Effects of mycotoxins in ruminants

RuminantsThe effects of mycotoxins in ruminants is a research area that highly depends on economic factors that arise when it comes to planning and conducting a trial.1 Effects of mycotoxins in ruminants are dependent upon multiple factors that include: type of mycotoxin and duration of exposure, type of diet (ruminant diets are quite complex and involve the use of different types of ingredient and protein sources), status of the animal (age, sex, breed, dry matter intake (DMI), general health, immune status, nutritional strategies), and environmental parameters (farm management, hygiene and biosecurity).1,2 Of relevance is the multiple unknown metabolites whose presence can increase the toxicity of other known mycotoxins via synergistic and additive interactions.1,3 Normally, ruminants are considered more resistant to mycotoxins due to the complexity of their gastrointestinal tract which is populated by a broad variety of different microorganisms, some of which are capable to biotransform mycotoxins.1,4,5 However, feed commodities are usually contaminated by more than one mycotoxin, and due to the composition of the diet, ruminants are more exposed to the a mixture of toxins that occur in the field and during storage.3

Aflatoxins

Aflatoxins (Afla) is a potent carcinogen for both animals and humans (listed as a group 1 carcinogen by the International Agency for Research on Cancer, IARC).1,6,7 Afla is rapidly absorbed and metabolized in the body, and appears in the bloodstream and milk after a minimum of five minutes.5,8,9,10,11 The main metabolite of aflatoxin B1 (AfB1) is aflatoxin M1 which is even more carcinogenic and contaminates milk and other dairy products, which is why the presence of AfB1 in dairy feed is strictly regulated in the majority of markets worldwide.1,5,10 The aflatoxin metabolite AFM1, is carried over into the milk from around 1 to 6% of the aflatoxin consumed (see compendium for Ref). In addition, AfB1 demonstrates antimicrobial activities, as reported by some studies where cows fed AfB1 contaminated feed showed a reduction of gas production, ammonia and volatile fatty acid (VFA) concentrations, together with an increased bioavailability of AfB1 in the rumen fluid.5,6,10,12 Aflatoxins are highly immunosuppressive as well, and effects on animals such as sheep and dairy cows can be significant, even at low doses.1,5,10,11 In general, calves are more sensitive to aflatoxins than adult cattle.1  

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Ergot Alkaloids

Ergot alkaloids may induce neurotoxic effects, leading to reduced feed intake because the birds are reluctant to move and may suffer from respiratory difficulties.34 Birds affected by ergot alkaloids showed poor growth and decreased egg production. The most obvious pathological changes are gangrenous lesions on the toes, beak and claws.35

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Fumonisins

Fumonisins (FUM) are poorly degraded in the rumen. Common symptoms in ruminants are diarrhea and hematological changes such as an increase in the serum cholesterol.1,5,20 Other symptoms reported in the literature include hepatocellular injuries and neoplasia in the biliary epithelial cells, changes in hematological parameters including an increase of serum aspartate aminotransferase (AST), lactate dehydrogenase (LDH), bilirubin and cholesterol.5,20,21,22 One study conducted on calves reported on histological changes after feeding with 15, 31 and 148 mg FBs/kg diet for 31 days.20

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Ochratoxins

Ochratoxin (OTA) is largely degraded by rumen microflora into OTα.13 The literature generally does not report the effects on nutrient digestibility and feed intake, suggesting that animals have developed tolerance mechanisms.14 Portions of OTA that are not degraded can however be transferred to the milk, although the concentration is usually too low to present a threat to consumers.5,15  

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Trichothecenes

Type A Trichothecenes

The effects of type A trichothecenes such as T-2 and HT-2 have been investigated in young ruminants.1,13 Their main effects include hemorrhages, lesions in the gastrointestinal tract, and changes in the immune status.1,13 Effects on the semen quality were observed in bulls, but no information is currently available on dairy cows or beef animals.19

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Zearalenone

In the rumen, zearalenone (ZEN) is converted into α-zearalenol (α-ZEL) and β-zearalenol (β-ZEL), with the α-metabolite (which is approximately ten times more estrogenic than the parental compound) being the predominant one.1,2,23 Common ZEN post-exposure symptoms include reproductive problems, such as edema and hypertrophy of the genitalia, decrease in embryo survival, alteration in uterine tissues morphology, decreased testosterone production and subsequent feminization in males, and infertility.2,24,25,26,27 

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Synergistic effects in ruminants

Although ruminants are thought to be less susceptible to the effects of mycotoxins, the protective effect of the rumen can be compromised when the health status of the animal is altered, or when the latter is exposed to mixtures of mycotoxins. A typical agricultural commodity contains on average 25-30 different bacterial and fungal secondary metabolites, thus mycotoxin mixtures can be quite heterogeneous.3

The literature reports that a mixture of DON and other Fusarium mycotoxins including ZEN, nivalenol, and masked forms of DON (DON-3-glucoside) are able to interfere with the activity of cellulolytic bacteria, which are very important for ruminants.1,13,26 An increase in rumen ammonia concentration, and a reduced duodenal flow of microbial proteins suggesting alteration of microbial population, was also reported in cows consuming feed contaminated by mixtures of Fusarium mycotoxins.28 The latter, in combination with AfB1 were able to interfere with the dry matter intake and nutrient digestibility in lactating dairy cows, stressing the importance of synergistic interactions.1,5,27 Mycotoxins such as Afla, DON, gliotoxin, FUM, roquefortine C and mycophenolic acid are quite stable in the rumen environment and can potentially reach the intestinal intact.29

Mixtures of Aspergillus mycotoxins can be harmful for ruminants. These include gliotoxin which exhibits antimicrobial, antiprotozoal and immunosuppressive effects (ROS and apoptosis of lymphocytes), and Kojic acid and cyclopiazonic acid, which both show antimicrobial activities (disruption of calcium homeostasis, degeneration and necrosis of liver).13,29,30

Strains of Penicillium such as P. roqueforti and P. paneum produce immunosuppressive and antibacterial secondary metabolites. Consumption of feed contaminated with these fungi can result in loss of appetite, impaired nutrient efficiency, ketosis, ulceration and gastroenteritis.2,13,29,30 In some cases, paralysis and abortion were observed as well.1 Some mycotoxins, and mixtures of them, produced by strains of Penicillium such as OTA, citrinin, patulin, mycophenolic acid, can inhibit macrophage proliferation, rendering cattle more susceptible to diseases.29 Other symptoms observed in animals consuming moldy silages were oxidative stress and dysfunction of lipid metabolism.25

Co-occurrence of Monascus ruber toxins such as citrinin and OTA are able to generate symptoms such as pruritus, pyrexia, and hemorrhages as well as fever and diarrhea. Moreover, citrinin shows antimicrobial effects and can have a negative impact on the rumen microflora.29

Effects of Mycotoxins in Ruminants

AFB1 – Aflatoxin B1 | AFM1 – Aflatoxin M1 | DON – Deoxynivalenol | FUM – Fumonisins | OTA – Ochratoxin A | T-2 – T-2 Toxin | HT-2 – HT-2 Toxin | ZEN - Zearalenone | Ergots – Ergot, Alkaloids

References
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