Why do Mycotoxins Lead to Decreased Productivity and Profitability in Animal Production?18 March 2016
Mycotoxins are secondary metabolites produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by higher animals.
Currently, there are more than 400 known mycotoxins. Those of most concern can be divided into six major categories: aflatoxins, trichothecenes, fumonisins, zearalenone, ochratoxins, and ergot alkaloids.
Fusarium, Aspergillus, and Penicillium are the most abundant moulds that produce these toxins and contaminate human foods and animal feeds through fungal growth prior to and during harvest, or during (improper) storage. Mycotoxin producing moulds damage crops which can result in great economic losses at all stages of food and feed production.
Mycotoxin levels in grain vary from year to year and between regions. The key factors affecting mycotoxin risk in wheat are: preceding crop, crop residues, variety, field management, and weather at flowering and harvest.
- Crop residue on the soil surface is the major source of head blight inoculum, especially after (in order of relevance) grain maize, forage maize and wheat.
- Ploughing helps to reduce overwintering fungi by lowering levels of infected crop debris on the soil surface. Deep tillage should effectively bury infected crop debris.
- Straw should be removed to help reduce crop debris. Crop debris needs to be buried by ploughing or mixing into the upper soil layer. A range of broad-leaved and grass weeds, as well as some insects, can carry Fusarium leading to infected weed and crop debris as well as a carry-over of spores.
- During flowering, crops are particularly susceptible to severe head blight infection. Further rainfall after infection, particularly after ripening, allows secondary infections. The risk of mycotoxin infection is more pronounced during warm and dry than wet and cold weather.
- At harvest, Fusarium mycotoxins may increase if wet weather causes delays. Set combine, especially fan speed, to minimize retention of light Fusarium-damaged grains and chaff as the highest concentrations of mycotoxins are found in Fusarium-damaged grains and chaff.
Stress factors such as drought, poor fertilization, high crop densities, weed competition, insect or mechanical damage on the field or during harvest, storage and distribution can weaken the plant’s natural defense. This then promotes colonization by mycotoxin-producing fungi as well as mycotoxin formation.
Mycotoxins can be found in every variety of grains and forage produced for food or feed. They accumulate in food and feed crops in the field, during transportation or improper storage.
Mycotoxins may be present in feedstuff which has shown negative analytical findings.
It is well understood that mycotoxins are not homogeneously dispersed in feedstuffs but usually occur in “hot-spots”. This makes sampling difficult and the mycotoxins may not be detected during analytical testing even with good sampling procedures.
Therefore, a negative result is not always conclusive and should not give reassurance in all situations.
Mycotoxins may also be masked from analytical detection by small molecules (glycosides) attached to the toxin thus giving a false negative result. Consequently, conventional analytical methods do not always detect these masked mycotoxins. However, the attached molecules may be removed during digestion, releasing the mycotoxin to affect the animal.
The negative impact of moulds and mycotoxins on animal production is an ever increasing concern. In addition, many of the mycotoxins interact with the digestibility of nutrients, impair health, cause diseases and death in humans and animals after consuming contaminated food or feed.
Negative effects of mycotoxins in livestock
Various sources provide information about the effects and symptoms of mycotoxins in animals.
It should be noted that the effects of mycotoxins are very complex and it is possible that symptoms different to the ones presented in this paper may occur. With some exceptions, generally, younger animals are more susceptible than older animals.
Feeding mycotoxins to pigs, what can we expect?
Generally, pigs are the most sensitive farm animals to mycotoxins.
Aflatoxins suppress the immune system and the first sign of aflatoxin contamination in the diet is decreased feed intake. Clinical signs, depending on the contamination level can range from reduced growth, hepatosis, to death.
Among the trichothecenes, deoxynivalenol and T-2 toxin are the most relevant for the pig industry. T-2 toxin inhibits feed intake.
Deoxynivalenol also reduces feed intake, decreases growth of the pigs and causes vomiting.
Ochratoxins are hepatotoxic and nephrotoxic causing other particular chronic toxicities. The effects of ochratoxin intoxication are reduced growth, decreased weight gain and renal lesions.
Zearalenone mainly causes estrogenic effects in pigs. In pregnant sows it increases the occurrence of abortions and stillbirths. In others, zearalenone contaminated feed induces swelling and reddening of vulva, false heats and false pregnancy. Fumonisins target the liver, lungs and pancreas and causes pulmonary oedema in pigs.
Ruminants: continuously affected by mycotoxins
Aflatoxins, trichothecenes and zearalenone are equally as important in ruminants as they are in monogastric animals. However, mature ruminants are generally more resistant to the effects of mycotoxins than monogastric animals. This results from the mycotoxin detoxification ability of some rumen microbes.
In general, calves are more sensitive to aflatoxins than adult cattle. Among the most common mycotoxins, aflatoxins, trichothecenes and zearalenone are of importance to cows.
Clinical signs of ingestion of aflatoxin contaminated feed include reduced feed consumption and milk production, diarrhoea, acute mastitis, weight loss, respiratory disorders, hair loss, liver damage and immune suppression.
The aflatoxin metabolite AFM1 is carried over into the milk from around 1 to 6 per cent of the aflatoxin consumed.
Numerous studies have shown that ruminants are less affected by deoxynivalenol (DON) because it is metabolised into its less toxic de-epoxyde in the rumen.
Nevertheless, DON is associated with reduced feed intake and lower milk production in dairy cattle. T-2 toxin results in loss of appetite and weight, slower growth, gastroenteritis, lowered milk production, and reduced immune response in calves.
In addition, T-2 toxin has been implicated in haemorrhagic bowel syndrome by impairing immune function. Zearalenone causes among other things abnormal reproductive processes in cattle, sheep and other ruminants resulting in false heats, anoestrus, premature mammary development and abortions.
Poultry suffer hidden performance losses due to the mycotoxins
Poultry are sensitive to mycotoxins resulting in several toxic effects.
Broiler chickens are less affected by aflatoxins than other poultry like ducks, geese or turkeys. Predominantly, aflatoxins are the most immunosuppressive toxins.
Type A trichothecenes (T- toxin, HT-2 toxin, diacetoxyscripenol) are of major concern to poultry industries and cause economic losses in productivity.
They are highly toxic for poultry, especially for chickens due to their very low LD50. Particularly, T-2 toxin reduces feed intake, body weight, quality of breeding eggs and causes oral lesions.
Young chicks and turkey poults are highly sensitive to ochratoxins. These nephrotoxins can suppress feed intake, growth, egg production, and poor egg shell quality.
Fumonisins are associated with spiking mortality in poultry. Signs of dietary fumonisin are immune suppression, decreased body weight and average daily weight gain as well as increased gizzard weights.
In comparison to other species like pigs, poultry appear to be less affected by zearalenone while combinations of mycotoxins might cause significant losses in fertility and hatchability.
Nutriad mycotoxin management focuses on binding and inactivation of mycotoxins as well as reducing the detrimental effects of mycotoxins in animals by organ protection, immune system stimulation and support of the antioxidant system.
The use of effective mycotoxin management under conditions where mycotoxins are thought to be present even at low levels appears to restore, to a large extent, productivity and profitability.