the adaptation period in the feedlot than the control group. The higher feed intake can partly explain the improved performance of the two groups compared to the control group. However, over the total period of the trial, no differences were observed in body weight, dry matter intake as a percentage of body weight, or feed conversion ratio between the groups. Since mycotoxin adsorbents and/or deactivating feed additives are known to improve the performance of cattle, these similarities were attributed to the overall low naturally occurring mycotoxin challenge experienced during the trial. Further, no differences were observed in slaughter parameters, including carcass weights, dressing percentage, or fat content classification. Finally, despite the increased feed costs from the addition of the feed additives, no differences were observed in the margin above feed cost.

AFRIKAANSE OPSOMMING: Die wêreldwye voorkoms van mikotoskiene in landboukommoditeite, insluitend veevoer, is ‘n groot bron van kommer. Navorsing dui daarop dat tot 88% van wêreldwye- en 89% van Suid-Afrikaanse voerkommoditeite met mikotoksiene besmet is. Die blootstelling of inname van hierdie natuurlike toksiene lei tot gesondheidsprobleme en produksiesteurings in vee en veroorsaak noemenswaardige ekonomiese verliese. Gevolglik hou die voorkoms van mikotoksiene ‘n beduidende bedreiging vir voer- en voedselsekerheid wêreldwyd in. Die teenwoordigheid van mikotoksiene in voerkommoditeite word deur verskeie faktore bv. verbouingsmetodes, omgewingstoestande, verwerkings-, bergings- en vervoertoestande beïnvloed. Gevolglik wissel die voorkoms van mikotoksiene tussen seisoene en verskillende geografiese gebiede. ’n Nasionale opname is gedoen om die huidige omvang van mikotoksiene in voerkommoditeite wat algemeen in Suid-Afrikaanse beesvoerkraaldiëte gebruik word, en die daaropvolgende risiko wat vir die bedryf ingehou word, te bepaal. Vyf voerkommoditeite, naamlik mielies, mieliekuilvoer, mieliekiemmeel, gluten 20 en koringsemels is uit vier provinsies, nl. Vrystaat, KwaZulu-Natal, Noordwes en Wes-Kaap, evalueer. Die resultate het getoon dat die belangrikste mikotoksiene wat in Suid-Afrika teenwoordig is, deoksinivalenol, fumonisien en zearalenoon is. Die teenwoordigheid en konsentrasievlakke van ander mikotoksiene wat wêreldwyd algemeen waargeneem word, soos aflatoksien, okratoksien en ergot-alkaloïede was beduidend laer in die huidige studie. Aangesien hierdie toksiene as bergingsmikotoksiene beskou word, kan hierdie waarneming toegeskryf word aan optimale hantering, vervoer- en bergingstoestande in die plaaslike landbousektor. ‘n Totaal van 3.33, 6.67, 92.50, 62.90, 10.83 and 67.50% van die voermonsters was onderskeidelik met aflatoksien, ergot-alkaloïede, deoksinivalenol, fumonisien, okratoksien en zearalenoon besmet. Daarbenewens was die meerderheid van die mikotoksiene teenwoordig teen matige tot hoë risikovlakke vir vleisbeeste. 'n Beduidende interaksie (P < 0.01) tussen die hoofeffekte (kommoditeit en provinsie) is waargeneem in onderlinge kontaminasie. Daar was ook betekenisvolle (P < 0.01) verskille in die konsentrasie van deoksinivalenol tussen die onderskeie voerkommoditeite, waar mieliekiemmeel, volg deur gluten 20, die hoogste konsentrasievlakke gehad het. Hierdie waarneming kan verklaar word deur die ongelyke verspreiding van deoksinivalenol in die verskillende maalfraksies van mielies. Daarteenoor is geen verskille in fumonisien- of zearalenoonkonsentrasies tussen die verskillende voerkommoditeite waargeneem nie. Ten spyte van die wisselende klimaatstoestande regoor Suid-Afrika, is geen beduidende verskille in mikotoksienkonsentrasies tussen die onderskeie provinsies waargeneem nie. Hierdie opname het tot die gevolgtrekking gekom dat die huidige voorkoms van mikotoksiene in voerkommoditeite in Suid-Afrika beduidend is en 'n groot risiko vir die beesvoerkraalbedryf inhou. Hoewel herkouers as meer bestand teen die negatiewe effek van mikotoksiene beskou word, is hul inherente detoksifikasievermoë veranderlik en versadigbaar. Hoëproduserende voerkraalbeeste ontvang diëte ryk aan energie, wat hul mikrobiese bevolking kan verander en die voerdeurvloeitempo kan verhoog, wat gevolglik die kapasiteit en tyd wat beskikbaar is om mikotoksiene af te breek, verminder. Boonop ervaar voerkraalbeeste aansienlike produksiestres, wat hul immuunweerstand verlaag en hul sensitiwiteit vir mikotoksiene verder verhoog. Doeltreffende strategieë moet dus geïmplementeer word om die nadelige effek van mikotoksikose te verlaag. Mikotoksien-adsorberende middels of deaktiverende voerbymiddels het bewese doeltreffendheid om die negatiewe effek van mikotoksikose in vee te verlaag of te voorkom. Om die doeltreffendheid daarvan op voerkraalosse te bepaal, is twee mikotoksien-deaktiverende voerbymiddels, naamlik Mycofix® Secure en Mycofix® Select 5.0 (Biomin [DSM], Getzersdorf, Oostenryk), ondersoek. ‘n Totaal van 186 kruisgeteelde osse van soortgelyke ouderdom en liggaamsmassa is ewekansig in drie behandelingsgroepe verdeel wat uit 62 diere elk bestaan het. Die eerste groep het as 'n kontrolegroep gedien, terwyl die tweede en derde groep Mycofix® Select 5.0 en Mycofix® Secure teen 'n insluitingskoers van 15 g/dier/dag onderskeidelik ontvang het. Die diere is deur die loop van studie met natuurlike mikotoksienvlakke uitgedaag. Die groep wat Mycofix® Select 5.0 ontvang het, het verbeterde liggaamsgewigtoename en voeromsetdoeltreffendheid oor die totale duur van die proef getoon, in terme van gemete gemiddelde daaglikse toename (P = 0.03) en berekende Kleiber-verhouding (P = 0.04). Daarbenewens het beide behandelingsgroepe hoër droëmateriaal-innames, as ‘n persentasie van liggaamsmassa, as die kontrolegroep gedurende die aanpassingsperiode in die voerkraal gehad. Die hoër voerinname gedurende hierdie tydperk kan die verbeterde prestasie van die twee groepe in vergelyking met die kontrole groep deels verklaar. Oor die totale tydperk van die proef is daar egter geen verskille in liggaamsmassa, droëmateriaalinname as persentasie van liggaamsmassa of voeromsetverhouding tussen die groepe waargeneem nie. Aangesien dit wel bekend is dat mikotoksien-deaktiverende voerbymiddels die prestasie van beeste verbeter, word hierdie ooreenkomste toegeskryf aan die algehele lae natuurlike mikotoksien- uitdaging wat tydens die proef ondervind is. Verder is geen verskille in slagparameters, insluitend karkasmassa, uitslagpersentasie of vetinhoudklassifikasie waargeneem nie. Ten spyte van die verhoogde voerkoste weens die byvoeging van die voerbymiddels, is geen verskille in die marge bo voerkoste waargeneem nie.

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