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Importance of Mycotoxins In Pigs

Mycotoxins are secondary metabolites produced by moulds (microscopic fungi) growing in feedstuffs. Moulds such as Fusarium spp. can grow on grain and produce mycotoxins before harvest. Other moulds infect grain before harvest but produce most mycotoxins during storage. The moulds that produce mycotoxins are not always visible, but feed stuffs that become visibly mouldy during storage are very likely to reduce productivity.

There are several key questions that should be considered when faced with options on either the purchase of fungus-infected (often weather-damaged) grain or the use of feed that has become mouldy in storage. Some are:

  • whether fungal toxins (mycotoxins) are present in concentrations sufficient to affect pig health and performance;
  • whether the palatability and nutrient content has been altered for better or worse, and the most important question of all;
  • whether the lower price of the grain or other feed component, compensates for these effects and the risks involved.

Many moulds cause only a slightly reduced growth rate or poor feed conversion, but some mycotoxins with more drastic effects are aflatoxins, ochratoxins, zearalenone, trichothecenes (deoxynivalenol, nivalenol), fumonisins . These mycotoxins do occur in particular regions and in particular situations, so that prior knowledge of these circumstances will greatly reduce the risk of mycotoxicosis.

The fungi that produce aflatoxins (Aspergillus flavus and A parasiticus) most commonly grow during storage of summer crops (Corn, Soya and sorghum) but wheat and barley can also be affected.

Typically, aflatoxin occurs on farms that mix their feeds from home-grown grain. Failure to dry grain, or moisture condensation and accumulation favour the growth of moulds, which is accompanied by heating - these moulds grow best at 30-40 degrees. Aflatoxins can be produced within 2-6 weeks and signs of mycotoxicosis of pigs may be noticed within a week of it being introduced to the diet.

The clinical signs of aflatoxin poisoning are not characteristic. Pigs go off their feed and some may die, some are anaemic (pale) and jaundiced (yellowish in colour). Characteristic damage is caused to the liver, that can be detected when it is examined post mortem, and a diagnosis of aflatoxiicosis is confirmed when the feed and tissues from dead animals are analysed at a laboratory.

There is no specific treatment for affected pigs. Replace or dilute the mouldy feed with clean feed containing adequate protein, as the effects of aflatoxin poisoning are made worse by low dietary protein. Pigs may take several weeks to recover and never reach their normal growth potential.

Overall, the main risks are grain that has been stored moist and heated in the silo. Although less frequent, mouldy corn, barley and wheat can on occasion contain enough aflatoxins to seriously affect pigs.

Ochratoxin A is produced by a number of Aspergillus and Penicilllum fungi. Ochratoxin A may occur in combination with citrinin, and both of these mycotoxins cause kidney damage. Depressed appetite and reduced growth rate may result. Ochratoxin A is a common contaminant of barley grown in cool to wet conditions in northern Europe and Canada. . However, ochratoxicosis of pigs is not common in Latin America.

Zearalenone is the most detrimental mycotoxin in Pigs with some properties of the female sex hormone oestrogen. Several Fusarium moulds produce it in grains, particularly corn, grown in cool, wetter regions. The fungus actually grows on the grain before harvest when rainfall is high and insect damage prevalent, but damp, cool storage after harvest increases the hazard. When fed to female grower pigs, zearalenone causes swelling and reddening of the vulva similar to that seen at natural heat. This can progress to straining and prolapse of the rectum and vagina. Zearalenone also causes slight development of the teats of gilts and occasionally swelling of the prepuce of boars. A dark purple discolouration of maize or pink tips on bleached wheat may be an indication of infection with zearalenone-producing mould, but it can also be present in weather-damaged sorghum. Diagnosis is confirmed by analysis of the feed. Zearalenone toxicosis is increasing in North and South America.

This group of mycotoxins includes deoxynivalenol, which is occasionally detected in Corn, Wheat . If the pigs are hungry when the feed is first offered, they may eat and then vomit, which is why deoxynivalenol is also called vomitoxin. . A purple-red mould (Fusarium graminearum) infecting wheat, corn and Soybeans before harvest produces these mycotoxins, often in conjunction with zearalenone. There are a few other trichothecenes, including T2-toxin, HT-2,which could potentially affect pigs.

Fumonisins are common in maize infected with Fusarium moniliforme in most temperate regions of the world.. Fumonisins can be produced before harvest. They have been associated with pulmonary oedema (fluid in the lungs) of pigs in the USA.

Effects of moulds on palatability and nutrients

The only mycotoxins that have so far been shown to affect pigs are aflatoxins, zearalenone, deoxynivalenol . As described above, these occur in particular circumstances, and knowledge of those circumstances will help to reduce risk of Mycotoxicosis.

Mould growth before harvest
In general, changes in palatability and nutrient content of grain infected with mould before harvest (weather-damage) is slight, and there may even be some improvement in nutritive value as a result of starch hydrolysis similar to that seen in early germination. Deteriorated grain will be lighter in weight, be discoloured and darkened if mould invasion is extensive and the endosperm is likely to have a chalky appearance due to the partial hydrolysis of the nutrient stores. Gross energy on a weight basis may be unaffected, but fiber and non-protein nitrogen may be increased. The minor nutritional deficiencies of weather-damaged grains can generally be ignored in dietary formulation, but if desired, increasing the digestible energy with fat can easily compensate .

Mould growth in storage
Many moulds can grow in stored feed when hygiene is poor. Mould spores are always present in feed and the main factor stopping mould growth is lack of moisture. Condensation, leaks, rodent and insect damage all lead to mould growth. When this has occurred, the main affects are reduced palatability and worsening of feed conversion. These effects should not be ignored, as the effects on profits can be severe. Mould infection of grain decreases its feed value for pigs through the removal of storage starch and the hydrolysis of protein and losses in fat content also occur. Consequently, in material with extensive mould invasion during storage, the relative amount of fibre in the grain will increase in proportion to the decline in starch, protein components and fats, leading to reductions in digestible energy content. Vitamins and other essential nutrients can also be affected. The result of these changes is poor conversion of feed . Regular cleaning of silos and feed handling equipment, and rapid feed turn over are very important to maintain feed quality.

Sometimes in times of high humidity, feed may become slightly mouldy despite good hygiene and there is a need to use this material. Damaged feed that has undergone fungal growth during storage may exhibit 'off' aromas and flavours and be unpalatable when first offered to pigs. Usually, this poor palatability lasts only a few days before pigs become accustomed to the taste and smell. If it persists longer than this, it might indicate infectious disease or dietary imbalance, although mycotoxins are a possibility.

Economic factors
The decision whether or not to feed weather-damaged grain or mouldy feed is a matter of balancing the risk of reduced growth with lower feed costs Avoid feeding any unpalatable feed to young pigs, as reduced intakes when young will compromise later performance. . Finishers are a better proposition for unpalatable feed as slightly reduced intakes may be desirable to reduce fat deposition, and actually improve feed conversion slightly. Should feed conversion be adversely affected, as will happen if nutrients are unbalanced or if there are toxins in the feed, profits will reduce substantially. Risks can also be minimised by checking for zearealenone contaminated feed for sows in the gestation/lactation phase where possible.

Prepared by:
Ing: Jos E. Ferrer