Feed and water

Mycotoxins are toxins produced by mould in the feed and pose a serious risk to pigs. Toxins can be divided into two main groups: field toxins and storage toxins. Field toxins are formed while the crops are growing in the field and are often linked to stressed plants e.g. due to poor weather conditions, pests and similar.  Examples of field toxins are deoxynivalenol (DON) and zearalenone. On the other hand, storage toxins occur after harvest if the crops are stored under moist or warm conditions and typical examples are penicillium and ochratoxin.

How do mycotoxins occur?

Mould always precedes toxins meaning that visible mould on grain is a warning about a potential toxin threat. Mould can taste and smell bad which leads to the animals losing their appetite and eating less. Even though mould can partly be removed by processing the grain, the mycotoxins remain. They have no taste nor smell and can therefore be present in the feed without being discovered. It is therefore important to keep an eye on signs of mould but also be aware that the toxins may still be present even though the mould is not visible.

Different types of mycotoxins in feed and their effect on pigs

Mycotoxins can have various adverse health effects on pigs and other domestic animals. The most common toxins in pig feed include trichothecenes, zearalenone, ochratoxin and penicillium, but there are also other types which may affect the pigs’ health.

Trichothecenes are a group of mycotoxins produced by Fusarium fungi and can be divided into two main groups:

Trichothecene A which includes the toxins HT-2 and T2 toxin. These are extremely toxic and even small amounts in the feed may lead to severe symptoms. When the levels cause problems is much debated. In our experience, when the levels exceed 40-50 ppm the animals may show symptoms such as reduced feed intake and general unthriving.

Trichothecene B includes deoxynivalenol (DON) also known as “vomitoxin” which is one of the most common mycotoxins in pig feed. DON impedes the animals’ appetite, resulting in reduced feed intake and slower growth. The pigs typically react to DON by eating less or completely refusing the feed which may lead to large production-related losses.

Zearalenone is another mycotoxin from Fusarium fungi which affects the animals. This toxin imitates oestrogen which may lead to hormonal disturbances in sows such as infertility, uterine prolapse and premature farrowings. Zearalenone can be particularly harmful for young sows as it disrupts their reproductive cycle which may in the end lead to less productive herds.

Aflatoxins are one of the most dangerous types of mycotoxins and are produced by Aspergillus fungi. Aflatoxin is extremely toxic and can severely harm the liver, affect the immune system and, in the worst-case scenario, cause acute poisoning and death. Even though aflatoxins are rare in Denmark, they are known for their high toxicity, and they are used as reference for toxin measurements as their toxicity is a 1:1 comparison with other toxins. Aflatoxins can be particularly problematic in warm, moist climate conditions and good storage and drying of grain are therefore crucial in order to avoid them.

Penicillium is a storage toxin which may also cause problems for pigs. This toxin has many adverse health effects: it can lead to increased saliva production, damage the liver, expand the blood vessels and disrupt intestinal flora. When the intestinal flora changes, the feed consumption is affected which may lead to diarrhoea and reduced growth. Penicillium contains substances with antibacterial traits which may kill bacteria. This can disrupt the balance in the intestinal flora and cause problems such as poor feed conversion. It is particularly dangerous if it gets into feed for cows as it may destroy the rumen flora which is catastrophic for a cow. The sow’s “rumen”, which is the large intestine, can be similarly affected.

How reliable are toxin analyses?

In addition to the known mycotoxins, there are also masked toxins – chemical connections which are not always discovered in traditional tests. This means that risk assessments often underestimate the toxin load in the feed, and it is therefore always important to consider the overall health condition of the animals. It is also essential to test feed samples regularly and take into account new mycotoxins which are discovered every year.

When is there a risk of mycotoxins?

A number of factors increase the risk of mycotoxins in grain and straw. Crop rotation plays a crucial part where repeated growing of the same crop, e.g. maize after maize, creates a favourable environment for fungal growth and toxins. Similarly, non-ploughing cultivation can be a challenge as fungi thrive in soil that is not turned over which increases the risk of toxins in both grain and straw.

The time of harvest is also critical. Wet weather, which delays the harvest, creates optimal conditions for fungal growth and thereby increases the risk of toxins. Effective handling of harvest and storage are therefore crucial to minimise the risk of toxins. Grain should be dried quickly, preferably within 5-6 days to avoid development of storage toxins. Grain must be stored under optimal conditions – ideally with a humidity of 15% and a temperature of 8 °C to be storage stable.

How do you test feed and straw for mycotoxins?

To ensure that grain and straw do not contain harmful amounts of mycotoxins, it is important to take representative samples. A correct sample involves taking a total of 1 kg grain but from several places. It is even more difficult to take samples of straw as this requires small random samples from many bales in order to get a representative picture.

Even though laboratory tests can detect the presence of many known risk factors, you should note that testing is not done for all toxins and that new toxins are continuously discovered – approx. one a year.  Furthermore, some laboratory tests might underestimate the risk if the toxins are masked or bound to other agents.

Therefore also look at the animals – they will show you if there is an issue.

Risk of mycotoxins in straw for pigs

Straw can contain significant amounts of toxins even though the grain looks fine. It is a challenge to assess how much straw the sows eat particularly in deep litter stables where they can eat large amounts. It is important to take this into consideration as straw consumption is often not included of the normal feeding plan and toxins in the straw may affect the animals’ health.

Toxin binders are often used as a safety measure to reduce the effects of mycotoxins. The dosage is typically 1-2 kg per ton dry feed, but it is important to remember that the binder only works in wet feed as it requires liquid to activate the binding of the toxins. With dry feed, the binding therefore only takes place inside the animal.

Symptoms of mycotoxins in feed and straw for pigs

Regardless of the test results from the laboratory, it is important to observe the animals closely. They will often reveal whether they are affected by toxins even if the analyses do not show alarming values. Signs of a toxin load may include:

• Diarrhoea
• Reduced feed intake
• Less milk
• Small litters
• Lack of growth
• Ear lesions or tail necroses
• Acute deaths
• Prolapse
• Hard udder

These symptoms may be a sign that the toxin levels in the feed or the straw are too high even though it cannot necessarily be seen in the laboratory results.

Prevention and handling of mycotoxins

To reduce the risk of mycotoxins in grain and straw, it is important to focus on good cultivation and storage practices. Crop rotation with crops such as rape or ploughing can help reduce the occurrence of fungi in the soil.

Effective storage of grain involves regular ventilation. The grain must be blown through every three weeks (the entire season) and indoor silos should be emptied and cleaned every six weeks to avoid fungal growth. A thorough cleaning of silos and grain are just as important as cleaning of liquid feeding systems as old grain can be a source of mould and toxins.

To learn more about mycotoxins – listen to our podcast which you can find via this link: https://www.spreaker.com/podcast/o-vet-podcast–5965728