» Moulds and Yeasts
Moulds and Yeasts
Many of homegrown feeds contain some fungal spores. When the temperature and humidity are correct, these spores will grow and multiply to create fungi (“moulds”). Consequently, mycotoxins can be produced by these moulds and can reduce animal health and productivity. Feeds containing significant levels of moulds can usually be diluted down to a safer level. Feeds containing very high levels of total moulds (over 1,000,000 cfu/g) generally should not be fed at all, or only in low restricted amounts. Tolerable levels are much lower for non-ruminant animals than for ruminants. Without exception, significant levels of moulds will affect performance.
Symptoms of mould induced problems
- Liver, lung or kidney damage
- Reduced weight gain and performance
- Abortions and reproductive problems
- Digestive upset and reduced feed intake
- Compromised immune function
- Diarrhea, bloating and hemorrhage
Some common fungal genera are listed below in alphabetical order along with their affiliation to particular fungal divisions (in parenthesis).
Even though the toxin is not produced, the mold spores are there and will be inhaled causing irritation of the lungs, respiratory problems (pneumonia, etc.), throwing off of the rumen, mycotic abortions caused by the production of histamines. Possibly mix with silage to reduce the dust. People dealing with this product may also develop what is known as farmer's lung.
A maximum of 50,000 cfu/g (colonies forming units per gram) is advised, however potential problems may be encountered at lower levels, exercise care and caution at levels above 10,000 cfu/g – above the maximum level, potential problems may start to be seen. Even though some moulds do not produce toxins (zygomycetes Mucor and/or Rhizopus, and some ascomycetes, such as Cladosporium spp.), the spore dust may be inhaled and cause respiratory problems and raise the potential of mycotic abortions.
Some of possible pathogens of mycotic abortion include: Mucor rhizopodiformis, Absidia corymbifera, Absidia ramosa, Aspergillus flavus, Aspergillus nidulans, Aspergillus terreus, Mucor psillus, Rhizopus arrhizus, Aspergillus niger, Rhizopus boyinus, Allescherica boydii, Aspergillus versicolor, Kontospora lanuginose, Mortierella polycephala, Polystictus versicolor, Mucor disperses, Mortierella zychae, Mortirella wolfii, Aspergillus fumigatus, Candida tropiculis, Nicardia asterodies.
Mycotic infections are a common cause of abortion in individual animals, causing some 3 to 10 % of all abortions. The infection usually occurs after an episode of grain overload or fungal pneumonia. The toxins in moldy feeds will enter the bloodstream and the pregnant uterus. Abortions and infertility may result if the toxic elements from the moldy feed enter and infect the placenta. Severe infection of the placenta may result; it is seen as a leathery thickening of areas in between the cotyledons.
In 25 % of mycotic abortions, the fungus invades the fetus, and red or white rings and worm-like lesions are seen. If the fetus remains in the uterus for any length of time after death, these lesions may no longer be visible. The afterbirth may be retained, causing even more problems. The infection may pass through the placenta and into the fetus, so plaques or crusts of fungus will develop on the skin of the fetus. Culturing the organism from aborted tissues will provide the diagnosis. Abortion can occur any time from the fourth month of pregnancy to full term. Penicillium roqueforti is sometimes found on moldy grains and silage. It is associated with abortion, retained placenta and reduced fertility in cattle, as this species can produce a variety of different mycotoxins. Concentration of 1,000 – 2,000 cfu/g can already cause problems and concentration above 10,000 cfu/g will definitely lead to rumen disfuntion.
Moldy sweet clover can cause reproductive problems in cattle herds. Sweet clover hay and silage are difficult to make because the moist nature of the plant encourages mold growth. Coumoral is a chemical normally found in sweet clover. However, it changes to dicoumarol by fungal action after harvest. This is the same substance found in rat poisons. Dicoumarol is a potent anti-clotting compound and can result in excessive bleeding. Newborn calves are especially susceptible to dicoumarol effects, although older animals and even adults may be affected. Symptoms include abortion or death of a calf shortly after birth, extensive bleeding from the genital tract of the dam and hemorrhage into the tissues of the calf.
– Maximum 50,000 cfu/g - again similar problems as above in that the moulds dust may cause respiratory problems and there may also be an added impact of reduced feed intake.
Mycelia sterilia (imperfect fungi)
- do not usually produce toxins but may seriously affect intake at elevated levels 10,000 cfu/g will in most cases result in complete feed refusal for non-ruminant animals and levels as low as 500 cfu/g will result in reduced feed intake – for ruminant animals, intake may be affected above 5,000 cfu/g. (exercise extreme caution).
Yeast-like fungi (Candida albicans)
- does not produce toxins, maximum 1,000 cfu/g and exercise caution above 500 cfu/g. Can produce mouth yeast infections (thrush) and may also contribute to vaginal yeast infection.
Signs of moldy feed:
-Poor feed flow
-Feed refusal by animals, decreased palatability
-Poor reproductive performance
-Increased somatic cells/mastitis
-Any amount of heating in feeds or grains
-Darkening of feed and grain
-Slight off-smell of feed grains
Moulds in feeds (both hay and grain) - problems and dealing with them
1. Send a representative sample of the feed to a feed testing laboratory for toxic mold analysis. Grain samples should not be ground or rolled. The procedure takes two to four weeks, as a culture of the mold must be grown before it can be determined if it has the potential to be toxic.
2. Presence of a toxic mold does not always mean a mycotoxin was produced, but a risk is considerably higher; you may want to consider testing still for the mycotoxins it may produce.
3. Many moulds are known to produce one or more toxins, some of which cannot be identified at present. Clinical signs vary with the particular mold and toxin. However, it helps to remember that cattle are generally more resistant to mold toxins than either swine or poultry. Young animals are more susceptible than mature animals.
4. It must also be taken into consideration that mycotoxins can persist in the feeds/foods for long time after their producers (fungi) have lost vitality, i.e. mycotoxin may be present in the substrate even when we do not see any fungus (fungi as living organisms are being more sensitive, while the toxins are molecules in some cases very resistant to adjacent environment).
5. Balance moldy feeds with good quality ingredients. Loss in feed value can be significant (10% +) when moulds are present in a feedstuff. Adjustments to the ration should be made accordingly.
6. Some moulds (Rhizopus, Aspergillus) can cause mycotic abortions.
7. When inhaled, mould spores can cause the lungs to become abnormally sensitive to these particular spores. Chronic respiratory disease and even death can occur if exposure to the moldy feedstuff is continued.
8. If problems are encountered, stop using the moldy feed and seek help from a competent source.
9. The most important step for eliminating fungi growth in the silage is compacting and a good covering of the silage. It means the oxygen has to be removed completely in order to inhibit moulds. If moulds remain in the silage mycotoxin contamination can increase, therefore special attention should be given to air pockets and defficient sealing. Closed related to the compacting is the particle length. There is a rule: the higher the dry matter content, the shorter the particle length.
A combination of anaerobiose and low pH value, a sign of a good fermentation, can stop completely the growth of fungi, decreasing the risk of futher mycotoxin contaminations. However, the field mycotoxins will remain in the silage since they can not be degraded by fermentation.
A high pH value decrease can be reached using biological silage inoculants containing homolactic lactic acid bacteria (lactic acid is the major end product). Heterolactic acid bacteria (besides lactic acid bacteria, they also produce acetic acid) are specially important for the inhibition of yeasts and moulds after the opening of the silo. Acids or their salts can be also used in the upper silage layer which is more prone to spoil since the compacting is generally speaking lower, or as silage additive when the dry matter content is relatively high (over 50%) and the risk of mould growth is higher due to air pockets.
10. If feed is ensiled and you have not followed proper procedure in the ensiling process (e.g. not properly packed, not enough moisture, too mature, opened pit < 50 days after sealing, excessive aerobic degradation) be cautious in using the feed and be aware of things that you can do differently in the future. Also be critical in how you manage the silage face.
Table 1. Attachment No.3 to Government regulation 438 Slovak republic of 21 June 2006, On undesirable substances in animal feed and other indicators of safety and availability of the feed