The prefix ‘myco-‘ means fungus, so mycotoxins are toxins produced by fungi. Fungi are found everywhere – including in pastures and in bought-in feed. That means that mycotoxins can also be found in pastures and feed. Mycotoxins can have beneficial effects: some of them provide plants with protection against insect attack. However, some mycotoxins have the side effect of causing animal health issues.
In ryegrass-based pastures, troublesome mycotoxins can build up in leaf sheaths and flower stalks. They are produced by the endophyte Neotyphodium lolii, a fungus that grows inside ryegrass plants. This endophyte produces two mycotoxins – lolitrem B and ergovaline. Lolitrem B causes the characteristic tremors seen in ryegrass staggers, while ergovaline reduces the heat tolerance of animals.
Animals affected by endophyte mycotoxins eat less, so milk production suffers. Stock can also become more temperamental and may be more inclined to kick off the cups while in the shed.
The endophyte grows mainly in the seed, seed head, tillers and leaf sheaths, rather than in the actual leaf blade. This means that stock are more at risk of developing problems if they graze hard into the base of the pasture, or graze seed-heavy pasture. In addition, the risk increases when there is a long, hot period of weather followed by rain.
There are a few simple strategies that can help reduce the chance of stock being affected by ryegrass mycotoxins:
- Avoid grazing pastures hard, so that stock have less chance of ingesting high levels of mycotoxin
- Top pastures to remove seed heads
- Graze stock on pastures that contain either no endophyte, or one of the newer, novel endophytes that offer the plant protection but do not carry thesame level of risk to stock
- Encourage clover growth in pastures: this helps to dilute out the concentration of mycotoxin ingested by stock
- Take special care after a drought, as mycotoxin levels are likely to be higher
- Feed a high-quality supplement such as silage, hay, turnips or maize
- Young stock are particularly susceptible to the effects of mycotoxins, so extra care should be taken with their grazing set-up.
Mycotoxins can also be found in supplementary feed, and are produced by different fungi to those found in ryegrass. Any conditions that promote the growth of fungi in the feed will increase the chance of mycotoxins being present. Warm, humid storage conditions are most likely to increase fungal growth.
Any type of supplementary feed can be affected: blended feed, pellets, cereals, silage and baleage. Feed can be affected if it is bought from vendors or made on farm. Reputable vendors of supplementary feed ensure that their product is well managed throughout its life: from growing, through harvesting, processing and storage. The same precautions should be taken for feed produced on farm.
Good storage conditions are essential: protect the product from damp and use it as soon as possible.
If you suspect stock have been affected by mycotoxins, move them onto safe pastures (e.g. tall fescue, lucerne, chicory) and/or feed high-quality supplement. Leave them undisturbed as much as possible, and separate them from the main herd. If milking, reduce the frequency to once a day.